ALMA MEMO 429 Fixed-tuned waveguide 0.6 THz SIS Mixer with Wide band IF 28-July-2002

The Atacama Large Millimeter Array (ALMA) requires low noise SIS receivers for frequencies from about 80 GHz to 950 GHz with a very large IF bandwidth (8 GHz SSB upper or lower sideband, 8 GHz DSB or 4 GHz dual sideband, upper and lower sideband). Since there will be a large number of antennas in the array (currently 64), additional requirements such as high reliability, low cost, and the production of a relatively large number of mixers have to be addressed. In this paper we report the results of a waveguide mixer with a fixed backshort for ALMA band 9 (602 – 720 GHz). The mixer is based on standard Nb/AlOx/Nb SIS junction technology. This mixer was tested with a wide band IF amplifier with and without an isolator. Mixer measurement results for different LO frequencies across a wide IF band (4-12) GHz) will be presented. DSB Receiver noise across the both RF and IF band was measured, and receiver noise as low as 136 K at 650 GHz was demonstrated over the wideband IF. Finally, the possibility of a small production series of such a mixer is discussed with results on a first batch of mixer-blocks will be presented.