MASTER: Millimetre and sub-millimetre triple heterodyne receiver

We will describe a system of three heterodyne receivers. Its mixers are based on SIS tunnel junctions which allow a very sensible downconversion of the detectable signal from 94 GHz, 225 GHz and 345 GHz to 1.5 GHz. This will allow the detection of molecular rotational transition lines from diffuse molecular clouds. Current status of a 94 GHz receiver, prototype of MASTER, will also be described. Technical design and cryogenic problems solution will be shown and we will focus our attention on the optical coupling technique based on gaussian beam analysis.