On Modelling of Balanced Filters

In this paper, a lattice-based model of balanced filters is proposed. The symmetric lattice model is derived directly from the transversal circuit model of coupled-resonators filters through a series of equivalent transformations. Expressions for S-parameters of general symmetric lattice network are derived, as well as equations for S-parameters of balanced bandpass and bandstop filters utilizing the lattice model; the dualism of their transmission and reflection coefficients is demonstrated. Two numerical examples of modelling balanced bandpass and bandstop filters are presented.