Research On Pulse Generators Based On Arrayed Photoconductive Semiconductor Switches

Three topics are discussed for ultra-wide band Radar sample transmitter in this dissertation: firstly, high power electric pulse source is developed which is based on Photoconductive Semiconductor Switches (PCSS); some research work has been done on the transmission properties of transient pulses according to a simplified model; finally, ultra-wide band Radar transmitter system is set up on basis of such pulse sources and transmission properties.When PCSS made from semi-insulating (SI) Gallium Arsenide (GaAs) is illuminated by laser pulse with its 1064 nanometers wavelength, the parameters of output pulse from the load can be calculated if absorption coefficient of GaAs and capture coefficient are given. Firstly, in terms of Fermi-Dirac statistics approximation, the density of unionized EL2 center is calculated and absorption coefficient of SI GaAs for sub-gap laser pulse was determined. Secondly, it is the enhancement of capture coefficient by electric field via EL2 centers that leads to output pulse with a nanosecond rise-time. Thirdly, three cases are discussed when PCSS is operated under linear mode: the wavelength of laser pulse is 532, 1064 nanometers, respectively, and the capacitance from Blumlein transmission line is 27.2 pF with a biased high voltage. The last section of this topic is related to the nonlinear mode of PCSS. In this section, a proposal is given: PCSS is operated under the nonlinear mode if electric field is higher than 3.5kV/cm when the laser pulse turned off, on the contrary, PCSS is still in linear mode.As for PCSS fabrication and the test of PCSS, research work has been done as follows.First, mechanic structure and insulation package of PCSS are developed for PCSS excellent performance. Second, the layers of refractory Ohmic electrode consist of Pd/Ge/Ti/Pt/Au for longetivity of PCSS.1500 PCSSes have been fabricated by such electrode layers.When 50? load is used for measurement of the output power and pulse width (more than 2MW, less than 1 nanosecond), each PCSS lasts more than 3.6×106 shots if repetitition frequency of the triggering signal is set to 1kHz.Third, two types of test circuit are designed for the research of differences between linear and nonlinear mode of PCSS. One of test circuits is charged by direct current voltage module, while another is charged by pulse charged module.Some research on properties of transient electromagnetic pulse has been done as follows: the z-axis properties of transient pulse coming from PCSS array such as transmission, power combination and beam formation are simulated by a model where each antenna is at its own location; the ouput efficiency of Blumlein transmission line is discussed by Laplace technique when the resistance of PCSS is taken into account.The impulse radar system is made up of some modules such as pulse charged module, laser generation and optical fibre transmission module, the module for the control of time sequence between two triggering signals, the antenna package module integrated with Blumlein transmission line and antenna.Among those modules,the pulse charged module is independently designed,developed and tested by the author.Other modules are designed,developed and tested by the collaboration of our research group.After the impulse radar system is completed, properties of transient electromagnetic pulse such as transmission, power combination and beam formation are explained and verified when simulation results and experimental results are in their comparison.