A SIMPLE MULTIPLE-BEAM LO COUPLER FOR SIS HETERODYNE ARRAYS

The construction of SIS heterodyne imaging arrays for submillimetre wa velengths requires multiple coupling of the local oscillator signal. T he quasi-optical analogue of a multiple cross-guide coupler, employing 45-degrees beam-splitters successively stacked along the local oscill ator beam, allows for individual adjustment of local oscillator power to each channel. We analyse the coupling as a function of the focal ra tio of the incident beams and the number of beam widths off-axis throu gh which the coupler is extended, and describe a simple construction m ethod to realise a compact and effective design.