Canonical synthesis of transversal bandpass filters

Abstract

The objective of this study is to try to find a canonical solution to realise transversal bandpass filters (BPFs), especially transversal BPFs with high order. For this purpose, first, a new configuration composed of coupled lines and transmission lines is proposed. After a series of simple transformations and approximations executed, the proposed configuration is simplified to a circuit with four paths between the source and load, and each path contains one half-wavelength resonator. Then based on the modularity of transversal filters, a dual-mode resonator is used to replace the half-wavelength resonator in each path. Thus, the order of transversal BPF could be extended to five, six and even higher. It is shown that the proposed configuration could realise arbitrary BPFs specified by a transversal coupling matrix, including single-passband filter with multiple transmission zeros, self-equalised BPF and multi-passband filters. In final, a class of BPFs is synthesised, designed and measured to prove the validity of the approach.