MM/FE CAD and Optimization of Rectangular Combline Filters

A rigorous and fast hybrid mode-matching (MM)/finite-element (FE) technique is presented for the CAD and optimization of coax-fed rectangular combline filters. The novelty of the formulation consists in the very efficient EM based modeling of these filter types including immediately three common coax feed forms (direct post, disc or probe coupling). The attractive feature of the hybrid approach is the combination of the computational speed of the MM technique with the flexibility of the FE method. This achieves the direct optimization of combline filters within typically an overnight run on a PC. Design examples for a variety of combline filters demonstrate the flexibility of the CAD method, experimental results show its validity for practical applications.