To reach the ambitious goal of the ALMA Wideband Sensitivity Upgrade (WSU) to quadruple the instantaneous bandwidth from 4 to 16 GHz a wide range of receiver components need to be upgraded including the junctions, the intermediate frequency (IF) hybrids and the Cryogenic Low Noise Amplifiers (CLNA). The latter component has a critical role, as its location early in the analogue part of the signal chain means it has a substantial contribution to the overall receiver noise and affects the quality of sideband separating receivers. Moreover, the IF bandwidth of the CLNA is often the limiting factor for the overall receiver bandwidth, making the CLNA one of the key components to upgrade for the WSU. The same CLNA can be installed in most upgraded receivers.
Development study on wideband low noise amplifiers kicks off
Visit of the Yebes laboratory, with Isaac Lopez showing the test cryostat to characterise the cryogenic low noise amplifier components
A recently completed study under the ESO Technology Development Programme led by the Observatorio de Yebes (Spain) has produced a new prototype CLNA covering the full 4-20 GHz IF range (see López-Fernández et al, ESO Messenger 191). While this prototype displays a spectacular performance fully compatible with the ambitious WSU specifications, it is still possible to improve the technology to simplify the fabrication and assembly of the final CLNAs. This will make easier producing the large number of units needed to upgrade over 70 ALMA receivers per band (four CLNAs are needed per receiver). In a new ALMA development study that kicked off on 21 September 2023, the Yebes team will now endeavour to obtain similar performance using monolithic microwave integrated circuits (MMIC), where most of the circuitry is integrated in a single chip. To obtain the optimal cryogenic MMIC wafers based on InP substrate material, Yebes will collaborate with the Diramics foundry in Switzerland. If successful, this study will open the path towards cost-effective production of WSU-compliant CLNAs in large volume.