Patterns of primary beam non-redundancy in close-packed 21 cm array observations

Understand

Radio interferometer arrays such as HERA consist of many close-packed dishes arranged in a regular pattern, giving rise to a large number of `redundant' baselines with the same length and orientation.

• Since identical baselines should see an identical sky signal, this provides a way of finding a relative gain/bandpass calibration without needing an explicit sky model.
• In reality, there are many reasons why baselines will not be exactly identical, giving rise to a host of effects that spoil the redundancy of the array and induce spurious structure in the calibration solutions if not accounted for.
• In this paper, we seek to build an understanding of how differences in the primary beam response between antennas affect redundantly-calibrated interferometric visibilities and their resulting frequency (delay-space) power spectra.