1Waveguide Filter Design with Finite Element Method and Mode Matching

Abstract — In this paper, a hybrid method that combines the finite element method (FEM) and the mode matching technique is proposed to analyze waveguide filters consisting of perforated metal screens. Such structures can be considered as a cascading of sections of homogenous waveguides with different cross sections. The FEM is applied to each section to compute the waveguide modes. The use of the FEM enables the incorporation of arbi-trarily shaped cross section in the structure. At the junction of two adjacent waveguides, the corresponding modes are matched and a scattering matrix is computed. Finally, scattering matrices for different junctions are cascaded to generate a composite scat-tering matrix for the whole structure. Since only two-dimensional problems are involved in this method, the computation time and memory usage are drastically reduced compared to the three-dimensional volumetric modeling. The resultant efficiency makes the method most suitable for combining with optimization methods to obtain optimal designs, as demonstrated in the numerical examples. Index Terms — finite element method, mode matching, waveg-uide filter design I