Design of Ultra-Narrowband Miniaturized High Temperature Superconducting Bandpass Filter

This paper proposes a novel clip-shaped meander-line resonator (CSMLR) to realize miniaturized ultra-narrowband (UNB) bandpass filter design. The main advantage is that it can achieve very weak coupling between adjacent resonators with keeping them very close and introduce transmission zeros (TZs). To further demonstrate the feasibility of using this configuration, a six-pole UNB filter with a fractional bandwidth (FWB) of 0.20% at the center frequency of 1915 MHz was designed on double-sided YBCO high temperature superconducting (HTS) thin films with a thickness of 0.5mm and dielectric constant of 9.8. The measured responses agree rather well with the simulated ones. The measured results show a maximum insertion loss of 0.31 dB and return loss of 15.5 dB in the passband. Two TZs are generated to improve the passband selectivity, which causes the band-edge steepness better than 50 dB/MHz in both transition bands.