Optimum Bias Conditions for K-Band Microwave Mixing Using YBaCuO Step-Edge Microbridge Josephson Junction

Characteristics of the K-band microwave mixing using a YBaCuO step-edge microbridge Josephson junction were systematically investigated, and the optimum bias conditions were experimentally determined. A large intermediate frequency (IF) output signal was observed at every midway between the Shapiro steps, and the maximum IF output was obtained between the 0th and 1st steps (0-1) for the local oscillation (LO) power level of I 0/I c=0.2-0.3 (absolute LO power of -49.9 dBm). The maximum conversion efficiency was estimated to be -26.6 dB. Although the IF output (0-1) was observed for a wide range of LO power, it vanished or decreased radically under some peculiar conditions (I 0/I c?0 and ?(I 0/I c)/?I LO?0). These characteristics were qualitatively accounted for by the basic Josephson-mixing theory.