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 low-frequency 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 E- and 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′. |
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CITATIONS
Cited by 2 scholarly publications.
Polarization
Antennas
Telescopes
Angle measurement
Reflectors
Transmittance
Calibration