A Direct Method of Synthesis for a Class of Waveguide Filters

A direct method of synthesis on insertion loss basis is presented for symmetrical waveguide filters which can be modelled by a cascade chain of lumped parameter, reactive, symmetric two-ports and lengths of unimodal waveguide sections (Fig. 1). The presented method is rather general, easy to implement numerically and sheds physical insight into the complex propagation phenomena in waveguide filters. Hereby the synthesis of a N-section symmetric filter, where N is an odd integer, is reduced to the simultaneous solution of (N+l)/2 nonlinear equations which can be written down by inspection for given design perspectives. The achieved degree of accuracy in the design is remarkably good over bandwidths in excess of 60%.