Dual-Band Superconducting Bandpass Filter Using Stub-Loaded Resonators With Controllable Coupling and Feeding Structures

A four-pole dual-band bandpass filter is designed with stub-loaded resonators and dual-feeding structure. The stub-loaded resonator generates two resonant modes, and the interstage couplings between the resonators at the two modes can be controlled independently. A dual-feeding structure is proposed to meet the required external couplings of the two passbands simultaneously. The filter is successfully designed and fabricated on a MgO substrate with a compact size of 29.2 mm × 13.8 mm. The measured results show high performance and agree well with the simulations.