Informing antenna design for sky-averaged 21-cm experiments using a
  simulated Bayesian data analysis pipeline
  Global 21cm experiments aim to measure the sky averaged HI absorption signal
from cosmic dawn and the epoch of reionisation. However, antenna chromaticity
coupling to bright foregrounds can introduce distortions into the observational
data of such experiments. We demonstrate a method for guiding the antenna
design of a global experiment through data analysis simulations. This is done
by performing simulated observations for a range of inserted 21cm signals, then
attempting to identify the signals with a data analysis pipeline. We
demonstrate this method on five antennae that were considered as potential
designs for the Radio Experiment for the Analysis of Cosmic Hydrogen (REACH); a
conical log spiral antenna, an inverted conical sinuous antenna and polygonal-,
square- and elliptical-bladed dipoles. We find that the log spiral performs
significantly better than the other antennae tested, able to correctly and
confidently identify every inserted 21cm signal. In second place is the
polygonal dipole antenna, which was only unable to detect signals with both
very low amplitudes of 0.05K and low centre frequency of 80MHz. The conical
sinuous antenna was found to perform least accurately, only able to detect the
highest amplitude 21cm signals, and even then with biases. We also demonstrate
that, due to the non-trivial nature of chromatic distortion and the processes
of correcting for it, these are not the results that could have been expected
superficially from the extent of chromatic variation in each antenna.
