Research overview
LiteBIRD is a planned space mission to map the large-scale polarization of the cosmic microwave background. Its low-frequency telescope covers 34–161 GHz over an 18° × 9° field of view, and its optics are predicted to rotate polarization angles by up to about 1.5° across the field. To separate the faint B-mode signal from E-modes, these angles must be known to within a few arcminutes. The authors measured a 1/4-scale model of the antenna in a compact antenna test range at 140–220 GHz, which corresponds to 35–55 GHz at full scale. They placed a collimated wave source near the aperture and rotated the feed polarization. On-axis results matched the rotation of the collimated wave’s polarization to within about 15 arcminutes. Across the field, the measurements agreed with simulations, with polarization angles determined to an uncertainty below 1.9 arcminutes.
Key findings
- Wide-field polarization angle measurements of a 1/4-scale LiteBIRD low-frequency telescope antenna
- Measured at 140–220 GHz, equivalent to 35–55 GHz at full scale
- Polarization angles determined with an uncertainty below 1.9 arcminutes
- Measurements agreed with optical simulations across the field of view
