基于散射模型的空间目标ISAR成像

发布时间：2018-07-02 13:42

本文选题：几何光学物理光学法 + 电磁散射　；参考：《西安电子科技大学》2014年硕士论文

【摘要】：通过电磁仿真模拟雷达回波,研究空间目标的逆合成孔径雷达(ISAR)成像,能获得其运动态势和基本结构特征,同时也能为目标分类、识别等提供理论模型和技术支撑。尽管ISAR成像技术已发展到较高水平,但由于空间目标的特殊性,仍有不少问题有待解决。论文基于目标电磁散射的基本原理和模型,开展运动空间目标ISAR成像仿真的研究工作,主要内容包括:1、针对空间目标(卫星)的天线结构特点,利用几何光学-物理光学法(Geometrical optics and Physical optics,GOPO)混合高频近似算法计算空间目标的电磁散射特性。首先通过简单目标(二面角反射器和简单组合体)验证GOPO的可行性和有效性。着重利用该算法分别计算了飞机模型和卫星模型在不同方位角和入射角下的垂直极化和水平极化的雷达散射截面(Radar Cross Section,RCS)。由于卫星结构的对称性和在计算散射场时采用PO算法,垂直极化(VV极化)散射结果与水平极化(HH极化)差别不大。对比计算了完整卫星模型和去掉天线结构的卫星模型在不同方位角和入射角下的RCS,可以发现:由于卫星天线具有明显的角形结构,使得多次散射效应加强,因此在一定角度范围内,天线的多次散射占主导因素。2、综述逆合成孔径雷达(Inverse Synthetic Aperture Radar,ISAR)成像的基本原理,分析了ISAR成像中散射场与成像函数的关系。模拟了飞机和卫星模型的一维距离像和一维方位像,并给出了完整卫星模型和无天线结构模型的二维ISAR像,讨论不同带宽和采样点数对飞机成像结果的影响。基于距离-多普勒(Range-Doppler)成像算法,分析了目标方位向的多普勒频移效应,利用频率步进信号(SFCW)分别模拟了飞机点散射模型和实际卫星模型的雷达回波,在距离-多普勒域进行ISAR成像仿真。由卫星成像结果可以明显看出有无天线的影响,加强论证了角反射器对目标电磁散射特性的影响。3、研究了ISAR成像中运动补偿算法。讨论了ISAR成像过程由于目标运动出现的多普勒效应,由于目标的运动可能会引起方位像模糊和距离徙动的现象,因此需要在ISAR成像过程中进行平动补偿和旋转运动补偿。对标准的平动补偿和转动补偿过程做了简要的分析,并据此提出了最小熵法和联合时频分析的运动补偿方法,从结果可以看出,前者主要补偿目标的平动分量,后者则可以补偿目标的平动和转动分量,有效提高了成像质量。并以卫星模型为算例,基于GOPO算法模拟的雷达电磁回波,仿真了不同参数(带宽、运动速度等)情况下的ISAR成像。结果表明:当增加雷达带宽时,图像中目标散射强点在距离向的分布更加清晰;当增大目标转动速度时,图像中目标散射强点在方位向的分布更加清晰,同时卫星翼板部分有一定增强。
[Abstract]:The inverse synthetic Aperture Radar (ISAR) imaging of space targets can be studied by electromagnetic simulation to simulate the radar echo, which can obtain the motion situation and basic structural characteristics, and also provide theoretical model and technical support for target classification and recognition. Although ISAR imaging technology has been developed to a higher level, there are still many problems to be solved because of the particularity of space targets. Based on the basic principle and model of target electromagnetic scattering, the research work of ISAR imaging simulation of moving space target is carried out in this paper. The main contents include: 1, aiming at the antenna structure characteristics of space target (satellite). The hybrid high-frequency approximation algorithm of geometric optics and physical optics (GOPO) is used to calculate the electromagnetic scattering characteristics of space targets. Firstly, the feasibility and effectiveness of GOPO are verified by simple target (dihedral reflector and simple combination). The radar cross section (RCS) of vertical and horizontal polarization of aircraft model and satellite model at different azimuth and incident angles are calculated respectively by using this algorithm. Due to the symmetry of satellite structure and the use of PO algorithm in the calculation of scattering field, the vertical polarization (VV polarization) scattering results are not different from horizontal polarization (HH polarization). The RCSs of the complete satellite model and the satellite model without antenna structure at different azimuth and incident angles are compared and calculated. It is found that the multiple scattering effect is enhanced because of the obvious angular structure of the satellite antenna. Therefore, in a certain range of angles, multiple scattering of antenna is the dominant factor. This paper summarizes the basic principle of inverse synthetic Aperture radar (ISAR) imaging, and analyzes the relationship between scattering field and imaging function in ISAR imaging. The one-dimensional range profile and one-dimensional azimuth image of the aircraft and satellite model are simulated, and the complete satellite model and the two-dimensional ISAR image without antenna structure are given. The effects of different bandwidth and sampling points on the imaging results of the aircraft are discussed. Based on Range-Doppler imaging algorithm, Doppler frequency shift effect of target azimuth direction is analyzed. Radar echo of aircraft point scattering model and actual satellite model is simulated by frequency step signal (SFCW). ISAR imaging simulation is carried out in range-Doppler domain. The influence of antenna can be clearly seen from the results of satellite imaging. The influence of angle reflector on the electromagnetic scattering characteristics of target is demonstrated. The motion compensation algorithm in ISAR imaging is studied. This paper discusses the Doppler effect in ISAR imaging process due to the target motion, because the target motion may cause azimuth image blur and range migration, so it is necessary to compensate for translation and rotation motion in ISAR imaging process. Based on the analysis of the standard translation compensation and rotational compensation process, the minimum entropy method and the motion compensation method of joint time-frequency analysis are proposed. From the results, it can be seen that the translational component of the former is the main compensation target. The latter can compensate the translational and rotational components of the target and improve the imaging quality effectively. Taking the satellite model as an example, the ISAR imaging with different parameters (bandwidth, velocity, etc.) is simulated based on the radar electromagnetic echo simulated by the GOPO algorithm. The results show that when the radar bandwidth is increased, the distribution of the target scattering intensity in the range direction is more clear, and when the target rotation velocity is increased, the distribution of the target scattering strength in the azimuth direction becomes clearer. At the same time, the satellite flange part has certain enhancement.
【学位授予单位】：西安电子科技大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TN957.52

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