Wide-field polarization angle measurements of a LiteBIRD low-frequency telescope scaled antenna

Abstract

LiteBIRD is a space mission intended for the late 2020s that aims to observe the large-angular-scale polarization pattern of the cosmic microwave background. The lowfrequency telescope (LFT) aboard LiteBIRD has a crossed-Dragone design and observes at 34 to 161 GHz with a field of view (FoV) of 18 deg × 9 deg. The LFT antenna optics is predicted to induce polarization angle rotation by up to around 1.5 deg in its FoV, while polarization angles among the detectors should be corrected to a few arcminutes level to distinguish Eand B-mode polarizations. To characterize the polarization angle rotation by the antenna optics and to develop a ground calibration method, we performed polarization angle measurements with a small compact-antenna-test-range setup. We measured the polarization angles of a 1/4-scaled LFT antenna across the FoV at correspondingly scaled frequencies of 140 to 220 GHz (35 to 55 GHz for the full-scale LFT). We placed a collimated-wave source near the scaled-LFT aperture and rotated the scaled-LFT feed polarization. The measured polarization angles agree with those measured by rotating the collimated-wave polarization at the 15″ level for the on-axis case. The measurements are consistent with simulation and determined the polarization angles with an uncertainty of less than 1.9′.

Holographic phase-retrieval method of near-field antenna pattern measurement for bolometer-array-equipped millimeter-wave telescopes

“…In this study, we used a 1/4-scaled antenna of the LiteBIRD LFT 14,23,31 as an AUT. The aperture is 100 mm in diameter, and the size of the focal plane is 105 mm × 52.5 mm.…”

“…32, and its parameters and beam shapes are described in Ref. 31; the aperture diameter and length are 9.086 and 16.2 mm, respectively.…”