Holographic field-retrieval method of near-field measurements of wide field of view millimeter-wave telescopes using reference phase shifting

Wide-field-of-view millimeter-wave telescopes have been developed for astronomical observations, such as cosmic microwave background (CMB) polarimetry. These telescopes often employee phase-insensitive detectors that are fabricated with the on-chip feed antennas. A holographic field-retrieval method is useful for near-field antenna measurements of such telescopes. Among several variations of the methods, we present the one using the phase shifting of the reference waves, which do not require a fine frequency sweeping. This method aims at application to the ground testing of the LiteBIRD Low-Frequency Telescope (LFT) antenna, which observes the CMB and foreground radiations at 34–161 GHz. In our experiments conducted with a LFT 1/4-scaled antenna, the new method indicated an accuracy of −56 dB levels, which is required for the sidelobe levels of the LFT.