1.中国科学院紫金山天文台南京210023;2.中国科学技术大学天文与空间科学学院 合肥 230026;3.中国科学院射电天文重点实验室 南京 210023;4.上海师范大学数理学院 上海 200234)
1. Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210023;2. School of Astronomy and Space Science, University of Science and Technology of China, Hefei 230026;3. Key Laboratory for Radio Astronomy, Chinese Academy of Sciences, Nanjing 210023;4. School of Mathematics and Physics, Shanghai Normal University, Shanghai 200234;
天线反射面的面形精度直接影响天线效率, 是望远镜的关键指标之一. 近场射电全息具有测量精度高, 便捷高效的优点, 是毫米波和亚毫米波射电望远镜面形检测最为常用的方法之一, 卡焦近场全息可以完整测量望远镜光路中整体的面形误差. 斜轴式机架结构能够更好地适应太赫兹望远镜在极端台址环境下的整体保温和热控需求, 但斜轴天线特殊的转动特性会在近场全息测量过程中引入额外的系统误差. 针对斜轴式天线的卡焦近场全息测量, 分析了数据处理中需要额外考虑的参考路接收机位置和副面衍射的影响, 并在1.2m口径斜轴式太赫兹天线上开展了测量实验. 实验结果表明, 卡焦近场全息测量的重复测量精度优于2.0μm RMS (Root Mean Square), 面形误差分布与摄影测量所得结果一致, 验证了误差分析与修正的正确性.
The surface accuracy of the reflector antenna directly affects the antenna efficiency, and is one of the key performance indicators of the telescope. Near-field radio holography, which features the advantages of high measurement accuracy and convenience, is one of the most commonly used surface alignment methods for millimeter and submillimeter wave radio telescopes. Near-field radio holography under Cassegrain mode can measure the overall deformation error in the optical path of the telescope. The slant-axis mount is more adaptable to the extreme site environment of terahertz telescopes, and can provide better thermal protection and control for the overall telescope. However, the unique rotation characteristics of the slant-axis antennas will introduce additional error factors during the holography measurements, and devoted study on the near-field holography of slant-axis terahertz antennas under Cassegrain mode has not been reported. In this paper, the influence of the reference receiver position and diffraction of the secondary mirror has been analyzed. The near-field holography measurements have been conducted on a 1.2 m slant-axis terahertz antenna. The repeatability of the experimental system has been evaluated to be better than 2μm RMS (Root Mean Square), and the comparison between near-field holography and photography has been performed to verify the correctness of the error analyses and corrections.