Planar Compact Waveguide Step Matching Structure

Impedance matching technology has extensive and important applications in microwave transmission systems.When two waveguides with different characteristic impedances are connected,the power capacity and transmission efficiency of the transmission system will be reduced due to reflection,and in serious cases,the system will not work properly.To solve the problem of impedance mismatch,an impedance matching circuit needs to be designed.For the impedance matching circuit,under the condition that the specified operating bandwidth and the length of the matching section are fixed,to shorten the length of the matching section as much as possible,the forefathers of the international microwave community have done a lot of theoretical research.For the convenience of calculating the size of the matching structure and the reflection coefficient,many restrictions have been added before,and the "best matching scheme" is designed,which is the traditional quarter-wavelength ladder impedance matching.But because of the constraints,these design options are not optimal.As the development of threedimensional electromagnetic simulation software becomes more and more mature,it is easy to use the software to perform complex numerical calculations.Therefore,it is possible to consider gradually releasing the restrictions and optimizing to obtain a matching circuit with better performance.The purpose of this paper is to design a matching circuit that is shorter in length than the traditional ladder impedance matching circuit and has a lower maximum reflection coefficient.The design idea is: First,let go of the restrictions in the traditional ladder impedance matching circuit for optimization,to try to obtain a matching circuit with better matching performance.Then,symmetric and asymmetric complex cross-section transmission lines are used for design,and a single-stage complex transmission line impedance matching circuit and dual-stage complex transmission line impedance matching circuit are designed.Compare the highest reflection coefficient of each design and the length of the matching section to finally obtain the best design.Considering people's demand for low manufacturing costs,all the design schemes in this paper adopt quasi-planar design.The research work of this article is as follows:1.Theoretically calculate and model the initial structural parameters of the traditional a single-stage quarter-wavelength transmission line impedance matching circuit.The initial model was gradually released from the constraints to optimize the design,and then a a single-stage complex cross-section transmission line was used to design the impedance matching circuit.Comparing the performance indexes of various design schemes,the best design scheme of a single-stage waveguide ladder impedance matching circuit is obtained: a single-stage asymmetric fifth-order complex crosssection transmission line impedance matching circuit.2.Theoretically calculate and model the initial structural parameters of the traditional second-order quarter-wavelength transmission line impedance matching circuit.The initial model was gradually released to limit the conditions for optimal design,and a two-stage complex transmission line was used to design the impedance matching circuit.Compare the performance indicators of each design.The best design scheme of the two-stage waveguide ladder impedance matching circuit is obtained: an asymmetric two-stage fifth-order complex section transmission line impedance matching circuit.3.To verify the correctness of the simulation results,choose an optimization program for processing test,and analyze the test results.4.Summarize the design of this paper and prospect the next step.