ALMA Band 5 (163-211 GHz) Sideband Separation Mixer

Abstract

We present the design of ALMA Band 5 sideband separation SIS mixer and experimental results for the double side band mixer and first measurement results 2SB mixer. In this mixer, the LO injection circuitry is integrated on the mixer substrate using a directional coupler, combining microstrip lines with slot-line branches in the ground plane. The isolated port of the LO coupler is terminated by wideband floating elliptical termination. The mixer employs two SIS junctions with junction area of 3 μm2 each, in the twin junction configuration, followed by a quarter wave transformer to match the RF probe. 2SB mixer uses two identical but mirrored chips, whereas each DSB mixer has the same end-piece configuration. The 2S mixer has modular design such that DSB mixers are measured independently and then integrated into 2SB simply by placing around the middle piece.Measurements of the DSB mixer show noise temperature ofaround 40K over the entire band. 2SB mixer is not fullycharacterized yet, however, preliminary measurement indicates SSB (un-corrected) noise temperature of 80K