# The impact of station far sidelobes on EoR/CD power spectra

**Authors:** Cathryn M. Trott  
**arXiv:** [2112.00904](https://arxiv.org/abs/2112.00904)  
**Date:** 2021-12-02  
**Summary page:** https://www.summarizepaper.com/en/arxiv-id/2112.00904v1/

## Key points

- Study focuses on impact of station far sidelobes on Epoch of Reionisation (EoR) and Cosmic Dawn (CD) power spectra in the context of dipole antennas for SKA1-Low
- Stations consist of 256 elements spread over a 38~m diameter area
- Effect of residual unsubtracted sources located well outside the main beam investigated for different numbers of unique station configurations
- Beam sidelobes imprint power that renders cosmological signal unobservable unless compact sources are subtracted beyond \theta_Z=30 degrees from zenith
- Station apodization may be necessary to control far sidelobes effectively
- Array with four unique station configurations (N_b=4) deemed sufficient, minimal improvement seen when increasing to eight (N_b=8)
- Beam sidelobe level contributes significantly to excess power in EoR window, while beam chromaticity plays a less significant role
- To access relevant modes of power spectrum at z=8.5 in EoR, necessary to subtract sources above 200~mJy out to \theta_Z=45 degrees
- Study highlights importance of considering station far sidelobes and their impact on cosmological signal observations

## Summary

This study focuses on the impact of station far sidelobes on Epoch of Reionisation (EoR) and Cosmic Dawn (CD) power spectra in the context of dipole antennas for SKA1-Low. The stations consist of 256 elements spread over a 38~m diameter area. The researchers investigate the effect of residual unsubtracted sources located well outside the main beam for different numbers of unique station configurations. Using simulations and theoretical considerations, the authors find that beam sidelobes imprint power that renders the cosmological signal unobservable across various scales unless compact sources are subtracted beyond a certain angle from zenith (\theta_Z=30 degrees). They also suggest that station apodization may be necessary to control far sidelobes effectively. To reduce contamination, an array with four unique station configurations (N_b=4) is deemed sufficient, as increasing it to eight (N_b=8) shows minimal improvement. Comparing their findings with an achromatic Airy disk beam model, they conclude that beam sidelobe level contributes significantly to excess power in the EoR window, while beam chromaticity plays a less significant role. In order to access relevant modes of the power spectrum at z=8.5 in the EoR, it will be necessary to subtract sources above 200~mJy out to \theta_Z=45 degrees. This study highlights the importance of considering station far sidelobes and their impact on cosmological signal observations; it provides insights into what is required for reducing contamination and accessing relevant modes in both EoR and CD scenarios using dipole antennas for SKA1-Low.