Kavli Affiliate: George Efstathiou
| First 5 Authors: Oscar S. D. O’Hara, Quentin Gueuning, Eloy de Lera Acedo, Fred Dulwich, John Cumner
| Summary:
We investigate the impact of Mutual Coupling (MC) between antennas on the
time-delay power spectrum response of the core of the SKA-Low radio telescope.
Using two in-house tools – Fast Array Simulation Tool (FAST) (a fast full-wave
electromagnetic solver) and OSKAR (a GPU-accelerated radio telescope simulator)
– we simulate station beams and compute visibilities for various array layouts
(regular, sunflower, and random). Simulations are conducted in an Epoch of
Reionisation subband between 120-150~MHz, with a fine frequency resolution of
100~kHz, enabling the investigation of late delays. Our results show that MC
effects significantly increase foreground leakage into longer delays,
especially for regular station layouts. For 21-cm science, foreground
spill-over into the 21-cm window extends beyond $k_{parallel} sim
2$~h$^{-1}$Mpc for all station layouts and across all $k_{perp}$ modes,
completely obscuring the detection window. We find that attempting to remove
the foreground contribution from the visibilities using an approximated beam
model, based on the average embedded element pattern or interpolating the
embedded element patterns from a coarse channel rate of 781~kHz, results in
residuals around 1% ($sim 10^{11}~mathrm{mK}^2$h$^{-3}mathrm{Mpc}^3$) which
is still around 7 orders of magnitude brighter than the expected level of the
EoR signal ($sim 10^{4}~mathrm{mK}^2$h$^{-3}mathrm{Mpc}^3$). We also find
that station beam models with at least 4-5 significant digits in the far-field
pattern and high spectral resolution are needed for effective foreground
removal. Our research provides critical insights into the role of MC in SKA-Low
experiments and highlights the computational challenges of fully integrating
array patterns that account for MC effects into processing pipelines.
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