High‐selectivity bandpass filter using six pairs of quarter‐wavelength coupled lines

Abstract

A novel high-selectivity bandpass filter (BPF) with multiple transmission poles (TPs) and transmission zeros (TZs) using six pairs of quarter-wavelength coupled lines has been presented. By employing two pairs of side-coupled lines and four pairs of open/shorted coupled lines, high roll-off skirt characteristic, and good stopband rejection can be achieved with five TPs and six TZs. Theoretical analysis is explained and simulated results are illustrated for this high-performance filter. Finally, a BPF example with a centre frequency of 1.9 GHz and a 3 dB fractional bandwidth of 9% is designed, fabricated, and measured. It is shown that the measured lower and upper stopband rejections are better than 38 and 16 dB, respectively. Good agreement between the simulations and measurements validates the design method.