Berkhout, Lindsay M.Jacobs, Daniel C.Abdurashidova, ZuhraAdams, TyroneAguirre, James E.Alexander, PaulAli, Zaki S.Baartman, RushelleBalfour, YangaBeardsley, Adam P.Bernardi, GianniBillings, Tashalee S.Bowman, Judd D.Bradley, Richard F.Bull, PhilipBurba, JacobByrne, RubyCarey, StevenCarilli, Chris L.Chen, Kai FengCheng, CarinaChoudhuri, SamirDeBoer, David R.de Lera Acedo, EloyDexter, MattDillon, Joshua S.Dynes, ScottEksteen, NicoEly, JohnEwall-Wice, AaronFagnoni, NicolasFritz, RandallFurlanetto, Steven R.Gale-Sides, KingsleyGarsden, HughGehlot, Bharat KumarGhosh, AbhikGlendenning, BrianGorce, AdelieGorthi, DeepthiGreig, BradleyGrobbelaar, JasperHalday, ZiyaadHazelton, Bryna J.Hewitt, Jacqueline N.Hickish, JackHuang, TianJosaitis, AlecJulius, AustinKariseb, MacCalvinKern, Nicholas S.Kerrigan, JoshuaKim, HonggeunKittiwisit, PiyanatKohn, Saul A.Kolopanis, MatthewLanman, AdamLa Plante, PaulLiu, AdrianLoots, AnitaMa, Yin ZheEdward MacMahon, David HaroldMalan, LourenceMalgas, CresshimMalgas, KeithMarero, BradleyMartinot, Zachary E.Mesinger, AndreiMolewa, MathakaneMorales, Miguel F.Mosiane, TshegofalangMurray, Steven G.Neben, Abraham R.Nikolic, BojanNunhokee, Chuneeta DeviNuwegeld, HansParsons, Aaron R.Pascua, RobertPatra, NipanjanaPieterse, SamanthaQin, YuxiangRath, EleanorRazavi-Ghods, NimaRiley, DanielRobnett, JamesRosie, KathrynSantos, Mario G.Sims, PeterSingh, SaurabhStorer, DaraSwarts, HiltonTan, JianrongThyagarajan, Nithyanandanvan Wyngaarden, PieterWilliams, Peter K.G.Zheng, HaoxuanXu, Zhilei2025-05-302025-05-300004-6280WOS:001204550400001http://www.scopus.com/inward/record.url?scp=85190746749&partnerID=8YFLogxKhttps://hdl.handle.net/1885/733754966This paper presents the design and deployment of the Hydrogen Epoch of Reionization Array (HERA) phase II system. HERA is designed as a staged experiment targeting 21 cm emission measurements of the Epoch of Reionization. First results from the phase I array are published as of early 2022, and deployment of the phase II system is nearing completion. We describe the design of the phase II system and discuss progress on commissioning and future upgrades. As HERA is a designated Square Kilometre Array pathfinder instrument, we also show a number of “case studies” that investigate systematics seen while commissioning the phase II system, which may be of use in the design and operation of future arrays. Common pathologies are likely to manifest in similar ways across instruments, and many of these sources of contamination can be mitigated once the source is identified.This material is based upon work supported by the National Science Foundation under grant Nos. 1636646 and 1836019 and institutional support from the HERA collaboration partners. This research is funded by the Gordon and Betty Moore Foundation through grant GBMF5215 to the Massachusetts Institute of Technology. HERA is hosted by the South African Radio Astronomy Observatory, which is a facility of the National Research Foundation, an agency of the Department of Science and Innovation. L.M.B. acknowledges that this material is based upon work supported by the National Science Foundation Graduate Research Fellowship under grant No. 2233001. J.S.D. gratefully acknowledges the support of the NSF AAPF award #1701536. A.L. acknowledges support from the New Frontiers in Research Fund Exploration grant program, the Canadian Institute for Advanced Research (CIFAR) Azrieli Global Scholars program, a Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant and a Discovery Launch Supplement, the Sloan Research Fellowship, and the William Dawson Scholarship at McGill. Y.-Z.M. acknowledges the support of the National Research Foundation of South Africa with grant No. 150580. D.S. acknowledges that this material is based upon work supported by the National Science Foundation Graduate Research Fellowship Program under grant No. DGE-1762114. Any opinions, findings, and conclusions expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation. M.G.S. and P.K. acknowledge support from the South African Radio Astronomy Observatory (SARAO) and the National Research Foundation (grant No. 84156). G.B. acknowledges support from the Ministero degli Affari Esteri della Cooperazione Internazionale-Direzione Generale per la Promozione del Sistema Paese Progetto di Grande Rilevanza ZA18GR02 and the National Research Foundation of South Africa (grant No. 113121) as part of the ISARP RADIOSKY2020 Joint Research Scheme. N.S.K. acknowledges support from NASA through the NASA Hubble Fellowship grant #HST-HF2-51533.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. E.d.L.A. acknowledges the financial support of STFC. R.B. is supported by the National Science Foundation under Award No. 2303952.29enPublisher Copyright: © 2024. The Author(s). Published by IOP Publishing Ltd on behalf of the Astronomical Society of the Pacific (ASP). All rights reserved21 cm cosmologyBase-line calibrationBeam variationsCosmic dawnFundamental limitationsI.ImpactInterferometerPower spectrum estimationSky202410.1088/1538-3873/ad312285190746749