基于双波束的天马望远镜主反射面面形快速测量

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

天马望远镜的主反射面受重力、热等因素的影响会发生大尺度形变.主动反射面是补偿大尺度形变,保证望远镜电性能最有效的手段.对主反射面形变的快速测量是主动反射面高效率工作的核心问题.目前的测量耗时约为20 min,耗时较多.本文提出了一种基于双波束的相位恢复法,此方法基于双波束的天线方向图具有相似性和重叠性的特点,在保证测量信噪比的同时,通过减少扫描区域来缩短测量时间.与单波束测量相比,可将测量时间缩短1/2以上,提高了观测时间利用率.通过测量两个波束的一组部分聚焦和两组部分离焦天线方向图,再经过最小二乘数据处理得到大尺度形变.在天马望远镜对重力和热形变的实测表明,本方法可在8 min内测量得到不同情况下的主反射面面形,测量精度可达55μm.此方法有效地改善了望远镜波束,提高了望远镜效率,可应用于其他具有多波束接收系统的大型射电望远镜.

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 55μm.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.