Design of Tri-Band Superconducting Bandpass Filters with Independently Controllable Bandwidths

A high-temperature superconducting tri-band bandpass filter (TBPF) has been developed. The TBPF is realized by combining a three-pole dual-band bandpass filter (DBPF) which uses stub-loaded meander line resonators with an additional capacitance-loaded microstrip line, and a three-pole single band bandpass filter (SBPF) which uses folded stepped-impedance resonator with common input and output. The DBPF constructs the first and third bands, and the SBPF forms the second band. The DBPF enables independent control of the center frequencies of the first and second bands. The bandwidths of the DBPF can be flexibly adjusted using the additional microstrip lines. The TBPF was designed and analyzed using an electromagnetic simulator based on moment method. The TBPF was fabricated using YBa₂Cu₃O_y thin film on a 25×25×0.5 mm Al₂O₃ substrate. The center frequencies of the three-pass-bands are 3.5, 4.25, 5.0 GHz; three bands have a 2% bandwidth. The measured frequency response of the TBPF was in good agreement with the simulated one.