Dual-Band Superconducting Bandpass Filter Using Quadruple-Mode Resonator

A dual-band high-temperature superconducting (HTS) bandpass filter (BPF) using a quadruple-mode resonator is realized in this paper. The resonator consists of a half-wavelength uniform impedance resonator, an open stub in a symmetrical plane, and two spiral open stubs at the two sides of the symmetrical plane. Distinct characteristics of the quadruple-mode resonator are investigated by using even/odd mode theory, and the design graphs are given to analyze the dual-band filter. A dual-band HTS BPF with central frequencies of 1.8 GHz for GSM applications and 2.4 GHz for wireless local area network applications is designed using the proposed quadruple-mode resonator, which is fabricated by depositing YBCO films on a 0.5-mm-thick MgO substrate. Its size occupies only 13 mm × 17 mm. Measured results demonstrate that an insertion loss within the passbands is less than 0.25 dB. In addition, a transmission zero is achieved in-between two passbands, and two transmission zeros are realized in the upper stopband of the higher passband, which improve the skirt selectivity and stopband characteristics of the filter.