Radiometer Design for the REACH 21cm Global Experiment

Detecting signals from the Cosmic Dawn using “global” experiments requires an unprecedented level of instrumental calibration, especially to remove possible systematics which arise from the interaction between the antenna and receiving systems. In this paper we describe the calibration methods which can be applied to a range of experiments including the Radio Experiment for the Analysis of Cosmic Hydrogen (REACH) which is an instrument being designed to detect such signals. We use the functions described by noise wave parameters in a fast Bayesian pipeline to determine physical calibration coefficients which can describe the systematics. This approach when used in the field and on the fly could calibrate the absolute temperature measured by the antenna down to sub-kelvin levels. In this paper we present the Bayesian framework and simulated results of our pipeline using models derived from early laboratory measurements. A major advantage of this approach is that we can properly model the uncertainties in our measurement system.