Demonstrator of Cryogenic Multibeam Receiver with MMIC LNAs for 75-116 GHz

We describe the design of a nine-element multibeam receiver demonstrator for the 75-116 GHz (W-band). The design consists of a cryogenic 3×3 dual-polarization focal plane array (FPA) based on individual reimaging optics for the corrugated horns, and employs an innovative "active OMT" with two cascaded mHEMT MMIC LNAs packaged in each of the polarization channels of the OMT waveguide structure. The RF signals from the cryogenic array active OMT outputs are linked, through WR10 waveguides, to three-pixel sideband separating mixer (2SB) modules located at room temperature, attached to the baseplate of the cryostat. One of such modules converts six RF signals from one line of the array (1×3×2 pols) down to the 4-12 GHz IF band, thus providing a total of 12 IF outputs (USB and LSB). The optics of the FPA demonstrator was designed and optimized for high-efficiency broadband operation on the IRAM 30-m telescope at Pico Veleta, Spain.