Parallel-coupled linear-phase superconducting filter

A novel double coupling planar structure (a single microstrip line coupled with two resonators coincidental) is presented for the first time. Based on this structure, a six-pole parallel-coupled high-temperature superconducting band-pass filter with both linear phase response and quasi-elliptic function response is designed. The filter has a 40 MHz passband with a center frequency of 2,000 MHz. Its dimension is 18.67 mm × 25.96 mm. At 77 K, minimum insertion loss is 0.26 dB in passband. The group delay variation is <3 ns over 70 % of the filter bandwidth.