A holographic phase-retrieval method of aperture-field evaluation for bolometer-array-equipped radio telescopes

Abstract

We verified a method of near-field antenna pattern measurement for a wide-field telescope with a bolometric detector array, based on a holographic phase-retrieval technique. A signal emitter scans the telescope aperture and a reference emitter, which is phase-locked to the signal, is located at a fixed position to allow a bolometric detector to receive the both. It generates a hologram on the focal plane as a function of the signal emitter location. Since the hologram is obtained in a receiving mode, we can use the telescope-equipped detector as it is. It is beneficial for the case where such detector is integrated with a feed antenna, which characterizes the telescope performance. The new method also has an advantage that we do not need the phase calibration of the reference emitter since it is constant. We experimentally demonstrated this method with a crossed-Dragone antenna whose field of view is 18◦ × 9 ◦ at 180 GHz for three representative detector positions in the focal plane. The antenna patterns were consistent with those measured by a vector near-field measurement at the level of −60 dB, which directly acquires both the phase and the amplitude of the electric field.