Determination of the spectral response of sis-junctions by a direct detection measurement

We present a simple method to determine the spectral response of an SIS detector in the millimeter and submillimeter wavelength range from its current response to a chopped cold-load. This direct detection response is also a good indicator of quantum efficiency and mixer noise temperature when using the SIS junction in heterodyne mode. A simple experimental setup without local oscillator, cryogenic IF-amplifier or any quasioptical interferometer allows a quick diagnosis of integrated planar impedance matching structures.