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在140呎望远镜上,以1.3公分的波长绘制的波束图表明了极强的旁瓣,当指向遥远的西方时,就连续出现四个旁瓣。不同的观察型式及彗形波瓣的理论导出了与下述完全一致的结论——望远镜具有大的横向散焦,即指向变化90°时,东西方向有7.2公分的变化,而南北方向有2.8公分的变化。因为馈源支腿的横向变形只有0.5公分,必然是以光轴移动为主。用一种最佳吻合抛物面的滑动旋转来达到此目的,即是沿着稍有变形的表面滑动而且又绕表面的平均曲率中心旋转。据表明,引起的横向焦点偏置可能是比引起的表面变形更大。这种滑动旋转还可以用结构分析来证明。此种观察和分析方法的描述也适用于其它望远镜。例如140呎的极轴座架,可以表示出两个方向影响:东西方向和南北方向;当用俯仰一方位座架时,可以用唯一的方向表示:上一下。每当边缘部分比中心部分更有柔性时,横向散焦的影响在其它望远镜中也有同样现象;每当重力在误差估算中是主要的时候,引起的效率和波束的劣化将是重要的。在此情况下,望远镜应当在初级焦点处提供一种可变的支架横偏,用计算机控制指向角的变化,随后进行轴向移动。对这种望远镜而言,这种附加的自由度可以大大改善短波长的性能,这种望远镜的面板比自重引起变形的背架结构更精确。
On the 140-foot telescope, the beam pattern plotted at a wavelength of 1.3 centimeters shows very strong side lobes, and when viewed in the far west, four side lobes appear. The different types of observations and the theory of the co-lobes lead to the exact conclusion that the telescope has a large lateral defocus, ie a change of 7.2 cm in the east-west direction when pointing changes by 90 ° and a 2.8-cm change in the north-south direction Change of centimeter Because the lateral deformation of the feed leg is only 0.5 cm, it is necessary to move the optical axis. This is accomplished with a sliding fit that best matches the paraboloid by sliding along a slightly deformed surface and rotating about the mean center of curvature of the surface. It has been shown that the resulting lateral focus offset may be greater than the resulting surface distortion. This sliding rotation can also be proved by structural analysis. The description of such observation and analysis methods also applies to other telescopes. For example, a 140-foot polar-axis mount can indicate two directions: the east-west and north-south directions. When using the pitch-bearing one, you can represent it in one direction only: up. Whenever the edge portion is more flexible than the center portion, the effect of lateral defocusing is the same in other telescopes; the resulting efficiency and beam degradation will be important whenever gravity is the primary factor in error estimation. In this case, the telescope should provide a variable cross-arm deflection at the primary focus, using a computer to control the change of the pointing angle, followed by an axial shift. For such telescopes, this additional degree of freedom can greatly improve the performance of short wavelengths, the telescope’s panel is more accurate than the self-weight deformation of the back frame structure.