A 16-GHz Bandwidth Cryogenic IF Amplifier With 4-K Noise Temperature for Sub-mm Radio-Astronomy Receivers

The major mm and sub-mm radio-astronomy observatories are prioritizing instantaneous bandwidth widening for their current or planned upgrades this decade. We present an ultra-wideband and ultra-low-noise cryogenic hybrid amplifier with 4 K ( NF = 0.06 dB) average noise temperature in the 2-18 GHz band when cooled to 6 K. It is based on a 100 nm gate pseudomorphic indium-phosphide HEMT with outstanding characteristics. This demonstration amplifier meets the noise and IF bandwidth demands of atacama large millimiter/submillimeter array (ALMA) next-generation receivers, doubling the present maximum IF instantaneous bandwidth with state-of-the-art noise performance, with a gain flatness of ±0.8 dB, and output return loss better than 15 dB over 85% of the band. It can be used in the 1-19 GHz range with negligible degradation, and a tentative test has been performed with a 602-720 GHz ALMA band-9 double sideband SIS mixer, showing a flat-average and low-ripple IF noise level in an 18-GHz wideband down to near dc. A balanced configuration is feasible to improve the input matching.