Research On Phaseless Near-Field Antenna Measurements Based On The Interpolation Algorithm And The Source Reconstruction Method

Traditional antenna testing technique requires to use a linearly polarized probe to obtain the amplitude and phase of the electric field in the near-field.When the near-field data is sampled at the uniform discrete points on the scanning plane,the sampling interval is supposed to satisfy the Nyquist Sampling Theorem.However,for the high-frequency antennas,such as the microwave and millimeter wave antennas,the sampling interval is much too small and the phase presents a cyclical shock.Thus,the requirement for the antenna measurement system and the costs of antenna measurements will become high.A high-reliability and low-cost near-field measurement scheme for the high-frequency antennas will be provided in this thesis.In order to solve the problems above,interpolation algorithm is imported to obtain electrical intensity data,and phaseless planar near-field antenna technique based on source reconstruction method is introduced to overcome the difficulty of phase acquisition.Firstly,the applications of several common interpolation algorithms in various fields are deeply studied,and the theoretical derivations are detailed.The calculation amount of nearest neighbor interpolation algorithm is the smallest.Only when the values of the matrix elements fluctuate with a narrow range,can the nearest interpolation algorithm achieve a satisfactory effect.The B-spline interpolation algorithm has high accuracy and stable performance,but it needs to solve equations,and cannot be controlled locally.The bilinear interpolation algorithm integrates the advantages of the above two algorithms,and makes a good compromise between calculation amount and accuracy.The accuracy of the far-field pattern is highly sensitive to the near-field amplitude,and the near-field amplitude usually has a certain fluctuation.Therefore,in this thesis,the electrical intensity is sampled by the sampling interval l,then the bilinear interpolation algorithm is used to obtain the amplitude at the unsampled points.Secondly,on the basis of traditional near-field antenna measurement technique,planar phaseless near-field antenna measurement technique based on source reconstruction method is proposed to solve the phase acquisition problem of high-frequency antennas.Specifically,the near-field amplitude of AUT is used as the reference,equivalent current elements are placed on an enveloping surface of the antenna,and the current distribution is optimized using the particle swarm optimization.And then the near-field phase generated by the preprocessed current distribution is taken as the initial iterative phase.Lastly,the phase is further refined by the iterative Fourier transformation algorithm,and the restored phase on a scanning plane is obtained.Finally,the half-wave dipole array antenna and pyramidal horn antenna are used as models to simulate the near-field to far-field transform algorithm,the interpolation algorithm and the phaseless near-field antenna measurement technique based on the source reconstruction method.The simulation results show that the interpolated amplitude by the bilinear interpolation algorithm is in good agreement with the theoretical amplitude.In the phase retrieval process,the source reconstruction method can obtain a set of superior initial iterative phase.And compared to the random initial phase,it can avoid falling into the local optimal solution,and can reach the convergence accuracy more quickly.Finally,the antenna far-field pattern also meets the experimental requirements.