Study Of Some Problems In Electromechanical Coupling Theory Of Large Microwave Reflector Antennas

Reflector antenna has been widely applied in areas,such as radar,communication,radio astronomy.With its development of large aperture,high frequency,high gain,and high pointing accuracy,electromechanical couping problem is gradually revealed.Based on previous works,several problems existing in electromechanical couping problem are investigated for large microwave reflector antenna.The main works can be summarized as follows.(1)The root mean square of surface errors is always adopted as a parameter to characterize reflector's electromagnetic performance.But only one root mean square value is not enough to describe error distribution form.For this problem,firstly,an optimization model is constructed to analyze the effect of the error distribution form on electromagnetic performance,where peak gain loss and first sidelobe level are taken as two objectives,the variances of surface errors in different annular regions as design variables,and the same root mean suqare values of surface errors for whole reflector as constraint.Then,weighting function for surface errors is derived and the influencing characteristics on peak gain and first sidelobe level are discussed.Lastly,the derived weighting function is applied in reflector's quality evaluation with non-uniform surface errors along radius.Results show that the weighted root mean square value can be used to measure the electrical quality of reflector surface more effectively.(2)The pattern approximation analysis is of great importance for improving the efficiency of integrated structural-electromagnetic design.But the existing methods are only suitable for small deformations.Thus,a new pattern approximation model based on piecewise linear fitting is presented.The exponential error term is approximated by a series of straight lines,the structure deformations are separated from integral operation with several assumptions,and based on the stiffness matrix assembly process in finite element method,the integration of pattern analysis can be simplified to be a matrix operation.Simulation results show that the proposed pattern approximation model is feasible and effective.Then,based on the proposed model,an optimization model for producing a contoured beam is proposed with good results.(3)The information transfer from structure elements to electromagnetic grids is a key point for integrated structural-electromagnetic design.For the shortcomings in the method of producing electromagnetic grids by refining structure elements,a new information transfer method is developed by constructing quadratic surface over each structure element.Firstly,the node normal vectors of distorted reflector are constructed using node coordinates of structure elements.Then,for each structure element,a quadratic surface is constructed to be the approximation surface of the distorted reflector.Lastly,the electromagnetic grids can be obtained by refining all the quadratic surfaces.Results show that the proposed method is feasible and effective.(4)Reflector antenna working in complex and harsh environment needs to be calibrated periodically,but the panel adjustment process is inconvenient and has a long period generally,thus,the feed adjustment is a conventional method for non-active main reflector antenna.Based on reflector's far field pattern,the feed adjustment amounts of distorted reflector is derived and the results of feed position errors and pointing errors determined from reflector's far field pattern are discussed,and some useful data and figures are obtained.The methods metioned above are applied in feed adjustment of someone non-active main reflector antenna and good results are obtained.(5)With reflector's development of large aperture and high frequency,the effect of thermal deformations caused by solar radiation on reflector's performance cannot be neglected.For this problem,a real-time adjustment process for beam pointing under the effect of solar radiation is presented,real-time estimation method of temperature field is proposed,and adjustment amounts of beam pointing is derived.Reflector's temperature field can be estimated in real-time through a small amount of sensors,based on which,the real-time adjustment for beam pointing can be achieved easily.The simulation on a 7.3 m reflector antenna is done well,showing the effectiveness of the proposed method.