Ahmed A. Kishk - US grants

This Research Initiation Award project will study the electromagnetic scattering and radiation from impedance surfaces in the presence of dielectric materials and analyze some new antennas and scatterers. The proposed study will be based on the use of the surface integro-differential equations to generate different formulations. While exact boundary conditions will be applied on the dielectric surfaces, the concept of the impedance boundary conditions will be introduced on the impedance surfaces. The use of this concept provides the means for modeling different surface types of practical significance such as complex composite objects. The solution will be carried out numerically using the method of moments. The solution accuracy will be established through comparison with other available analytical and numerical results as well as new experimental data. Many problems will be investigated such as the internal resonance problem. The proposed approach is particularly useful in studying the radiation and scattering from axisymmetric complex composite objects such as the new microslab antenna. the microslab antenna is similar to the microstrip one except that the conducting patch is replaced by a physically thin disc of high dielectric constant to reduce the conduction losses from the radiating conducting patch. The study of the radiation characteristics of microslab antennas will be carried out numerically and experimentally. Different excitation techniques are also under consideration for economic use in the phased array antennas.

In this project it is proposed to investigate the characteristics of dielectric resonator radiating structures. Antennas comprising dielectric material are expected to be more efficient and more economical in the high microwave frequency range than are microstrip and similar metal antennas. The circular dielectric disk radiator will serve as the fundamental radiating element for the study, but other configurations, such as the use of several layers of dielectric to make the element suitable for use over an increased range of frequencies, may also be investigated to better understand the effects of various parameters on the performance of the antenna. Rigorous numerical modeling of the dielectric structure will be based on the Surface Integral Equation Formulation, but other numerical methods such as the Finite Integration Technique will also be used where appropriate. Precision measurements will consist of radiation pattern, radiation efficiency, and input impedance investigations, and will serve to validate the theoretical results obtained for various configurations. Different excitation methods for the conductorless dielectric resonator antenna, as well as different antenna configurations, will be analyzed. The three investigators will cover the numerical aspects, the electromagnetic system aspects, and the experimental aspects of the conductorless antennas.

9809862
Kishk

The Deparment of Electrical Engineering at The University of Mississippi will purchase a mircorwave receiver which will be dedicated to support research on antennas and scatterers. The equipment will be used to pursue studies of new, innovative antennas for several research projects, including studies of dielectric resonator antennas, cylindrical wire antenna scatterers in multi-layeted media, antenna for a ground coupled radar, and meander and spiral antennas for wireless communication.
RF and Microwave technology has been used and is being proposed for a variety of military and commercial applications based on the rapid growth of wireless and personal communication usage. The availability of reasonably priced components and propagation characteristics in the RF and GHz. range are, however, contributing factors for the rapid growth of RF and wireless applications in this country. Personal communications systems have generated a great deal of interest by industry and research organizations with a need for new antenna technology. As a result, this group of six faculty members has been very active in the development of dielectric resonators for communications applications. This has led us to begin research related to the development of technologies for the design and application of dielectric resonators for microwave networks and antennas. It is foreseen that the proposed equipment is required for the study of new types of dielectric resonators for use as antennas for future applications. In addition, the investigation of now meander and spiral-type antennas for RF and wireless applications has been initiated to discover new antenna configurations for these applications
In another research project, a multi-wire, cage model has been developed to solve the important problem of the determination of the radiation pattern and longitudinal current distribution along and around a wire antenna protruding through a multi-layer medium. This research is of significant merit because the longitudinal directed current distribution on a wire antenna near the interface between two layered medium is not uniform as a function of angle around the antenna because of proximity effects, and current simulation programs cannot model these structure's accurately. In this research, directed towards investigation of a more accurate simulation model for these type wire structures, several different cases are being analyzed using a cage model used in this research for verification of a model, and antenna current distributions, impedance, and radiation patterns are to be measured for discovering the characteristics of this class of wire antenna structures in the presence of lossy media.
The fourth project that is currently under investigation is a study of an optimized antenna for a ground coupled radar system for location of unexploded artillery shells and mines. The location of unexploded munitions is currently a high priority area of interest, and this research is being pursued in an effort to discover new technology for the solution of this widely recognized problem.
The proposed equipment is to provide a wide-band microwave receiving system (<20GHz) for magnitude and phase measurements of current and charge distribution, input and mutual impedance, and radiation patterns for the advancement of antenna technology by this research group. 'Me availability of this equipment, which includes the proposed receiver and University of Mississippi provided signal source and test set, will have a significant impact on the quality and type of research that can be pursued for creating new knowledge antennas, as well as on the level of instruction for training engineers for the future with backgrounds in RF, wireless, and microwave technology.

9810448
Kishk
It is proposed to study artificially soft and hard surfaces for practical applications. Artificially soft and hard surfaces can be realized by a reactive and anisotropic loading of a conducting material, This loading can, for example, be done by using the well-known corrugations or using a cheaper method of etching conducting strips on a grounded dielectric slab. To perform this study, it is necessary to modify some existing numerical codes to adopt modeling these surfaces and develop analytical solutions of some canonical problems for verification purposes. The numerical tools will be general witch can be employed to easily model any detailed structure of antennas and scatterers. Two numerical techniques will be adopted, the finite difference time domain technique (FDTD) the method of moments techniques. The two methods will be used to complement each other and model many complicated structures. The graduate student will be trained to learn these techniques and to be able to do the modifications to the codes. Then, the process of designing new antennas and scatterers will begin. Some of the interesting problems are reducing the coupling between microstrip array elements to eliminate the blind effect with lower scanning elevation angles, reducing leakage of electromagnetic waves from microwave ovens, reducing the heat consumption in high power applications to increase device efficiency and reducing the cost of the cooling system. Smart antennas used in base stations require a decrease of the support structure effect on the radiation patterns and many other applications. Base stations requires the study of the radiation from antennas such as dipoles, slots, and microstrip antennas in the presence of infinite cylinders with arbitrary cross-section of composite materials. Many of these applications will be constructed and tested and verified with the numerical results.
To analyze strips loaded surfaces and corrugated surfaces in an efficient way, new asymptotic boundary conditions are developed and will be implemented in the numerical codes. These asymptotic boundary conditions are referred to as asymptotic strip boundary conditions (ASBC) for strips loaded surfaces and asymptotic corrugation boundary conditions (ACBC) for corrugated surfaces. These boundary conditions will facilitate the study of arbitrary and finite surfaces that have periodic strip loading or corrugations. The new boundary condition will simplify the numerical modeling of these surfaces and Facilitate using them in practical applications. Therefore, these new asymptotic boundary conditions will be implemented in the method of moment codes and FDTD code.
In some applications, the impedance boundary condition (EBC) can also be used efficiently whenever it is possible to accurately obtain the equivalent surface impedance. Therefore, the EBC will be also considered. We have presented a few examples to show that these boundary conditions can be successfully implemented and used with practical applications.
This study also may develop novel ideas to obtain the desired radiation characteristics of antennas by simple implementation of the soft and hard surfaces. This may be used to improve the performance of the wireless communication devices, and microwave ovens, and simultaneously reduce the danger of the electromagnetic waves and their biomedical effects on human bodies. The findings of this work will be published in the literature, and introduced to the class room, and a comprehensive study may be published in a book.

This proposal addresses two areas of critical emerging technology in the microwave and millimeter wave regions. The first area is the fundamental characteristics of dielectric resonator antennas and finite antenna arrays operating in a cylindrical waveguide environment. The study and analysis of single dielectric resonator antenna element show the advantages of this new antenna type at millimeter wave frequencies in comparison with traditionally used microstrip and patch printed antennas. This new radiator is expected to be an excellent element in antenna arrays used in many critical applications. This part of the project focuses on the development of new analytical and numerical tools for full-wave analysis of antenna radiation characteristics and on the investigation of performance of dielectric radiators as elements in waveguide-based antenna arrays. Based on the understanding of dielectric resonator antenna performance in cylindrical waveguides, the second part of the project addresses the issue of modeling a fully integrated cylindrical waveguide-based spatial power combining amplifier array. A cylindrical spatial power combining architecture, which utilizes an array of dielectric resonators, is proposed. In this system, dielectric resonator antennas play a critical role, which is justified by their radiation characteristics and high power handling capabilities. Our goal here is to develop an integrated modeling scheme for the full-wave analysis of a complete waveguide-based spatial power combining system, including the interaction of passive (dielectric resonator and hard-horn antennas) elements and active (amplifier) circuits. The newly proposed system will allow to operate in dual and circular polarization regimes.

A high level educational component is considered here by training two graduate students during the course of this project that merge the basic research with high level practical applications. In order to broaden the scope of benefits, a new course will be developed to involve and expose more graduate students to this area. The course will be developed based on the study of dielectric resonator antennas in an array environment and the use of hard surfaces as an artificial magnetic surface.

The Department of Electrical Engineering (EE) and the Center for Applied Electromagnetic Systems Research (CAESR) at The University of Mississippi (UM) seeks support from the National Science Foundation to acquire near-field antenna range instrumentation which will be dedicated to support ongoing research on antennas and scatterers in the commonly known technology areas of RF, wireless, microwave, millimeter wave, infrared, and optics. The equipment will be used to pursue studies of new, innovative antennas and scatterers, and large planar phased array antennas for research projects, including studies of dielectric resonator antennas, printed antennas, cylindrical wire antenna scatterers in multi-layered media, radar/sensor antennas, spatial power combiners, and meander and spiral antennas for wireless communication. This instrumentation is needed because EE and CAESR do not currently have capability for large aperture antenna measurements.

UM EE programs supporting this research have grown to an enrollment of about 100 undergraduate students and over 45 graduate students with a faculty having 11 tenure track, instruction/research positions. The department research areas are in electromagnetic applications and telecommunications. Seven faculty members are in the area of electromagnetics and their research will benefit from these facilities. In addition, two professors emeritus of electrical engineering who are very active in research and RF measurements will be using this instrumentation.

Intellectual Merit: The research objectives are 1) to continue investigation of developing new DR antennas with wideband performance and to study the performance of these radiators in large antenna array environments and 2) to investigate technological advances in providing basic, state-of-the-art building blocks for advanced phased array radar systems.

Currently, design and construction of new and innovative large aperture antennas are in progress, and full-scale testing is needed for design validation. This instrumentation will contribute significantly to the quality of ongoing research and will add new research capability and greatly enhance research-relate education, because UM does not have facilities for testing and measurement of large aperture and phased array antennas.

Broader Impact: This equipment will have significant impact on our research and the development of highly efficient antenna arrays such as dielectric resonator antennas. Also, this equipment will help the engagement of the University with the industry in the area and help in the economical development of the area. As widely noted by the industry, a shortage of RF, wireless, and microwave engineers has been evident in the past few years, and this growing problem must be addressed in order to maintain the leadership of the United States in the rapidly growing and demanding information and communication intense areas in the 21st century. The instrumentation supported by this proposed grant will provide the latest technology for instruction in antenna design and testing to facilitate technology research and education. The graduates of our program will be able to use new methods of antenna design and be able to build and test large array, state-of-the-art antenna components needed for RF, wireless, microwave, and millimeter-wave systems of the future based on experiences with this new instrumentation as well as existing facilities.

ECS-0524042
M. El-Shenawee, U of Arkansas

This integrative systems proposal focuses on developing a new compact microwave imaging system (hardware and software) aiming to reconstruct tumor images of diameters less than 5 mm. The investigators intend to answer two main questions associated with microwave imaging systems as; (i) what are the most efficient antennas to be used as transmitter and/or receivers in a radar-based imaging system for breast cancer detection? (ii) which imaging algorithms are capable of processing the received signals and produce reconstructed images in realistic time frame? The investigators are proposing to build an advanced ultra wideband compact imaging sensor that is specifically designed for breast cancer imaging. This sensor will be an antenna array composed of dielectric wideband elements. Each element will be a dielectric resonator antenna that can be flexible in shape, small in size and light in weight, making the sensor practical for use on the breast. Also, the investigators are proposing to develop and hybridize potential imaging algorithms to efficiently and rapidly reconstruct the tumor shape and location using received signals. The intellectual merits of this proposal focus on designing and building an advanced compact ultra wideband lightweight microwave sensor; developing efficient and robust imaging algorithms to be integrated with the hardware part of the system; and validating the developed algorithms on real data to be collected by the sensors. The proposed hardware sensor will be used to validate the imaging algorithm and once proven successful the investigators will seek funding in collaboration with medical researchers for clinical use.
The broader impact of this project will be on women's health in general and on breast cancer disease in particular. The new system will offer an economical and less painful option for many women. This project will influence the sensor technology and data acquisition techniques associated with the microwave imaging modality. The proposed research will have significant bearing on the graduate and the undergraduate research opportunities at the University of Arkansas and the University of Mississippi.