The Study Of Ultra-wide-band Through-the-wall Radar Imaging Under Complex Background

Through-the-wall detection based on ultra-wide-band is an emerging non-invasive detection technique. Electromagnetic wave is utilized for penetration of nonmetallic obstacles, as well as detection and imaging of targets. For the excellent penetration capability and high down-range resolution, through-the-wall detection based on ultra-wide-band is of great demand for military and civil applications. In the applications of UWB through-the-wall radar, the desired signals are generally overwhelmed by strong wall clutter, and it has serious impacts on the target detection and imaging. In addition, imaging with original echo signals received via the tilted antenna array may affect the accuracy of target location. To resolve the problem above-mentioned, the main content of this paper is summarized as follow.(1) The existing wall clutter mitigation algorithm based on data entropy is studied. However, the problems may come that the range of threshold is restricted in a finite interval, and the concentrated antenna positions for scanning are needed.Based on the existing algorithm, theory of entropy of expanded antenna source is employed, and an improved wall clutter mitigation algorithm is proposed in this paper. Compare with the existing one, it is obvious that the proposed algorithm can provide imaging with higher quality for the same measurement. And it requires fewer scans with the same quality of imaging as well. Thus, the complexity of TWRI can be reduced.(2) False detection and imaging distortion due to tilted scanning track or tilted antenna array are discussed. In the existing algorithms of TWRI, it is assumed that the scanning track or array of antennas is close and parallel to the wall, which is denoted as standard model. However, this standard model cannot be guaranteed in real applications. Results of simulation show that the unknown tilt angle between the antenna and the wall would result in invalidation of existing algorithms. It may induce an inevitable imaging distortion and even lead to a false detection, and the accuracy of target location cannot be ensured as well. To deal with the problem, a datum correction algorithm based on the backward propagation of EM wave in reverse time is proposed in this paper. Simulation results show that the proposed algorithm is effective and it can effectively eliminate the negative influence caused by the unknown tilt angle.