Multiport MM/FE technique for the efficient CAD of folded and cross-coupled rectangular combline filters

The hybrid mode-matching/finite-element (MM/FE) technique extended to multiports yields generalized scattering matrix (GSM) building blocks for the CAD of advanced coax-fed rectangular combline filters of improved performance. The novelty of the formulation consists in the very efficient EM based modeling of folded and cross-coupled rectangular combline filters that allows their optimization within typically an overnight run on a PC. Usual coax feeds (direct post, disc, probe or loop coupling) are directly included. The attractive feature of the hybrid MM/FE approach is the combination of the computational speed of the MM technique with the flexibility of the FE method also for this class of components. Design examples demonstrate the flexibility of the CAD method; experimental results show its validity for practical applications.