An SIS mixer based focal-plane array at 230 GHz

Efficiently mapping large areas of the sky with high spectral resolution at mm and sub-mm wavelengths will require a new generation of heterodyne focal-plane array receivers. The number of pixels in such arrays has not increased particularly rapidly in the last two decades, with maximum achieved pixel numbers between 16 and 64 (e.g. [1] and [2]). Thus new approaches are needed to address such problems as local oscillator (LO) injection, feed horn fabrication and SIS mixer design, fabrication and repeatability. Here we describe a prototype focal-plane array unit based on unilateral finline SIS mixers, fed with smooth-walled feed horns. LO injection power diplexing is achieved by a combination of directly machined waveguide Y-power splitters and bow-tie cross waveguide couplers. The 1×4 prototype array, currently under construction, will demonstrate several technologies relevant to the construction of large format arrays.