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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  &#x003D; 0.06 dB) average noise temperature in the 2&#x2013;18 GHz band when cooled to 6 K. It is based on a 100 nm gate pseudomorphic indium&#x2013;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 &#x00B1;0.8 dB, and output return loss better than 15 dB over 85&#x0025; of the band. It can be used in the 1&#x2013;19 GHz range with negligible degradation, and a tentative test has been performed with a 602&#x2013;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.

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