Dual-band bandpass filter using two simple coupled microstrip rings

Abstract

A new dual-band bandpass filter (BPF) using two very simple coupled microstrip rings is proposed in this paper. The two identical 3λg/2 microstrip rings are coupled each other with λg/2 coupled length, resulting in the generation of dual frequency bands with multiple transmission zeros (TZs). Theoretical deduction is presented to verify the proposed structure. The center frequencies and bandwidths of the two passbands can be tuned by controlling the impedance parameters of the microstrip rings. For demonstration, a prototype example of this dual-band BPF is fabricated and characterized. The measured results show that it has high selectivity and great return losses of passbands with multiple TZs at the stopband.