太赫兹天线变形测量方法及有限元模型可靠性优化研究

Terahertz telescopes require very high accuracy for the reflector surface shape and for the subreflector alignment. As an antenna suffers from the thermal and gravitational deformations during operation, both the subreflector alignment and main dish surface are continuously changing. In order to meet the overall equivalent surface accuracy requirement of the antenna, subreflector positioning must be performed in real time. In addition, an antenna is desired to have its best surface accuracy at the middle elevation of the usually operation range. If measurements of the surface error can not be made at this optimum elevation (it is often the case for terahertz antennas), we need to preset the deviations for surface shape deformations when aligning the panels. Thus, it is important to establish a model for deformations of the reflector system. In this proposal, we will evaluate the accuracy of several applicable methods for deformation measurements of the reflector system, and propose an approach for establishing the model for deformations of the reflector system, which fuse measurement results be several different methods. We will also make efforts to explore an algorithm for optimizing the finite element model (FEM) based on measurement results, by which we can optimize the FEM of the antenna reflector system, according to measurements of the deformation induced deviations of the subreflector position and main dish surface under finite working conditions, and to meet the measurement results. The works are important for the proposed Dome A 5-m terahertz telescope (DATE5) to improve its on-site antenna efficiency. The proposed methods are also applicable to similar radio telescopes.

因重力和热变形影响，天线工作过程中无论是副面相对位置还是主反射面面形都在发生变化。太赫兹望远镜对天线主面面形精度和副面定位精度要求均非常高。副面相对位置偏差必须要通过实时调整才能满足天线整体等效反射面精度要求；主面测量时的天线俯仰与期望获得最好天线增益的俯仰往往不同，为在调整时预置出与要求俯仰位置的形变偏差，需要知道精确的主面面形重力变形特性。因而，建立一个精确预测天线反射面系统变形的模型非常重要。本项目将根据南极5米太赫兹望远镜（DATE5）的性能和台址特点，在评估多种可能适用方法对天线反射面系统变形测量精度的基础上，建立一套适用于DATE5天线副面位置及主面面形重力和热变形模型、融合多种测量手段的高精度测量方法；建立一种依据测量结果优化天线有限元模型可靠性的方法，并探索有限元模型可靠性优化算法的收敛条件。本项目工作对提高DATE5天线效率具有重要意义，提出的方法对类似望远镜同样适用。

受大气透过率限制，太赫兹望远镜往往工作在极端环境台址，其性能对天线变形极其敏感，且台址现场难以开展系统的天线变形测量，因而一个真实、可靠的天线有限元模型尤为重要。然而由于材料、结构特性参数差异（尤其是复合材料），以及模型简化等原因，初期建立的天线有限元模型与实际天线往往存在差异，使有限元模型不能精确预测实际天线结构在各种载荷下的变形特性，需要依据在有限工况下的重力和热变形测量结果对有限元模型进行修正；另一方面，太赫兹天线精度要求极高，高精度的变形测量方法也是挑战。. 根据规划建设的南极5米太赫兹望远镜(DATE5)的性能要求和台址特点，采用实验或仿真方法评估了多种可能适用的天线反射面系统变形测量方法的测量精度，包括全息测量法、摄影测量法以及天文观测法等。对天线变形近场全息测量系统中的多种测量误差修正开展了深入的理论和实验研究，取得了优于2μm的测量精度。提出并实现了基于增益测量和波前扰动的天线反射面变形测量调整新方法，在3mm波段实现了优于1/100波长的测量调整精度。提出并实现了多频同时近场全息测量，并以NI PXIe-5785高速双通道数字收发仪为硬件平台，自主研发了基于FFT的互相关谱实时处理和梳状谱发生器FPGA内核软件。开展了太赫兹天线有限元模型修正优化方法研究，并且基于摄影测量方法，对实验室1.2m太赫兹天线和德令哈13.7m毫米波天线，开展了天线有限元模型修正实验研究，取得了高精度修正结果。. 项目研究成果为我国太赫兹/亚毫米波望远镜建设和高精度运行打下了良好基础。