7 GHz-Band Quasi-Elliptic Function Narrow-Band Superconducting Filter on Sapphire Substrate

We have developed a 7 GHz band superconducting 8-pole quasi-elliptic function filter on sapphire substrate. To realize a high Qu microstrip line resonator at 7 GHz band, the structure was used for a resonator so as to suppress the radiation, which consists of two adjacent radiation points with opposite phase. Also, the radiation decreased in proportion to odd times of half-wavelength. Hairpin microstrip line resonator with 1.5 times wavelengths realized sharp-cut filter characteristic by both high Qu and transmission zeros. Measured center frequency of the 8-pole quasi-elliptic function filter agreed with the designed value. Given these features, a superconducting filter with a sharp skirt characteristic for next-generation RF applications is expected to be realized by applying these filters