3 GHz-band superconducting wide-band filter for small microwave receiver

We have developed a low-insertion-loss and wideband bandpass filter using a superconducting microstrip filter, in order to reduce the noise of a small microwave receiver in the 3 GHz band. For the superconducting microstrip filter, it is necessary to suppress the radiation loss of the resonator in order to achieve low insertion loss and to couple resonators strongly with each other to achieve wide passband, too. Therefore, by adopting an interdigital hairpin resonator whose ends are both comb-shaped, we have aimed to suppress the radiation loss and to strengthen the coupling between resonators. Using the interdigital hairpin resonators, we designed and fabricated a 5th-order Chebyshev filter and evaluated its frequency characteristics. As a result, it is confirmed that the insertion loss is less than 0.06 dB and the fractional passband width is 26.8%.