Influence Mechanism Of Mechanical Factors On Electrical Performance Of Reflector Antenna And Its Applications

This work was supported by a grant from the National Program on Key Basic Research Project (973 Program). On the basis of the predecessor work, this thesis is mainly concerned with the influence mechanism of mechanical factors on the electrical performance of reflector antenna and its application in surface panel adjustment. The main research work can be described as follows.1. In accordance with the characteristic that the large parabolic reflector antenna surface are divided into panels, the ETM (Error Transformation Matrix) between panel positional errors and aperture phase errors is derived. Based on the ETM, the influence mechanism of panel positional error on the electrical performance of reflector antenna is analyzed. And the effect model of panel fabrication error and sub-reflector positional error on the electrical performance of reflector antenna is given. Then, an experiment is implemented on a 3.7m reflector antenna with 12 panels which verified the method mentioned above. At last, a 6m reflector antenna is simulated and some useful data and figures are obtained.2. Based on the precise analysis of antenna structure, a gravity deformation model was derived by superposition which described the main reflector distortion over the entire range of elevation angles. The corresponding formulae were also deduced based on the analysis of antenna structure. The BFP (Best-Fit Paraboloid) of the deformed reflector surface is calculated by the LSM (Least Squares Method). In accordance with convention, the distortion RMS (Root Mean Square) of the deformed reflector surface was considered with respect to the BFP. The aperture efficiency and gain loss is calculated using Ruze formula. An optimization method was presented to calculate the best rigging angle for reflector surface accuracy. To verify the present equations, a finite element model of 12m parabolic antenna structure was created and input to the ANSYS program for numerical simulation.3. After the analysis of the characteristic of panel adjustment for large segmented reflector antenna, the BFP is chosen as an objective surface shape. Then, an efficient method of panel setting is given, which can be used to optimize the quantity of panel adjustment. Based on the theoretical derivation, a software platform for surface measurement and panel adjustment of reflector antenna is developed. The simulation on a 6m parabolic reflector antenna with Ku band is done and the panel adjustment quantity is calculated. At last, the efficiency of the method mentioned in the thesis is discussed. The numerical simulations showed that the results may be applied to antennas with realistic panel schemes, for prediction of their electrical performance and surface adjustment.4. To improve the efficiency of panel adjustment of large segmented reflector antenna, a method for determination of panel adjustment quantity from far field pattern is presented. Using the method of Physical Optics (PO), the relationship between the far field value and the node displacement is derived. Then the panel adjustment vector is related to far field pattern with linear equations. Singular Value Decomposition (SVD) is used to find out a vector of panel adjustment quantity, which will be used for quick adjusting. An experiment is implemented on a 3.7m reflector antenna with 12 panels and some useful data and figures are obtained. The applicable range of the proposed method is also discussed, and the results are going to be useful guide for panel adjusting of large reflector antenna efficiently and precisely.5. On the degradation of electrical performance due to the main reflector deformation of large shaped Cassegrain antennas, a method for compensation by moving sub-reflector is presented. A group of best-fit paraboloids are found by least-square fitting the theoretical discrete data. The group of paraboloids is used to fit the deformed main reflector, with the constraint of all these focuses being in line. The best-fit parameters are optimized and the adjustments of sub-reflector are derived with the ratio of main reflector and sub-reflector. The adjustments at various attitudes are saved in a look-up table to real-time compensate for main reflector deformation. From the simulation testing on a 65m reflector antenna, satisfactory results are obtained and will be used in practice.