Coplanar-Waveguide Quarter-Wavelength Resonator with Open Stubs for Miniaturizing High-Temperature Superconducting Bandpass Filter

This paper presents a newly developed compact coplanar-waveguide (CPW) quarter-wavelength resonators with open stubs for use in a miniaturized high-temperature superconducting (HTS) bandpass filter (BPF). The proposed resonator has a structure in which the open stubs are aligned close to the center conductor of the resonator. This is because strongly-coupled resonators have widely-split resonant frequencies, and the lowest resonant frequency is employed as the fundamental resonant frequency of the resonator in order to achieve miniaturization. A four-pole Chebyshev HTS BPF is designed and fabricated using the proposed CPW resonators to investigate the validity of the proposed resonator. The filter achieves a size reduction of at least 50% compared to previously reported filters without any degradation in the frequency characteristics.