Measurement of the direct-detection responses of a 500-GHz and a 660-GHz waveguide superconducting SIS mixer

This paper presents the direct-detection responses of a 500-GHz and a 660-GHz waveguide superconducting SIS (superconductor-insulator-superconductor) mixer measured with a Fourier transform spectrometer (FTS). The two superconducting SIS mixers adopt the same type of junction tuning circuit (i.e., parallel connected twin SIS junctions), but are of different designs for the junction feed point where RF signals are coupled and then transmitted to the SIS junction tuning circuit and have different mixer design criteria. The experimental results are discussed in detail.