射电天文研究组知识库

大型天线口径大、精度高、结构复杂且长时间在室外工作,日照对天线反射体产生非均匀、实时变化的热变形误差对天线电性能的影响日益突出.本文以景东120 m天线为具体研究对象,通过有限元方法计算在不同的观测姿态和日照环境下天线反射体的非均匀温度分布及其变化规律,探讨主反射面面形在实时变化日照影响下的演变规律,并针对面形非均匀热变形的实时误差开展补偿研究.结果表明,受太阳东升西落的影响,改变天线观测方位角可影响反射体温差变化达4°C,改变天线俯仰角可影响反射体温差变化达1.5°C,说明相同日照环境下,观测方位角对反射体的热影响更大;天线结构热变形在一天中呈现时变性与非均匀性,其中14时的变形量最大.受日照年度变化的影响,改变天线观测方位角将影响反射体温差呈增大、减小再增大的变化规律,其中夏季中午温度标准差最小,为0.1;对应地,反射体热变形全年呈增大、减小再增大的变化规律,其中冬季热变形最大,达2.6 mm,其余季节最大为2 mm,说明冬季日照对天线反射体的热影响更大.基于反射体热误差变化规律,引入误差耦合原理,分析反射体热变形误差,并通过馈源调整机构实现补偿.本文提出的反射体热变形仿真技术及馈源补偿方法可为提升大型天线指向精度提供理论基础与技术支持. 

Large antennas are characterized by large apertures, high precision, complex structures, and extended outdoor operation. The effect of a non-uniform and real-time thermal deformation error of an antenna reflector caused by sunlight on the electrical performance of an antenna is considerable. Herein, the Jingdong 120-m antenna is considered the research object. The finite element method is employed for determining the non-uniform temperature distribution and the law for its variation for the antenna reflector under different observation attitudes and sunlight environments. The evolution law of the main reflector surface shape under the influence of real-time varying sunlight is discussed, and the real-time error of the non-uniform thermal deformation of the surface shape is compensated. The findings reveal that due to the influence of the sunrise in the east and the sunset in the west, changing the observation azimuth and elevation angle of the antenna can affect the temperature experienced by the reflector by 4°C and 1. 5°C, respectively. This indicates that the observation azimuth has a greater effect on the heat experienced by the reflector as compared to the elevation angle under the identical sunlight environment. The thermal deformation of the antenna structure exhibits time variation and nonuniformity throughout the day, and the largest deformation is observed at 14:00. Affected by the annual variation in sunlight, the change in antenna observation azimuth angle will affect the change rule of reflector temperature difference, which increases, decreases and then increases. The standard deviation of temperature at noon in summer is the least (0. 1); therefore, the thermal deformation of the reflector increases, decreases and increases again throughout the year. Further, thermal deformation in winter is the highest, reaching 2. 6 mm, and the maximum in other seasons is 2 mm, indicating that the sunlight in winter has a considerable thermal effect on the antenna reflector. Based on the variation law of the reflector thermal error, the error coupling principle is introduced to analyze the thermal deformation error of the reflector, and the compensation is realized by the feed adjustment mechanism. The reflector thermal deformation simulation technology and feed compensation method proposed in this paper can provide a theoretical basis and technical support for improving the pointing accuracy of large antennas.