4. The Study on the Adjustment Model of Sub-reflector and Engineering Realization Method

The gravity deformation of large reflector antenna causes the deterioration of antenna performance. In order to solve the problem, the method of real time adjustment of sub-reflector to reduce the influence of gravity deformation is proposed in the paper. The influence of the position translation and rotation of sub-reflector on antenna gain and pointing is analyzed. The mathematical model about the posture change of sub-reflector with the adjustment of antenna elevation angle is built. A set of data about the main reflector deformation of 35 m antenna for different elevation angles was obtained through digital photogrammetry. The best fit was conducted. And then a set of optimum position coordinate of sub-reflector obtained through best fit were superposed with the measured displacement data of sub-reflector under the action of gravity with respect to different elevation angle. And then a set of final adjustment data of sub-reflector was obtained and substituted into the mathematical model. The best fit was conducted again by using the least squares to calculate the parameters of mathematical model. The model was used to adjust sub-reflector in real time to reduce the influence of gravity deformation on the antenna performance. The simulation results show that the gain of 35 m antenna in X and Ka band can be increased by 0.52 and 1.95 dB after the sub-reflector position is adjusted in real time by using the model.