| With the development of large fully steerable reflector antenna towards the trends of high frequency,high gain,wide band and high pointing accuracy,it is a great challenge to the design of antenna structure.For example,the National Key Basic Research Program of China(the National 973 Program)will build the world's largest fully steerable reflector antenna(Qi Tai radio Telescope: QTT)with 110 m aperture in Qi Tai County,Xingjiang,China.The main reflector area of QTT is about equal to 22 basketball courts,and its final accuracy is required to be better than 0.2mm.Therefore,the difficulty is conceivable.In addition,its subreflector has a diameter of 12 m.If the structure of subreflector is till designed as a rigid structure,it will greatly increase the difficulty and cost of the main reflectors structure design and even the whole antenna structure system.Based on the electromechanical coupling theories and the ideal of subreflector compensation,the method of considering the subreflector compensation in large reflector antennas electromechanical coupling design is proposed.It is expected to reduce the requirements for the accuracy of the main reflector,thus reducing the difficulty and cost of the structure design and building.The main contributions are described as follows.1.The homology calculating method is proposed for the large subreflector.This research expanded the homology idea from paraboloid reflector to standard subreflector.The parameters of semi-major and semi-minor axes are used to describe the shape change of subreflector.Establish the transformation relationship between the deformation of subreflector and its homologous fitting surface by the change of path length,and the homology parameters can be calculated by matrix operations of minimizing the path length error.Then the parameters can be used to realize the homologous design for the subreflector structure.The simulation results verify the correctness and feasibility of the proposed method.2.A best fit shaped surface calculation method for the shaped reflector antennas is presented.Firstly,“Focal Line” is introduced to transform the shaped dual reflector antennas into two matching systems of “Main Reflector-Focal Line” and “Feed-Subreflector-Focal Line”.In “Main Reflector-Focal Line” system,the quantitative relationship between the displacement of “Focal Line” and the change of the shaped reflector surface is derived,and then the fitting parameters of the shaped surface are determined which solves the problem that the shaped surface has no specific parameters to describe the homologous surface.Through the matrix operation of the minimum antennas half optical path length error,the best fitting parameters of the distorted shaped main reflector can be calculated and then the best fitting shaped surface can be determined.The simulation results show the effectiveness of the presented method.3.A fast design method of correcting a subreflector to compensate the error of main reflector is proposed.Starting from the GO/PO method,the method calculates the corrections of subreflector by iteration to minimum the antennas path length error,and combines the orthogonal polynomials(Zernike polynomials)to determine the corrected subreflector quickly.Therefore,the way is also called the Path-length Error Iteration Compensation method.The simulation results show that the proposed method is simple,effective and adaptable to a wide frequency range.4.A method of determining the error of main reflector relaxed by the corrected subreflector is proposed.First of all,the error of main reflector is decomposed into independent items.Then based on the Path-length Error Iteration Compensation method,the relaxation of independent main reflector error can be quantitatively described by the corrected subreflector under the condition that the antennas has the specific gain loss.It is very meaningful refer to the engineering. |
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