The Transmission Characteristic Study Of Ultrashort Electromagnetic Pulse Based On Photoconductive Switches

The ultrashort electromagnetic pulses have a broad applied foreground in ultra-wideband randar, ultra-wideband communication and THz imaging systems. As far as the power and band width of the electromagnetic pulses are concerned , the generation of electronic pulses by photoconductive switches is more effective.It is a new technology that combine the photoconductive switch with the ultra-short pulse laser to generate the ultrashort electromagnetic pulse . The base principle that generate the nanosecond or sub-nanosecond is changing the conductance of Semi-insulating(SI)GaAs , which the DC voltage across the switch , by using the ultrashort laser pulse . Photoconductive Switches (PCSS's) are a completely different type of switch than those currently used in pulsed power applications . The most important attributes of PCSS's are jitter free triggering , low inductance and capacitance , fast rise time , fast recovery time , and high repetition rate . Due to the energy of the circuit of high pulsed power is occupied unavoidably by residual components especially transmitting with bandwidth of GHz electromagnetic pulse , the influence by the dispersion of power couldn't be ignored . Accordingly , it is important that studying the transmission characteristic and making the PCSS's matching of the external circuit is a key problem needed to be resolved in high power electromagnetic weapons , which is also signifiable to ultra-wide-band signal.In this paper , the PCSS's ciucuit structure , gap size , the microstrip figure , coupling interface , transimission line configure are investigated. Because the PCSS's are the apparatus which operate by triggering of laser with photoconductor , and photoconductor's attributes are decided by the evolvement of carriers . Based on the results of our tests, we analyse the variation of the carriers and obtain the expression of the varying equivalent resistance of PCSS's and figures. We propose the equivalent circuit model and explain the voltage transmission efficiency of 93% . We also simulate different voltage waves produced by different characteristic loads.Finally , based on the physical model of NDR effect of GaAs materials, transferred electron effect, impact ionization and radiation recombination effect in high field , we establish an understandable three-ports non-linear PCSS's transient circuit model which associates dynamics parameter with electrics parameter and simulate the voltage waves between the electrodes.