Signatures in the cosmic radio background from spin flip and recombination in cosmological hydrogen

The cosmological evolution of baryons through recombination and reionization are predicted to manifest as faint spectral features in the cosmic radio background. Pathfinder experiments that aim to detect global phase transitions in the ionization state of the gas in redshifted 21-cm may well be the first radio wavelength constraints on the astrophysics that drive the thermal evolution during reionization and the timing of critical events as first stars and galaxies form. This challenging problem is a motivation for innovative design in radio astronomy receivers. We present progress at the Raman Research Institute in the system design of precision radiometers for detecting spectral deviations in the radio background, design and test measurements of novel antennas, space beam splitters and receiver configurations, and present results from observations to date. The precision radiometer elements developed for the detection of cosmological phase transitions is a step towards building out SKA arrays that operate as interferometers to detect the spatial fluctuations in hydrogen during these critical epochs.