Design of a Superconducting Ultra-Wideband (UWB) Bandpass Filter With Sharp Rejection Skirts and Miniaturized Size

This letter presents a superconducting ultra-wideband (UWB) bandpass filter (BPF) with sharp rejection skirts and miniaturized size using multiple-mode resonator (MMR). The MMR is formed by loading a stepped-impedance open-end stub in shunt to a modified stepped-impedance resonator (SIR). The modified SIR generates three resonant modes within the 3.1-10.6 GHz UWB band, whereas the stepped-impedance open-end stub creates two transmission zeros and two additional resonant modes improving the bandedge steepness. Interdigital coupled-lines are used for the external couplings to enhance the coupling strength. A superconducting UWB BPF is realized with a compact size of 20 mm × 11 mm. The measured results without any tuning show good performance. The insertion loss at the center frequency is 0.58 dB, the return loss is greater than 10.6 dB, and the group delay variation is less than 1.76 ns. Furthermore, the experimental results of the filter are in good agreement with the simulated ones.