Vol 18, No 7

B-spline surface fitting and simplified GO/PO analysis of subreflector correction for large Cassegrain antenna distortion compensation

You Ban, Cong-Si Wang, Shu-Fei Feng, Wei Wang, Bao-Yan Duan


Abstract The main surface of a large Cassegrain antenna consists of a large number of panels. There are inevitably random and systematic errors which will degrade the antenna pattern and limit its applicability when working at high frequencies. Correcting the subreflector surface is difficult to describe by a global expansion effectively with a small amount of data. This paper presents a simple and clear way for correcting the subreflector surface of a large Cassegrain antenna for achieving such compensation. The advantage of the method is that the geometrical optics (GO) analysis is extremely simplified by the concept of equivalent prime-focus paraboloid, and corrected deformations of the subreflector surface are determined by simple formulas which represent the relationship between distortions of the subreflector surface and phase of the main surface current. The final shape of the subreflector surface is represented by a B-spline surface. To obtain a satisfactory antenna pattern with the simplest subreflector surface, the optimal number of B-spline patches are searched by particle swarm optimization (PSO). The shaping process is verified by compensating a 22-m Cassegrain antenna whose main reflector has 96 panels. The results are satisfactory and demonstrate the simplicity and effectiveness of the approach.


Keywords telescopes — reflector antennas — subreflector shaping — compensation

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