Efficient hybrid MM/MoM technique for the CAD of circular combline filters with resonators of more general shape

A hybrid mode-matching (MM) / method-of-moment (MoM) technique is presented for the efficient CAD and optimization of circular combline filters involving more general elements like corrugated circular post and re-entrant resonators. Using the free-space Green's function, the proposed technique combines the high flexibility of the MoM with the efficiency of the MM method. A locally refined adaptive triangular surface mesh and the application of Rao-Wilton-Glisson (RWG) basis functions achieve the reliable modeling of arbitrarily shaped structures. The building blocks are combined by the generalized scattering matrix (GSM) allowing typical MM elements like irises to be efficiently included. The attractive feature of the proposed method is its short computation time (order of a few seconds per frequency point) achieving the full-wave optimization of such filters within reasonable times. The high versatility of the hybrid method is demonstrated at examples of practical interest; its efficiency and accuracy is verified by available measurements.