Gain Stabilization of a Submillimeter SIS Heterodyne Receiver

TL;DR

This paper presents a gain stabilization system for submillimeter SIS heterodyne receivers that compensates for thermal fluctuations, significantly improving stability by monitoring temperature and adjusting IF amplifier gain.

Contribution

The authors developed and implemented a gain stabilization scheme that reduces IF power fluctuations caused by cryocooler-induced temperature variations in SIS receivers.

Findings

Achieved a receiver gain stability of 1 part in 6,000.

Improved stability by an order of magnitude over uncorrected systems.

Effective compensation for 4 K temperature fluctuations in cryocooled receivers.

Abstract

We have designed a system to stabilize the gain of a submillimeter heterodyne receiver against thermal fluctuations of the mixing element. In the most sensitive heterodyne receivers, the mixer is usually cooled to 4 K using a closed-cycle cryocooler, which can introduce ~1% fluctuations in the physical temperature of the receiver components. We compensate for the resulting mixer conversion gain fluctuations by monitoring the physical temperature of the mixer and adjusting the gain of the intermediate frequency (IF) amplifier that immediately follows the mixer. This IF power stabilization scheme, developed for use at the Submillimeter Array (SMA), a submillimeter interferometer telescope on Mauna Kea in Hawaii, routinely achieves a receiver gain stability of 1 part in 6,000 (rms to mean). This is an order of magnitude improvement over the typical uncorrected stability of 1 part in a few hundred. Our gain stabilization scheme is a useful addition to SIS heterodyne receivers that are cooled using closed-cycle cryocoolers in which the 4 K temperature fluctuations tend to be the leading cause of IF power fluctuations.