K-band dual-band superconducting bandpass filter using uneven coupled SIRs and stub-loaded combining network

Abstract

A K-band millimeter dual-band superconducting filter with uneven coupled step-impedance resonators (SIRs) and stub-loaded combining network is proposed in this paper. The novel uneven internally coupled SIR introduces a notch to the classical internally coupled SIR, enhancing the Q-factor for narrow-band filter design. The performance of the uneven coupled SIR is theoretically
analyzed, and two single-passband superconducting filters based on the proposed resonator are designed and demonstrated its high Q-factor. A novel stub-loaded combining network is then investigated theoretically to integrate the two single passband filters into a dual-band filter. To validate the design concept, a dual-band superconducting filter is designed on a magnesium oxide (MgO) substrate
using the yttrium barium copper oxide (YBCO) superconducting film. The measured results reveal insertion losses of 0.91-1.2 dB of the first passband at 24.21-24.41 GHz with the bandwidth of 0.82% and 0.43-1.3 dB of the second passband at 24.67-25.2 GHz with the bandwidth of 2.12%, respectively. Both passbands exhibit return loss levels exceeding 8 dB, a maximum out-of-band suppression of approximately 65 dB, and a rejection level of about 35 dB between the two passbands.