Characterisation of millimeter and submillimeter wave mixers based on high-T/sub c/ superconductor structures

We report on our experimental studies of noise properties and conversion efficiency of high-T/sub c/ Josephson mixers and high-T/sub c/ hot-electron bolometric (HEB) effect mixers at frequencies between 90 GHz and 550 GHz. Noise measurements using a Josephson mixer at 90 GHz gave noise temperatures of 2900 K at 20 K. Measurements in a quasi-optical setup at 430 GHz and 546 GHz showed mixer noise temperatures of 1200 K and 1100 K at 4.2 K, respectively. Heterodyne mixing experiments using high-T/sub c/ HEB mixers have been performed at temperatures around 78 K and at frequencies between 78 GHz and 119 GHz. The uncorrected conversion efficiency at an intermediate frequency of 3 GHz was measured to be -30 dB.