Photoconductive Switch Transient Electromagnetic Pulses

Ultra-wideband (UWB) sources and antennas are of interest for a variety of potential applications that range from transient radar systems to communications systems. The generation of ultra-wideband 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. Photoconductive switches are a completely different type of switch than those currently used in pulsed power applications. The most important attributes of photoconductive semiconductor switches'(PCSS) are jitter free triggering, low inductance and capacitance, fast rise time, fast recovery time and high repetition rate. Among PCSS, GaAs PCSS have many advantages over Si in response speed,the transfer efficiency of light into electricity and high voltage resistant,especially they can operate in a nonlinear mode with high gain which can reduce the triggering optical energy by 3-5 orders of magnitude comparing to the conventional linear mode. This makes it realistically possible to realize the miniaturization,practicality and integration of the system of PCSS。So it will be applied widely in ultra-wideband source circuit.In this paper, Auston circuit, blumlein pulse forming line is introduced and give their difference. The experiment system is set up and the PCSS samples are tested. A Blumlein microstrip photoconductor switch is designed and the voltage transmission efficiency of 98.9% has been obtained in experiment. Moreover, the ultrashort pulse is radiated through slot antenna. after simulating time-space distribution of electron and hole in photoconductor, the relations of laser energy, laser character and photoconduction are analyzed and the fundamental principles of nonlinear phenomenon is introduced. At the same time the effection of some important recombinations are discussed and the relation of photoconduction versus time is given.The research of slow-decay effect is the advanced task of the electromagnetism, which can be widely used in many fields: ultra-wide radar, ultra-wide secrecy communication ,high-power microwave and etc. The detailed analysis of the slow-decay effect of pulse propagation is presented in this paper. Near or far field and law of energy propagation are presented at axes of disk.