A Hybrid MOM/FEM Technique for Modeling Broadband Cavity-Coupled Microstrip Vertical Transitions

In this paper, a hybrid solution that combines the advantages of the MoM and FEM solutions is proposed to calculate the frequency response of the cavity-coupled vertical transitions. This technique differs from other boundary integral techniques in one major way: the FEM solution only serves as the replacement of the closed form Green's function. The formulation in fact is identical to pure MoM. In this method, the original problem are divided into two kinds of regions: the spatially unbounded regions where Green's functions are available but the FEM fails to accurately satisfy the radiation conditions or requires huge computational resource; and the regions with complex geometries where their Green's functions are not available but the FEM can be used to calculate equivalent ones. The separation of the original problem into the two kinds of regions makes the selection of the basis functions for the MoM solutions independent of that for the FEM solutions. It also retains the sparsity and symmetry of the finite element matrix, reducing the storage space and improving computational efficiency. By enforcing the continuity conditions of the electromagnetic fields across the boundary separating these regions, the solutions are coupled and form matrix equations for equivalent currents, which can be used to calculate the desired parameters of the original problem