Tri-band superconducting bandpass filter with controllable passband specifications

A compact tri-band bandpass filter is designed by combining a dual-band sub-filter and a single-band one. The dual-band sub-filter comprises four stub-loaded resonators. The single-band sub-filter is inserted into the gaps of the dual-band sub-filter for size miniaturisation. Both the centre frequencies and the bandwidths of the three passbands can be independently controlled. The measurements of the fabricated superconducting filter exhibit high performance and match well with the simulations.