Research On Millimeter Wave Near Field Beamforming Algorithms

With the increasing improvement of security requirements in public places,the accuracy and security of security imaging has become a research hotspot in recent years,and millimeter wave imaging has the dual advantages of penetration and security.In this dissertation,the near-field response model is firstly introduced according to the characteristics of near-field security inspection imaging.Secondly,the conventional beamforming algorithm and adaptive beamforming algorithm is simulated by this model.In addition,combining the beamforming algorithm with the non-uniform fast Fourier transform?NUFFT? imaging algorithm,the imaging target image can be restored more clearly.According to the characteristics of millimeter-wave near-field security inspection imaging site,the signal propagation equation of near-field array for security inspection imaging system is deduced.Based on this equation,the relationship between the number of antennas and the beam width is simulated by combining with conventional beamforming under the condition of one-dimensional uniform linear array.The simulation results show that the larger the number of antennas,the narrower the main lobe beam and the higher the spatial resolution.Aiming at the shortcomings of the conventional beamforming algorithm that can filter out the interference signals effectively,the adaptive beamforming algorithm is applied to the near-field array signal propagation equation.By simulating the three adaptive beamforming algorithms in the distance dimension and the angle dimension respectively,we can find that the adaptive beamforming algorithm can form the depression at the interference signal.At the same time,it is better to locate the desired signal in the distance dimension.The NUFFT two-dimensional imaging algorithm is combined with a near-field beamforming algorithm.After the beamforming process is performed on the echo signals received by the antennas,the azimuth FFT transform is performed,multiplied by the matching function,and then subjected to two-dimensional inverse NUFFT transform to obtain the target scattering coefficient and restore the target image.The simulation results show that the NUFFT two-dimensional imaging algorithm can achieve image reconstruction well.Under the condition of reducing the computational complexity greatly,the output error with discrete Fourier transform?DFT? is 10^-6.Then the increasing number of elements can better restore the spatial point target image with low noise power.In addition,the NUFFT algorithm combined with adaptive beamforming can better reduce the influence of noise and identify targets more clearly than the conventional beamforming NUFFT algorithm.