| The parabolic reflector antenna is an important device for mankind to observe the universe.However,due to the influence of various environmental factors,many small deformations will occur on the surface of the antenna over time.These deformations will greatly affect the efficiency of the antenna.In order to eliminate the influence of surface deformation on observation,large antennas are always equipped with actuators behind the antenna panel to tune the shape of the antenna surface.However,it is necessary to know the deformation distribution to guide the actuator to adjust the antenna surface accordingly.The current methods of detecting antenna surface deformation include phase correlation method and phase retrieve method.However,these two methods have disadvantages such as long measurement time and the need for complex measurement devices.In recent years,some researchers have proposed another method to restore deformation through the amplitude of the electric field radiated by the antenna,which is referred to as the amplitude method.The amplitude method first establishes the relationship between the antenna’s near-field electric field amplitude and the surface deformation,which is called the deformation-amplitude equation,and then uses an iterative algorithm based on Fourier transform to solve the deformation-amplitude equation(DAE).In the amplitude method,only one set of near-field data needs to be measured,which make the amplitude method have the advantage of short measurement time and can possibly be used for real-time surface deformation recovery.However,the deformation solved by the amplitude method still has a certain error.The error of deformation solved by the amplitude method mainly comes from two aspects.On the one hand,the DAE has some error;on the other hand,the iterative algorithm used to solve the DAE has some error.The main work of this paper is to modify the amplitude method for these two aspects,so as to improve the accuracy of the deformation solved by this method.The content includes:1.To eliminate the error caused by the approximation of the energy conservation formula during the derivation of the DAE,this paper adopts a more accurate energy conservation formula based on the radius of curvature to re-derive the equation,thereby obtaining a new DAE.2.To eliminate the error caused by treating the antenna feed approximately as a point source during the derivation of the DAE,this paper adopts a Gaussian feed model which matches better with the antenna feed used in real world.The new DAE has been further modified due to the influence of Gaussian feed.Simulation results show that the corrected equation has a higher accuracy.3.To eliminate the error caused by the discrete Fourier transform in the iterative algorithm,this paper improves the iterative algorithm by means of zero padding.Simulation results show that this improvement can eliminate the offset phenomenon in the solved deformation.4.To eliminate the error caused by the iteration in the algorithm,this paper utilized the new DAE to replace the old DAE in the iteration.Simulation results show that the deformation solved by the improved iterative algorithm is more accurate than the one solved by the original iterative algorithm.A nearfield experiment verifies that the above four improvements will improve the accuracy of the retrieved deformation in real world.In addition,the amplitude method is currently only applicable to single reflector antennas.However,most of the large antennas in service are dual-reflector antennas.In order to make the amplitude method have a wider application range,this article also derives the amplitude method which is applicable to dual-reflector antennas by means of the equivalent feed method.Simulation results show that this method can restore the surface deformation of the main reflection surface of the dual-reflector antenna. |
