The IEEE AP-S Distinguished Lecturer Program provides AP-S chapters
around the world with talks by experts on topics of interest and
importance to the AP community. The chapters incur little or no
cost in making use of this program. Each chapter can request a maximum
of two visits per year by our Distinguished Lecturers (DLs). (One
of the two visitors is allowed to be a former Distinguished Lecturer,
if the chapter prefers.) Requests must be approved prior to making
an official commitment by contacting the Chair of the Distinguished
Lecturer Program. The AP-S Society will normally reimburse Distinguished
Lecturers up to $1,250 for presentations to AP-S Chapters located
inside the DL's IEEE geographic region. Travelling outside the DL’s
geographic region is currently reimbursable at up to $2,500. (One
exception is that Canada and the U.S. are considered as one region
for reimbursement purposes.) Each additional chapter visited on
the same trip, within the same geographical region, is normally
reimbursable at the rate of $1,250. Exceptions to the above reimbursement
limits require approval from the Chair of the Distinguished Lecturer
Program. To receive reimbursement, the lecturers are required to
keep all expense receipts and send them electronically to the AP-S
Secretary/Treasurer along with an expense report on a standard IEEE
reimbursement form, which is available from the Chair of the Distinguished
All Distinguished Lecturers are outstanding in their fields of
specialty. Collectively, the Distinguished Lecturers possess a broad
range of expertise within the area of AP. Thus, the chapters are
strongly encouraged to use this program as a means to make their
local AP community aware of the most recent scientific and technological
Although the Chair selects and appoints the Distinguished Lecturers,
the Chair is open to suggestions from members of the IEEE AP-S and
the AP Chapter Chairs for the selection of appropriate topics and/or
the nomination of future Distinguished Lecturers, and suggestions
are welcome. The Distinguished Lecturer Program Handbook can be found here.
Kwok Wa Leung was born in Hong Kong. He received the B.Sc. degree in Electronics and Ph.D. degree in electronic engineering from the Chinese University of Hong Kong, in 1990 and 1993, respectively.
From 1990 to 1993, he was a Graduate Assistant with the Department of Electronic Engineering, the Chinese University of Hong Kong. In 1994, he joined the Department of Electronic Engineering at City University of Hong Kong (CityU) and is currently a Professor and an Assistant Head of the Department. He is also the founding Director of the Innovation Centre of the Department. From Jan. to June, 2006, he was a Visiting Professor in the Department of Electrical Engineering, The Pennsylvania State University, USA.
Professor Leung was the Chairman of the IEEE AP/MTT Hong Kong Joint Chapter for the years of 2006 and 2007. He was the Chairman of the Technical Program Committee, 2008 Asia-Pacific Microwave Conference, Hong Kong, the Co-Chair of the Technical Program Committee, 2006 IEEE TENCON, Hong Kong, and the Finance Chair of PIERS 1997, Hong Kong. His research interests include RFID tag antennas, dielectric resonator antennas, microstrip antennas, wire antennas, guided wave theory, computational electromagnetics, and mobile communications. He was an Editor for HKIE Transactions and a Guest Editor of IET Microwaves, Antennas and Propagation. Currently, he serves as an Associate Editor for IEEE Transactions on Antennas and Propagation and received Transactions Commendation Certificates twice in 2009 and 2010 for his exceptional performance. He is also an Associate Editor for IEEE Antennas and Wireless Propagation Letters. He has been appointed as a Distinguished Lecturer by the IEEE Antennas and Propagation Society for 2012-2014.
Professor Leung received the International Union of Radio Science (USRI) Young Scientists Awards in 1993 and 1995, awarded in Kyoto, Japan and St. Petersburg, Russia, respectively. He received Departmental Outstanding Teacher Awardsin 2005, 2010, and 2011. He is a Fellow of IEEE and HKIE.
Development of the Dielectric Resonator Antenna
The fundamentals and development of dielectric resonator antenna will be discussed in this talk. For many years, dielectric resonators (DRs) have only been used as high-Q elements in microwave circuits until S. A. Long and his collaborators showed that they can also be used as efficient radiators. The studies were motivated by an observation that carrier frequencies of modern wireless systems had gradually progressed upward to the millimeter-wave region, where efficiencies of metallic antennas can be reduced significantly due to the skin effect. In contrast, DR antennas (DRAs) are purely made of dielectric materials with no conductor loss. This feature makes DRAs very suitable for millimeter-wave systems.
As compared to the microstrip antenna, the DRA has a much wider impedance bandwidth (~ 10 % for dielectric constant ~ 10). This is because the microstrip antenna radiates only through two narrow radiation slots, whereas the DRA radiates through the whole DRA surface except the grounded part. Avoidance of surface waves is another attractive advantage of the DRA over the microstrip antenna. Nevertheless, the DRA and microstrip antenna have many common characteristics because both of them are resonators. For example, both of them can be made smaller in size by increasing the dielectric constant because the dielectric wavelength is smaller than the free-space wavelength. Furthermore, basically all excitation methods applicable to the microstrip antenna can be used for the DRA.
Although the DRA received attention originally for millimeter-wave applications, it is also widely investigated at microwave or even RF frequencies. It is because the DRA is a volume device that offers designers more degrees of freedom than 2D-type antennas (e.g., microstrip antennas) or 1D-type antennas (e.g., monopole antennas). Other advantages of the DRA include its light weight, low cost, low loss, and ease of excitation.
The following DRA topics will be covered in this talk:
Circularly polarized DRAs
Dualband and wideband DRAs
Transparent Antennas: From 2D to 3D
Transparent antennas are very attractive. They can be integrated with clear substrates such as window glass, or with solar cells to save surface areas of satellites. Transparent antennas are normally realized using (2D) planar structures based on the theory of patch antenna. The optical transparency can be obtained by fabricating meshed conductors or transparent conductors on an acrylic or glass substrate. Transparent designs using the meshed-conductor approach are straightforward because optical signals can pass through the opening of the meshes, while microwave signals can be transmitted or received by the conductors. The transparency and antenna property can be optimized by refining the width of the mesh. In this talk, results of a transparent antenna with meshed conductors will be presented.
In the transparent-conductor approach, transparent conductive films are used as radiators. Commonly used transparent conductive films include indium tin oxide (ITO), silver coated polyester film (AgHT), and fluorine-doped tin oxide (FTO). A sheet resistance of at least 1-2 ohm/square is required to obtain an optical transmittance of better than 70%. However, antennas made of such transparent conductor films are not efficient because of the high sheet resistance. This is one of the major obstacles to the widespread application of transparent antennas. A method that alleviates this problem will be discussed in this talk.
For a long time, transparent antennas have been of planar (2D) structures. Very recently, 3D transparent antennas have also been developed. This is a new topic. The principle of 3D transparent antenna is based on the theory of dielectric resonator antenna; the resonance is caused by the whole 3D structure rather than a confined cavity as found in the patch-antenna case. For glass, it is usually assumed that its refractive index is ~1.5, giving a dielectric constant of ~ 2.25. This value is too low for a DRA to have good polarization purity. However, it was generally overlooked that this dielectric constant was obtained at optical frequencies instead of microwave frequencies. Recently, a dielectric constant of ~7 was measured for glass at 2 GHz and this value is sufficient for obtaining a good radiator. Since crystals are basically glass, they can also be used for antenna designs. In this talk, the characteristics of glass DRAs will be shown. In addition, the idea of using a 3D glass antenna as a light cover will be presented. It has been experimentally found that the lighting and antenna parts do not affect each other because they are operating in totally different frequency regions. Interesting results will be presented in this talk.
Finally, it will be shown that 3D transparent antennas can be designed as aesthetic glass (or crystal) wares or artworks. This idea is especially useful when invisible antennas are needed due to psychological reasons. The idea has been demonstrated successfully using a glass swan and apple bought from the commercial market. The results will be presented in this talk.
Analyses of Spherical Antennas
The spherical antenna is an interesting and useful topic. For example, a spherical helical antenna can radiate circularly polarized fields over a wide beamwidth. An antenna array with its elements distributed over a spherical surface is able to determine the direction-of-arrival and polarization of an incoming wave. Further, a spherical antenna array can be used to avoid the scanning problem of a planar array at low elevation.
The spherical antenna is also important from the theoretical point of view. Since a spherical structure does not have any edge-shaped boundaries as found in cylindrical and rectangular structures, its closed-form Green’s function is obtainable. As a result, an exact solution of a spherical problem can exist, and the solution can be used as a reference for checking the accuracy of numerical or approximation techniques.
In this talk, the general solution of Helmholtz equation in the spherical coordinates will be briefly reviewed. The solution will be used to solve different spherical antenna problems, including the spherical slot antenna, spherical microstrip antenna, and grounded hemispherical dielectric resonator antenna (which is equivalently a dielectric sphere after imaging). Derivations of their exact modal Green’s functions will be described. Both electric and magnetic current sources will be considered, and their integral equations will be formulated using the Green’s functions. The method of moments (MoM) will be used to solve for the electric or magnetic current sources. From the currents, the input impedances and radiation patterns of the spherical antennas can be obtained easily.
When a field point coincides with a source point, the Green’s functions will become singular and care has to be exercised in evaluating their MoM integrals. Around a singular point, an extensive number of modal terms are needed to calculate the Green’s functions accurately. This may lead to practical problems because amplitudes of high-order Hankel functions can be too large to be handled numerically. A method that tackles the singularity problem will be presented. In this talk, integrals involving spherical Bessel functions or associate Legendre functions will be evaluated rigorously through analytical integration or their recurrence formulas. Since numerical integration is avoided, the evaluations of the integrals are computationally very efficient. Numerical convergence of the modal solutions will also be examined. Excellent agreement between theory and experiment is observed and the results will be presented in the talk. Finally, it will be shown that a spherical solution can be used to solve a planar annular problem.
Stefano Maci is a Professor the University of Siena (UNISI), with scientific responsibility of a group of 15 researchers (http://www.dii.unisi.it/~lea/). He is the Director of the UNISI PhD School of Information Engineering and Science, which presently includes about 60 PhD students. His research interests include high-frequency and beam representation methods, computational electromagnetics, large phased arrays, planar antennas, reflector antennas and feeds, metamaterials and metasurfaces.
Since 2000, he was responsible of 5 projects funded by the European Union (EU); in particular, in 2004-2007 he was WP leader of the Antenna Center of Excellence (ACE, FP6-EU) and in 2007-2010 he was International Coordinator of a 24-institution consortium of a Marie Curie Action (FP6). He also carried out several projects supported by the European Space Agency (ESA-ESTEC), the European Defense Agency (EDA), the US-Army Research Laboratory (ARL), and by various industries and research institutions: EADS-MATRA, (Tolosa, Francia), IDS (Pisa, Italia), TICRA (Copenhagen), ALENIA MARCONI SYSTEM (Rome, Italy), SAAB-ERICSON SPACE (Gotheborg, Svezia), THALES (Paris, France), TNO (L'Aia, Olanda), OTO MELARA (La Spezia, Italia), OFFICINE GALILEO (Florence, Italy), SELEX Communication (Rome), Thales Alenia Space (Rome).
Since 2001 he was a member the Technical Advisory Board of 11 international conferences, member of the Review Board of 6 International Journals; in the same period, he organized 23 special sessions in international conferences, and he held 10 short courses in the IEEE Antennas and Propagation Society (AP-S) Symposia about metamaterials, antennas and computational electromagnetics. He was an Associate Editor of IEEE Trans on EMC and of IEEE Trans. on AP and two times Guest Editor of special issues of the latter journal. In 2003 he was elected Fellow of IEEE.
In 2004 he founded the European School of Antennas (ESoA), a PhD school that presently comprises 30 courses on Antennas, Propagation, Electromagnetic Theory, and Computational Electromagnetics. ESoA counts about 150 among the best teachers of Europe (which include eleven IEEE Fellows) and it is frequented by an average of 220 students per year. The ESoA consortium presently comprises 33 European research centers and offers 12 one-week courses per year.
In 2005-2007, he was Italian National representative of the NATO SET-TG 084 "Emerging Technology for Sensor and Front-ends”, and he is presently involved as co-representative in the NATO SET-181 RTG on "Metamaterials for Defense and Security Applications".
Stefano Maci was co-founder of two spinoff-companies and since 2008 he is honorary President of LEAntenne e Progetti SPA (Valeggio sul Mincio, VE).
Stefano Maci is presently Director of ESoA, a member of the Board of Directors of the European Association on Antennas and Propagation (EuRAAP), a member of the Technical Advisory Board of the URSI Commission B, a member elected of the AdCom of IEEE Antennas and Propagation Society, a member of the Governing Board of the European Science Foundation (ESF) Project “NewFocus”, a member of the Governing board of the FP7 coordination action “CARE” (Coordinating the Antenna Research in Europe), a member of the Award Committee of the IEEE Antennas and Propagation Society (AP-S), a member of the Antennas and Propagation Executive Board of the Institution of Engineering and Technology (IET, UK), and a member of the Focus Group on METAMATERIALS in the Finmeccanica project “Mind-Share”.
His research activity is documented in 10 book chapters, 110 papers published in international journals, (among which 76 on IEEE journals), and about 300 papers in proceedings of international conferences. His h index is 24, with a record of more than 2000 citations (source Google Scholar).
Metasurfing Wave Antennas
Metasurfaces constitute a class of thin metamaterials, which can be used from microwave to optical frequencies to create new electromagnetic engineering devices. They are obtained by a dense periodic texture of small elements printed on a grounded slab without or with shorting vias. These have been used in the past for realizing electromagnetic bandgaps (EBG) or equivalent magnetic-walls. Changing the dimension of the elements, being the sub-wavelength 2D-periodicity equal, gives the visual effect of a pixelated image and the electromagnetic effect of a modulation of the equivalent local reactance. The modulated metasurface reactance (MMR) so obtained is able to transform surface or guided waves into different wavefield configurations with required properties. This MMR-driven wavefield transformation is referred to as “Metasurfing”. The MMR allows in fact a local modification of the dispersion equation and, at constant operating frequency, of the local wavevector. Therefore, the general effects of metasurface modulation are similar to those obtained in solid (volumetric) inhomogeneous metamaterial as predicted by the Transformation Optics; namely, re-addressing the propagation path of an incident wave. However, significant technological simplicity is gained.
When the MMR is covered by a top ground plane (Parallel-plate waveguide Metasurfing) the real part of the Poynting vector follows a generalized Fermat principle as happen in ray-field propagation in inhomogeneous solid medium. This may serve for designing lenses or point-source driven beam-forming networks. When the MMR is uncovered, wave propagation is accompanied by leakage; i.e., a surface wave is transformed into a leaky-wave, and the structure itself becomes an extremely flat antenna. In every case, introducing slots in the printed elements allows a polarization control. In such cases, the metasurface associated with can be described by an anisotropic surface impedance.
In this lecture, after illustration of the design method of metasurfing-wave antennas, various examples are presented and discussed, including Luneburg lenses, Maxwell’s Fish-eyes, isoflux antennas, Doppler-guide antennas and new transmission lines.
Retrieval of Constitutive Parameters in Metamaterials
The amazing interest on metamaterials, which has been growing for a decade, has in parallel posed a lot of questions about the most reliable and accurate approach to the characterization of their electromagnetic behavior. Most of the metamaterials can be described as a periodic repetition of some inclusions in a host medium; the inclusions can be made resonant despite their small dimension in terms of a wavelength. It is well accepted in various scientific communities to consider this type of artificial structures as effective media, described by a set of equivalent constitutive parameters. These parameters can be obtained by using analytical models, measurements or full-wave simulations in conjunction with numerical retrieval algorithms. However, the procedure for the definition of the equivalent parameters is not univocally defined, and different approaches may be used depending on the metamaterial characteristics and on the goal of the homogenization process.
The analysis methodologies for retrieval of constitutive parameters include those based on a microscopic-equivalence and those based on a macroscopic-equivalence. The former set up a model relating each element of the periodic arrangement to an equivalent particle with electric and/or magnetic dipolar moment. This requires constituent particles small in terms of a wavelength, since the response of the single particle is approximated by the dominant term of a multi-polar expansion. On the other hand, macroscopic-equivalence approaches identify equivalent wave impedance and propagation constant for the field propagating inside the metamaterial, and they look for a homogeneous medium supporting the same modal structure. In this case the restrictions on the electrical size of the inclusion may be less severe, and it is possible to correctly retrieve the scattering parameters from a metamaterial sample. However, there could be some intrinsic ambiguities in the extraction of the equivalent parameters.
In this lecture, after the review of the literature, an original method of retrieval of the metamaterial constituent parameters is described, with emphasis on removing ambiguity and on the role played by the spatial dispersivity of the constituent parameters. The special class of metamaterials formed by periodic multilayer arrangements of 2D printed structures will be considered with much attention. Anisotropy and special case of gyrotropy, as well as bianisotropy and the special case of chirality will be considered in the parameter retrieval.
Scattering Matrix Domain Decomposition Method Formalized with Different Wave Propagators
In most of the real applications, antennas need to be located in a complex operative environment; accurate analysis is needed to take into account interaction with antenna platform or other surrounding antennas. A rigorous numerical analysis of these large problems is a very complex task, due to the prohibitive number of unknowns; furthermore, the simultaneous presence of electrically large structures and small features may lead to ill conditioning.
The Domain Decomposition Method is a general approach for the solution of complex multiscale problems, which allows one to overcome the above mentioned impairments; it consists in dividing the original problem into simpler, more tractable non-overlapped subdomains that are solved separately, and then obtaining the overall solution by imposing proper connections among different subdomains. In particular, if the sub-domains boundaries are associated with ports through which a proper set of modes flow, the interactions among different sub-domains can be rigorously described through an equivalent network representation. Depending on the propagation mechanism within each sub-domain, different types of modes or ”wave objects” can be used. In particular, beam-type fields or radiated modes are conveniently used when dealing with radiation and scattering problems, while waveguide modes are well suited for representing guided waves.
Different choices of the wave objects used for field representation lead to different implementations of the generalized network formulation. The optimal choice is the one maximizing the efficiency of the overall numerical analysis, and depends on the problem under consideration. In this talk, two particular implementations are considered: the first one uses complex point source (CPS) beams as wave objects, while the second one uses spherical waves (SW) for the representation of radiated field and waveguide modes at the antenna input port. In the first case, thanks to the angular selectivity of the CPS beams, only a small fraction of the beams contribute to the subdomain interactions, thus, leading to an efficient numerical procedure. In the second case, the choice of spherical waves offers the advantage of direct interfacing with the output of spherical near-field measurements or numerical simulations, while the inclusion of waveguide modes provides the information about the reflection coefficient at the antenna input port.
Dr. Brian M. Kent, Fellow, IEEE/AMTA/AFRL Aerospace Consultant and Adjunct Professor (Michigan State University)
C/O 385 Lightbeam Dr, Dayton, OH 45458-3632
Primary email: Brian.firstname.lastname@example.org
Secondary email: email@example.com
Dr. Brian M. Kent is a Consultant in Aerospace, Science, and Technology, and an adjunct professor of Electrical Engineering with Michigan State University's Department of Electrical Engineering. He recently completed 37 years of Service to the United States Air Force having most recently served as the Chief Technology Officer of Air Force Research Laboratory, Wright-Patterson Air Force Base, Ohio. As CTO, he was AFRL’s principal scientific and technical expert for a 6,500 person organization while overseeing a $2.2B+ research portfolio. He is an internationally recognized scientific expert, and provided technical advice to AFRL management and the professional staff. He has significant experience in engineering education, radar, radar signature, and other radio frequency technologies.
During his previous tenure as AFRL’s Sensor’s Directorate Chief Scientist, he served as the directorate's principal scientific and technical adviser and primary authority for the technical content of the science and technology portfolio. He collaborated on numerous interdisciplinary research problems that encompass multiple AFRL directorates, customers from other DOD components, as well as the manned space program managed by NASA.
Dr. Kent also served the USAF as Senior Scientist for Low Observables and Electromagnetics, Air Force Research Laboratory, where he performed and directed research, and development activities at the Multi-Spectral Radar Signature Measurement Facility, His primary responsibilities include the development and transition of advanced low observable electromagnetic analysis and measurement techniques to the Department of Defense and their aerospace industrial partners, and profoundly impacted the development and deployment of the F-117, B-2, F-22, and F-35 for the USAF. Dr. Kent's fundamental research interests encompass extremely broadband electromagnetic test and evaluation techniques, with special emphasis on the acquisition of measured performance data from basic 6.1/6.2 technology components through fully fielded and sustained weapon systems. Dr. Kent held a variety of positions, making pioneering and lasting contributions to the areas of signature measurement technology, and successfully established international standards for performing radar signature.
Dr Kent was a lecturer for Georgia Tech Research Institute for over 9 years, and concurrently became an adjunct professor in 1998 at Michigan State University, and has served the department on the Visiting Committee, ABET accreditation, ECE Chair Search Committee, Deans Search Committee, and Dean’s advisory Committee. He has also participated in reforming the Senior Design Project classes, and has served for many years as a judge at the Spring and Fall Engineering “design day”.
Dr. Kent has authored and co-authored more than 90 archival articles and technical reports and has written key sections of classified textbooks and design manuals. He has delivered more than 200 lectures, and developed a special DOD Low Observables Short Course that has been taught to more than 3,000 scientists and engineers since its inception in 1989. Dr. Kent has provided technical advice and counsel to a wide range of federal agencies, including the Department of Transportation, the Department of Justice and NASA's Space Shuttle Program.
Contributions of the US Air Force Laboratory’s Sensor’s Directorate to the Columbia Accident Investigation - shedding light on the mystery of the flight day two object and our role in returning the Shuttle to safe flight.
In the wake of the Columbia tragedy, Air Force Space Command carefully reviewed records of all radar objects in space during the time the Shuttle was on orbit. To everyone’s surprise, a post accident review revealed that a mysterious object separated from the Orbiter on Flight Day 2 and subsequently de-orbited 60 hours later, burning up on re-entry. Reentry ballistics revealed an estimate of the object’s area to mass. Four ground based tracking radars gave a hint of the objects radar cross section at the UHF frequency of 433 MHz. The Columbia Accident Investigation Board (CAIB) wanted to know what the object was, and whether it could be related to the accident. Three weeks after the accident, the CAIB eventually contacted Dr Brian Kent of the Air Force Research Laboratory Multi-spectral Advanced Compact Range measurement facility, for their help in assessing the mysterious object. For the next two months, RCS measurements performed at the AFRL advanced compact range ultimately narrowed the mystery of the Flight Day 2 object to a very few possibilities. Their work became so visible that Dr Kent provided public testimony to the CAIB on May 6, 2003. In light of the accident cause, NASA made many changes to the Shuttle system and supporting ground sensors. Dr Kent was involved in the fielding of a debris radar system that allows NASA to closely monitor ascent debris from ascending rockets, including the Shuttle. Come hear how a solid engineering analysis, good teamwork, and a bit of sleuthing shed light on what turned out to be one of the most intriguing issues in the Columbia investigation, leading eventually to returning the Shuttle to operational flight status.
Air Force Research Laboratory Sensors Directorate: An Update on the organization, Our Major Research Interests, and On-going Laboratory Construction and Modernization Activities
The AFRL Sensor Directorate mission is to “Lead the discovery, development, and integration of affordable sensor and countermeasure technologies for our warfighters.” Sensors is being transformed by a $45M military construction office and laboratory modernization effort related to consolidating our research workforce and laboratories from Rome, New York and Hanscom AFB, Massachusetts. This talk will outline Sensors vision for the future work in antenna design, multi-input/multi-output passive and active RF systems, and other research interests of the US Air Force. We will also describe the major new Sensors laboratory facilities recently completed, and provide insight into collaborative research opportunities.
Electro-Magnetic Interference Measurements on the Shuttle Orbiter "Discovery" in Preparation for Return to Flight - A Case Study
As NASA prepared the Space Shuttle for its first return to flight mission (STS-114) in the July 2005 timeframe, a number of new visual and radar sensors were used during the critical ascent phase of the flight to assess whether any unintentional debris was liberated from the Shuttle as it raced into orbit. New high-resolution C-Band and X-Band radars were used to help ascertain the location and speed of any released debris, and were also used to monitor routine flight events such as Solid Rocket Booster (SRB) separation. To assure these new radars did not interfere with flight-critical engine subsystems, an Electromagnetic Interference (EMI) measurement was performed on the Shuttle Orbiter "Discovery" in January 2005, using the Air Force Research Laboratory's Mobile Diagnostic Laboratory (MDL). This portable EM Measurement system performed a large number of attenuation measurements the night of January 17-18, 2005. This paper describes how the attenuation data was acquired, and the methodology used to reduce the data to predict average attenuation of the radar energy from the outside world to the inside of the aft engine bay of the Orbiter. This data, when combined with a separate NASA performed equipment level EMI analysis, demonstrated the new C and X-Band Debris Radars could be operated without adversely interfering with the Orbiter electronic systems in the aft avionics and engine bays.
Characterization of Space Shuttle Ascent Debris Based on Radar Scattering and Ballistic Properties --Evolution of the NASA Debris Radar System told in two parts
This is a two-part presentation (with break) that introduces the NASA Debris Radar (NDR) system developed to characterize debris liberated by the space shuttle (and any follow-on rocket system) during its ascent into space. Radar technology is well suited for characterizing shuttle ascent debris, and is especially valuable during night launches when optical sensors are severely degraded. The shuttle debris mission presents challenging radar requirements in terms of target detection and tracking, minimum detectable radar cross-section (RCS), calibration accuracy, power profile management, and operational readiness. In Part I, I describe the NDR system consists of stationary C-band radar located at Kennedy Space Center (KSC) and two X-band radars deployed to sea during shuttle missions. To better understand the signature of the shuttle stack, Xpatch calculations were generated at C and X band to predict the radar signature as a function of launch time. These calculations agreed very well with measured data later collected. Various sizes, shapes, and types of shuttle debris materials were characterized using static and dynamic radar measurements and ballistic coefficient calculations. After a break, Part II discusses the NASA Debris Radar (NDR) successes, which led to a new challenge of processing and analyzing the large amount of radar data collected by the NDR systems and extracting information useful to the NASA debris community. Analysis tools and software codes were developed to visualize the shuttle metric data in real-time, visualize metric and signature data during post-mission analysis, automatically detect and characterize debris tracks in signature data, determine ballistic numbers for detected debris objects, and assess material type, size, release location and threat to the orbiter based on radar scattering and ballistic properties of the debris. Future applications for space situational awareness and space-lift applications will also be discussed.
Dynamic Radar Cross Section and Radar Doppler Measurements of Commercial General Electric Windmill Power Turbines -- Predicted and Measured Radar Signatures
Commercial windmill driven power turbines (“Wind Turbines”) are expanding in popularity and use in the commercial power industry since they can generate significant electricity without using fuel or emitting carbon dioxide “greenhouse gas”. In-country and near-off shore wind turbines are becoming more common on the European continent, and the United States has recently set long term goals to generate 10% of national electric power using renewable sources. In order to make such turbines efficient, current 1.5 MW wind turbine towers and rotors are very large, with blades exceeding 67 meters in diameter, and tower heights exceeding 55 meters. Newer 4.5 MW designs are expected to be even larger. The problem with such large, moving metallic devices is the potential interference such structures present to an array of civilian air traffic control radars. A recent study by the Undersecretary of Defense for Space and Sensor Technology acknowledged the potential performance impact wind turbines introduce when sited within line of site of air traffic control or air route radars. In the Spring of 2006, the Air Force Research Laboratory embarked on a rigorous measurement and prediction program to provide credible data to national decision makers on the magnitude of the signatures, so the interference issues could be credibly studied. This paper will discuss the calibrated RCS and Doppler measurement of the turbines and compare this data (with uncertainty) to modeled data.
Dr. Monai Krairiksh
King Mongkut’s Institute of Technology Ladkrabang
Bangkok 10520, Thailand firstname.lastname@example.org
Monai Krairiksh was born in Bangkok, Thailand. He received the B.Eng., M.Eng. and D.Eng. degrees from King Mongkut’s Institute of Technology Ladkrabang (KMITL), Thailand in 1981, 1984, and 1994, respectively.
He was a visiting research scholar at Tokai University in 1988 and at Yokosuka Radio Communications Research Center, Communications Research Laboratory (CRL) in 2004. He joined the KMITL and is currently a Professor at the Department of Telecommunication Engineering. He has served as the Director of the Research Center for Communications and Information Technology during 1997-2002. His main research interests are in antennas for mobile communications and microwave in agricultural applications.
Dr.Krairiksh was the chairman of the IEEE MTT/AP/Ed joint chapter in 2005 and 2006. He served as the General Chairman of the 2007 Asia-Pacific Microwave Conference, and the advisory committee of the 2009 International Symposium on Antennas and Propagation. He was the President of the Electrical Engineering/ Electronics, Computer, Telecommunications and Information Technology Association (ECTI) in 2010 and 2011 and was an editor-in-chief of the ECTI Transactions on Electrical Engineering, Electronics, and Communications.
He was recognized as a Senior Research Scholar of the Thailand Research Fund in 2005 and 2008 and a Distinguished Research Scholar of the National Research Council of Thailand.
Remote Sensing of the Physical Qualities of Fruits
Nondestructive determination of dielectric properties of materials is essential in various applications to monitor the nature of an object. Apart from many techniques like near infrared (NIR), X-ray, ultrasonic, and so on, a microwave based technique is of interest due to its low cost, high accuracy, and small size. In this talk the objective is to describe and present a novel way to determine in situ the ripening of fruits and how they can be applied in real time applications. This methodology has been applied to determine the quality of fruits like Durian, Banana, Mangosteen and the like.
A number of techniques exist for characterization of lossy dielectric objects at microwave frequencies. Many such techniques have been extensively developed, e.g. resonant and non-resonant methods. For the resonant method, the cavity perturbation technique is well suited for measuring low dielectric loss materials and the accuracy is limited only by the size of the cavity. For a non-resonant method, the transmission line technique needs an adequate thickness of the sample. An open-ended probe technique, which has been successfully commercialized, can measure over a wide frequency range with moderate accuracy, but the material sample must be sufficiently thick and the contact surface of the probe must be flat and free of air gaps.
In this methodology we propose to use a free space measurement technique used in RCS measurements and use the natural resonant frequency concepts to estimate the variation of the dielectric properties with time, and thereby relate to the physical characteristics of the fruit. What makes the problem challenging is that both the real and the imaginary parts of the dielectric constant for most frits is extremely high and even much greater than that of sea water! The variation of these electrical properties as a function of frequency will be described and how the singularity expansion method can be applied to estimate the variation of the natural resonant frequency of the various fruits as it ripens changing the sugar content with time will also be discussed.
In a free-space measurement technique, the amplitude and the phase of the returned probing signal are measured from a sample of interest which is placed between a transmitting and a receiving antenna. Thus, the measurement setup is quite complicated since one needs to measure both the magnitude and phase of the scattered signal. There have been attempts to simplify the measurement system. An interesting method is to omit the phase and measure only the reflection and the transmission coefficients instead.Subsequently, a coupled-dipole sensor using the magnitude of S_11 and S_21 has been developed.
This talk will provide an overview of the various measurement techniques and try to relate the electrical properties to the physical properties of the various fruits.
An Adhoc Wireless Communications Network to Monitor Fruits on Trees in a Rural Environment
A wireless sensor network plays an important role in various applications, e.g., surveillance, defense, environmental monitoring, rescue, etc., including agriculture. An example of interest is to apply this methodology for farm management and perform in-situ quality control of agricultural products.
For an effective design of a wireless communications system in a rural environment, measured channel characteristics are highly desirable. Much work has been conducted on characterizing propagation through foliage but very few of them are really applicable for characterizing a propagation channel under a tree canopy. Although the physical principles are not different from a conventional system characterization, but the details are significantly different. The channel model in an orchard and on a tree will be described including environmental effects. The obtained channel model enables the system designer install suitable antennas for wireless communications under a tree canopy.
Specifically, the use of a wireless sensor network for pre-harvesting control of fruits will be presented in this talk.
A Phased Array Consisting of Switched Beam Elements in Improving Channel Capacity
Due to a dramatic increase of users in any application, the channel capacity is always invariably insufficient. A number of techniques have been introduced to address this problem by reducing multipath fading, delay spread and co-channel interference. A smart antenna system; classified into diversity, switched-beam, and adaptive antennas are possible good candidates. However, a switched-beam antenna is interesting due to its simplicity and thus low cost.
A phased array of switched-beam elements (PASE) has been developed based on a circular array in which the elements are capable of beam switching. It has been applied for improving signal to interference ratio (SIR). Instead of using PIN diodes for beam switching in the elements, a probe switching methodology to the implementation simpler has been proposed.
This beam switching element has been further developed for dual band operation. To form a circular array of PASE, study on the mutual coupling has been conducted for appropriate feed design for the antennas. Along with the phased array concept the constant modulus algorithm (CMA) for fast convergence is proposed for further improving the rate of convergence. Recently, PASE has been proposed for angle of arrival (AOA) measurement and dual band PASE is introduced for dual band operation.
This talk describes the principle of PASE and illustrates some of its applications.
Prof. Yahia Antar
Department of Electrical and Computer Engineering
Royal Military College of Canada
PO Box 17000, Station Forces
Kingston, Ontario CANADA
K7K 7B4 email@example.com
Dr. Yahia Antar received the B.Sc. (Hons.) degree in 1966 from Alexandria University, and the M.Sc. and Ph.D. degrees from the University of Manitoba, in 1971 and 1975, respectively, all in electrical engineering.
In 1977, he was awarded a Government of Canada Visiting Fellowship at the Communications Research Centre in Ottawa where he worked with the Space Technology Directorate on communications antennas for satellite systems. In May 1979, he joined the Division of Electrical Engineering, National Research Council of Canada, Ottawa, where he worked on polarization radar applications in remote sensing of precipitation, radio wave propagation, electromagnetic scattering and radar cross section investigations. In November 1987, he joined the staff of the Department of Electrical and Computer Engineering at the Royal Military College of Canada in Kingston, where he has held the position of professor since 1990. He has authored or co-authored close to 200 journal papers, many chapters in books ,about 350 refereed conference papers, holds several patents, chaired several national and international conferences and given plenary talks at many conferences . He has supervised and co-supervised over 80 Ph.D. and M.Sc. theses at the Royal Military College and at Queen’s University, of which several have received the Governor General of Canada Gold Medal, the outstanding PhD thesis of the Division of Applied Science as well as many best paper awards in major international symposia. He served as the Chairman of the Canadian National Commission for Radio Science (CNC, URSI,1999-2008), Commission B National Chair (1993-1999),held adjunct appointment at the University of Manitoba, and, has a cross appointment at Queen's University in Kingston. He also serves, since November 2008, as Associate Director of the Defence and Security Research Institute (DSRI).
Dr. Antar is a Fellow of the IEEE (Institute of Electrical and Electronic Engineers), a Fellow of the Engineering Institute of Canada (FEIC), a Fellow of the Electromagnetic Academy, serves as an Associate Editor (Features) of the IEEE Antennas and Propagation Magazine, served as Associate Editor of the IEEE Transactions on Antennas and Propagation, IEEE AWPL, and was a member of the Editorial Board of the RFMiCAE Journal. He served on NSERC grants selection and strategic grants committees, Ontario Early Research Awards (ERA) panels, and on review panels for the National Science Foundation.
In May 2002, Dr. Antar was awarded a Tier 1 Canada Research Chair in Electromagnetic Engineering which has been renewed in 2009. In 2003 he was awarded the Royal Military College of Canada “Excellence in Research” Prize and in 2012 the Class of 1965 Teaching Excellence award. He was elected by the Council of the International Union of Radio Science (URSI) to the Board as Vice President in August 2008, and to the IEEE Antennas and Propagation Society Administration Committee in December 2009. On 31 January 2011, Dr Antar was appointed Member of the Canadian Defence Science Advisory Board (DSAB).
Dielectric Resonator Antenna for Wireless and Other Applications
Pioneering investigations with the dielectric resonator as a radiator date back to the work of Long and his associates in 1983. Since then many groups of researchers all over the world have been active in this area of research and have made remarkable advances during the last two decades. The main goals have been to explore efficient feeding techniques, methods to obtain wide and ultra wide impedance bandwidth, high gain, new geometrical shapes for improved features, etc. Indeed from the very beginning of DRA research, it has been regarded as a variant of the planar radiator like a microstrip patch , but compared to microstrip it is more advantageous in many aspects and also there are some disadvantages too. Some new efforts have also been made to integrate microstrip structures with a DRA to achieve better performances. As has been demonstrated, DRAs offer a high degree of flexibility and versatility over a wide frequency range allowing the designer to suit many requirements. Many new elements and arrays with attractive characteristics for wireless and other applications have been implemented and a description of some of these is included in the literature.
Even after many new developments and achievements, practical design, fabrication and implementation of these DRAs are still challenging in many cases. In recent years, more focus has been given to enhance antenna bandwidth efficiency and gain which are more relevant to the requirement of modern wireless applications. Many new techniques have been explored; most of them apply various composite and hybrid type structures. Furthermore, due to the mature technology of microwave and millimetre wave integrated circuits, on-chip DRAs have recently received a great deal of attention because they can be more efficient, reduce the size, weight and cost of many transmit and receive systems.
This presentation will address the basic fundamentals of DRAs, most recent development and research directions.
New Considerations for Antenna Electromagnetic Near Fields
This presentation focuses on introducing a new fundamental approach to some electromagnetic phenomena with particular focus on antenna systems. The theme chosen here is the near-field zone of electromagnetic radiation which is crucial and pertinent to the scientific understanding of how electromagnetic devices work and consequently is critical for product design and development. Starting with the familiar radiation expressions obtained from Maxwell’s equations, we proceed to build a new formulation of radiation and interaction, coupling and energy transfer, all at a general level. One of the main thrusts considered will be a look at possible future directions of research into new potentials for viewing and monitoring the structure of electromagnetic radiation. In particular, we will discuss new paths towards a deeper understanding of electromagnetic radiation that go beyond the usual measures of impedance parameters and radiation pattern. A new perspective on the origin of radiation in the near field zone will be introduced.
These new theoretical development start from the classical Wilcox and Weyl expansions in electromagnetic theory, where they are deployed in a new fashion in order to provide insights into the nature of electromagnetic radiation and antenna systems in particular. The conventional concepts of reactive and stored energies are revisited and formulated on a new basis that is general and comprehensive. As an example, a distinction between various genera of energy processes in the near field zone is proposed and verified by careful exposition of the physical content of the electromagnetic field viewed here as a moving quantum of energy. The theory leads naturally to new generalizations of the classical Poynting theorem in order to take into account the interaction between propagating and non-propagating modes, a topic that needs to be given more attention in both theoretical and applied electromagnetics. The formulation links the spatial (Wilcox) and spectral (Weyl) perspectives by deriving a new hybrid expansion and suggests possible organic connections between the far and near fields. Some of the applications of the near field theory involve an attempt to characterize and understand the phenomena of electromagnetic interactions and mutual coupling between various antenna/scatterer systems. It is hoped that this comprehensive rigorous theory for the near fields would help in providing new understanding and new mechanisms for dealing with some important phenomena in applied electromagnetics.
A Class of Printed Leaky Wave Antennas
Leaky wave antennas form one type of traveling wave antennas in which an aperture is illuminated by the fields of a traveling wave. Usually a leaky wave stems from a close guiding structure that supports traveling waves but has some means of continuous power leakage into the exterior region. The illuminated aperture extends over several wavelengths and is limited by wave attenuation caused by power leakage. In a typical leaky wave antenna structure, an incident mode travels inside a wave guiding structure with one of the sides allowing power leakage causing some perturbation to the propagating mode. Therefore, assuming propagation in the z direction, the mode longitudinal wave number bzs in a completely closed waveguide will be slightly changed to, say bz, and there appears, in addition an attenuation factor az. Therefore, a leaky mode is one having a complex wave number kz = bz – jaz, where bz is less than the free space wave number k0 rendering the leaky mode to be a fast wave. A leaky mode will radiate in a direction q given by q = sin-1(bz/k0). Since bz is a function of frequency, it follows that the radiation beam can be steered by frequency scanning between broadside and end fire. The beamwidth depends on the attenuation rate az. As az is reduced, the illuminated aperture extends over larger area resulting in higher directivity and lower beamwidth.
The basic properties of leaky wave antennas were founded in the pioneering work of Tamir and Oliner back in the early 1960s and later in the work of Jackson and Oliner. Recently, the need for high gain microstrip antennas has revived interest in leaky waves resulting in a great number of papers on printed leaky wave antennas also by Jackson and others. In here we discuss leaky waves and their supporting structures. We describe a leaky wave mathematically as a complex plane wave. The leaky mode supporting structure is treated as a perturbation of a closed waveguide. A planar antenna configuration with a partially reflecting screen will be studied in detail as an example of a leaky wave antenna structure. Another example of such a structure is a multilayered planar antenna with the capability of gain enhancement. Analysis of these two structures reveals the main properties of leaky wave antennas and provides some physical insight into their nature. In addition, we present practical designs of one-dimensional and two-dimensional leaky wave antennas that radiate fan-shaped beams and conical or pencil beams respectively, along with some planar feeding schemes.
Dept. of Electrical and Electronics Engineering
Director, Computational Electromagnetics Research Center (BiLCEM)
TR-06800 Bilkent, Ankara Turkey firstname.lastname@example.org
Levent Gürel (S'87-M'92-SM'97-F'09) received the B.Sc. degree
from the Middle East Technical University (METU), Ankara, Turkey,
in 1986, and the M.S. and Ph.D. degrees from the University of Illinois
at Urbana-Champaign (UIUC) in 1988 and 1991, respectively, all in
He joined the Thomas J. Watson Research Center of the International
Business Machines Corporation, Yorktown Heights, New York, in 1991,
where he worked as a Research Staff Member on the electromagnetic
compatibility (EMC) problems related to electronic packaging, on
the use of microwave processes in the manufacturing and testing
of electronic circuits, and on the development of fast solvers for
interconnect modeling. Since 1994, he has been a faculty member
in the Department of Electrical and Electronics Engineering of the
Bilkent University, Ankara, where he is currently a Professor. He
was a Visiting Associate Professor at the Center for Computational
Electromagnetics (CCEM) of the UIUC for one semester in 1997. He
returned to the UIUC as a Visiting Professor in 2003-2005, and as
an Adjunct Professor after 2005. He founded the Computational Electromagnetics
Research Center (BiLCEM) at Bilkent University in 2005, where he
is serving as the Director.
Prof. Gürel's research interests include the development of
fast algorithms for computational electromagnetics (CEM) and the
application thereof to scattering and radiation problems involving
large and complicated scatterers, antennas and radars, frequency-selective
surfaces, high-speed electronic circuits, optical and imaging systems,
nanostructures, and metamaterials. He is also interested in the
theoretical and computational aspects of electromagnetic compatibility
and interference analyses. Ground penetrating radars and other subsurface
scattering applications are also among his research interests. Since
2006, his research group has been breaking several world records
by solving extremely large integral-equation problems, most recently
the largest involving as many as 540 million unknowns.
Among the recognitions of Prof. Gürel's accomplishments, the
two prestigious awards from the Turkish Academy of Sciences (TUBA)
in 2002 and the Scientific and Technical Research Council of Turkey
(TUBITAK) in 2003 are the most notable.
He is a member of the USNC of the International Union of Radio
Science (URSI) and the Chairman of Commission E (Electromagnetic
Noise and Interference) of URSI Turkey National Committee. He served
as a member of the General Assembly of the European Microwave Association
(EuMA) during 2006-2008.
He is currently serving as an associate editor for Radio Science,
IEEE Antennas and Wireless Propagation Letters, Journal of Electromagnetic
Waves and Applications (JEMWA), and Progress in Electromagnetics
Prof. Gürel served as the Chairman of the AP/MTT/ED/EMC Chapter
of the IEEE Turkey Section in 2000-2003. He founded the IEEE EMC
Chapter in Turkey in 2000. He served as the Cochairman of the 2003
IEEE International Symposium on Electromagnetic Compatibility. He
is the organizer and General Chair of the CEM’07 and CEM’09
Computational Electromagnetics International Workshops held in 2007
and 2009, technically sponsored by IEEE AP-S.
Hierarchical Parallelization of the Multilevel Fast Multipole
It is possible to solve electromagnetics problems several orders
of magnitude faster by using MLFMA. Without exaggeration, this means
accelerating the solutions by thousands or even millions of times,
compared to the Gaussian elimination. However, it is quite difficult
to parallelize MLFMA. This is because of the already-too-complicated
structure of the MLFMA solver. Recently, we have developed a hierarchical
parallelization scheme for MLFMA. This novel parallelization scheme
is both efficient and effective. This way, we have been able to
parallelize MLFMA over hundreds of processors. By using distributed-memory
architectures, this accomplishment translates into an ability to
use more memory and to solve much larger problems than it was possible
before. Unlike previous parallelization techniques, with the novel
hierarchical partitioning strategy, the tree structure of MLFMA
is distributed among processors by partitioning both clusters and
samples of fields at each level. Due to the improved load-balancing,
the hierarchical strategy offers a higher parallelization efficiency
than previous approaches, especially when the number of processors
is large. We demonstrate the improved efficiency on scattering problems
discretized with millions of unknowns. We present the effectiveness
of our algorithm by solving very large scattering problems.
Solution of World’s Largest Integral-Equation Problems
Accurate simulations of real-life electromagnetics problems with
integral equations require the solution of dense matrix equations
involving millions of unknowns. Solutions of these extremely large
problems cannot be achieved easily, even when using the most powerful
computers with state-of-the-art technology. However, with MLFMA
and parallel MLFMA, we have been able to obtain full-wave solutions
of scattering problems discretized with hundreds of millions of
unknowns. Some of the complicated real-life problems (such as, scattering
from a realistic aircraft) involve geometries that are larger than
1000 wavelengths. Accurate solutions of such problems can be used
as reference data for high-frequency techniques. Solutions of extremely
large canonical benchmark problems involving sphere and NASA Almond
geometries will be presented, in addition to the solution of complicated
objects, such as metamaterial problems, red blood cells, and dielectric
photonic crystals. For example, by solving the world’s largest
and most complicated metamaterial problems (without resorting to
homogenization), we demonstrate how the transmission properties
of metamaterial walls can be enhanced with randomly-oriented unit
cells. Also, we present a comparative study of scattering from healthy
red blood cells (RBCs) and diseased RBCs with deformed shapes, leading
to a method of diagnosis of blood diseases based on scattering statistics
of RBCs. We will present solutions of extremely large problems involving
more than 500 million unknowns.
Novel and Effective Preconditioners for Iterative Solvers
Solutions of extremely large matrix equations require iterative
solvers. MLFMA accelerates the matrix-vector multiplications performed
with every iteration. Despite the acceleration provided by MLFMA,
the number of iterations should also be kept at a minimum, especially
if the dimension of the matrix is in the order of millions. This
is exactly where the preconditioners are needed. We have developed
several novel preconditioners that can be used to accelerate the
solution of various problems formulated with different types of
integral equations. For example, it is well known that the electric-field
integral equation (EFIE) is worse conditioned than the magnetic-field
integral equation (MFIE) for conductor problems. Therefore, the
preconditioners that we develop for EFIE are crucial for the solution
of extremely large EFIE problems. For dielectric problems, we formulate
several different types of integral equations to investigate which
ones have better conditioning properties. Furthermore, we develop
effective preconditioners specifically for dielectric problems.
In this talk, we will review three classes of preconditioners:
We will present our efforts to devise effective preconditioners
for MLFMA solutions of difficult electromagnetics problems involving
both conductors and dielectrics, such as the block-diagonal preconditioner
(BDP), incomplete LU (ILU) preconditioners, sparse approximate inverse
(SAI) preconditioners, iterative near-field (INF) preconditioner,
approximate MLFMA (AMLFMA) preconditioner, the approximate Schur
preconditioner (ASP), and the iterative Schur preconditioner (ISP).
Prof. Ari Sihvola
Aalto University, Department of Radio Science and Engineering
Box 13000, FIN-00076 Aalto
Ari Sihvola was born in 1957, in Valkeala (Finland). He received the degrees of Diploma Engineer in 1981, Licentiate of Technology in 1984, and Doctor of Technology in 1987, all in Electrical Engineering, from the Helsinki University of Technology (TKK), Finland. Besides working for TKK and the Academy of Finland, he was visiting engineer in the Research Laboratory of Electronics of the Massachusetts Institute of Technology, Cambridge, in 1985–1986, and in 1990–1991, he worked as a visiting scientist at the Pennsylvania State University, State College. In 1996, he was visiting scientist at the Lund University, Sweden, and for the academic year 2000–2001 he was visiting professor at the Electromagnetics and Acoustics Laboratory of the Swiss Federal Institute of Technology, Lausanne. In the summer of 2008, he was visiting professor at the University of Paris XI, France. Ari Sihvola is professor of electromagnetics in Aalto University School of Electrical Engineering (Aalto University was created in 2010 as a merger of three universities: Helsinki University of Technology, Helsinki School of Economics, and the University of Art and Design). His scientific interests range from electromagnetic theory, complex media, materials modeling, remote sensing, and radar applications, into engineering education research and history engineering and technology. Ari Sihvola is Chairman of the Finnish National Committee of URSI (International Union of Radio Science), Vice Chairman of the Commission B (Fields and Waves) of the international URSI, and Fellow of IEEE. In 1990’s, he has served as Chairman of the IEEE AP–MTT Chapter for several years. He was awarded the five-year Finnish Academy Professor position in 2005–2010. He is also director of the Finnish Graduate School of Electronics, Telecommunications, and Automation (GETA). Author of several books and hundreds of publications, Ari has been active in organizing conferences and workshops, convening and chairing sessions, and serving in advisory, technical, and organizing committees for numerous national and international scientific symposia as member, secretary, or chairman. In TKK and Aalto University, Ari Sihvola has received several teaching awards, like the “Teacher of the Year” Prize in 1995 from the Student Union of TKK.
Characterization and Effective Description of Heterogeneous and Composite Electromagnetic Materials
In the analysis of electromagnetic fields interacting with material structures, the response of medium is condensed in dielectric and magnetic material parameters, like permittivity, conductivity, and permeability. In complicated and anisotropic media, these material parameters may need to be generalized from scalar quantities into matrices, or equivalently dyadics. The complicated response of materials is very often of structural origin, in other words the manner in which a heterogeneous mixture is formed determines its macroscopic electromagnetic material parameters. This lecture deals with the variety of ways how one is able to characterize and effectively describe the macroscopic dielectric and magnetic behavior of composite materials with given properties of the constituents and the geometrical microstructure. The rich history of homogenization of mixtures will be reviewed, including Clausius−Mossotti, Lorenz−Lorentz, Maxwell Garnett, Bruggeman, and other homogenization principles, and their ranges of applicability will be assessed. Mixing principles will be applied to mixtures that display very interesting properties that differ strongly from those of the constituent materials, like, for example, aqueous, strong-contrast, lossy, plasmonic, chiral, and bianisotropic mixtures.
Boundary Conditions and Extreme-Parameter Materials in Electromagnetics
In electromagnetics, the distinction between a boundary and an interface is fundamental. It is essential to emphasize the difference between these two concepts because very often in applied electromagnetics and in metamaterials studies, confusions exist. One often hears the question: “What is the material behind the surface on which a boundary condition is assumed?” The answer is, of course, that such a question is meaningless: nothing in the space on the other side of the boundary affects the fields in the domain of interest. On a boundary of a given spatial domain, electromagnetic fields have to be forced to satisfy a certain boundary condition in order to uniquely determine the field solutions. An interface problem is fundamentally different: the fields in the two domains have an interaction through tangential continuity conditions across the interface. The boundary–interface issue has a special significance in metamaterials studies where quite often the focus is on media with extreme constitutive parameters. Even if the boundary problem is different from the interface problem, they can be approximations or idealizations of each other. However, here it is important to keep clear what is the starting point and what is the approximation. Sometimes the interface problem is approximated by a boundary problem, which idealizes the situation and hence simplifies the analysis. The complementary procedure is a synthetic approach, where the boundary problem is primary and the question is how to construct and synthesize a real-world material structure that would best approximate the starting-point situation with the ideal boundary. In this lecture, I focus on this important distinction and show how well certain boundary conditions and complex surfaces can be simulated by material structures.
Philosophy of Metamaterials and Metasystems
Metamaterials have entered into the mainstream of electromagnetics, high-frequency engineering, and materials science research within a relatively short period. Even if the rapid progress in this field owes very much to earlier studies, it has managed to find a distinct profile and visibility within the first decade of the 21st century. Seminars, workshops, sessions, and even congresses dedicated to metamaterials are being organized, and the journal Metamaterials, published by Elsevier, runs already its sixth yearly volume (in 2012). Several books on the topic have appeared during the latest years. The potential for applications of metamaterials in the nanoscale, by manipulation of optical waves, has given rise to the field of metatronics. The prominence of metamaterials research wave is affecting the way electromagnetics problems and questions are approached even to the extent that one may talk about a metamaterials paradigm in research. The essential property in metamaterials is their unusual and desired qualities that appear due to their particular design and structure. These advantageous properties are not straightforward linear functions of the constituents from which the metamaterial is built up. A sample of metamaterial is more than a sum of its parts, analogously to the taste of ice-cream, which is not a direct sum of the flavors of ice and cream. Taking a more general perspective, we may observe that in the field of electromagnetic materials, there are several examples of media that fully deserve to be labeled metamaterials. Chiral (spatial-parity-breaking structures) materials, artificial magnetism, magnetoelectric materials, percolation processes, extremely anisotropic media, and other special media are complex enough to fall in the category of metamaterials. This lecture discusses fundamental issues associated with metamaterials, like possibilities to find a unique definition for them, the spatial scales and geometrical constellations for which one can talk meaningfully about metamaterials, and meta-type characterization of engineering structures and systems in general.
Mats Gustafsson received the M.Sc. degree in Engineering Physics in 1994, the Ph.D. degree in Electromagnetic Theory in 2000, was appointed Docent in 2005, and Professor of Electromagnetic Theory 2011, all from Lund University, Sweden.
He co-founded the company Phase holographic imaging AB in 2004. His research interests are in scattering and antenna theory and inverse scattering and imaging with applications in microwave tomography and digital holography. He has written over 60 peer reviewed journal papers and over 75 conference papers.
Prof. Gustafsson received the best antenna poster prize at EuCAP 2007 and the IEEE Schelkunoff Transactions Prize Paper Award 2010.
Convex Optimization for Analysis of Small Antennas
Design of small antennas is challenging as the Q-factor, efficiency, and radiation resistance must be controlled simultaneously. In this presentation, it is shown that convex optimization together with closed form expressions of the stored electromagnetic energies provide a general method for analyzing many fundamental antenna problems. The solution to the convex optimization problem determines optimal currents, offers insight for antenna design, and presents performance bounds for antennas.
We present optimization formulations for the maximal gain Q-factor quotient, minimal Q for superdirectivity, and minimal Q for given far field. The effects of antennas embedded in metallic structures and effects of losses are also discussed. Results are shown for various antenna geometries and compared to state of the art designs. It is also shown that many antennas perform almost optimally. A tutorial description of a method of moment implementation together with a Matlab package for convex optimization to determine optimal current distributions on arbitrarily shaped antennas is also presented.
Sum Rules and Physical Bounds in Electromagnetics
Sum rules can be used to construct physical bounds on many types of physical systems. The physical bounds answer questions like; what is the minimal temporal dispersion of passive metamaterials, how does the thickness influence the performance of absorbers and high-impedance surfaces, how does the inter-element coupling affect frequency selective surfaces, how does the bandwidth and directivity depend on the size of antennas, and what is the available bandwidth in extra-ordinary transmission of electromagnetic waves through sub-wavelength apertures. These types of identities and bounds are of great interest in many areas of physics and engineering. They also provide insight into the relationship between design parameters. The mathematical analysis is based on integral identities for Herglotz (or positive real) functions. These integral identities are referred to as sum rules and generalize the classical Kramers-Kronig dispersion relations to physical systems satisfying the underlying principles of linearity and passivity.
In the talk, we present the mathematical background based on time domain passive systems, Herglotz (or positive real) functions, and integral identities (sum rules) for passive systems. We analyze and present physical bounds for; broadband matching, radar absorbers, high-impedance surfaces, temporal dispersion of metamaterials, sub-wavelength scatterers, extraordinary transmission, and small antennas. We also compare the theoretical results with state of the art designs.
Near-field Diagnostics of Antennas and Radomes
Visualization of electromagnetic field and currents facilitates our understanding of the interaction between fields and devices. This is easily done in numerical simulations where the electromagnetic fields can be computed directly. It is much harder in most measurement situations where the fields cannot be measured directly and must instead be reconstructed from measurements of the fields outside the object or volume of interest. This reconstruction requires the solution of an inverse source problem. Reconstructions of field and current distributions are useful in applications such as non-destructive diagnostic of antennas and radomes and assessment of specific absorption ration (SAR) in the human body due to base station radiation.
In this presentation, we show how the field and current distribution can be reconstructed and visualized from near- and far-field measurement data. We illustrate how they can be used in antenna and radome diagnostics to, for example, identify faulty components. We discuss recent developments in inverse source problems to accurately reconstruct electromagnetic fields on a surface or volume from near- and far-field measurements. We review the theory for inverse source problems, non-uniqueness, and regularization. We present formulations based on equivalent currents using integral equations and integral representations for planar, spherical, body of revolution, and general geometries.
Prof. Ahmed Kishk
Department of Electrical and Computer Engineering
1455 De Maisonneuve Blvd. West, EV 005.139
Montreal, QC, Canada H3G 1M8
Dielectric Resonator Antennas
The dielectric resonator antenna (DRA) is made from high dielectric constant materials and mounted on a ground plane or on a grounded dielectric substrate of lower permittivity. DRAs have many attractive features such as small size, high radiation efficiency, wide bandwidth, and high power capability that make them attractive for radar applications and base stations. An overview for the development of the dielectric resonator antennas will be given to provide understanding of dielectric resonator characteristics, operation, and design. DRA arrays characteristics are provided with discussion on the mutual coupling level and the wide scanning capabilities. Finally, several examples of DRA for wideband, multifunction applications, and proposed new application of embedded DRA in energy harvesting environments.
Dielectric Resonator Antenna Arrays Excited by Waveguide Slots and Probes
Excitation of dielectric resonator antennas (DRAs) using rectangular waveguide slots and probes is studied. A method of moments (MoM) procedure is used to analyze a single DRA element as a first step. For slot excitation, transverse, longitudinal and tilted slots are considered and prove to be a weak coupling mechanism to DRAs, thus can be used for large arrays. Probe excitation, however, exhibits the possibility of strong coupling to the DRA with the proper choice of the design parameters, and thus a wide matching bandwidth can be achieved. An equivalent circuit model for both excitation mechanisms is developed to facilitate the extension of the study from the single element to the array. A simple design procedure for the array is developed based on the circuit model and the array performance is studied. Results show that the developed analysis and design tools give accurate predictions of the element and array return loss and radiation patterns.
UWB Antennas for Wireless Communication and Detection Applications
Ultra-wide band (UWB) wireless communication occupies a bandwidth from 3.1 to 10.6 GHz, referred to as UWB band, to achieve high data rate over a short distance. Two competing schemes, namely multiband orthogonal frequency division multiplexing (MB-OFDM) and direct sequence ultra wide band (DS-UWB), were proposed to make use of the allocated bandwidth. Ideally, a transmitting/receiving UWB antenna pair comprising a communication channel should operate as a band-pass filter covering the UWB band and have a flat magnitude response and a linear phase response with frequency. It requires an UWB antenna well matched, with frequency independent phase center, and linearly increasing gain with frequency over the entire UWB band.
An omnidirectional UWB antenna is especially attractive to wireless communications at either base station or terminal side. For an omnidirectional UWB antenna, besides the aforementioned three requirements, its radiation performances over the UWB band should also be independent of the azimuth angle. A good impedance matching over the UWB band is not difficult, and many types of antenna can achieve that. Frequency independent phase center is achievable for most antennas except for those with multi-resonant structure spatially separated. But, after the first three requirements are met, a wideband omnidirectional radiation is still challenging for UWB antenna design. Omnidirectional UWB antennas with a non-planar conducting structure as well as DRA are presented for an UWB access point.
Another recently addressed problem is the interference problem with the WLAN bands. To prevent interference problems due to existing nearby communication systems within an Ultra-wideband operating frequency, the significance of an efficient band notched design is increased. Two novel antennas are presented. One antenna is designed for one band-notch. The second antenna is designed for dual band-notches
Several UWB antennas with unidirectional patterns are presented for detection applications. Dielectric resonator is used to tremendously shrink an UWB antenna’s size to be used as a sensor for breast cancer detection and microwave imaging. Another 3D conducting self-grounded Bow-Tie sensor is presented. The application of such a DR UWB antenna for thro-wall radar detection is also investigated showing better performance as compared to the Vivaldi antenna.
EM Modeling ofArtificial Magnetic Conductors
The term soft and hard surfaces is recently used with surfaces based on the direction of propagation along the surface. Soft surfaces are long been used in horn antennas as transverse corrugations to improve the radiation characteristics. A grounded dielectric slab loaded with transverse metallic strips can realize also soft surfaces. Longitudinal corrugations or longitudinal strips can realize hard surfaces. Such surfaces have recently found some applications and relation with the electromagnetic band gap surfaces (EBG) and artificially magnetic conducting surfaces (AMC). The analysis of these surfaces using exact boundary conditions is tedious and sometimes is limited to certain geometrical constraint when periodicity has to be analyzed using Floquet modes. Recently, simplified boundary conditions have been developed to analyze such surfaces. Such boundary conditions remove the geometrical restrictions and able the analysis of complex surfaces with different types. These asymptotic boundary conditions are used under the condition that the structure period is very small compared to the wavelength and ideally when the period approaches zero. Three types of asymptotic boundary conditions are considered. The asymptotic strips boundary conditions (ASBC) to be used with strips loaded surfaces. The asymptotic corrugations boundary conditions (ACBC) to be used with corrugated surfaces. The third type can be used with strips or corrugations under the assumption of ideal soft or hard conditions. The surfaces can be model as periodic surface of perfect electric conducting strip (PEC) attached to a perfect magnetic conducting strip (PMC). This boundary condition is referred to as PEC/PMC surface. Also, the classical model of surface impedance boundary condition can be used with some of these surfaces.
A review related to these boundary conditions will be given. We will show the implementation of these boundary conditions in method of moments (MoM) based on surface integral equations and the finite difference time domain method (FDTD). The advantages of using the asymptotic boundary conditions will be illustrated. The relation between the soft surfaces and the electromagnetic band gap (EBG) surfaces will be discussed. We will present several examples of applications such as compact horn antennas with soft or hard surfaces, reduction of blockage from cylindrical objects and others applications.
A newly developed guiding structure will be presented, which is based on the properties of the AMC with low loss. Also, a demonstration of using AMC in packaging microwave circuits will be presented.
Analysis and Design of Wideband Dielectric Resonator Antenna Arrays for Waveguide-Based Spatial Power Combining
Dielectric resonator antennas (DRAs) have attractive features such as small size, high radiation efficiency, wide bandwidth, and high power capability. These advantages made them attractive for use in different applications. Probe-fed dielectric resonator antenna arrays in an oversized dielectric loaded waveguide with hard horn excitation are investigated for their use in waveguide-based spatial power combining systems. The horn excitation could be considered as a space fed network for the dielectric resonators. A design of thin walled hard waveguide and hard horns are presented to provide uniform field distribution to provide uniform excitations for the array inside the hard structure. Design procedures for the special power combiner using the DRA are presented. The design starts from a single DRA inside a hard waveguide. A single dielectric resonator antenna element excited by a coaxial probe is analyzed first inside a hollow rectangular waveguide and a TEM waveguide to show the needs for the hard waveguide (TEM waveguide) to provide the uniform field distribution. Then, one-dimensional dielectric resonator antenna arrays are studied inside the H-plane sectoral hard horns. An entire spatial power combining system with a two-dimensional dielectric resonator antenna array is analyzed inside a hard pyramidal horn. The analysis of the entire system is based on the finite-difference time-domain method with region-by-region discretization and sub gridding schemes. All these designs are constructed by the student using very limited resources. Simulation results are compared with measurement results and show good agreement.
Another design of wideband dielectric resonators system is analyzed and tested as a special power combiner. Use of the special power combiner as a space feed for a radiating array will also be considered. As still open research area hints for possible future work will be provided.
Study of SIW Circuits Using an Efficient Hybrid Method
As the substrate integrated waveguide (SIW) is constructed by emulating the solid side walls of the waveguide using two rows of metal posts, the thin wire approximations for these posts are found to be inadequate and the current variations around the posts must be considered. A numerical modeling for the posts as cylinders is found to be more realistic, but that presents a numerical burden in the analysis. Therefore, a two-dimensional efficient full wave method is developed to analyze non radiating SIW circuits. The method combines the cylindrical eigenfunction expansion and the method of moments to avoid geometrical descretization of the posts. The formulations for an SIW circuit printed on either homogeneous or inhomogeneous substrate are presented. With the ability to model inhomogeneous substrate, the cylindrical eigenfunction expansions are used to model the inhomogeneity. Therefore, circuits with metal and/or dielectric posts are analyzed. This facilitates designs of filters based on SIW structures are designed with metallic or dielectric resonators embedded inside the substrate. The talk also covers the microstrip-to-SIW transition and the speed-up technique for the simulation of symmetrical SIW circuits. Different types of SIW circuits will be presented using the proposed method.
Wideband Dually Polarized Microstrip Air Patch Antennas and Dielectric Resonator Antennas
For today’s communication, wide frequency band, low cross-polarization and high isolations are required for dually polarized antennas. In this presentation, several designs for air patches, Huygens’ source antenna, and dielectric resonator antennas are presented. Several excitation techniques are presented to achieve wideband width and high isolations. Bandwidths between 25-50% are achieved with isolation between 30-40dB.
Ahmed A. Kishk received the BS degree in Electronic and Communication Engineering from Cairo University, Cairo, Egypt, in 1977, and BSc. in Applied Mathematics from Ain-Shams University, Cairo, Egypt, in 1980. In 1981, he joined the Department of Electrical Engineering, University of Manitoba, Winnipeg, Canada, where he obtained his M.Eng and PhD degrees in 1983 and 1986, respectively. From 1977 to 1981, he was a research assistant and an instructor at the Faculty of Engineering, Cairo University. From 1981 to 1985, he was a research assistant at the Department of Electrical Engineering, University of Manitoba. From December 1985 to August 1986, he was a research associate fellow at the same department. In 1986, he joined the Department of Electrical Engineering, University of Mississippi, as an Assistant Professor. He was on sabbatical leave at Chalmers University of Technology, Sweden during the 1994-1995and 2009-2010 academic years. He was a Professor at the University of Mississippi (1995-2011). He was the director of the Center of Applied Electromagnetic System Research (CAESR) during the period, 2010-2011. Currently he is a Professor at Concordia University, Montréal, Québec, Canada (since 2011) as Tier 1 Canada Research Chair in Advanced Antenna Systems. He was an Associate Editor of Antennas & Propagation Magazine from 1990 to 1993. He is now an Editor of Antennas & Propagation Magazine. He was a Co-editor of the special issue, “Advances in the Application of the Method of Moments to Electromagnetic Scattering Problems,” in the ACES Journal. He was also an editor of the ACES Journal during 1997. He was an Editor-in-Chief of the ACES Journal from 1998 to 2001. He was the chair of Physics and Engineering division of the Mississippi Academy of Science (2001-2002). He was a guest Editor of the special issue on artificial magnetic conductors, soft/hard surfaces, and other complex surfaces, on the IEEE Transactions on Antennas and Propagation, January 2005. He was a technical program committee member in several international conferences.
His research interest includes the areas of design of Dielectric resonator antennas, microstrip antennas, small antennas, microwave sensors, RFID antennas for readers and tags, Multi-function antennas, microwave circuits, EBG, artificial magnetic conductors, soft and hard surfaces, phased array antennas, and computer aided design for antennas. Design of millimeter frequency antennas; Feeds for parabolic reflectors. He has published over 220-refereed Journal articles and 380 conference papers. He is a coauthor of four books and several book chapters and editor of one book. He offered several short courses in international conferences.
Dr. Kishk and his students are the recipient of many awards. Dr. Kishk received the 1995 and 2006 outstanding paper awards for papers published in the Applied Computational Electromagnetic Society Journal. He received the 1997 Outstanding Engineering Educator Award from Memphis section of the IEEE. He received the Outstanding Engineering Faculty Member of the Year on 1998 and 2009, Faculty research award for outstanding performance in research on 2001 and 2005. He received the Award of Distinguished Technical Communication for the entry of IEEE Antennas and Propagation Magazine, 2001. He also received The Valued Contribution Award for outstanding Invited Presentation, “EM Modeling of Surfaces with STOP or GO Characteristics – Artificial Magnetic Conductors and Soft and Hard Surfaces” from the Applied Computational Electromagnetic Society. He received the Microwave Theory and Techniques Society Microwave Prize 2004. Dr. Kishk is a Fellow of IEEE since 1998, Fellow of Electromagnetic Academy, and Fellow of the Applied Computational Electromagnetic Society (ACES). He is a member of Antennas and Propagation Society, Microwave Theory and Techniques, Sigma Xi society, U.S. National Committee of International Union of Radio Science (URSI) Commission B, Phi Kappa Phi Society, Electromagnetic Compatibility, and Applied Computational Electromagnetics Society.
Dr. Christophe Caloz
Professor, Electrical Engineering
Canada Research Chair
École Polytechnique de Montréal
Building Lassonde, Office M6025
2500, ch. de Polytechnique
Montréal (Québec), H3T 1J4, Canada email@example.com
Metamaterials: Past, Present and Future
In the history of humanity, scientific progress has frequently been associated with the discovery of novel substances or materials. Metamaterials represent a recent incarnation of this evolution. As suggested by their prefix “meta”, meaning “beyond” in Greek, metamaterials (artificial materials owing their properties to sub-wavelength but supra-atomic scatterers) even transcend the frontiers of nature, to offer unprecedented properties with far-reaching implications in modern science and technology.
This talk presents some research highlights in electromagnetic metamaterials over the past decade, with emphasis on applications providing performances or functionalities that outperform state-of-the-art technologies. The first part of the talk reviews some history, principles and properties of metamaterials from a global perspective. The second part presents a series of microwave metamaterial applications exploiting these properties, in particular negative refraction, near-zero index propagation, coupling amplification, full-space scanning leakage radiation, and agile temporal and spatial dispersions. This part culminates with the introduction of the concept of radio real-time signal processing, enabled by “phasers” (components with fully designable group delay versus frequency responses), which might play a central role in tomorrow’s radio. The third part introduces magnet-less non-reciprocal metamaterials (MNMs), which have been recently invented and developed in the speaker’s group. While non-reciprocal gyrotropic materials, first reported by Faraday in 1845, have always required a biasing magnet to date, MNMs, which are composed of transistor-loaded rings mimicking electron-spin precession in ferrites, only require a biasing voltage, and are therefore fully compatible with semiconductor technology. This new class of metamaterials might therefore be considered a breakthrough and seem to have a strong potential for commercial electronic and photonic applications. Finally, the talk explores perspectives for next-generation of metamaterials, which will arguably be muli-scale (micro, nano, atomic) and multi-substance (e.g. semiconductors, ferroelectrics, magnetic nanoparticles, multiferroics, carbon nanotubes, graphene, etc.) in nature.
Leaky-Wave Antennas: the Dawn of a New Era!
Leaky-wave antennas (LWAs) have a history of over 70 years. This history started with a patent on a leaky slit waveguide by Hansen in 1940, and the field was then really developed in the late 1950ies and 1960ies by the Brooklyn Polytechnic (now NYU Poly) microwave group, involving Oliner, Tamir and Hessel. Since then, much LWA research has then been carried out by various groups around the world. However, despite some of their unique features, LWAs have been plagued by fundamental issues that have limited their utilization in practical systems. These issues have been recently solved, bringing us to the doorstep of a new area in LAWs.
The unique benefits of LWAs is that they provide high directivity and (frequency or electronic) beam scanning with much smaller form factor, lower cost and higher gain than antenna arrays, as they do not require a complex feeding network. In uniform LWAs, these benefits are annihilated by the restriction of forward-only scanning. Periodic LWAs have been capable of radiating both in forward and backward directions, using leaky space harmonics, since their introduction by Rotman in the late 1950ies. However, their aforementioned LWA benefits have been countered by the collapse of the radiation efficiency at broadside. A definite solution to this persistent issue came in 2002 with the advent of metamaterial Composite Right/Left-Handed (CRLH) LWAs, the first LWAs capable of efficient full-space scanning, which made LWAs potentially superior to arrays. The secrets for this long sought solution were revealed by the groups of D. R. Jackson and of the speaker over the past decade, and then extended to non-metamaterial LWAs: 1) presence of two resonators in the unit cell, 2) closure of the open-stop band by mutual cancellation of the two resonances, 3) satisfaction of a Heaviside-like condition to equalize gain through broadside. Moreover, fundamental relations between the (transverse and longitudinal) symmetries of the periodic unit cell and the LWA properties were recently unveiled by the speaker and collaborators at the University of Duisburg, providing prescriptions completing the broadside radiation ones for most efficient and diverse LWA designs. The talk first overviews historical milestones, explains the physics of LWAs (including their fundamental connection with the Smith-Purcell effect in particle physics) and provides basic electromagnetic tools for their analysis. Next, it presents and illustrates the solution to the broadside radiation issue as well as the unit cell symmetry rules. Finally, it demonstrates a number of novel concepts, structures, systems and applications, including active LWA beam forming, gain enhancement via power recycling, LWA direction-of-arrival estimation, non-reciprocal LWA diplexers, direction diversity enhanced MIMO systems, smart reflectors, graphene-tunable THz antennas, real-time spectrogram analyzers, and vortex beam launchers for orbital angular momentum multiplexing.
Radio Analog Signal Processing for Tomorrow’s Radio
Today's exploding demand for faster, more reliable and ubiquitous wireless connectivity poses unprecedented challenges in radio technology. To date, the predominant approach has been to put increasing emphasis on digital signal processing (DSP). However, while offering device compactness and processing flexibility, DSP suffers of fundamental limitations, such as poor performance above the K band, high-cost A/D conversion, low processing speed and high power consumption.
Recently, Radio Analog Signal Processing (R-ASP) has emerged as a novel paradigm to potentially overcome these issues, and hence address the aforementioned challenges. R-ASP processes radio signals in their pristine analog form and in real time, using “phasers”. A phaser is a temporally – and sometimes also spatially – dispersive electromagnetic structure whose group delay is designed so as to exhibit the required (quasi-arbitrary) frequency function to perform a desired operation, such as for instance real-time Fourier transformation. Phasers can be implemented in Bragg-grating, chirped-waveguide, magnetostatic-wave and acoustic-wave technologies. However, much more efficient phasers, based on 2D/3D metamaterial structures and cross-coupled resonator chains, were recently introduced, along with powerful synthesis techniques. These phasers can manipulate the group delay of electromagnetic waves with unprecedented flexibility and precision, and thereby enable a myriad of applications in communication, radar, instrumentation and imaging, with superior performance or/and functionality. This talk presents an overview of R-ASP technology, including dispersion-based processing principles, historical milestones, phasing fundamentals, phaser synthesis, and many applications.
Graphene, a monolayer of carbon atoms arranged in a honeycomb lattice, is the first truly two-dimensional material ever produced by humanity. For this reason, and also due to its exceptional mechanical, thermal, chemical and electronic properties, it won Geim and Novoselv the Nobel Prize in Physics in 2010, only 6 years after their first experimental report on the topic. Since then, this Holy Grail material has spurred huge interest in both the scientific and engineering communities, with over 1000 papers published per month on graphene related topics.
In the area of electronics, during its first lustrum (starting in 2004), graphene research was mostly focused on transport devices (transistors, mixers, switches, etc.), exploiting the high mobility and ambipolarity of the material for higher performance or functionality. However, many researchers have recently directed their attention to the potential of graphene for electromagnetics, due to the discovery of novel phenomena and to the recent availability of large area graphene sheets. One of the key interests in this area graphene’s capability to provide tunable material properties via simple or patterned electrostatic gating. Moreover, fascinating and unprecedented effects occur when the graphene is immersed in a static magnetic field, in which case the electron and hole charge carriers are drawn into cyclotron orbits described by a tensorial conductivity. This area may be called graphene magneto-plasmonics, as graphene essentially behaves as a two-dimensional electron or hole gas. At microwaves, graphene is a transparent conductor whose phase difference between the right-handed and left-handed circularly polarized eigenstates is so significant that electromagnetic waves traveling across it experience giant Faraday rotation, with the possibility of voltage-induced Faraday reversal based on ambipolarity. This phenomenon enables a diversity of unique Faraday devices, such as gyrators, isolators, non-reciprocal radomes and perfect electromagnetic boundaries. At terahertz frequencies, graphene supports tunable surface magneto-plasmons with exotic properties, such as for instance directional concentration and splitting counter-propagating modes, strongly depending on the nature of doping (chemical or electrical). These magneto-plasmons might pave the way for efficient non-reciprocal terahertz electromagnetic components, which are critically missing today. The talk first recalls the fundamentals of graphene and describes some key electronic applications. Next, it introduces magneto-plasmonics, and sequentially presents the microwave Faraday rotation and the terahertz surface magneto-plasmonic phenomenology and applications. Finally, it discusses some multi-scale and multi-physics metamaterial structures involving graphene as a gyrotropic element.
Localized Waves or Molding Electromagnetic Waves
Localized waves (LW), also sometimes called non-diffractive waves or non-diffractive beams, are currently spurring revived interest in the radio and optical communities. A LW is characterized by a strong confinement of the field on a distance that is proportional to the size of the radiating aperture. LWs are solutions to the wave equation. There exist a great diversity of LWs, exhibiting various and fascinating properties. For instance, Bessel LWs exhibit a Bessel constant cross section, vortex LWs feature spiral wave fronts, i.e. carry orbital angular momentum (OAM), which may be applied to OAM multiplexing or particle tweezing, X-LWs are pulsed Bessel waves, of order larger than one and also carrying OAM, that may be designed to produce superluminal centroids, and Airy LWs are accelerated beams, following prescribed curved trajectories.
Until recently, LWs have been mostly restricted to theoretical studies, and have been little exploited in practical applications. However, technological progress in optics technology, where LWs are generally produced by sophisticated spatial light modulators, has brought the area of LWs to the forefront of the stage. At microwave, millimeter-wave and terahertz frequencies, other approaches are required to generate LWs. However, two promising roads – metasurfaces and, more recently, leaky-wave antennas – have been recently opened to meet this new challenge. Moreover, the group of the speaker has introduced two systematic techniques to synthesize metasurfaces producing arbitrary LWs within the limits of the laws of physics: a spatial technique, based on electromagnetic boundary conditions and providing the metasurface susceptility and polarizablities, and a spectral technique, based on the conservation of the total wave momentum and providing the metasurface transfer function in phase and magnitude; the latter includes a reverse propagator technique which allows to control LWs are an arbitrary distance from the source. The talk will first present the fundamentals of LWs and describe some of the most common LWs. It will next introduce the aforementioned spatial and spectral synthesis techniques, and demonstrate their unprecedented capabilities via several examples of exotic waves existing either in the Fresnel region or in the Frauenhofer region of the aperture. Then, a number of metasurface and antenna implementations and applications will be presented. Applications pertaining to communications, security, sensing, imaging, spectroscopy biotechnology, nanotechnology, and astronomy will be presented or discussed.
Christophe Caloz received the Diplôme d'Ingénieur en Électricité and the Ph.D. degree from École Polytechnique Fédérale de Lausanne (EPFL), Switzerland, in 1995 and 2000, respectively. From 2001 to 2004, he was a Postdoctoral Research Fellow at the Microwave Electronics Laboratory, University of California at Los Angeles (UCLA). In June 2004, Dr. Caloz joined École Polytechnique of Montréal, where he is now a Full Professor, the holder of a Canada Research Chair (CRC) in Metamaterials and the head of the Electromagnetics Research Group. He has authored and co-authored over 500 technical conference, letter and journal papers, 12 books and book chapters, and he holds many patents. His works have generated over 11,000 citations. In 2009, he co-founded the company ScisWave, which develops CRLH smart antenna solutions for WiFi. Dr. Caloz received several awards, including the UCLA Chancellor’s Award for Post-doctoral Research in 2004, the MTT-S Outstanding Young Engineer Award in 2007, the E.W.R. Steacie Memorial Fellowship in 2013, the Prix Urgel-Archambault in 2013, and many best paper awards with his students at international conferences. He is an IEEE Fellow. His research interests include all fields of theoretical, computational and technological electromagnetics, with strong emphasis on emergent and multidisciplinary topics, including particularly metamaterials, nanoelectromagnetics, exotic antenna systems and real-time radio.
Prof. Steven Gao
Chair of RF and Microwave Engineering
School of Engineering and Digital Arts
University of Kent
Canterbury CT2 7NZ
Low-Cost Smart Antennas Abstract
Smart antennas are the key technology for wireless communications and radars. They can adjust their radiation patterns adaptively, i.e., forming maximum radiation towards the desired users and nulls towards the interference sources. Thus, they can improve the capacity of wireless communication networks significantly, increase the spectrum efficiency and reduce the transmit power. Traditionally, smart antennas are, however, too complicated, bulky, heavy and expensive for civil applications. For commercial applications, it is very important to reduce the cost, size, mass and power consumption of smart antennas.
This lecture will first give an introduction to smart antennas and their types such as passive and active phased arrays, digital beamforming smart antennas, adaptive arrays, multi-beam antennas, beam-switching antennas, multiple inputs and multiple outputs (MIMO) antenna systems, etc. The basic principles of each type of smart antennas will be explained. The advantages and disadvantages of each type of smart antennas will be highlighted.
The lecture will then describe different types of low-cost smart antenna technologies, such as Electrically-Steerable Parasitic Array Radiator (ESPAR) antenna, compact MIMO antennas, beam-switching array antennas and low-cost phased arrays. Many practical examples of antenna configurations and designs will be shown, explained and their performance discussed. These will include folded-monopole ESPAR (FM-ESPAR) for wireless communications, high-gain ESPAR using small director array, small-size MIMO, beam-switching reflectarray antennas for satellite communications, low-cost phased array antennas, etc.
Space Antennas Abstract
Due to the special environment of space and the launch vehicle dynamics to get there, spacecraft antenna requirements and designs are quite different from those of terrestrial antennas. Onboard a satellite, there are a number of different antennas and arrays for various functions, such as Telemetry, Tracking and Command (TT&C), high-speed data downlink, GPS navigation and positioning, remote sensing, inter-satellite links, deep-space communications, etc. Since the launching of 1st man-made satellite “Sputnik” in 1957, a large variety of antennas and arrays have been developed for space applications and the antennas employ different frequency bands including UHF/VHF, L, S, C, X, Ku, Ka and V band.
This lecture will first explain the satellites, orbits, the space environment and special requirements of space antennas. Different types of satellites and orbits will be explained. Space environments such as extreme thermal conditions, materials outgassing, radiation environment, multipaction effects, passive inter-modulation, corona phenomenon, electro-static charging, atomic oxygen, etc, will be discussed and their impact on the antenna designs will be explained. Other issues, e.g., the interactions amongst antennas, satellite bodies and solar panels, will also be described. Key challenges for space antenna designs will be illustrated.
The lecture will then provide an overview of space antennas developed for different applications. This part will show many examples of the real-world space antennas for different applications such as TTC, navigations, high-speed data downlink, GPS reflectometry remote sensing, inter-satellite links, deep-space communications, etc. The operating principles of each antenna will be explained and their performance will be discussed. Finally, an outlook to the future development of space antennas will be presented.
Multi-Band Antennas for Global Navigation Satellite Systems (GNSS) Receivers Abstract
Global Navigation Satellite System (GNSS) is a satellite based radio navigation system that provides precise information about the spatial coordinates (longitude, latitude and altitude) of an object anywhere on the earth or in the air. Global Positioning System (GPS) is the single fully operational navigation system available for commercial and military users around the globe while Galileo, GLONASS and COMPASS (European, Russian and Chinese respectively) are in the development stage with GLONASS operating with partial capability. GNSS operates at different frequency bands including L1, L2, L5, E5, etc. The use of a compact multi-band antenna instead of multiple single-band antennas can reduce the size, mass and cost of GNSS receivers significantly. During recent years, a variety of multi-band antennas have been developed for GNSS receivers.
This lecture will give an introduction to the GNSS system and the antenna design requirements for GNSS receivers. Various issues such as multipath mitigation, phase center stability, compact size, multi-band operation, etc, will be discussed. Techniques of multipath mitigation such as choke rings, electromagnetic-band-gap (EBG) antennas, etc, will be presented and their principles will be explained.
The lecture will then give a review of compact multi-band antennas and arrays for GNSS receivers. Many examples of GNSS antenna designs will be shown, and the antenna configurations and design principles will be explained. These will include the dual-band multipath mitigating GNSS antenna using the cross plate reflector ground plane (CPRGP), multi-band QHA antennas, active multi-band antennas, small multi-band GNSS array antennas, high-gain beam-switching multi-band GNSS arrays, etc. The performance of each antenna will be described.
Antennas for Synthetic Aperture Radars Abstract
Synthetic aperture radars (SAR) is an imaging radar which produces high resolution radar images of the earth’s surface by using microwave signals. Unlike optical sensors which are limited by day lights and weather conditions, SAR can be used day and night and can see through clouds. SAR has important wide-ranging applications for earth observations in remote sensing and mapping of the surfaces of both the Earth and other planets. SAR is used in various fields of research ranging from oceanography, geology, to archaeology. Antenna for SAR is usually very complicated and expensive. SAR antenna is often one of the most expensive components onboard the aircraft or spacecraft.
This lecture will first give an introduction to SAR systems and how SAR works. Key parameters of SAR systems such as range resolution, azimuth resolution, frequency bands, etc, will be explained. Different SAR modes such as stripmap, scanSAR, spotlight and interferometric SAR (InSAR) will be described. SAR system design considerations and key challenges for SAR antenna designs will also be presented.
The lecture will then provide a review of antennas for SAR. An overview of antenna development for space-borne SAR will be illustrated and some examples will be given. The design principles of each example antenna will be explained and their performance discussed. Finally the lecture will give a discussion of future development such as the digital beam-forming SAR for satellite constellations, etc.
Steven (Shichang) Gao was born in Anhui, P.R. China. He received a PhD from Shanghai University, China, in 1999. He is a Professor and Chair of RF and Microwave Engineering at School of Engineering and Digital Arts, University of Kent, UK. His research covers antennas, smart antennas, phased arrays, space antennas, RF/microwave and mm-wave circuits and systems, satellite communications, synthetic-aperture radars, UWB radars and GNSS receivers.
He started his career at China Research Institute of Radiowave Propagation in 1994-1996. Afterwards, he worked as a Post-doctoral Research Fellow at National University of Singapore in 1999-2001, a Research Fellow at Birmingham University (UK) in 2001-2002, a Senior Lecturer (2002-2006), Reader (2006-2007) and Head of Active Antenna and RF Group (2002-2007) at Northumbria University (UK) and a Senior Lecturer and Head of Space Antennas and RF System Group (2007-2012) at Surrey Space Center, University of Surrey, UK. Also he was a Visiting Scientist at Swiss Federal Institute of Technology (ETHZ, Switzerland) in 2003, a Visiting Professor at University of California at Santa Barbara (US) in Jan-July 2005, and a Visiting Fellow at Chiba University (Japan) in Aug-Sept 2005 and June-July 2013. Since Jan. 2013, he joined the University of Kent as a Full Professor and became a Chair of RF and Microwave Engineering since Feb. 2014.
He is General Co-Chair of Loughborough Antennas and Propagation Conference (LAPC), UK, 2013, and Chair of Special Session on “Satellite Communication Antennas” in IEEE/IET International Symposium on Communication Systems and Networks, 2012, etc. He is a Guest Editor of IEEE Transactions on Antennas and Propagation for a Special Issue on "Antennas for Satellite Communication"(Feb. 2015 issue). He is an Invited Speaker at IWAT'2014 (Sydney, 2014), SOMIRES'2013 (Japan, 2013), APCAP'2014 (Harbin, 2014), etc. He is an Associate Editor of Radio Science and also the Editor-in-Chief of Wiley Book Series in Microwave and Wireless Technologies. He is a Fellow of Institute of Engineering and Technology (IET), UK.
He has two book including Space Antenna Handbook (Wiley, 2012, co-editors: Imbriale and Boccia) and Circularly Polarized Antennas (Wiley-IEEE Press, 2014, co-authors: Luo and Zhu), published over 180 technical papers, 10 book chapters and holds three patents in smart antennas and RF. He received "URSI Young Scientist Award”, 2002, “JSPS Fellowship Award”, Japan, 2005, “Best Paper Award”, LAPC, UK, 2012, “JSPS Fellowship Award”, Japan, 2013, etc. He has been a leader and principal investigator of a number of research projects in areas of smart antennas for satellite communications on the move, space antennas, compact-size low-cost smart antennas for wireless communications, phased arrays for synthetic aperture radars, active integrated antennas for mobile communications, millimeter-wave antennas arrays, high-efficiency RF/microwave power amplifiers, UWB radars, GNSS receiver front end, adaptive small-size multi-band antennas for mobile phones, etc.
Prof. Qing Huo Liu Department of Electrical and Computer Engineering
Durham, NC 27708, USA firstname.lastname@example.org
Multiscale Computational Electromagnetics and Applications
Electromagnetic sensing and system-level design problems are often multiscale and very challenging to solve. They remain a significant barrier to system-level sensing and design optimization for a foreseeable future. Such multiscale problems often contain three electrical scales, i.e., the fine scale (geometrical feature size much smaller than a wavelength), the coarse scale (geometrical feature size greater than a wavelength), and the intermediate scale between the two extremes. Most existing commercial solvers are based on single methodologies (such as finite element method or finite-difference time-domain method), and are unable to solve large multiscale problems. We will present our recent work in solving realistic multiscale system-level EM design simulation problems in time domain. The discontinuous Galerkin method is used as the fundamental framework for interfacing multiple scales with finite-element method, spectral element method, and finite difference method. Numerical results show significant advantages of the multiscale method.
Subsurface Sensing and Super-Resolution Imaging: Application of Computational Acoustics and Electromagnetics
Acoustic/seismic and electromagnetic waves have widespread applications in geophysical subsurface sensing and imaging. In these applications, often the problems of understanding the underlying wave phenomena, designing the sensing and imaging measurement systems, and performing data processing and image reconstruction require large-scale computation in acoustics and electromagnetics. It is very challenging to solve such problems with the traditional finite difference and finite element methods. In this presentation, several high-performance computational methods and super-resolution imaging in acoustics and electromagnetics will be discussed along with their applications in oil exploration and subsurface imaging.
Progress and Challenges in Microwave Imaging and Microwave Induced Thermoacoustic Tomography
Breast cancer imaging by microwaves bas been investigated intensively over the past two decades due to the potentially high contrasts in permittivity and conductivity between malignant tumors and normal breast tissue. In comparison with the conventional ultrasound imaging where the acoustic impedance contrast between malignant tumors and normal breast tissue is low (typically a few percent), the dielectric contrast is indeed one to two orders of magnitude higher. Nevertheless, progress toward a clinically mature system for microwave breast imaging is painfully slow, primarily due to the low resolution of microwaves that can provide adequate penetration only at a relatively low frequency. We will describe challenges in achieving such a system, and ways to improve the resolution of microwave imaging. In the meantime, recent progress in microwave induced thermoacoustic tomography (MITAT) provides a new impetus for combining microwave and ultrasound modalities. In MITAT, we use millisecond-pulsed microwaves to produce ultrasound through thermal expansion, thus the induced ultrasound source represents the high contrast in electrical conductivity, while the collected ultrasound signals provide the high resolution corresponding to a short wavelength of ultrasound. We will describe our recent progress in both microwave imaging and MITAT, in both computational methods and system development.
Spectral Element Method for Nanophotonics
Nanophotonics is a major technological frontier with numerous new applications. However, a significant challenge in design optimization of nanophotonic devices is the huge computational costs in large-scale simulations. Advances in high-precision, high-efficiency computational methods will have significant impact on this emerging area. In this presentation, we will discuss our recent efforts to improve the methods for computational electromagnetics in nanophotonics. Particular topics will include the spectral-element method and spectral integral method in frequency domain for Maxwell's equations with applications in photonic crystals and plasmonics, and for nonlinear effects such as second harmonic generation. We use the spectral element method in the frequency domain for the simulation of nonlinear optical effects and the associated second harmonic generation (SHG). In most materials the SHG effect is weak in general because their nonlinear optical coefficients are usually small. Moreover, as optical materials are usually dispersive, there is a phase mismatch between the fundamental frequency and second harmonic fields, further weakening the SHG effect. With our accurate and efficient computational method, we design an air-bridge multiple layer photonic crystal slab based on the structure of GaAs/AlAs distributed Bragg reflector. We show that the SHG effect can be enhanced by ten orders of magnitude.
Qing Huo Liu (S’88-M’89-SM’94-F’05) received his B.S. and M.S. degrees in physics from Xiamen University in 1983 and 1986, respectively, and Ph.D. degree in electrical engineering from the University of Illinois at Urbana-Champaign in 1989. His research interests include computational electromagnetics and acoustics, and their applications in inverse problems, geophysics, nanophotonics, and biomedical imaging. He has published over 230 refereed journal papers and 300 conference papers in conference proceedings. His H index is 42 and has been cited over 7000 times (Google Scholar). He was with the Electromagnetics Laboratory at the University of Illinois at Urbana-Champaign as a Research Assistant from September 1986 to December 1988, and as a Postdoctoral Research Associate from January 1989 to February 1990. He was a Research Scientist and Program Leader with Schlumberger-Doll Research, Ridgefield, CT from 1990 to 1995. From 1996 to May 1999 he was an Associate Professor with New Mexico State University. Since June 1999 he has been with Duke University where he is now a Professor of Electrical and Computer Engineering.
Dr. Liu is a Fellow of the IEEE, a Fellow of the Acoustical Society of America. Currently he serves as the Deputy Editor in Chief of Progress in Electromagnetics Research, an Associate Editor for IEEE Transactions on Geoscience and Remote Sensing, and an Editor for the Journal ofComputational Acoustics. He was recently a Guest Editor in Chief of the Proceedings of the IEEE for a 2013 special issue on large-scale electromagnetics computation and applications. He received the 1996 Presidential Early Career Award for Scientists and Engineers (PECASE) from the White House, the 1996 Early Career Research Award from the Environmental Protection Agency, and the 1997 CAREER Award from the National Science Foundation.
Using Model-Based Parameter Estimation to Increase the Efficiency and Effectiveness ofComputational Electromagnetics Abstract
Science began, and largely remains, an activity of making observations and/or collecting data about various phenomena in which patterns may be perceived and for which a theoretical explanation is sought in the form of mathematical prescriptions. These prescriptions may be non-parametric, first-principles generating models (GMs), such as Maxwell’s equations, that represent fundamental, irreducible descriptions of the physical basis for the associated phenomena. In a similar fashion, parametric fitting models (FMs) might be available to provide a reduced-order description of various aspects of the GM or observables that are derived from it. The purpose of this lecture is to summarize the development and application of exponential series and pole series as FMs in electromagnetics. The specific approaches described here, while known by various names, incorporate a common underlying procedure that is called model-based parameter estimation (MBPE).
MBPE provides a way of using data derived from a GM or taken from measurements to obtain the FM parameters. The FM can then be used in place of the GM for subsequent applications to decrease data needs and computation costs. An especially important attribute of this approach is that windowed FMs overlapping over the observation range make it possible to adaptively minimize the number of samples needed of an observable to develop a parametric model of it to a prescribed uncertainty. Two specific examples of using MBPE in electromagnetics are the modeling of frequency spectra and far-field radiation patterns. An MBPE model of a frequency response can provide a continuous representation to a specified estimation error of a percent or so using 2 or even fewer samples per resonance peak, a procedure sometimes called a fast frequency sweep, an example of which is shown below. Comparable performance can be similarly achieved using MBPE to model a far-field pattern. The adaptive approach can also yield an estimate of the data dimensionality or rank so that the FM order can be maintained below some threshold while achieving a specified FM accuracy. Alternatively, the data rank can be estimated from singular-value decomposition of the data matrix. FMs can be also be used to estimate the uncertainty of data while it is being generated or data that is pre-sampled that is being used for the FM computation. Topics to be discussed include: a preview of model-based parameter estimation; fitting models for waveform and spectral data; function sampling and derivative sampling; adaptive sampling of frequency spectra and far-field patterns; and using MBPE to estimate data uncertainty.
Conductance and susceptance of a fork monopole having unequal length arms from NEC and an MBPE model using a frequency sample and 4 frequency derivatives at the 2 different wavelengths (WLs) shown by the solid circles.
An Exploration of Radiation Physics
All external electromagnetic fields arise from the process of radiation. There would be no radiated, propagated or scattered fields were it not for this phenomenon. In spite of this self-evident truth, our understanding of how and why radiation occurs seems relatively superficial from a practical viewpoint. It’s true that physical reasoning and mathematical analysis via the Lienard-Wiechert potentials show that radiation occurs due to charge acceleration. It’s also true that it is possible to determine the near and far fields of rather complex objects subject to arbitrary excitation, making it possible to perform analysis and design of EM systems. However, if the task is to determine the spatial distribution of radiation from the surface of a given object from such solutions, the answer becomes less obvious.
One way to think about this problem might be to ask, were our eyes sensitive to X-band frequencies and capable of resolving source distributions a few wavelengths in extent, what would be the image of such simple objects as dipoles, circular loops, conical spirals, log-periodic structures, continuous conducting surfaces, etc. when excited as antennas or scatterers? Various kinds of measurements, analyses and computations have been made over the years that bear on this question. This lecture will summarize some relevant observations concerning radiation physics in both the time and frequency domains for a variety of observables, noting that there is no unanimity of opinion about some of these issues. Included in the discussion will be various energy measures related to radiation, the implications of Poynting-vector fields along and near wire objects, and the inferences that can be made from far radiation fields. Associated with the latter, a technique developed by the author called FARS (Far-field Analysis of Radiation Sources) will be summarized and demonstrated in both the frequency and time domains for a variety of simple geometries. Also to be discussed is the so-called E-field kink model, an approach that illustrates graphically the physical behavior encapsulated in the Lienard-Wiechert potentials as illustrated below. Brief computer movies based on the kink model will be included for several different kinds of charge motion to demonstrate the radiation process.
Depiction of the E-field lines for an initially stationary charge (a) that's abruptly accelerated from the origin to a speed v = 0.3c to then coast along the positive x-axis until time t1 (b) when it is abruptly stopped (c).
Verification and Validation of Computational Electromagnetics Software
For the past several decades, a computing-resource of exponentially expanding capability now called computational electromagnetics (CEM) has grown into a tool that both complements and relies on measurement and analysis for its development and validation, The growth of CEM is demonstrated by the number of computer models (codes) available and the complexity of problems being solved attesting to its utility and value. Even now, however, relatively few available modeling packages offer the user substantial on-line assistance concerning verification and validation. CEM would be of even greater practical value were the verification and validation of the codes and the results they produce be more convenient. Verification means determining that a code conforms to the analytical foundation and numerical implementation on which it is based. Validation means determining the degree to which results produced by the code conform to physical reality. Validation is perhaps the most challenging aspect of code development especially for those intended for general-purpose application where inexperienced users may employ the codes in unpredictable or inappropriate ways.
This presentation discusses some of the errors, both numerical an example of which is shown below, and physical, that most commonly occur in modeling, the need for quantitative error measures, and various validation tests that can be used. A procedure or protocol for validating codes both internally, where necessary but not always sufficient checks of a valid computation can be made, and externally, where independent results are used for this purpose, is proposed. Ideally, a computational package would include these capabilities as built-in modules for discretionary exercise by the user. Ways of comparing different computer models with respect not only to their efficiency and utility, but also to make more relevant intercode comparisons and to thereby provide a basis for code selection by users having particular problems to model, are also discussed. The kinds of information that can be realistically expected from a computer model and how and why the computed results might differ from physical reality are considered.A procedure called “Feature Selective Validation” that has received increasing attention in the Electromagnetic Compatibility Community as a means of comparing data sets will be summarized. The overall goal is to characterize, compare, and validate EM modeling codes in ways most relevant to the end user.
The magnitude of the finely sampled induced tangential electric field along the axis (the current is on the surface) of a 2.5-wavelength, 50-segment wire 10-3 wavelengths in radius modeled using NEC. For the antenna case (the solid line) the two 20-V/m source segments are obvious as are the other 48 match points (the solid circles) whose values are generally on the order of 10-13 or less. For the scattering problem, the scattered E-field (the dashed line) is graphically indistinguishable from the incident 1 V/m excitation except near the wire ends. The IEMF and far-field powers for the antenna are 1.257x10-2 w and 1.2547x10-2 w, respectively. For the scattering problem, the corresponding powers are 5.35x10-4 and 5.31x10-4 watts.
Two Novel Approaches to Antenna-Pattern Synthesis
The design of linear arrays that produce a desired radiation pattern, i.e. the pattern-synthesis problem, continues to be of interest as demonstrated by the number of articles that continue to be published on this topic. A wide variety of approaches have been developed to deal with this problem of which two are examined here. One of them, a matrix-based method, begins with a specified set of element currents for a chosen array geometry. A convenient choice, for example, is for all of the current elements to be of unit amplitude. Given its geometry and currents, an initial radiation pattern for the array can be computed. A matrix is constructed whose individual coefficients are comprised of the contribution each element current makes to the various lobe maxima of this initial radiation pattern. Upon forming the product of the inverse of this matrix with a vector whose entries are the desired amplitudes of each maxima in the radiation pattern to be synthesized, a second set of element currents is obtained. The lobe maxima of the pattern that this second set of element currents generates usually change somewhat in angle relative to those of the initial pattern while their amplitudes will also not match those specified. The process is repeated as an iterative sequence of element-current and pattern computations. When the locations of the lobe maxima no longer change in angle and their maxima converge to the values specified the synthesis is complete. Results from this approach are demonstrated for several patterns an example of which follows below.
The pattern of a 15-element array synthesized to have a pattern increasing monotonically in 5 dB steps from left to right.
The second approach is based on a pole-residue model for an array whose element locations (the poles) and currents (the residues) are developed from samples of the specified pattern. One way of solving for the poles and residues is provided by Prony’s Method, and another is the Matrix-Pencil procedure. However found, the spacing between the array elements derived using such tools can in general be non-uniform, a potential advantage in reducing the problem of grating lobes. There are three parameters that need to be chosen for the pattern sampling: 1) the number of poles in the initial array model, for each of which two pattern samples are required; 2) the spacing of the pattern samples themselves, being required to be in equal steps of , with the observation angle from the array axis; and 3) the total pattern window that is sampled. The pattern rank is an important parameter as it establishes the minimum number of elements that are needed for the array, and can be determined from the singular-value spectrum of the matrix developed from the pattern samples. The pole-residue approach is summarized and various examples its use are also demonstrated.
Some Computational “Tricks of the Trade”
Numerical computations have become ubiquitous in today’s world of science and engineering, not least of which is the area of what has come to be called computational electromagnetics. Students entering the electromagnetics discipline are expected to have developed a working acquaintance with a variety of numerical methods and models at least by the time they reach graduate studies, if not earlier in their undergraduate education. Most will have obtained some experience with the broader issues involved in numerically solving differential and integral equations. However, there are a variety of specialized numerical procedures that contribute to the implementation and use of numerical models that are less well known, and which form the basis for this lecture. Among such procedures are:
1) Acceleration techniques (e.g., Shank’s method, Richardson extrapolation, Kummer’s method) that enable estimating an answer for an infinite series or integral using many fewer terms;
2) Adaptive techniques such as one based on Romberg quadrature that permit more efficient numerical evaluation of integrals;
3) Model-based techniques that can reduce the number of samples needed to estimate a transfer function or radiation pattern.
4) “Backward” recursion that develop classical functions from noise together with an auxiliary condition.
5) Ramanujan’s modular-function formula for Pi whose accuracy increases quartically with each increase in the computation order.
This lecture will survey some of these procedures from the perspective of their applicability to computational electromagnetics. A specific example of an acceleration technique is the Leibniz series for pi, which provides N-digit accuracy after summing approximately 10N terms. Shank’s method, on the other hand provides N-digit accuracy after N terms of the Leibniz series as shown in the triangle array below.
A Personal Retrospective on 50 Years of Involvement in Computational Electromagnetics
This presentation briefly reviews some selected aspects of the evolution and application of the digital computer to electromagnetic modeling and simulation from a personal perspective. First considered are some of the major historical developments in computers and computation, and projections for future progress. Described next are some of the author’s personal experiences in computer modeling and electromagnetics resulting from his research activities in industry, government laboratories and academia dating from introduction of the IBM 7094. Some aspects of the impact that computer modeling has had more generally on the discipline of computational electromagnetics (CEM) is then summarized. Issues of potential interest not only to CEM but also to scientific computing in general are then briefly considered. These include: 1) verification and validation of modeling codes and their outputs; 2) the importance of statistics and visualization as computer models become larger and more complex; and 3) some issues related to first-principles or micro-modeling and reduced-order or macro-modeling of physical observables and their connection with signal processing. Various illustrative examples are shown to demonstrate some of these issues with the talk concluding with a few personal remarks.
The growth of computer speed in FLOPs/sec since 1953. The cross marks the time of the author’s first involvement in computational electromagnetics.
Evolution of the Digital Computer and Computational Electromagnetics Abstract
The development and evolution of the digital computer is a fascinating and still-unfolding story. This presentation briefly surveys this fascinating topic beginning with the origin of numbers and mathematics and concluding with present and anticipated future capabilities of computers in terms of their impact on computational electromagnetics (CEM). Numerous intellectual and technological breakthroughs over millennia have contributed to the current state-of-art. The development of arithmetic and computing might be said to begin with an ability to count. The first “recorded” number that has been found, a slash mark on the fibula of a baboon and apparently signifying the number 1 is about 20,000 years old. Counting and numbers eventually followed some 15,000 years later due to the Babylonians who invented the abacus as the first calculating tool at about the same time that the Egyptians introduced the first known symbols for numbers using a base-10 system. The number zero appeared about 500 CE in India with fractions and negative numbers coming a little later as did the Arabic number system, also credited to India.
It was about a thousand years later that the appearance of the first computational device beyond the abacus occurred, the “Pascaline” invented by Pascal for addition and subtraction in 1642. Leibniz added the capability for multiplication and division in 1671 with the “Leibniz wheel” which is still used in electromechanical calculators. Related computational developments include the invention by de Vaucanson of the punched wooden card for controlling a special loom that was later perfected by Jacquard. Babbage proposed his “difference” engine for calculating tables in 1822, followed in 1833 by his “analytical” engine, the first programmable computer. Punched cards were first used in a numerical setting by Hollerith for the 1890 US census with his company becoming part of IBM in 1911. The light bulb and the “Edison effect” began the electronics revolution with Fleming’s and De Forest’s work leading to the first triode in 1906.
The computer revolution began in earnest in the 1930s with a series of electromechanical computers due to Vennevar Bush at MIT, Konrad Zuse in Germany, and Howard Aiken with the IBM Mark 1. The latter was used during World War II for computing artillery-firing tables. The first all electric computer was built at Iowa State College by Atanasoff and Berry in 1939 and the first all electronic computer, Colossus, was developed in 1943-1944 in Britain for code breaking on a project headed by Alan Turing. A series of “AC” or “automatic computers” followed, such as ENIAC, EDSAC, ILLIAC I, ORDVAC, EDVAC and UNIVAC. The first transistor-based system, the IBM 7090, was introduced in 1959 with the IBM 7094 using ferrite-core memory following a few years later.
The onset of CEM can probably be said to date to the 1940’s using electromechanical calculators. These were still being used as late as 1960 at the Radiation Laboratory at the University of Michigan for computing tables of special functions and related quantities. The IBM 704 and 7094 soon took over this role that the author exploited in developing a computational thesis from 1963 to 1965. A special issue of the IEEE Proceedings in 1965 highlighted EM computations with the moment method popularized by the Harrington book in 1968. What were once considered “big” problems in the 1960’s using an integral-equation model having 200 or so unknowns have expanded to millions of unknowns now, even on personal computers, with an expanding set of tools and models. The growth rate in performance from the UNIVAC until now has been one of unparalleled progress, by a factor of 10 every 5 years. If this were to continue until 2053, computing speed will have grown to ~1023 FLOPS! ensuring a commensurate impact on CEM.
From the abacus to the IBM 7094 and beyond.
Since earning his PhD in Electrical Engineering at the University of Michigan, E. K. Miller has held a variety of government, academic and industrial positions. These include 15 years at Lawrence Livermore National Laboratory where he spent 7 years as a Division Leader, and 4+ years at Los Alamos National Laboratory from which he retired as a Group Leader in 1993. His academic experience includes holding a position as Regents-Distinguished Professor at Kansas University and as Stocker Visiting Professor at Ohio University. Dr. Miller wrote the column “PCs for AP and Other EM Reflections” for the AP-S Magazine from 1984 to 2000. He received (with others) a Certificate of Achievement from the IEEE Electromagnetic Compatibility Society for Contributions to Development of NEC (Numerical Electromagnetics Code) and was a recipient (with others) in 1989 of the best paper award given by the Education Society for “Computer Movies for Education.”
He served as Editor or Associate Editor of IEEE Potentials Magazine from 1985 to 2005 for which he wrote a regular column “On the Job,” and in connection with which he was a member of the IEEE Technical Activities Advisory Committee of the Education Activities Board and a member of the IEEE Student Activities Committee. He was a member of the 1992 Technical Program Committee (TPC) for the MTT Symposium in Albuquerque, NM, and Guest Editor of the Special Symposium Issue of the IEEE MTT Society Transactions for that meeting. In 1994 he served as a Guest Associate Editor of the Optical Society of America Journal special issue “On 3 Dimensional Electromagnetic Scattering.” He was involved in the beginning of the IEEE Magazine "Computing in Science and Engineering" (originally called Computational Science and Engineering) for which he has served as Area Editor or Editor-at-Large. Dr. Miller has lectured at numerous short courses in various venues, such as Applied Computational Electromagnetics Society (ACES), AP-S, MTT-S and local IEEE chapter/section meetings, and at NATO Lecture Series and Advanced Study Institutes.
Dr. Miller edited the book "Time-Domain Measurements in Electromagnetics", Van Nostrand Reinhold, New York, NY, 1986 and was co-editor of the IEEE Press book Computational Electromagnetics: Frequency-Domain Moment Methods, 1991. He was organizer and first President of the Applied Computational Electromagnetics Society (ACES) for which he also served two terms on the Board of Directors. He served a term as Chairman of Commission A of US URSI and is or has been a member of Commissions B, C, and F, has been on the TPC for the URSI Electromagnetic Theory Symposia in 1992 and 2001, and was elected as a member of the US delegation to several URSI General Assemblies. He is a Life Fellow of IEEE from which he received the IEEE Third Millennium Medal in 2000 and is a Fellow of ACES. His research interests include scientific visualization, model-based parameter estimation, the physics of electromagnetic radiation, validation of computational software, and numerical modeling about which he has published more than 150 articles and book chapters. He is listed in Who's Who in the West, Who's Who in Technology, American Men and Women of Science and Who's Who in America.
Dr. Sudhakar Rao
Technical Fellow, Engineering & Global Products Division
Northrop Grumman Aerospace Systems
1 Space Park Drive, Mail Stop: ST70AA/R9
Redondo Beach, CA 90278, USA
Advanced Antenna Systems for Satellite Communication Payloads Abstract
Recent developments in the areas of antenna systems for FSS, BSS, PCS, & MSS satellite communications will be discussed. System requirements that drive the antenna designs will be presented initially. Advanced antenna system designs for contoured beams, multiple beams, and reconfigurable beams will be presented. Shaped reflector antenna designs, multi-aperture reflector antennas for multiple beams, multi-band reflector antennas, reconfigurable antennas, phased array systems, and lens antennas will be discussed in detail. Design examples of direct broadcast satellites (DBS) covering national and local channels will be given. Topics such as antenna designs for high capacity satellites, large deployable mesh reflector designs, low PIM designs, and power handling issues will be included. High power test methods for the satellite payloads will be addressed. Future trends in the satellite antennas will be discussed. At the end of this talk, engineers will be exposed to typical requirements, designs, hardware, and test methods for various satellite antenna designs.
Feed Elements and Feed Assemblies for Space Applications Abstract
This talk presents various types of feed elements used for space applications. The first part of the talk discusses various feed elements suitable for space applications. These include feeds for reflectors, radars, phased arrays, global horns, and TT&C Omni-coverage feeds. Typical radiation patterns, scan performance, and design constraints will be presented along with hardware examples. The second part deals with the feed networks that go behind the radiating elements and includes OMTs, polarizers, filters/diplexers, combiners/dividers etc. Integrated design, analysis, and manufacture methods will be discussed. High power and PIM analysis and test methods will be discussed during the talk. Recent advances in the feed assembly design for low-loss and low cross-polar applications will be presented with examples. Feed elements suitable for array antennas and phased array systems for space applications will be discussed including practical examples.
Sudhakar K. Rao received B.Tech degree in electronics & communications from Jawaharlal Nehru Technological University, Warangal in 1974, M.Tech in Radar Systems Engineering from Indian Institute of Technology, Kharagpur in 1976, and Ph. D in Electrical Engineering from Indian Institute of Technology, Madras in 1980. During the period 1976-1977 he worked as a Technical officer at Electronics Corporation of India Limited, Hyderabad on large reflector antennas for LOS and TRPO microwave links, and during the period 1980-1981 he worked in the Electronics and Radar Development Establishment, Bangalore as a Senior Scientist and developed phased array antennas for airborne applications. He worked as a post-doctoral fellow at University of Trondheim, Norway during 1981-1982 and then as a research associate at University of Manitoba during 1982-1983. During1983-1996, he worked at Spar Aerospace Limited, Montreal, Canada, as Staff Scientist and developed advanced antennas for satellite communications. From 1996-2003 he worked as Chief Scientist/Technical Fellow at Boeing Satellite Systems and developed multiple beam antennas and reconfigurable beam payloads for commercial and military applications. During the period 2003-2010, he worked as a Corporate Senior Fellow at Lockheed Martin Space Systems and developed antenna payloads for fixed satellite, broadcast satellite, and personal communication satellite services. He is currently a Technical Fellow at Northrop Grumman Aerospace Systems, Redondo Beach, CA working on advanced antenna systems for space and aircraft applications. He authored over 160 technical papers and has 41 U.S patents. He co-edited three text book volumes on “Handbook of Reflector Antennas and Feed Systems” that are published in June 2013 by the Artech House.
Dr. Rao became an IEEE Fellow in 2006 and a Fellow of IETE in 2009. He received several awards and recognitions that include 2002 Boeing’s Special Invention Award for series of patents on satellite antenna payloads, 2003 Boeings’ technical achievement award, Lockheed Martin’s Inventor of Technology award in 2005 & 2007, IEEE Benjamin Franklin Key Award in 2006, Delaware Valley Engineer of the Year in 2008, and Asian American Engineer of the year award in 2008. He received IEEE Judith Resnik Technical Field Award in 2009 for pioneering work in aerospace engineering.