Fast measurement of primary reflector for the Tianma telescope based on two beams

Abstract

Primary reflector of a large radio telescope deforms considerably due to gravitational, thermal, and other effects. An active surface system alleviates these large-scale deformations and improves the electrical performance of the telescope. The fast reflector measurement is the major challenge for active-systems to work efficiently. Currently, the measurement takes approximately 20 min, which is a substantial amount of time. A phase-retrieval holography method based on two beams is proposed. The method employs the principle of overlap and similarity of the two beams and reduces the scanning area to shorten the observation time. Moreover, this method maintains the signal-to-noise ratio of the measured data. The time is reduced by half when compared with the single beam observation. The maximum time required for each measurement is below 8 min, and the achieved accuracy is approximately 55 μm. We performed several measurements to ensure the accuracy of the proposed method at the Tianma telescope. The proposed method successfully corrected gravitational and thermal deformations. Furthermore, it improved the aperture efficiency. We recommend that the proposed method can be used in other large radio telescopes that have multibeam systems.