Design and characterization of 225-370 GHz DSB and 247-360 GHz SSB full height waveguide SIS mixers

Abstract

We report on the design and characterization of two full height waveguide SIS mixers for astronomical applications: a Double Side Band (DSB) fixed-tuned mixer covering the 225-370 GHz band ( 50 % of relative bandwidth), and a tunable Single Side Band (SSB) mixer covering the 247-360 GHz frequency range. The DSB receiver noise temperature we have measured is below 50 K over a bandwidth larger than 100 GHz for the DSB mixer and has a minimum of 27 K (uncorrected) at 336 GHz; to our knowledge this is the lowest noise ever reported at this frequency. A receiver noise temperature below 80 K and an image band rejection around -14 dB were measured over most of the band of the SSB mixer. Both mixers use similar chips that integrate a parallel tuning inductor with a radial microstrip stub to compensate for the junction capacitance of 75 fF (junction size 1 μm 2 ). A stability criterion for intrinsically DSB and SSB mixers under typical operating conditions has been derived. The receiver designs have been optimised in order to guarantee a low mixer noise temperature while maintaining adequate gain and stable operation over the whole frequency bands of interest.