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 a 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