Coupling Parameter Extraction And Aided Tuning Of Cavity Filter

Cavity filter has the characteristics of high power capacity and low insertion loss.It is widely used in military and civil wireless communication systems such as satellite,radar,ship,and broadcast television.The performance of cavity filter is directly affects the quality of communication.Effective tuning is an essential step in filter production,but it needs to be based on complex and experienced manual tuning,which is time-consuming and labor-consuming.In order to reduce the manufacturing cost of the filter and shorten the production cycle,the coupling matrix synthesis theory of the cross-coupled filter is systematically analyzed in this paper.Based on this,the coupling parameter extraction is studied and the tuning of the filter is guided.The main work is as follows:Firstly,the basic theory of N*N and N+2 coupling matrix synthesis of generalized Chebyshev filter is deduced in detail.The rational polynomial coefficients are solved,the admittance matrix is expressed by the residue method and the circuit method respectively,and the equation relation is constructed,thus the N+2 type coupling matrix is constructed.The different topology structures of the coupling matrix and the simplification methods are introduced.Second,in view of the unknown transmission zero point,genetic algorithm is used to find the position of finite transmission zero point.Then,the coupling matrix synthesized at this time is used as the initial value to determine the position of non-zero elements,and the final actual coupling matrix is optimized.In order to improve the efficiency of the program,the coefficients of F,P and E polynomials are solved based on the improved Cauchy method,and then the phase is processed to improve the precision of parameter extraction,and then the coupling matrix is synthesized.Thirdly,MATLAB programming software is used to implement the coupling parameter extraction technology based on genetic algorithm.The GUI interface is designed,including ideal coupling matrix synthesis and actual coupling parameter extraction.Two examples are given to verify the feasibility of the algorithm and software design.The result of ideal synthesis is consistent with that of common coupling matrix synthesis software CST,which proves the correctness of the program.Fourthly,the coupling parameter extraction program based on improved Cauchy method was written by Visual Studio 2015.The operation speed is improved effectively,and the frequency response curve is well fitted.Then,the two cavity filters modeled by HFSS electromagnetic simulation software and the nine order with three zero point filter are tuned to make their response curves meet the acceptable index requirements,which verifies the accuracy of the algorithm and the feasibility of the program,and is beneficial to the rapid tuning of the filter.