Method of moments analysis of a waveguide crossed slot by using the eigenmode basis functions derived by the edge-based finite-element method

A hybrid analysis of the method of moments (MoM) and the finite-element method (FEM) is proposed for a waveguide crossed slot. The eigenmode functions of an X-shaped waveguide, with the geometry of the crossed slot in the cross section, are utilised as the basis functions of the magnetic currents in the MoM. They are derived as vectors by the edge-based FEM to express the current flow accurately around the crossing part. Reactions in the wall-thickness region of the rectangular waveguide can be simply and accurately evaluated without taking mode summation because of the orthogonality of the eigenmodes. The proposed method is advantageous for a crossed slot, especially with a wide slot width and a thick waveguide wall. For the verification of the analysis, the calculated results of the transmission coefficient, and the radiation pattern are compared with the measured ones using a 12 GHz model antenna. The agreement in the transmission coefficient is very good both in amplitude and phase from 10 to 15 GHz.