Design of a High-order Dual-wideband Superconducting Filter Using Stepped-impedance Cross Structures

This letter presents a broad dual-band filter design with stepped-impedance cross structure (SICS). Four stubs (two low frequency and two high frequency ones) are connected to the rectangular patch in the center to construct the proposed SICS. The center frequencies of the high-band and low-band can be controlled independently. The patch leads to the even- and odd-mode split to act as two non-degenerate dual-mode resonators to design dual-band filter, parallel-coupled structures are used to provide strong couplings for both passbands, and transmission zeroes are introduced on the two sides of the two passbands. An HTS broad dual-band filter operating at 2.91 and 5.98 GHz with -3dB FBWs of 27.6% and 24.3%, respectively is designed and fabricated. The measured results show good performance and agree well with the simulations.