Research On High Power Microwave Generation Technology Based On Linear Photoconductive Devices

Traditional high-power microwave(HPM)generation is mainly based on the relativistic vacuum electronic devices,which have disadvantages such as bulky volume,difficulties in frequency tuning,and requirement of vacuum system.In recent years,with the emerging of microwave photonics and the development of solid-state beamless HPM devices,the application of photoconductive semiconductor devices in generating microwave has attracted extensive attention.This thesis,by using vanadium compensated semi-insulating 6H-SiC photoconductive semiconductor switches(PCSS),verifies the potential of linear optical devices in producing HPM of high rep-rate and frequency tuning.The main work includes:1.The principle of a photoconductive microwave generator is introduced.The influence of the doping concentration,carrier recombination time and quantum efficiency of 6H-SiC on the photoelectric conversion efficiency is analyzed,and the formula of the dynamic resistance of the PCSS is derived.Extrinsic semiconductor,which can be triggered by a sub-band-gap laser and thus has deep penetration and high power operation,is utilized in this work.A PSpice circuit model of the PCSS is established,which helps to simulate and optimize the microwave generation using PCSS and a modulated laser pulse.2.Electrostatic field simulation is carried out to study the influence of the thickness of SiC wafer,electrode structure and filling material on the electric field distribution and high voltage insulation.A PCSS device with a vertical electrode structure and a silicone packaging is fabricated.To test the performance of the PCSS,the experiment is carried out using a 532 nm single pulse laser.With laser illumination of 17 ns and ～ 30 m J,the minimum conducting resistance of PCSS is about 7 Ω,the power capacity is up to 10.56 MW,and the breakdown field is up to 225kV/cm.3.The technology of photoconductive microwave generation and frequency tuning is verified by using burst-mode lasers with pulse width of 100 ns and modulation frequency ranged from 800 MHz to 1200 MHz,at 5.6kV and 4.9 Kv bias and two laser inputs of 1064 nm,8kW and 532 nm,33kW.The obtained electrical power is 1kW and15kW respectively.4.A Class B push-pull photoconductive microwave amplification circuit is proposed.Circuit simulation shows that when the quantum efficiency of PCSS reaches 0.2,the photoconductive microwave circuit can produce microwave power of 1.1 MW with 100kW laser and ?15kV bias.The electrical efficiency is 65.9% and the optical gain is 10 d B.Initial test is carried out with two time-complementary laser beams.The results show that increasing the quantum efficiency of PCSS is the key to improve the efficiency and gain of a photoconductive microwave generator.