Design of sharp-rejection and low-loss wide-band planar filters using signal-interference techniques

TLDR

The paper introduces a new class of sharp‑rejection, low‑insertion‑loss wide‑band planar filters. The filter employs transversal signal‑interference sections made of two parallel transmission‑line segments, producing multiple out‑of‑band transmission zeros and constructive in‑band combinations, with design equations that allow bandwidth and out‑of‑band performance to be tuned. Theoretical predictions are confirmed by fabricating and testing an ultra‑wideband microstrip filter prototype at 5 GHz.

Abstract

A new class of sharp-rejection, low insertion-loss wide-band planar filters is presented in this letter. The proposed filter topology uses transversal signal-interference filtering sections made up of two transmission-line segments connected in parallel. Thus, under signal-interaction principles, the filtering action comes about through the generation of multiple out-of-band power transmission zeros and constructive in-passband signal combinations. Design equations and guidelines to adjust both the bandwidth and the out-of-band performance of the filtering response through the design parameters of the transversal section are also provided. Furthermore, the theoretical results are validated with the manufacture and characterization of an ultra-wideband microstrip filter prototype at 5 GHz.