Highly Selective and Controllable Superconducting Dual-Band Differential Filter With Attractive Common-Mode Rejection

In this brief, a high-order dual-band differential bandpass filter (BPF) with two controllable passbands and attractive common-mode (CM) rejection is proposed. The designed filter is constructed by a novel symmetric stub loaded shunted-line resonator (SLSLR). The differential-mode (DM) circuit and CM circuit of the proposed resonator are investigated detailedly by employing the even- and odd-mode method for two times. By properly designing the resonator, two reasonable DM resonances can be obtained to build dual DM passbands. In addition, the DM bisection has two independent parameters for adjusting internal coupling, leading to the individual control of the bandwidths of two passbands. Attributing to the intrinsic transversal interference paths, multiple transmission zeros are produced, resulting in a high selectivity of passbands. Additionally, a broadband CM rejection is achieved by utilizing the frequency discrepancy technique. Lastly, an eighth-order superconducting dual-band differential filter is realized. Its two passbands are respectively working at 1.9 and 4.9 GHz. MgO substrate with deposited YBCO material is used to process the filter. Good agreement between the simulation and measured results is obtained, which clearly verifies the demonstrated structure and the designing method.