Broadband twin-junction tuning circuit for submillimeter SIS mixers

A 400–550-GHz fixed tuned quasioptical Nb/AlOx/Nb SIS heterodyne receiver has been built, and its performance has been evaluated. The receiver, operated at 3.5 K, showed noise temperatures ≤ 300-K DSB within the tuning range of the available LO source (440–520 GHz). The SIS junction capacitance was tuned out by a novel twin-junction circuit, which offered 130-GHz fixed tuned bandwidth at 480 GHz. Large-area SIS junctions (3.5 μm2, ωRnC ≈ 7.5 at 500 GHz), patterned by optical lithography, were used. © 1995 John Wiley & Sons, Inc.