Design of Balanced Dual-Band Superconducting Bandpass Filter with High Selectivity and Deep Common-Mode Suppression

In this work, a fourth-order balanced dual-band superconducting bandpass filter (BPF) is developed by using the newly symmetric-stub-Ioaded resonator (SSLR). The proposed SSLR has the advantage of two controllable differential-mode (DM) and more flexible control of the internal coupling. The DM bisection and common-mode (CM) bisection of the proposed SSLR are analyzed by applying the even- and odd-mode method and the corresponding resonant properties are investigated. With a proper design of SSLR, two controllable DM resonances that far away from CM resonance are obtained, which used to form the dual differential passbands. Finally, a balanced dual-band high-temperature superconducting (HTS) BPF operating at 1.9 GHz and 4.9 GHz for wireless communication application is successfully designed, and it demonstrates high selectivity for DM passbands and deep in-band CM suppression.