Study On The Protective Properties Of Cavity Filters For High Power Microwaves

With the in-depth study of strong electromagnetic pulses,the electromagnetic environment in which electronic equipment is located has become more severe.Especially with the development of high-power microwave(HPM)technology,the threat to antenna equipment such as radar is increasing,which also leads to a higher requirement for protection.The design difficulty of conventional antenna protection methods is gradually increasing,so it is very necessary to explore new protection methods.In addition,the conventional antenna protection methods need to add additional protective devices,which will inevitably affect the working performance of antenna.When cascading protection is required,the effect will be more serious.As a filter element commonly used in radar,cavity filter will not have concerns in this regard if it has the ability to defend high power microwave.In this thesis,the ability of cavity filter to defend high power microwave is studied.The main contents are as follows:In the first part,the possibility of cavity filter as high power microwave defense device is analyzed theoretically.Firstly,the application and working principle of cavity filter in RF link are analyzed,and the form of capacitive loading is found to make the cavity have a very strong resonance.The field strength between resonance gaps is much greater than that of the electric field in other locations,making it easy for air to breakdown.Under the effect of highpower microwave,air break-through will be more likely to occur.This makes cavity filters feasible as high-power microwave protection devices.Then,the critical electric field intensity of the air breakdown in the filter and the effect of the plasma formed after the breakdown on HPM are studied in detail.Studies have found that the plasma formed after the air breakdown in the cavity filter can reflect and attenuate HPM,and the transmission characteristics of the cavity filter can be changed by changing the loading capacitance,so that the cavity filter has the potential for protection against high-power microwaves.On this basis,the start threshold and isolation index describing the protective capability of cavity filter are proposed.In the second part,the coupling power of HPM at antenna port is analyzed.Firstly,the antenna gain is determined to calculate the coupling power.On this basis,the characteristics of HPM sources and the direction of receiving antennas are studied separately.The study of the characteristics of HPM source includes the analysis of pulse form and radiation antenna orientation.The directionality of HPM antenna and receiving antenna is analyzed by example of Cassergrain antenna and microband patch array antenna respectively,and the coupling power of the receiving antenna port is calculated according to the beam gain of the radiation antenna and the receiving antenna,which is equivalent to obtaining the input power of high-power microwave in the cavity filter input port.In the third part,the cavity filter is designed and manufactured.Firstly,according to the network synthesis theory of filter design,the impedance transformation and frequency transformation in the design process of cavity filter are analyzed,and the calculation formulas of coupling coefficient,external quality factor and other parameters which are very important for filter design are obtained.Then,according to the equivalent circuit of the cavity filter,the design of the filter is divided into four parts: resonant unit design,cavity coupling design,input and output structure design,full wave modeling and simulation.The design of the band-pass cavity filter with center frequency of 10 GHz and passband bandwidth of100 MHz is completed.Finally,the cavity filter is manufactured,and the debugging and testing are completed.The cavity filter model is used for simulation verification of protective performance,and the filter object is used to complete the test of protective performance.The fourth part verifies the HPM protection capability of the cavity filter through simulation,and calculates the isolation and start threshold of the filter.Firstly,the modeling process of FDTD method and plasma material is analyzed.The internal field strength of cavity filter under HPM is calculated by this method.The simulation of microwave and plasma synergy for single-order cavity filter shows that the filter has the ability to defend high power microwave.Then,for the X-band cavity filter designed,the relationship curve between isolation and input power and start threshold and pulse duration is obtained,and the role of filling argon and increasing initial electron concentration in reducing cavity filter starting threshold is analyzed by using the plasma module of COMSOL.Finally,the test configuration and experimental method of HPM protection performance of the cavity filter are given.