Mode Matching Method And Its Application In Microwave Windows

Mode matching method(MMM)is established on the generalized transmission line theory and is a sort of full wave analysis method based on electromagnetic field theory.This method has developed to the strictly analytic stage at present and has the advantages of high precision,fast calculation speed as well as small computer memory consumption.The method has been successfully used in the design of components including filters,couplers,impedance matchers,mode converters,antennas,multiplexers,power dividers,feedback networks,phase shifters,polarizers,compensation bend waveguides,etc.Mode matching method has also been applied to solving eigen value problem as well as the characteristic analysis of chiral media.As one of the most important component of the input and output system,microwave window is also an important passive component of high power microwave system.Besides vacuum sealing function,it also bears the function of microwave energy feed,microwave transmission and reducing the reflection.Therefore,the quality of microwave window affects directly the electric parameters of microwave devices and the life span.In this paper,mode matching method and its application in microwave windows are deeply studied.The detailed theoretical analysis and analytic formula derivation of this method are finished.S parameter calculation,relative convergence,the complex power conservation and the electromagnetic field matching are analyzed theoretically and verified numerically.The most four common types of window structures used in microwave tube are designed and simulated by using mode matching method,which greatly shortens the design cycle of the window on the premise of high precision.The designed window types include diaphragm-loaded rectangular waveguide window,multilayer dielectric circular waveguide window,coaxial window and high power pill-box-type window.The main contents and innovation points of this thesis are as follows:1.The mode matching method is studied systematically and deeply.By using electromagnetic field boundary conditions,the generalized scattering matrixes of five kinds of abrupt junctions are set up,respectively.The junctions include rectangular to rectangle,round to round,coaxial to coaxial,big rectangular to small circle,big circle to small rectangular.Using Green's theorem,discrete Fourier transform,coordinate system conversion and principle of normalization and orthogonality,the coupling matrixes of the five types of abrupt junctions are derived analytically and separately.2.Using matrix cascade and transmission line theory,the generalized scattering matrix of the regular passive component model is deduced and calculated analytically.Based on MATLAB language,the program package of mode matching method is written and named MMMS.The relative convergence of this method is analyzed.3.Under the framework of the mode matching method,the power amplitude coefficients of each mode are derived.The complex power of any cross section within the whole frequency band and the electromagnetic field distribution in the three dimensional space at arbitrary frequency are obtained successfully by using the coefficients.In the propagation process of the electromagnetic wave,the complex power conservation and electromagnetic field matching are verified.4.The most common four types of microwave windows are designed and simulated by mode matching method and the corresponding calculation results are compared with those from CST simulation,HFSS simulation and MTSS simulation.Because all of the results are in agreement,the correctness and reliability of the formula and the program code based on mode matching method are finally verified.