Superconducting narrow-band filter for 2 GHz-band transmitter

We have developed a superconducting microstrip resonator for the narrow-band transmitting filter application, in order to achieve both high power handling capability and high unloaded Q value. For the superconducting microstrip resonator, it is necessary to suppress the radiation loss of the resonator in order to achieve high unloaded Q value and to reduce the maximum current density in the resonator to achieve high power handling capability, too. Therefore, by adopting an interdigital resonator consisting of two coupled comb resonators, we have reduced current density and suppressed the radiation loss. Using the interdigital resonators, we have fabricated an 8-pole pseudo-elliptic function filter that has about 2.0 GHz center frequency and 0.975% fractional bandwidth, and evaluated the power handling capability. As a result, we have confirmed that the power handling capability of the filter exceeds 40 W.