Development of a 0.6 THz SIS Receiver for ALMA

The Atacama Large Millimeter Array (ALMA) requires low noise SIS receivers for frequencies from about 80 GHz to 950 GHz with very large IF bandwidth (4-12 GHz). Additional requirements for these receivers are high reliability, low cost and the possibility of series production. In this paper we report on mixer designs based on standard Nb/A10x/Nb SIS junction technology and an optics design for ALMA band 9 (602 - 720 GHz). We present the design of a tunerless balanced waveguide SIS mixer and a quasi-optical double slot-antenna mixer as well as an optical design to couple the telescope beam to the mixer. The waveguide balanced mixer is based on a magic T with integrated RF and LO feed horns. Losses in the Nb film increase at frequencies above the Nb gap frequency of 690 GHz and limit the mixer sensitivity at the high end of ALMA band 9. In this paper we present a layout concept of the optics and the mixers as well as an analysis of its RF properties which shows that efficient mixer operation is still possible across this band without changing the material of tuning elements.