Receiver design for the REACH global 21-cm signal experiment

TL;DR

This paper presents the design, simulation, and laboratory validation of the REACH radiometric system aimed at measuring the 21-cm hydrogen line, highlighting calibration techniques and initial results.

Contribution

It introduces a novel radiometer architecture for 21-cm measurements and demonstrates calibration accuracy using an over-constrained least squares approach.

Findings

Calibration RMSE of 80 mK achieved after five hours

Laboratory results validate the radiometer design and calibration method

System simulations support the design choices

Abstract

We detail the the REACH radiometric system designed to enable measurements of the 21-cm neutral hydrogen line. Included is the radiometer architecture and end-to-end system simulations as well as a discussion of the challenges intrinsic to highly-calibratable system development. Following this, we share laboratory results based on the calculation of noise wave parameters utilising an over-constrained least squares approach demonstrating a calibration RMSE of 80 mK for five hours of integration on a custom-made source with comparable impedance to that of the antenna used in the field. This paper therefore documents the state of the calibrator and data analysis in December 2022 in Cambridge before shipping to South Africa.