Wide-Stopband Superconducting Bandpass Filter Using Slitted Stepped-Impedance Resonator and Composite Spurline Structure

In this paper, a wide-stopband high-temperature superconducting (HTS) bandpass filter (BPF) is presented using slitted stepped-impedance resonators (slitted-SIRs). The use of SIR is essential in widening the filter stopband. Besides, it is found that introduced slits in SIRs provide additional freedoms to control resonance modes when compared with a conventional SIR. Hence, four types of slitted-SIRs are arranged at same fundamental mode f
₀
and different higher order modes by adjusting the slits. The coupling of higher order modes is reduced and wide stopband is achieved. In addition, a composite spurline structure is employed to generate two independently controllable transmission zeros, which further improves the stopband performance. Finally, a cascade quadruplet HTS BPF is designed and fabricated on an MgO wafer with double-sided YBCO films. Measurement shows the passband of the BPF is operated at 2.35 GHz and its minimum insertion loss is less than 0.15 dB. The rejection level is better than 21.9 dB in the stopband up to 13.26 GHz (about 5.64 f
₀
). The designed HTS filter tends to the potential application for the desired wide stopband and the high selectivity performance.