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The generation of ultra-wideband (UWB) pulses is a challenging problem that involves generating pulses with fast rise times on the order of 100 ps and voltages of more than 500 kV. Pulsewidths from 130 ps to a few nanoseconds (ns) are possible. A critical step involves switching high voltages with precision. The use of both gas and oil for the switching medium has been accomplished with varying results. The Air Force Research Laboratory (AFRL) is pursuing both media in the gas-switched H-series of pulsers and in studies of oil switches that promise good performance in compact packages. We are also pursuing solid-state switched systems that have demonstrated the potential for use in compact systems and in transient antenna arrays with steerable beams. This paper reviews recent progress in fast, high voltage switching and UWB transmitter development. These UWB pulsers and antennas have the potential for use in transient radar, target identification, and communications. Index Terms-Brewster angle window, gas switch, high power microwave, impulse radiating antenna, oil switch, photoconductive solid-state switch, radio frequency lens, silicon avalanche shaper, spark gap switch, transient antenna, ultra-wideband. I. BACKGROUND U LTRA-WIDEBAND (UWB) sources and antennas are of interest for a variety of potential applications that range from transient radar systems to communications systems. Predating the recent technology developments of the last several years were a number of important discoveries in the 1980's that led to the first UWB pulsers capable of transmitting high peak field signals through a variety of antennas. The Bournlea pulse generator is a good example of an instrument that is capable of fast rise times and a high repetition rate [1]. Using a CX1599 hydrogen thyratron as its basis, the original Bournlea pulser, made in 1986, could produce a 5-kV pulse with a rise time of 3 ns and a pulse repetition frequency (PRF) Manuscript

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Ultra-wideband (UWB) microwave sources and antennas are of interest for a variety of applications, such as transient radar, mine detection, and unexploded ordnance (UXO) location and identification. Much of the current research is being performed at the Air Force Research Laboratory (AFRL) at Kirtland AFB, NM. The approach to high power source development has included high pressure gas switching, oil switching, and solid-state-switched arrays. Recent advances in triggered gas switch technology and solid-state-switched shockline technology have opened up new possibilities for the development of much higher power systems and have thus opened the door to many new applications. The research into UWB transient antennas has also made significant contributions to the development and improvement of wideband continuous wave (CW) antenna designs and has brought new knowledge about the complex behavior of ferrites, dielectrics, and resistive materials in short pulse, very high voltage environments. This has in turn led to advances in the technology of transformers, transmission lines, insulators, and UWB optics. This paper reviews the progress to date along these lines and discusses new areas of research into UWB technology development. Index Terms-Highpower microwave, impulse-radiating antenna, oil switch, photoconductive solid-state switch, spark gap switch, transient antenna, ultra-wideband. William D. Prather (S'69-M'70-SM'89) was born in Odessa, TX, on March 9, 1947. He received the B.S.E.E. and M.S.E.E. degrees from the University of New Mexico, Albuquerque, NM , in 1970 and 1975, respectively. He was with the Air Force Weapons Laboratory from 1970 to 1990, and the Air Force Phillips Laboratory from 1990 to 1997. He is currently with the Plasma Physics Branch, Directed Energy Directorate, Air Force Research Laboratory. He has been active in electromagnetic interaction and coupling research, EMP simulation and testing, aircraft hardening design, design verification, and maintenance. He received special recognition from the Air Force for the development of hardness surveillance technology for use in aircraft assembly plants, maintenance depots, and operating bases. Since 1991, he has been responsible for the development of high power ultra-wideband microwave sources and antennas for the Air Force. He has written numerous technical papers, MIL-STD's, journal articles, and book chapters on the subject of aircraft coupling, shielding, transient electromagnetics, and high power sources. He is a Technical Advisor to numerous U.S. government agencies on EM-related matters and represents the USAF in exchanging EM coupling and hardening information with NATO countries.Mr. Prather is a Senior Member of Eta Kappa Nu. Robert J. Torres (M'94-SM'98) was born in Albuquerque, NM in 1963. He received the B.S.E.E. and M.S.E.E. degrees from the University of New Mexico in 1986 and 1995, respectively. He was with the Army Vulnerability Assessment Laboratory, now Army Research Laboratory from 1986 to 1991, where he was responsible for co...