Research On Electromagnetic Near-Field Far-Field Transformation Based On Multipole Expansion And Its Applications

Electromagnetic near-field far-field transformation is an important method to measure and analyze electromagnetic characteristics of radiation/scattering targets.The far field can be obtained by near-field far-field transformation with obtained data in nearfield measurement system,which avoids electromagnetic interference of outdoor measurement.At present,there are two traditional near-field far-field transform methods:spectral method and equivalent current method.The near-field far-field transformation based on multipole expansion has higher calculation accuracy than the spectral method,and the near-field measurement is more flexible.Compared with equivalent flow method,it has higher computational efficiency.Moreover,the commonly used sampling technology is uniform sampling technology.A large number of near-field sampling points are needed for both single-frequency and wide-band near-field measurement,and the measurement time cost is high.In view of the shortcomings of the two traditional nearfield far-field transformation methods and the high cost of near-field measurement,the following studies are carried out in this thesis.1.Multipole expansion model based on spatial compressive sampling: The electromagnetic near-field far-field transformation matrix equation based on multipole expansion is established,then a skeletonization-scheme-based compressive sampling method is proposed in the spatial domain to reduce the number of near-field sampling points required by the single frequency near-field measurement,and improve the efficiency.At the same time,the sampling parameters are systematically analyzed,and the factors affecting the compressive rate are studied.The numerical results show that the spatial compressive sampling technique reduces the number of near-field measurement samples obviously,and can realize accurate reconstruction of near field,which has high precision in nearfield far-field transformation.2.Parameterization model in frequency domain based on weighted Laguerre polynomials: In order to compress the samples in the wideband near-field measurement,the electric field matrix equation characterized by weighted Laguerre polynomials and expansion coefficient is established in this thesis to compress the wideband near-field samples in the frequency domain.At the same time,the spatial near field-sampling technology is combined to is reconstruct the whole wideband near-field through the nearfield at the spatial skeleton points at the frequency points,so as to realize the compressive sampling in the frequency domain and the spatial domain.Then the near-field far-field transformation is realized with the reconstructed wideband near-field.Numerical examples indicate that the proposed method has high compressibility in both frequency domain and spatial domain,and can reconstruct wideband near-field accurately with a high computational accuracy in near-far-field transformation.3.Wideband near-field reconstruction technology based on tensor CUR decomposition: Aiming at wideband scanning in frequency domain near-field measurement system,this thesis extends the matrix equation of multipole expansion model to tensor vector product equation,and realizes spatial compressive sampling by applying tensor CUR decomposition.After compression,the positions of spatial skeleton samples at different frequency are consistent,which is suitable for wideband scanning in near-field measurement.The numerical results show that the proposed method is effective and can realize the integrated spatial-frequency compressive sampling of wideband field.4.Practical and applied research of electromagnetic near-field far-field transformation based on multipole expansion: In order to improve the practical value of the proposed method,the scattering field measurement and near-field far-field transformation of the metal warhead cone are realized in this thesis.The measured data are used to conduct a quantitative analysis of its performance.And the electromagnetic characteristics analysis technology combined with the three-dimensional wave number domain imaging method is proposed.The near-field far-field transformation method is used to calculate the far field with high precision.Combined with the electromagnetic flow distribution obtained by imaging,the electromagnetic characteristics are analyzed from multiple angles and in all directions.