Reflectionless triple‐band BPF by reused even‐mode resonances of multi‐mode resonator

Abstract

A novel reflectionless triple-band bandpass filter (RTBPF) with compact structure and high controllability is proposed by combing the reused multi-mode resonator (MMR) with a coupled-line based absorptive network. The MMR is coupled to feeding lines to share its even-mode resonating points as transmission poles (TPs) in bandpass branch and transmission zeros (TZs) in bandstop branch. By employing the coupled-line based absorptive network, additional TZs and TPs are obtained in bandstop branch. Since these resonances in bandpass branch and the absorptive network are controlled independently, the bandwidth and centre frequency of the RTBPF can be tuned flexibly. The implemented RTBPF demonstrates a minimum insertion loss of 1.68 dB@2.4 GHz, 1.65 dB@3.2 GHz, 1.5 dB@4.3 GHz, three absorption peaks of − 6, −7 and −8 dB from dc up to 6 GHz. The overall circuit size is 0.22 λg 2.