de Lera Acedo, EloyEloyde Lera AcedoTrott, Cathryn M.Cathryn M.TrottWayth, Randall B.Randall B.WaythFagnoni, NicolasNicolasFagnoniBERNARDI, GIANNIGIANNIBERNARDIWakley, BrettBrettWakleyKoopmans, Léon V.E.Léon V.E.KoopmansFaulkner, Andrew J.Andrew J.Faulknerbij de Vaate, Jan GeraltJan Geraltbij de Vaate2020-09-112020-09-1120170035-8711http://hdl.handle.net/20.500.12386/27311This 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 analysed 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 2015 September 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.STAMPAenArticle10.1093/mnras/stx9042-s2.0-85020296460000406836200008https://academic.oup.com/mnras/article/469/3/2662/36053822017MNRAS.469.2662DFIS/05 - ASTRONOMIA E ASTROFISICAERC sectors::Physical Sciences and Engineering::PE9 Universe sciences: astro-physics/chemistry/biology; solar systems; stellar, galactic and extragalactic astronomy, planetary systems, cosmology, space science, instrumentation