Mode Matching Method And Its Application In Microwave Resonator

The microwave vacuum electronic devices which are of high power,high gain and high frequency are widely used in various applications,such as radar,wireless communication,medical and electronic countermeasures system.As the key part of microwave vacuum electronic devices,the performance of microwave window,impedance transformer and microwave cavity directly affects the bandwidth,power capacity,interaction efficiency,reliability of the devices.The accurate simulation and rapid design of the microwave passive components is crucial to shorten the development cycle,improve the tube performance and prolong its life span.In view of rapid optimization design of the critical components of electronic vacuum device,including microwave window,impedance transformer and microwave resonant cavity,the MMT(Mode Matching Technique)is studied in this thesis.Combining the multi-objective optimization algorithm NSGA-II(Non-dominated Sorting Genetic Algorithm II),an optimization model used for S parameter of microwave window is presented and the code named MWDK of corresponding algorithm is developed.Using the code,a coaxial window with operating frequency ranging from 1 to 35 GHz and a rectangle waveguide window for folding waveguide travelling wave tube of W-Band is designed simply and quickly.Meanwhile,the MMT is applied to the calculation and analysis of the resonant frequency,and eigen field distribution of microwave resonant cavity,and the high-frequency characteristics of microwave resonant cavity are calculated quickly.For the complex high-frequency structures of external cavity type devices such as klystrons and extended interaction klystrons,the MMT is extended to establish a theoretical model for the calculating the cold cavity field,which lay the foundation for further developing nonlinear beam-wave interaction of these kind of devices.The main contents and innovations in this paper are as follows:1 The mode matching technique is deeply studied.By using continuity boundary condition of electromagnetic field,the field matching formula of the method is deduced and the analytical expression of the coupling matrix of regular waveguide mutation is analyzed.It is used for calculating the S-parameters of the microwave window and analyzing intrinsic problem of microwave resonator.The resonant cavity solution code based on the MMT is written,and the resonant frequency and electromagnetic distributions of the corresponding resonant modes are solved.The computational performance and simulation results are compared with HFSS and CST.Under the same accuracy,the MMT achieve a faster solution speed.2 By studying non-dominated sorting genetic algorithm(NSGA-II)systematically and combining it with the MMT,a microwave window S-parameter optimization model is established in which three objective functions are designed to ensure low-reflection and wide-band.By analyzing the time complexity bottleneck of the entire optimization algorithm,the learning operator is further added on NSGA-II,which has the average convergence speed of the algorithm increase by 25%.3 Based on the idea of mode expansion and field matching,the theoretical model of cold cavity field of external devices is established.Firstly,the general telegraph equation satisfied by the electromagnetic field in the klystron resonator and the electron injection channel is obtained through the mode expansion.Ulteriorly,different forms coupling of field at the gap and at the coupling hole are tackled by combining with the idea of field matching.Finally,a complete theoretical model based on the MMT for external cavity resonator cold cavity field calculation is established.Simulating the cold cavity field of input and output cavity of klystron and comparing it with HFSS and CST,the results demonstrate the accuracy and the efficiency of the algorithm.