An Nb-based waveguide SIS distributed mixer employing coplanar inductor loaded microstrip transformer for the 800 GHz frequency band

We present a novel superconducting waveguide mixer for 800 GHz. In this mixer, a half-wave Nb/Al-AlO_x/Nb superconducting-insulator-superconductor (SIS) resonator is integrated with a microstrip superconducting transmission line loaded with coplanar inductors. This hybrid coplanar/microstrip transmission line acts as an impedance matching section between the distributed junction and the waveguide feed point of the mixer mount. We have designed mixers with a simple model which predicts that the insertion loss of the matching network is less than 10 percent up to 840 GHz. Preliminary experimental results show that the resonator can work up to 800 GHz but the parameters of the coplanar inductor loaded microstrip line need to be refined to improve power coupling to the resonator.