# Spectral performance of SKA Log-periodic Antennas I: Mitigating spectral artefacts in SKA1-LOW 21-cm cosmology experiments

## TL;DR

This paper investigates the spectral performance of SKA1-LOW log-periodic antennas, focusing on mitigating artefacts that affect 21-cm cosmology experiments, and proposes correction methods for passband ripple issues to improve calibration accuracy.

## Contribution

It provides a detailed electromagnetic analysis of SKA1-LOW antennas, introduces a correction for a specific ripple at 60 MHz, and compares antenna performance with HERA for EoR detection.

## Key findings

- Identified and characterized passband ripple at 60 MHz.
- Developed a correction method with minimal impact on performance.
- Demonstrated potential of SKA1-LOW antennas for EoR detection techniques.

## Abstract

This paper is the first in a series of papers describing the impact of antenna instrumental artefacts on the 21-cm cosmology experiments to be carried out by the low frequency instrument (SKA1-LOW) of the Square Kilometre Array telescope (SKA), i.e., the Cosmic Dawn (CD) and the Epoch of Reionization (EoR). The smoothness of the passband response of the current log-periodic antenna being developed for the SKA1-LOW is analyzed using numerical electromagnetic simulations. The amplitude variations over the frequency range are characterized using low-order polynomials defined locally, in order to study the impact of the passband smoothness in the instrument calibration and CD/EoR Science. A solution is offered to correct a fast ripple found at 60~MHz during a test campaign at the SKA site at the Murchison Radio-astronomy Observatory, Western Australia in September 2015 with a minor impact on the telescope's performance and design. A comparison with the Hydrogen Epoch of Reionization Array antenna is also shown demonstrating the potential use of the SKA1-LOW antenna for the Delay Spectrum technique to detect the EoR.