Study On Short Response Time Waveguide Limiter Under High Power Microwave

With the development of high power microwave technology and the miniaturization and integration of electronic equipment,the "front door" coupling problem of single aperture radar system with rectangular waveguide as transmission line in high power microwave environment is increasingly prominent.Aiming at the front door protection of radar system,a waveguide plasma limiter with short response time,short recovery time and high isolation is designed based on the reflection and absorption characteristics of plasma to electromagnetic wave.In order to solve the problem of insufficient protection ability of waveguide plasma limiter,the waveguide energy limiter is designed based on energy selection surface,which is used for secondary protection of receiving link.In order to take into account the protection of the transmission link,a high isolation ferrite circulator is designed,which effectively solves the "front door" protection problem of the radar system.The specific work of this paper is as follows:In the first part,the propagation characteristics of microwave in plasma are studied and the formula of critical breakdown field strength of inert gas at low and high pressure is analyzed.After simulating the formation process of argon plasma in BJ100 waveguide with COMSOL software,we think that the formation time of argon plasma in pure waveguide structure is too long,so resonant structure must be used to reduce the formation time of plasma.It is proposed that the critical breakdown field strength and response time should be taken as the constraints in the design to optimize the structure of waveguide plasma limiter and the gas pressure.In the second part,taking BJ100 waveguide as an example,the resonant window and resonant gap structure are designed by using CST software.On the basis of ensuring small insertion loss,the purpose of sealing gas and increasing local field strength are achieved respectively.The formulas of response time and recovery time are derived from the point of view of gas ionization and deionization,and the formula of isolation degree is derived based on the reflection and absorption characteristics of plasma to electromagnetic wave.Based on the structure of waveguide plasma limiter,the response time and isolation degree are calculated by COMSOL software.The analysis shows that the "best pressure" of argon ionization is 8torr,and the response time is about 10 ns and the isolation degree is up to 50 d B under the incident power of 1k W.In the third part,according to the engineering practice,it is considered that alumina ceramic is suitable for the material of dielectric window,which can obtain more power capacity,and the life of waveguide plasma limiter can be prolonged if the filling gas is slightly higher than the "optimum air pressure".The waveguide plasma limiter is tested by the test method of microwave electron tube.At the incident power of 1k W,the response is about 12 ns,and the isolation is up to 40 d B,which is basically consistent with the simulation results.In the fourth part,based on the design method of double layer band stop type energy selective surface,combined with the waveguide structure,an X-band waveguide energy selective limiter is designed,which can start to limit the amplitude under the incident power of 10 W.When the incident power is 200 W,the isolation degree can reach 18 d B,and the response time is ps level.After cascading with the waveguide plasma limiter,the protection ability is much greater than that of single-stage limiter,so that the receiving link will not be damaged by high-power microwave.For the protection of the transmission link,a ferrite circulator with an isolation degree of 45 d B is designed in this paper,so that the high-power microwave will not interfere with the transmission link,and finally complete the "front door" protection of the radar system,so that it can work in a more complex electromagnetic environment.