Prototype network synthesis for wideband microwave filters

A direct synthesis method is presented for folded bandpass filter prototype network. The prototype network consists of LC resonators coupled by frequency-dependent (L/C) couplings, which can model the filter responses over a wide frequency band. The synthesis method is generally applicable to a broad class of filtering characteristic functions. Commencing from transfer and reflection polynomials, a two-port [ABCD] transfer matrix is formed, enabling the extraction of variant circuit elements from the input and output ports of the prototype network. The extraction procedure is adequate for any cross-couplings, symmetric or asymmetric. The flexibility of the method makes it possible to configure the prototype network for the most realizable coupling topologies and the types of coupling elements.