Analysis of Nb superconductor-insulator-superconductor tunnel junctions with Al striplines for THz radiation detection

We study the gain and noise of a receiver consisting of a niobium junction embedded in an aluminum impedance matching circuit. The junction is operated in a waveguide mount with an adjustable backshort. The uncorrected double side band noise temperatures are 940 K to 1388 K for 820 to 980 GHz respectively. The total optical loss is obtained from the losses of the individual components, the losses in the stripline are calculated using the Reuter-Sondheimer equation in the extreme anomalous limit. The embedding impedance follows from the pumped curves and the Tucker equations which are also used to determine the noise and gain of the junction. The main limitation to the receiver sensitivity is shown to be the loss in the aluminum circuit.