Compact Dual-Band HTS Bandpass Filter Using Coplanar Waveguide Short-Circuited Stub-Loaded Ring Resonator

A compact coplanar waveguide (CPW) dual-band high-temperature superconducting (HTS) bandpass filter using a short-circuited stub-loaded ring resonator (SC-SLRR) is introduced in this paper. The equivalent circuit of the SC-SLRR is built and its resonant formulas are presented. The relationship between the parameters of electrical length and resonant performances are deduced. Resonant modes of the proposed resonators can be simultaneously excited and easily tuned for a dual-band application. To verify this methodology, a second-order CPW HTS dual-band bandpass filter operating at 2.36/4.93 GHz is designed. This filter is implemented on a 0.5-mm thick MgO wafer with a one-sided YBa 2 Cu 3 O 7 film, and it has the compact size of 0.146λg × 0.083λg. Measured results agree well with the simulated ones, which show that the minimum insertion losses of both bands are less than 0.15 dB.