FAST望远镜灵敏度优化及“回照”方式分析

发布时间：2018-08-18 21:18

【摘要】：500米口径球面射电望远镜(Five hundred meter Aperture Spherical radio Telescope-FAST)是目前国际上口径最大、最灵敏的单天线射电天文望远镜。与通常的射电望远镜不同,FAST在抛物面之外有金属反射面。这部分球面反射面可屏蔽地面热辐射,从而对馈源的照明设计提供了相对灵活的可能。但这部分球面反射面在屏蔽地面热辐射的同时,也对FAST的远场方向图有一定的影响:如旁瓣升高,天顶角不为零时方向图不对称等。本课题采用物理光学方法,利用GRASP软件计算了FAST的远场方向图,并对灵敏度进行计算和分析。首先介绍了在GRASP软件中建模过程和物理光学计算远场方向图的原理;然后研究了FAST在馈源为高斯照明时,不同边缘照明电平对望远镜灵敏度的影响;探讨了在天顶角大于26.4度时,采用“回照”方式优化望远镜灵敏度的方法;最后利用FAST各波段馈源仿真计算的方向图,计算了FAST各天顶角的远场方向图。当馈源为高斯照明时,边缘照明约为-12dB~-14dB时灵敏度达到极大值。当天顶角为30度、35度和40度,在“回照”方式下取回照角分别为15度、21度和26度时,望远镜的灵敏度分别提高了19%、48%和100%。本文的计算分析结果和方法可为今后FAST的电性能优化,及可能的防噪墙的建设提供参考。
[Abstract]:The 500m spherical Radio Telescope (Five hundred meter Aperture Spherical radio Telescope-FAST) is the largest and most sensitive single antenna radio telescope in the world. Unlike conventional radio telescopes, fast has metal reflectors outside the parabola. This part of spherical reflector can shield thermal radiation from the ground, which provides a relatively flexible possibility for the lighting design of the feed. However, this part of the spherical reflector not only shields the thermal radiation from the ground, but also has a certain effect on the far field pattern of FAST, such as the elevation of the sidelobe, the asymmetry of the azimuth angle not being 00:00, and so on. In this paper, the far-field pattern of FAST is calculated by using GRASP software and physical optics method. The sensitivity is calculated and analyzed. This paper first introduces the modeling process in GRASP software and the principle of calculating far field pattern by physical optics, and then studies the influence of different edge lighting levels on telescope sensitivity when the feed source is Gao Si illumination. This paper discusses the method of optimizing telescope sensitivity by "backlighting" method when the zenith angle is greater than 26.4 degrees, and finally calculates the far-field pattern of FAST zenith angle by using the simulated pattern of feed source in each band of FAST. When the feed source is Gao Si illumination, the sensitivity reaches maximum when the edge illumination is about -12 dB BU -14 dB. The sensitivity of the telescope is increased by 19% and 100% respectively when the peak angle is 30 degrees / 35 degrees and 40 degrees, and when the angle is 15 degrees / 21 degrees and 26 degrees respectively, the sensitivity of the telescope is increased by 19% and 100% respectively. The results and methods of calculation and analysis in this paper can be used as a reference for the optimization of electrical performance of FAST and the possible construction of noise proof wall in the future.
【学位授予单位】：贵州师范大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TH751

【相似文献】