We have described the mixer block design for a 7-element SIS heterodyne array being built for the HHT. The mixers employ half-height tunerless waveguide mounts with the junctions mounted in a suspended microstrip configuration. Details of the feed horn, IF matching network and fabrication issues were discussed. Scale model measurements were made of the embedding impedance offered by the waveguide mount and compared with numerical simulations using state-of-the-art electromagnetic simulators. A technique to combine FEA with optimizing circuit simulators was used to arrive at a design that provides a broad-band match for the entire frequency range of interest.
We wish to thank Neal Erickson for useful discussions on HFSS, and Jacob Kooi for discussions and help with the design of the SIS junctions.