A Sensitive and Permanent Josephson Mixer for Millimeter Waves

A new method to construct permanent Josephson mixers for millimeter waves is described. In contrast to conventional point contacts which are mechanically unstable and require adjustments after each cooldown, these point contact junctions are set at room temperature, stay mechanically stable and can be temperature cycled without readjustments. The junctions are packaged in a modified Sharples mixer wafer and exhibit a single-sideband noise temperature of 71° K at 47 GHz. Based on these results system noise temperatures of less than 100° K are predicted for practical broadband radiometers, radar and communications receivers up to at least 100 GHz.