|Organizer: IEEE Toronto Section, Electromagnetics and Radiation Joint|
|Title: The Minimum Q of Small Antennas (A Discussion of Recent Controversies)|
It is well known that small antennas exhibit a large input reactance, a small radiation resistance and, when tuned to resonance, a small bandwidth of operation. A measure of the small bandwidth and high input reactance is the Q of the small antenna. In 1948 Chu established the minimum Q of small antennas. His approach was to use a partial fraction expansion of the wave impedance of spherical modes that exist outside the smallest circumscribing sphere surrounding the antenna to obtain an equivalent ladder network from which the Q could be found by conventional circuit analysis. This work was expanded by Harrington. In 1964, Collin and Rothschild presented a method for evaluating the minimum Q without using the equivalent network. In 1969, Fante extended these results to multimode antennas. In a series of recent papers, beginning in 1994, D.M. Grimes and C.A. Grimes have challenged these results. They believe that small antennas can be designed that have smaller values of Q. In their most recent work they predict the possibility of a small antenna that has a zero Q. This would be a remarkable development and would be contrary to our understanding of small antenna behavior. The theories of Grimes and Grimes will be reviewed and it will be shown that their theories are based on a faulty hypothesis and are not valid. In addition some recent work by the author will be reviewed that provides a reaffirmation of the results obtained by Chu, Harrington, Collin and Rothschild, and others.
Professor Robert E. Collin
Case Western Reserve University
Cleveland, Ohio, USA
Robert E. Collin was born in 1928 in Alberta, Canada. He received the B.Sc. degree in engineering physics from the University of Saskatchewan in 1951. He attended Imperial College in England for graduate work and obtained the Ph.D. degree in electrical engineering from the University of London in 1954. From 1954 to 1958 he was a Scientific Officer at the Canadian Armament Research and Development Establishment where he worked on guided missile antennas, radomes, and radar system evaluations. He joined the Electrical Engineering Department at Case Institute of Technology in 1958, now Case Western Reserve University. During his tenure there he served as Chairman of the Department of Electrical Engineering and Applied Physics for five years and as Interim Dean of Engineering for two years. He has been an invited Professor at the Catholic University in Rio de Janeiro; at Telebras Research Center, Campinas, Brazil; the University of Beijing, People's Republic of China, and at the Technical University of Hamburg, Germany. He was also a Distinguished Visiting Professor at the Graduate School, Ohio State University during the 1982-83 academic year. Professor Collin is the author or co-author of five books and more than 150 technical papers. He is a life fellow member of the IEEE, a member of the National Academy of Engineering, and several other professional societies.
|Time and Location:|
Tuesday, July 28, 1998 at 3:00pm
Galbraith Building, Room 248
Faculty of Applied Science and Engineering
University of Toronto, 35 St. George Street
The Institute of Electrical and Electronics Engineers,
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