基于精确电磁建模的散射中心成像

【作者】 刘伟；

【导师】 胡俊；

【作者基本信息】 电子科技大学 ， 电磁场与微波技术， 2008， 硕士

【摘要】 成像雷达的出现扩展了原始的雷达概念,使它具有对运动目标(飞机、导弹等)、区域目标(山区、城市等)进行成像和识别的能力,并在微波遥感应用方面表现越来越大的潜力,为人们提供越来越多的有用信息。它对国防现代化、国民经济建设都具有深远的影响和重要的意义。因此,雷达成像技术受到国际上越来越多的关注和重视,是竞争激烈、发展迅速的技术领域。逆合成孔径雷达(ISAR)成像的研究近年来得到国内外的广泛研究,人们为此提出了多种运动补偿方法和成像算法。为了克服雷达在发射和接收等信号处理方而所而临的困难,现代雷达一般工作在高频区,而在高频区雷达目标的散射可以用多散射中心模型来近似。因此逆合成孔径雷达成像的研究都是基于散射中心模型的,本文从电磁学的角度解释了等效散射中心模型的有效性。另外,方法的有效性需要通过实测数据的检验。但是,实测数据的获得是非常困难和需要花费大量的时间,人力和物力的。得益于计算电磁学的发展,可以采用数值模拟的方法得到成像所需的数据。在本文中,分析和讨论了各种回波计算方法的优缺点,时域方法可以很好的计算宽带电磁散射,但不能计算电大尺寸目标。几何光学(GO)和物理光学(PO)方法计算速度比较快,但精确度不够高。而快速多极子方法不但可以计算电大尺寸而且精度高,计算快。因此本文的成像数据采用快速多极子方法计算。由于逆合成孔径雷达的目标一般是非合作目标,所以在成像之前必须进行运动补偿,本文在简单介绍了目前国内外的一些运动补偿方法,以及阐述了转台目标的距离多普勒成像原理后,实现了滤波逆投影成像算法和FFT成像算法,逆投影方法可以不受成像角度的限制,但计算量比较大,FFT计算方法速度快,但需要对回波数据进行插值,和成像角度不能太大。然后,本文在FFT成像算法的基础上提出了NUFFT成像算法,减少了FFT成像算法实现过程中的插值处理。另外,本文还提出了一种单频的微波成像的方法以及讨论了加窗对成像的影响,上述的方法在本文中都通过数值算例得到了验证。更多还原

【Abstract】 The emergence of imaging Radar expanded the original concept of radar, it has the ability to image and identify the moving object (aircrafts, missiles, etc.), regional targets (mountains, cities, etc.), shows greater potential in microwave remote sensing applications in, provides people with more and more useful information. It also has a far-reaching impact and significance in national defense modernization and the development of national economy. Therefore, the radar imaging technology is being more and more international attention and concern, intense competition, rapid technological development areas.In recent years, the research of inverse synthetic aperture radar (ISAR) imaging is widespread concerned both at home and abroad, people had put forward a variety of motion compensation method and imaging algorithm. In order to overcome the difficulty of processing in radar signal transmit and receive, modern radars often works in high frequency. In high frequency, radar target scattering can be modeled by multiple scattering centers approximation. Therefore, the study of inverse synthetic aperture radar imaging is based on the model of multiple scattering centers. In this paper, the effectiveness of the scattering center model is explained from the perspective of electromagnetism.In addition, the effectiveness of the method required being tested by the measured data. However, the obtaining of the measured data is very difficult and takes a lot of time, manpower and material resources. Benefit from the development of computational electromagnetism, the numerical simulation can be used to obtain the imaging data. In this paper, it disscusses the main methods to compute the scatter data, it elaborates the method to obtain the time-domain back-wave by the frequency domain computational method.Because the general object of the inverse synthetic aperture radar is non-cooperated, motion compensation must be carried out before imaging. In this paper, it briefly introduces some of the current methods of movement compensation in and abroad, expounds the Distance-Doppler imaging principle of the rotating object, realizes the FFT and inverse projection imaging algorithm, inverse projection imaging algorithm is none angle-limited, but is computal costly, FFT is fast but the imaging data need be interpolated before imaging, then in this paper puts forward the NUFFT imaging algorithm based on FFT algorithm. It has reduced the interpolation process in FFT algorithm. In addition, in the paper, it also describes a single-frequency microwave imaging method, as well as has a discussion about the window function ant its impact in imaging. The methods have been verified by numerical examples in this paper.更多还原