Design and High-Frequency Response of Resistive SQUID Frequency Converters

Several resistive SQUID frequency converters (R-SQUID) have been constructed and their properties studied in the frequency regimes 26.5–40 and 67–73 GHz. A brief outline of the theory of the device is presented together with constructional details for a Nb–Nb point-contact version. The device response is complicated by the effects on the ac Josephson current of distributed circuit elements, and a broad range of complex behavior is presented which is only partially understood. A useful amplification effect for the detected signal has been discovered, which gives the device good broad range sensitivity (∼ 10−7–∼ 10−12 W/Hz1/2) and reasonably narrow linewidths (Q-values of ∼ 104 at 70 GHz).