Analysis of millimeter wave microstrip circulator

A hybrid method that combines mode expansion and finite element method (FEM), which is based on Helmholtz Weak Form, is used to deal with inhomogeneous structure, shielded microstrip circulator. Mode expansion other than PML is used to truncate the FEM computing domain into the finite and smaller one. Here, S parameters of the shielded microstrip circulator are computed in two steps. Firstly, the field distribution and propagation constant of the modes of shielded microstrip can be obtained with 2-D FEM program. Secondly, the 3-D Vector-FEM is used to model the inhomogeneous structure and matched with the field of microstrip at interfaces, so a sparse matrix is obtained. Then SSOR-BCG algorithm is used to solve the matrix equation. The computation results are presented and compared with the measured results, and show the usefulness of this hybrid method.