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Ahmed Kishk

ahmed

Prof. Ahmed Kishk
Department of Electrical and Computer Engineering
Concordia University
1455 De Maisonneuve Blvd. West, EV 005.139
Montreal, QC, Canada H3G 1M8
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Dielectric Resonator Antennas Abstract 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 Abstract 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 Abstract 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 of Artificial Magnetic Conductors
Abstract
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
Abstract
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
Abstract
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
Abstract
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.

Biography
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.