Thursday, April 17, 2014 at Agilent Technologies, 5301 Stevens Creek Blvd., Building No. 5 Santa Clara, CA
Title “Non-Foster Circuits for Antenna Applications – Theory and Design”
Speaker: Steve Stearns, Technical Fellow, Northrop Grumman Information Systems.
Abstract: Non-Foster networks are active networks that use negative capacitors and negative inductors in addition to traditional passive lumped elements. Interest in non-Foster networks has been growing during the past decade for applications such as antenna loading and matching and making active metamaterials. Such networks are not subject to the Bode/Fano bound on match bandwidth. Network synthesis procedures have been found that, in principle, give infinite match bandwidth for arbitrary load impedance functions. Long-standing problems in linear circuit stability theory have been resolved . Non-Foster counterexample circuits have been found that demonstrate certain classical linear circuit stability tests or criteria are fundamentally incorrect. In this talk we demonstrate that a networks made from a small class of circuit elements can exhibit non-Foster behavior even if non-Foster elements are not allowed. In other words, negative capacitors and negative inductors are not necessary base elements for creating non-Foster behavior. Novel active non-Foster match networks for monopole and loop antennas will be described.
Biography: Stephen D. Stearns is a Technical Fellow of Northrop Grumman Corporation and works in San Jose, California, where he does research in new technologies for next generation systems. He has over 50 publications and presentations, and 10 U.S. patents. He is a Senior Member of the IEEE, is a past Vice President of the Silicon Valley chapter of the IEEE Information Theory Group, and serves as a reviewer for the Transactions of several IEEE societies. He is active in Amateur Radio, holds an FCC Amateur Extra class license, served as an Assistant Director of the of the American Radio Relay League’s Pacific Division, and is currently Vice President of the Foothills Amateur Radio Society. He writes a column on electromagnetics, antennas, and circuit theory.
Thursday, February 13, 2014 at Cogswell College, 1175 Bordeaux Drive, Sunnyvale, CA, 94089
Title: “Dielectric Resonator and Transparent Antennas”
Speaker: Dr. Kwok (Ben) Leong, IEEE APS Distinguished Lecturer, Professor at City College of Hong Kong.
The fundamentals and development of dielectric resonator antenna were presented 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. 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. 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.
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. 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. 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. 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. An example of a glass swan was presented.
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, a Guest Editor of IET Microwaves, Antennas and Propagation, and an Associate Editor for IEEE Antennas and Wireless Propagation Letters. He was also an Associate Editor for IEEE Transactions on Antennas and Propagation and received Transactions Commendation Certificates twice in 2009 and 2010 for his exceptional performance. Currently, he is the Editor-in-Chief of IEEE Transactions on Antennas and Propagation. He is a Distinguished Lecturer of the IEEE Antennas and Propagation Society.
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 CityU Research Excellence Award 2013 and Departmental Outstanding Teacher Awards in 2005, 2010, and 2011. He is a Fellow of IEEE and of Hong Kong Institute of Engineers (HKIE).