Design of a Low-Band Wideband Superconducting Filter Using Triple-Mode Resonator
A compact high-temperature superconducting wideband bandpass filter (BPF) based on a triple-mode resonator is developed in this paper. The triple-mode resonator is constructed by connecting a folded end-coupled open-loop resonator (FEOR) with two asymmetric stepped-impedance resonators (SIRs). The FEOR and asymmetric SIRs have the characteristics of harmonic frequencies suppression. A meander three parallel-coupled lines structure (MTPLS) is proposed to implement sufficient external coupling strength. Simulated results show that the filter is centered at 1GHz (fc) with 100% 3-dB fractional bandwidth (FBW) and has an upper stopband to 3.5 fc. The measured results show the return loss is larger than 20dB and the insertion loss is less than 0.06dB.