Series-cascaded rings dual-band filter

This paper presents a new topology of dual-band bandpass filter which is based on two series-cascaded ring resonators and fed via quarter-wavelength coupled-lines. Based on such topology, a microstrip dual-band filter is designed and realized on FR4 substrate. The passbands of the dual-band filter are centered at 0.89 GHz and 1.20 GHz with relative bandwidths of 18 % and 11 %. Simulated and measured results are presented throughout this paper to validate the idea.