Research On Wall Clutter Suppression And Fast Imaging Method Of Ultra-wideband Through-wall Radar

Ultra wideband through wall detection technology takes advantage of its low frequency and wide bandwidth to identify and image targets behind hidden objects such as trees,dense smoke and concrete walls.Compared with traditional narrowband radar detection,due to its good penetrability,with high range resolution and strong anti-interference,it has been further developed in military applications and civilian applications in recent years.In through wall radar detection,when electromagnetic waves penetrate wall obstacles,they will produce refraction and energy attenuation,the thickness and dielectric constant of the wall will affect the propagation speed of electromagnetic waves,resulting in non-existent,offset,out-of-focus or defocusing of the target during imaging.In addition,traditional imaging algorithms such as BP need to perform a large number of iterative calculations when performing high-resolution imaging of the detection scene,which has high computational complexity,large computer memory usage and slow imaging speed.In response to the above problems,this article has carried out the following research work,mainly including:(1)In the detection process of the through wall radar,the target echo signal is often submerged in the wall clutter,which makes it impossible to perform target positioning and imaging.To solve this problem,this paper proposes a through wall radar wall clutter suppression method based on combination entropy.In this method,the two sets of co-located antennas are placed parallel to the wall at equal intervals and emit electromagnetic waves successively;then the two sets of echo signals obtained are discretized,and their combination entropy is calculated,based on the target clutter It selects the best threshold adaptively,distinguishes the wall clutter from the target echo signal and filters out the useless clutter;finally,the filtered signal is used for BP target imaging.Simulation experiments show that compared with entropy method,background cancellation method and SVD method,the method proposed in this paper can filter out clutter interference signals more effectively,and image the target clearly without artifacts.Through calculation TCR and image Entropy analysis shows that the clutter suppression effect of the proposed method is better than other algorithms.(2)The traditional BP algorithm divided the imaging area into a grid of pixel points of the same size,calculated the time delay of sampling points in each echo signal to the pixel points,and carried out coherent superposition in the frequency domain to achieve high resolution imaging.In order to obtain high-quality or high-resolution through wall radar imaging,the traditional BP algorithm needs to finely divide the pixel grid,resulting in excessive calculation,high computer memory usage,and slow imaging speed.To address these problems,this article proposes fast BP imaging method for through wall radar based on fast Gaussian Gridding Nonuniform FFT is presented.This method eliminates the influence of Gaussian smoothing by deconvolving the pixel amplitude in the BP algorithm with the Gaussian kernel function,and performs fast Fourier transform on the processed pixel amplitude,and finally performs convolution operation on the obtained data Make the data output evenly and smoothly.In the calculation process,the exponents that need to be repeated are stored in advance to avoid repeated calculations.Simulation experiments show that compared with the traditional BP algorithm and NUFFT BP algorithm,the method proposed in this paper effectively reduces the computational complexity,memory requirements and imaging time while ensuring the imaging quality.(3)Realize the development of the through wall radar wall clutter suppression and rapid imaging test software based on Lab VIEW platform.Design and add corresponding input parameter controls in the front panel,and form the corresponding block diagram in the program panel.By using the MATLAB Script node to call the combination entropy method and the fast imaging method for clutter suppression and fast imaging,users can input different threshold adjustment factors to filter out interference signals,and finally display the imaging effect through the two-dimensional intensity map,three-dimensional scatter plot and corresponding output parameters in the front panel,thereby completing the development of the through wall radar wall clutter suppression and rapid imaging test software.