Biscoff, C.Brizius, A.Zwart, J.Buder, I.Chinone, Y.Cleary, K.Dumoulin, R.N.Kusaka, A.Monsalve, R.Naess, S.K.Newburgh, L.B.Nixon, G.Reeves, R.Smith, K.M.Vanderlinde, K.Wehus, I.K.Bogdan, M.Bustos, R.Church, S.E.Davis, RobertDickenson, C.Eriksen, H.K.Gaier, T.Gundersen, J.O.Hasegawa, M.Hazumi, M.Holler, C.Huffenberger, K.M.Imbriale, W.A.Ishidoshiro, K.Jones, M.E.Kangaslahti, P.Kapner, D.J.Lawrence, C.R.Leitch, E.M.Limon, M.McMahon, J.J.Miller, A.D.Nagai, M.Nguyen, H.Pearson, T.J.Piccirillo, L.Radford, S.J.E.Readhead, A.C.S.Richards, J.L.Samtleben, D.Seiffert, M.Shepherd, M.C.Staggs, S.T.Tajima, O.Thompson, K.L.Williamson, R.Winstein, B.Wollack, E.J.2017-07-142017-07-142013Biscoff, C. et al. (2013). The Q/U imaging experiment instrument. The Astrophysical Journal , 768 (9): 1-280004-637xhttp://hdl.handle.net/10566/3078The Q/U Imaging ExperimenT (QUIET) is designed to measure polarization in the cosmic microwave background, targeting the imprint of inflationary gravitational waves at large angular scales(∼1◦). Between 2008 October and 2010 December, two independent receiver arrays were deployed sequentially on a 1.4m side-fed Dragonian telescope. The polarimeters that form the focal planes use a compact design based on high electron mobility transistors (HEMTs) that provides simultaneous measurements of the Stokes parameters Q, U, and I in a single module. The 17-element Q-band polarimeter array, with a central frequency of 43.1 GHz, has the best sensitivity (69 μKs1/2) and the lowest instrumental systematic errors ever achieved in this band, contributing to the tensor-to-scalar ratio at r < 0.1. The 84-element W-band polarimeter array has a sensitivity of 87 μKs1/2 at a central frequency of 94.5 GHz. It has the lowest systematic errors to date, contributing at r < 0.01. The two arrays together cover multipoles in the range ∼ 25–975. These are the largest HEMT-based arrays deployed to date. This article describes the design, calibration, performance, and sources of systematic error of the instrument.enPublisher retains copyright. Authors may archive the published version in their institutional repository.Cosmic background radiationCosmologyObservationsInstrumentationDetectorsPolarimetersTelescopesArticle