超宽带稀疏阵列穿墙成像雷达栅瓣抑制方法研究

发布时间：2019-01-07 19:28

【摘要】：发射低频段的对墙壁等非金属障碍物有很好穿透能力的电磁波,超宽带穿墙成像雷达有着广阔的发展前景,在反恐、救援、安检等军事与民用领域具有重要的应用价值。基于多输入多输出(Multiple-Input Multiple Output,MIMO)阵列的超宽带雷达系统能够提供高分辨率的雷达图像,有利于后续的检测、跟踪等工作,并且具有高实时性、低成本等优点。考虑穿墙雷达系统的便携性,并为了节约成本,MIMO阵列通常采用稀疏阵,天线数量不多,间距大于波长。因此栅瓣将不可避免地出现,引起虚假像,降低成像质量。因此本文主要研究稀疏阵列所引起的栅瓣抑制问题。研究了单程阵列的方向图,从波形上分析了栅瓣的成因,指出均匀且等幅加权单程阵列的方位向分辨率较高且栅瓣水平较低。由于雷达用双程阵列成像,接着研究了双程阵列,引出等效阵列的概念,它是将双程阵列转化为单程阵列的重要工具。不同的双程阵列具有不同的单程等效阵列,栅瓣水平也不同。因此通过阵列配置,设计阵元的权重及位置,可以降低栅瓣水平,抑制栅瓣。而在成像角度,介绍了步进频信号的BP成像算法,指出各通道所成的像在主瓣与栅瓣处有不同的特点,为成像中的栅瓣抑制奠定基础。研究了三种阵列的配置方法,达到了较低的栅瓣水平。首先研究了收发分置MIMO阵列的配置问题,可以根据需要的栅瓣水平及分辨率设计阵列。然后研究了收发共置MIMO阵列,对天线数为4和大于4的情况分别提出一种性能优越的配置方法,并对后面一种方法做了改进,提高了阵列的效率。最后研究了二维阵列,分别提出了单程和双程阵列配置方法,比已有方法的栅瓣更低。接着在成像域研究抑制栅瓣的方法。介绍了相干因子(Coherence Factor,CF)与相位相干因子(Phase Coherence Factor,PCF),说明它们能够抑制方位向栅瓣而非距离向旁瓣。因而提出CF与PCF结合双切趾(Dual Apodization,DA)的方法,可以同时抑制方位向栅瓣与距离向旁瓣。为进一步抑制栅瓣,提出利用步进频信号子频段的CF与PCF的改进方法,比CF与PCF抑制栅瓣的能力更强,且能抑制距离向旁瓣。最后研究利用子孔径的栅瓣抑制方法,介绍了孔径差分方法和互相关方法,分析了这两种方法抑制栅瓣的优缺点,并提出了互相关加权孔径差分的方法,能够大幅抑制栅瓣。这些方法已成功应用于穿墙雷达成像,切实能够抑制栅瓣,提高成像质量。
[Abstract]:The electromagnetic wave which can penetrate the wall and other non-metallic obstacles in low frequency band has a broad prospect of development. It has important application value in the military and civilian fields such as anti-terrorism rescue and security inspection. The UWB radar system based on multiple input multiple output (Multiple-Input Multiple Output,MIMO) arrays can provide high resolution radar images, which is conducive to subsequent detection, tracking and other work, and has the advantages of high real-time, low cost and so on. Considering the portability of wall-penetrating radar systems and in order to save the cost MIMO arrays usually use sparse arrays with a small number of antennas and spacing larger than wavelength. Therefore, the gate lobe will inevitably appear, causing false images and reducing the imaging quality. Therefore, the problem of gate lobe suppression caused by sparse array is studied in this paper. The pattern of single pass array is studied and the origin of gate lobe is analyzed from the waveform. It is pointed out that the uniform and equal amplitude weighted single pass array has higher azimuth resolution and lower level of gate lobe. Because of the imaging of dual-pass array in radar, the concept of equivalent array is introduced, which is an important tool to transform two-pass array into single-pass array. Different dual-pass arrays have different single-pass equivalent arrays and different levels of gate lobes. Therefore, the weight and position of array elements are designed by array configuration, which can reduce the level of grid lobe and restrain gate lobe. From the point of view of imaging, the BP imaging algorithm of stepping frequency signal is introduced, and it is pointed out that the image generated by each channel has different characteristics at the main lobe and the gate lobe, which lays a foundation for the suppression of the gate lobe in the imaging process. Three kinds of array configuration methods are studied, and the lower gate lobe level is achieved. Firstly, the configuration of transceiver split MIMO array is studied. The array can be designed according to the level and resolution of grid lobe. Then we study the transceiver co-set MIMO array, and propose a superior performance configuration method for the antenna number of 4 and greater than 4, and improve the latter method to improve the efficiency of the array. Finally, the two-dimensional array is studied, and the single-pass and two-way array configurations are proposed, which are lower than the existing gate lobes. Then the method of suppressing the grating lobe is studied in the imaging domain. Coherence factor (Coherence Factor,CF) and phase coherence factor (Phase Coherence Factor,PCF) are introduced. It is shown that they can suppress azimuth gate lobe rather than range sidelobe. Therefore, a double toe cutting (Dual Apodization,DA) method combined with CF and PCF is proposed, which can suppress both azimuth gate lobe and distance sidelobe. In order to further suppress the gate lobe, an improved method using step frequency signal subband CF and PCF is proposed, which is more powerful than CF and PCF in suppressing the gate lobe and can suppress the distance sidelobe. Finally, using the subaperture gate lobe suppression method, the aperture difference method and the cross-correlation method are introduced. The advantages and disadvantages of these two methods are analyzed, and the cross-correlation weighted aperture difference method is proposed, which can suppress the gate lobe greatly. These methods have been successfully applied to wall penetrating radar imaging, which can effectively suppress the grating lobe and improve the imaging quality.
【学位授予单位】：国防科学技术大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TN957.52

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