Compact dual-polarization cryogenic receiver module for the 75-116 GHz band

We describe the design of a highly integrated cryogenic receiver module based on an "active" waveguide Orthomode Transducer (OMT) for dual-polarization radio astronomy observations across 75-116 GHz (3-mm band). The receiver module consists of passive and active sections incorporated in three mechanical blocks arranged in a very compact assembly. The module has external dimensions of 43×25×35 mm 3 ; it includes a square waveguide input (size 2.54×2.54 mm 2 ) and two standard WR10 waveguide outputs (size 1.27×2.54 mm 2 ) parallel to the input waveguide, suitable for integration in a focal plane array. The passive section of the receiver module employs a broadband backward-coupler waveguide OMT while the active section consists of two ultra-low noise MMIC (Monolithic Microwave Integrated Circuit) amplifiers in cascade, delivering a total gain of ≈45 dB for each of the polarization channels. The "active OMT" receiver will be cryogenically cooled at the physical temperature of ≈15 K. It is expected to provide state-of-the-art performance with noise in the range 25 to 50 K across 75-116 GHz. The module incorporates a DC power supply board along with discrete capacitors, resistors and DC bias connector for biasing the MMIC amplifiers.