Ultra-low-noise 100 GHz receiver based on parallel biased SIS arrays

Abstract

The possibility of overcoming the main drawbacks of the traditional series arrays by using a parallel connection of SIS junctions for DC and IF current has been experimentally demonstrated in full height 70-116 GHz waveguide mixers. This new array concept has been successfully developed to: (i) avoid the influence of junction non-uniformity in the array; (ii) provide optimal matching at both RF input and IF output even in the case of high gain, and (iii) tune out junction capacitance without any DC blocks. The experimentally tested arrays contain 10 or 11 trilayer 2.5 mu m2 Nb-AlOx-Nb junctions. Best values of Tr(DSB) as low as 20+or-2 K have been measured at the receiver room temperature horn in the 104-108 GHz LO range with a 4 GHz IF and at a mixer ambient temperature of 4.5-5.5 K. An SSB mixer noise temperature as low as 6+or-3 K was estimated. This value is very close to the quantum noise limit hf/k approximately=5 K.