新疆天文台25m南山射电望远镜日照温度场研究

中国科学院新疆天文台25 m南山射电望远镜(25 m NSRT)受日照导致天线结构温度不均匀,其指向精度和效率均有一定程度的损失.为研究25 m NSRT日照下的热力学特性,构建了晴空下射电望远镜热环境参数和热力学有限元模型,考虑了射电望远镜背架、面板等结构件对光线的反射和遮挡作用,通过比较25 m NSRT典型观测工况下各构件的平均温度、均方根温差、单位温差特征距离等特性参数,发现各部件热容量的差异是天线部件间存在大尺度温差现象的主要原因;分析了各类俯仰角和太阳照射角下天线背架结构的温度分布特征,表明日照区域的背架结构温度呈近似线性分布,平均梯度可达0.25℃·m^-1.     

65 m射电望远镜背架结构日照温度效应实验研究

借助精密工程测量手段,对65 m天线背架的日照温度效应进行了实验研究.在天线背架设计坐标系下分析实验数据,建立了日照温度变形模型,得出背架结构沿X方向变形系数为Kx=1.30×10-5,沿Z方向变形系数为Kz=-0.44×10-5,沿Y方向变形偏向太阳照射一侧.根据实验数据建立的背架变形模型,模拟分析了65 m天线背架日照温度变形对面形精度的影响,得出环境温度变化1℃带来的面形精度(均方根值rms)影响分量约为0.09 mm.实验结果为65 m天线主动面调节提供了很有价值的参考数据.     

超大口径射电望远镜温度场分析

随着天线口径增大、频率升高,日照热对其性能的影响愈发严重.针对待建的新疆110 m大口径全可动射电望远镜,建立其热分析有限元模型,研究天线在夏至日不同太阳时刻的温度场分布特性.结果如下:一天中,主反射面的最高温度可达42.86℃,出现在14时,同时刻撑腿的温度也达到峰值,为41.74℃.背架水平分区温差在5时、18时、19.5时均超过1℃,会对天线指向性能产生较大影响.夜间天线结构温度分布亦不均匀,俯仰结构的温差明显高于其他构件,最大温差为6.42℃,通过数值模拟与试验相结合的方法,证明了构件的壁厚差异是导致结构夜间温差较大的主要原因.     

A Study of the Fitting Accuracy of the Active Reflector for a Large Spherical Radio Telescope

We propose a spatial three-degree-of-freedom (DOF) parallel mechanism combining two degrees of rotations and one degree of translation to support the active reflector units of a large spherical radio telescope. The kinematics, workspace and accuracy of the mechanism are analyzed. One-dimensional and two-dimensional fitting errors to the working region of active reflector are investigated. Dimensional parameters of the mechanism and active reflector unit are examined with respect to the requirement of fitting accuracy. The result of accuracy analysis shows the effectiveness and feasibility of the proposed mechanism, and gives a design rule to guarantee the highest working frequency required by large radio telescope.     

大型射电望远镜主反射面调整方法研究

随着毫米波天文学和空间通信的重要性日益提高, 对天线性能提出了越来越高的要求, 而天线性能往往受到其反射器表面精度的限制. 微波全息技术是一种快速有效的检测反射面天线表面轮廓的测量技术. 通过微波全息测量得到天线口径场, 计算天马65m射电望远镜反射面与理想抛物面的偏差. 天马65m射电望远镜的主反射面板是放射状的, 有14圈. 面板的每个角都固定在面板下方促动器的螺栓上进行上下移动, 且相邻面板交点处的拐角共用一个促动器. 采用平面拟合的方法可以计算各块面板拐角处的调整值, 但是同一个促动器会得到4个不同的调整量. 通过平面拟合, 同时以天线照明函数为权重的平差计算方法得到相邻面板拐角的一个平差值, 即天马65m射电望远镜1104个促动器的最佳调整值. 通过多次调整和新算法的应用, 天马65m射电望远镜反射面的面形精度逐渐提高到了0.24mm.     

一种扩大FAST视场的方法

所有的大口径射电望远镜都存在这样一个问题：在其分辨率和灵敏度提高的同时，视场变小．而且口径越大，视场越小．这成为大口径望远镜不可回避的矛盾．要解决这个矛盾，可以在望远镜的焦平面上放置Ⅳ个分立馈源．让它们同时工作，这样可以看作把视场扩大了Ⅳ倍．望远镜的工作效率提高Ⅳ倍．但是这样做的缺点是——视场不连续．且馈源数目Ⅳ受到望远镜焦比(F／D)的限制．采用致密焦面阵(dense focal plane array)就可以很好地解决这个问题．致密焦面阵的单元不是喇叭口天线，而是无方向性的Vivaldi天线(Vivaldi antenna)．要把Vivaldi阵列应用到望远镜上，需要对单个Vivaldi天线和Vivaldi阵列的电性能有清楚的认识，并能根据需要来设计照明方向图．还要知道大望远镜的焦面上电磁场的分布情况，借此判断能否应用Vivaldi阵列，以及给出Vivaldi单元的分路赋权网络．主要给出了FAST的焦面场的分布情况．并说明应用Vivaldi阵列的可能性．     

Schemes for Segmenting the Main Reflector of the FAST

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基于全息测量的佘山25 m射电望远镜远场分析

首先分析了佘山25 m卡塞格伦天线结构,形变与噪声这2个因素影响下的远场进行仿真分析,理想情况比较,分析这2个因素对全息测量的影响。然后利用天线结构参数分别对天线面板表面获得了二维远场的幅度和相位分布图,并与     

Model Validation and Performance Evaluation for The Multi-Tethered Aerostat Subsystem of the Large Adaptive Reflector

The Canadian design for the Square Kilometre Array radio telescope includes a large multi-tethered aerostat to support the telescope’s receiver. To validate this design concept, two parallel tracks have been undertaken: a numerical simulation of the multi-tethered aerostat system has been assembled, and a one-third scale prototype of the system has been constructed. This paper describes the experimental facility, presents results from initial tests of the uncontrolled system and compares these results to the predictions of the computer model of the system. Generally, the results compare very favourably. Using the simulation, we arrive at two important design philosophies to be used in the design of the full-scale system: (a) perturbations on the confluence point should be minimized, and (b) the system stiffness should be maximized to ensure minimum response to disturbances.     

Development of Control Softwares for the SRAO 6-Meter Telescope Based on PCs Running Linux

We have developed a control system for the Seoul Radio Astronomy Observatory (SRAO) 6-meter telescope operating in the 85–115 Ghz frequency range. Four PCs running the Linux operating system control source tracking, take data, execute observations and handle user interface. The control system utilizes a modular and multiprocessing structure to facilitate easy upgrading and troubleshooting. Communication between the processes relies on the interprocess communication (IPC) resources on Linux such as shared memory, message queues, and TCP/IP sockets. Communication between PCs is made via an Ethernet link. We also use digital I/O lines for some status signals which require a short delay. The control system supports scheduling observations, updates observation logs automatically and also supports graphical user interfaces. These all makes the operation easy. By using a commercially available motion control card with an embedded microcomputer for antenna control, we achieved a tracking accuracy to better than 1 arcsec. This revised version was published online in July 2006 with corrections to the Cover Date.