Wideband SIS Receivers Using Series Distributed SIS Junction Array

We have developed an SIS mixer based on a 3-junction series distributed array. In this mixer layout, the three junctions are connected together by passive network elements, such that each junction is subjected to different local oscillator (LO) drive, and slightly different DC bias voltages. This design helps to reduce the output capacitance of the mixer at the intermediate frequency (IF) so as to achieve a wider IF bandwidth, while maintaining adequate RF bandwidth. The receiver performance of this type of mixer was evaluated in the 220 GHz band. The lowest noise temperature measured was ~30 K, and the noise temperature remains below 50 K over the IF range from 3 to 11 GHz. Receivers incorporating this new mixer design are currently in routine operation at the Submillimeter Array.