Design of fourth-order dual-band superconducting filter using dual-mode resonator

A compact dual-mode hairpin ring resonator (HRR) is proposed to implement dual-band superconducting bandpass filter (BPF) in this paper. Non-coupled and controllable dual-mode resonant characteristics of the proposed HRR are analyzed. Moreover, HRR can be easily extended to high-order filter design because of its unique structural characteristics. For demonstration, a fourth-order dual-band superconducting BPF is designed by using four coupled HRRs. Coupling structure for the adjacent HRRs with inverse orientation is used to excite multiple transmission zeros for high selectivity. The finally obtained fourth-order dual-band filter operating at 1.9 GHz and 2.6 GHz has desired frequency responses and compact size.