Tri-band superconducting filter using stub-loaded stepped-impedance resonators

• A stub-loaded stepped-impedance resonator is proposed to design a tri-band bandpass filter.
• The insertion losses are significantly reduced by using high-temperature superconducting thin films.
• The measured results exhibit high performance and agree well with the simulated ones.

A stub-loaded stepped-impedance resonator (SLSIR) with three resonant modes is proposed to design a tri-band bandpass filter (BPF). The couplings between adjacent resonators at different resonant modes can be controlled independently by properly selecting the geometric parameters of the resonator. A dual-feeding structure is used to realize the required external couplings of the three passbands simultaneously. A fourth-order tri-band BPF with the passbands centered at 1.73, 2.40 and 3.45 GHz, respectively, is successfully designed and fabricated with superconducting thin films. The measured results exhibit high performance and agree well with the simulated ones.