Development of the ALMA-North America Sideband-Separating SIS Mixers

TL;DR

This paper discusses the development and performance of sideband-separating SIS mixers used in ALMA's receivers, highlighting their design considerations, noise temperatures, and image rejection capabilities.

Contribution

It presents the design, implementation, and testing results of superconducting SIS mixers for ALMA's Bands 3 and 6, demonstrating their effectiveness in suppressing atmospheric noise.

Findings

Achieved low noise temperatures of 30 K in Band 3 and 60 K in Band 6.

Demonstrated typical image rejection of 15 dB.

Successfully delivered 73 dual-polarization receivers for each band.

Abstract

As the Atacama Large Millimeter/submillimeter Array (ALMA) nears completion, 73 dual-polarization receivers have been delivered for each of Bands 3 (84-116 GHz) and 6 (211-275 GHz). The receivers use sideband-separating superconducting Nb/Al-AlOx/Nb tunnel-junction (SIS) mixers, developed for ALMA to suppress atmospheric noise in the image band. The mixers were designed taking into account dynamic range, input return loss, and signal-to-image conversion (which can be significant in SIS mixers). Typical SSB receiver noise temperatures in Bands 3 and 6 are 30 K and 60 K, resp., and the image rejection is typically 15 dB.