This paper presents a synthesis design method for superconducting dual-mode dual-band filters. A low-pass to dual-band bandpass frequency transformation is proposed based on lossless lumped-element dual-mode resonator circuits. Formulas for extracting the coupling coefficient k and external quality factor Qe of dual-mode microstrip resonators are derived using the coupling matrix theory and the proposed frequency transformation formula. This makes the design process of dual-mode dual-band filters similar to that of the single bandpass filter. For the demonstration, four dual-band superconducting filters with different dual-mode resonator structures, such as stepped-impedance, stub-loaded, and embedded resonators are designed and fabricated. The measured results match well with the simulations.
Ma, P., Wei, B., Hong, J-S., Cao, B., Guo, X., & Jiang, L. (2017). Design of Dual-Mode Dual-Band Superconducting Filters. IEEE Transactions on Applied Superconductivity, 27(7), . https://doi.org/10.1109/TASC.2017.2732288