Analysis Of Complex Waveguide Discontinuities Based On Mode Matching Method

With the rapid development of modern microwave techniques, the demand for high precision microwave passive components such as filters, diplexers becomes more and more rigorous. Traditional equivalent circuit method can no longer keep up with the pace of the microwave technique development, because components designed by this method have low precision and are found to be hard to adjust. Based on the exact field theories, Mode Matching Method, which is a semi-analytic method, can be used to analyze the waveguide and its discontinuity. The finite thickness of metal irises and the effect of higher order modes are taken into account by this method rigorously. Therefore, the components designed by this method have very high effective.In the issues of the analysis the discontinuities, such as the waveguide step and iris, the mode functions are obtained by the wave equations. The tangential components in both TE wave and TM wave are expanded and then are matched according to the orthogonality with the equalities of transverse field continuity. Finally generalized scattering matrix can be obtained by the above relation.Generally speaking, microwave passive components are composed of a series of basic blocks. These blocks can be rigorously analyzed by mode matching method. Once the symmetry is considered, the analysis of the whole structure is simplified greatly, such as ridge waveguide or crossed rectangular waveguide. Finally, the generalized scattering matrix of microwave passive components can be obtained by mode matching method and matrix cascading technique.By this method, the curve results agree well with the simulations and the calculation time is greatly shortened too.