Calculation of the Best Fit Subreflector and Its Application in Eliminating the Harmless Error of Deformed Large Subreflectors

Abstract

For a dual reflector antenna whose subreflector is also equivalent to a large reflector antenna, its structure will inevitably be deformed due to the effect of gravity, wind, temperature, and so on. This article is inspired by the homologous idea applied to main reflectors and extends this idea to subreflectors to eliminate the harmless error of the distorted subsurface by using the best fit surface of the same type. This article proposes seven parameters to determine the best fit subreflector (BFS): five rigid parameters (three translation and two rotation parameters) and two parameters related to the change of the subreflector shape. These seven homology parameters are calculated by the least square method (LSM). The subreflector of the QiTai radio telescope (QTT) is used in two examples. The first example shows that the proposed method can effectively calculate the BFS surface and obtain the accuracy that has eliminated the harmless error of the distorted subreflector. In the second example, the accuracy without harmless error is used in the classical design so that the homologous design of the subreflector structure is realized. The excellent results show the validity of the proposed method and provide an important reference for the structure design of large subreflectors.