| Antenna near-field measurement is an important method to analyze antenna performance,it predicts the near-field distribution in unsampled region and far-field pattern according to the near-field model and the near-field sampling data,where the nearfield model and sampling method are key factors that determine the efficiency and accuracy of antenna near-field measurement.Common near-field models include wave spectrum model and equivalent current model,which are usually used together with uniform sampling method in practical applications,and suffer from high sampling cost.In addition,the wave spectrum model has a large error in predicting the extreme near field of the antenna,while the computational complexity of the equivalent current model is very high,which results in a rapid increase in time consumption with the size of the antenna under test.In view of the high sampling cost,large error or high computational complexity of the two near-field models,the following research works are carried out in the thesis.1.A skeletonization-scheme-based compressive spherical near-field sampling method: The interaction matrix between the spherical near field and the wave spectrum coefficients is constructed based on the spherical wave spectrum theory,then an interaction matrix preconditioning method is proposed by analyzing the variation characteristics of spherical wave spectrum with its order.A skeletonization-scheme-based compressive spherical near-field sampling method is established by the rowskeletonization-scheme-based compression of the preconditioned interaction matrix.The numerical results show that the proposed compressive sampling method siginificantly reduces the number of sampling points compared with the uniform spherical sampling method,and the preconditioning method siginificantly improves the condition number of the interaction matrix,so the near-field data can be decompressed accurately.2.Comparative analysis of the accuracy of plane wave expansion method: In order to verify the accuracy of the plane wave spectrum model for predicting the planar near field,the computational accuracy of the classical method and a novel one are compared and analyzed in the thesis.The novel model expands the plane wave spectrum by spherical wave expansion method,and obtains the expression of the complete plane wave spectrum according to spherical wave rotation theory,then the contribution of a part of evanescent waves can be considered.The numerical results show that the novel plane wave expansion method can obtain clearer near-field images compared with the classical method which completely ignores the contribution of the evanescent waves,but there is still a large error when predicting the extreme near field of the antenna.3.A fast reconstruction method for equivalent current: In order to reduce the computational complexity of the equivalent current model,a fast algorithm for matrix filling and inversion,which takes advantage of the low-rank properties of the interaction matrix between the equivalent current and the near field,are proposed in the thesis.Firstly,the adaptive cross approximation algorithm is used to quickly fill the interaction matrix,and then the number of equations is reduced by the row compression of the matrix U in the adaptive cross approximation,which greatly reduces the computational time for solving the equivalent current.The numerical results show that the proposed method can reduce the computational and storage complexity of matrix operations and improve the computational efficiency of the equivalent current method.4.Practical research on equivalent current method: In order to improve the practical value of the equivalent current method,the triangulation of Huygens and sampling surfaces of certain shapes is implemented,the influence of the shape of the sampling surface on the computational accuracy is analyzed,the fast acquisition method of sampling data is explored,a real-time solving technology of equivalent current based on inverse matrix compressive pre-storage is proposed,and the feasibility of applying the equivalent current method in the antenna near-field diagnosis is demonstrated in the thesis.Then the performances of the equivalent current model and wave spectrum model are compared,analyzed and verified by the measured data,and the recommendations for the use of the two models in the antenna near-field measurement are given. |
