PARALLEL BIASED SIS-ARRAYS FOR MM WAVE MIXERS - MAIN IDEAS AND EXPERIMENTAL-VERIFICATION

The possibility to overcome the main drawbacks of the traditional series arrays by parallel connection of the SIS junctions for dc and IF have been experimentally demonstrated. The proposed mixing elements i) avoid the influence of the junction nonuniformity in the array; ii) provide the optimal matching on both rf input and IF output; iii) tune out junction capacitance. Experimentally tested arrays contained up to 8 high quality Nb-AlO(x)-Nb junctions with R(n) = 20...70 Ohm at junction area 8 divided-by mu-m2. The best values T(r) (SSB) as low as 5 K have been measured on the mixer cold input flange in the 45-55 GHz bandwidth at ambient temperature 4.2 K. The mixer gain up to 10 dB was obtained, the gain values were limited by bias stability at very high or even negative array output impedance. The experimental receiver noise temperature (SSB) less than 20 K have been achieved referred to the room temperature horn.