Polarization angle measurement of LiteBIRD low frequency telescope scaled model

Hayato Takakura; Yutaro Sekimoto; Junji Inatani; Shingo Kashima; Masahiro Sugimoto

doi:10.1117/12.2560419

13 December 2020 Polarization angle measurement of LiteBIRD low frequency telescope scaled model

Hayato Takakura, Yutaro Sekimoto, Junji Inatani, Shingo Kashima, Masahiro Sugimoto

Proceedings Volume 11443, Space Telescopes and Instrumentation 2020: Optical, Infrared, and Millimeter Wave; 114436C (2020) https://doi.org/10.1117/12.2560419
Event: SPIE Astronomical Telescopes + Instrumentation, 2020, Online Only

Conference Poster

Abstract

LiteBIRD is JAXA Strategic Large Mission for the late 2020s that aims to observe the large-scale B-mode polarization pattern of the cosmic microwave background. One of its telescopes, the Low Frequency Telescope (LFT), has a crossed-Dragone design and observes at 34-161 GHz with a field of view of 18° x 9°. Because a miscalibration of the polarization angles mixes E- and B-mode polarization, we have measured the variation of the polarization angles in the field of view of a 1/4-scaled LFT antenna at 140-220 GHz, which corresponds to 35-55 GHz for the full-scale LFT, considering a scaling of the wavelength. We placed a collimated-wave source near the scaled-LFT aperture and rotated the polarization angle of the LFT feed. The measurements were explained well with a simple Jones matrix calculation, and the fitting errors of the polarization angles were less than 0.1’. We also measured the polarization angles by rotating the polarization direction in the scaled-LFT aperture, and the results were consistent with the angles measured by rotating the feed polarization at the ±10” level, except at the lowest frequencies. The polarization angle at the edges of the focal plane varied from that at the center by up to around a degree, with larger variation at lower frequencies. We evaluated the polarization angles for both Pol-X and Pol-Y feeds, and the results with Pol-Y showed a trend consistent with ray-tracing simulations. The results for Pol-X showed the opposite trend of the polarization rotation direction and larger angle variations.

Citation Download Citation

Hayato Takakura, Yutaro Sekimoto, Junji Inatani, Shingo Kashima, and Masahiro Sugimoto "Polarization angle measurement of LiteBIRD low frequency telescope scaled model", Proc. SPIE 11443, Space Telescopes and Instrumentation 2020: Optical, Infrared, and Millimeter Wave, 114436C (13 December 2020); https://doi.org/10.1117/12.2560419

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