Miniaturized Quadband High-Temperature Superconducting Bandpass Filter with a Wide Frequency Ratio

Abstract

This paper presents a miniaturized quadband high-temperature superconducting (HTS) bandpass filter based on a multistub-loaded resonator. Owing to the symmetrical structure of the proposed resonator, the odd- and even-mode analysis method can be used to derive its resonance frequencies. First, the frequency ratio between passbands may be significantly changed by adjusting the impedance ratio and fold spacing of the resonator. Moreover, the proposed filter exhibits well-controlled center frequencies and bandwidths for the four passbands, resulting in a considerably enhanced design possibility of quadband bandpass filters. A low insertion loss within each band is obtained using HTS technology. Additionally, the proposed filter was etched on an MgO substrate with a thickness of 0.5 mm and combined with YBCO thin films for demonstration. The results obtained were highly consistent with those of the simulation, validating the effectiveness and viability of the proposed method.