A subreflector system in the parabolic antenna of a 65 m radio telescope has been installed for compensating the gravitational deformation of the supporting frame in the antenna. This paper investigates the influence caused by the displacement of subreflector on the performance of the antenna and the corresponding compensation method. The investigation focuses on Ku-band frequencies and a new fitting formulation which is different from that of low-frequency bands is proposed to reduce the fitting error in the Y direction. In addition, the pointing deviation caused by the offset of the subreflector is analyzed and the model of pointing deflection caused by the displacement of subreflector is established, which can be used to improve the pointing accuracy. The model can determine the position and attitude of the subreflector with elevation and an extensive test shows that it can effectively improve the efficiency of the antenna at each elevation.
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