Measuring receiver noise parameters for global 21-cm experiments

Radiometer experiments to detect 21-cm Hydrogen line emission from the Cosmic Dawn and Epoch of Reionization rely upon precise absolute calibration. Noise generated by amplifiers within the radiometer receiver must be accounted for; however, it is difficult to measure as the noise power varies with source impedance. In this letter, we introduce a convenient method to measure the noise parameters of a receiver system, which is practical for low-frequency receivers used in global 21-cm experiments.