Novel Tri-Band High-Temperature Superconducting Bandpass Filters Using Asymmetric Shunted-Line Stepped-Impedance Resonator (SLSIR)

In this paper, a tri-band high-temperature superconducting (HTS) bandpass filter (BPF) is proposed with a pair of asymmetric shunted-line stepped impedance resonators (SLSIRs). Compared with the conventional SIRs, the proposed asymmetric SLSIR has more degrees of freedom in controlling multi-mode operating characteristics. Moreover, design graphs for the relationship of electric characteristic parameters and the resonant frequency ratio are built and applied to multiband device design. For demonstration, a two-order tri-band HTS BPF is well designed with center frequencies of 1.575/2.4/3.5 GHz. The external quality factor and the coupling coefficient have also been analyzed to satisfy the bandwidth of the BPF. The designed filter is fabricated on the YBCO superconducting material and measured under superconducting conditions (at the temperature of 77 K). The measurement results are in good agreement with the simulation results, indicating that the insertion loss of the three passbands is about 0.1 dB, showing the advantage of in-band insertion loss.