Ultra-narrowband HTS filter with 2.5-wavelength hairpin resonators in 7 GHz band

Abstract

We have developed an ultranarrowband high-temperature superconducting (HTS) filter with a fractional bandwidth of 0.14% in the 7 GHz band. To realize a filter with which a narrow bandwidth and low insertion loss are compatible, resonators with high unloaded Q (Qu) value are required. Hairpin microstrip resonators with 2.5 times wavelength were adopted to suppress the radiation loss and realize a high Qu value. With both the hairpin resonators and transmission zeros supplied by an 8-pole quasi-elliptic function filter construction, designed filter properties were realized. Next-generation RF applications are expected to be realized by applying these filters.