分布式星载雷达回波特性分析与仿真

【作者】 申成学；

【导师】 陈祝明；

【作者基本信息】 电子科技大学 ， 信号与信息处理， 2010， 硕士

【摘要】 分布式星载雷达是由一簇编队飞行的小卫星构成的稀疏阵列雷达,簇内各小卫星雷达协同工作,形成一个更大、更复杂的虚拟卫星雷达。不仅具有单星雷达的覆盖范围广、全天候、全天时等优点,更因其具有多个天线孔径和更长的基线,能够探测地面上低速运动目标。但分布式星载雷达轨道高度较高,小卫星速度较大,以及稀疏孔径所引入的栅瓣,使得对地面低速动目标的检测困难重重。为了实现地杂波的抑制和低速动目标的检测,本论文围绕着分布式星载雷达存在的主要问题及地杂波空时特性进行了研究,主要内容如下。在分布式星载雷达的观测几何方面,确定了观测中所涉及的三个坐标系,以及它们之间相互变换的关系式,研究了观测区域中地杂波散射单元的划分,最终确立了分布式星载雷达的地杂波的观测几何模型,并通过仿真分析验证所建模型的正确性。该模型为研究分布式星载雷达地杂波空时特性以及低速动目标的检测提供了基础。在介绍一般雷达地杂波生成机理的基础上,研究了分布式星载雷达地杂波存在的主要问题,相对于卫星平台,地球本身一直在自转,而地球的自转会在回波的多普勒频率中引入偏航角和偏航幅度。由于分布式星载雷达观测区域比较大,以及卫星轨道高度较高,地杂波存在距离模糊。而较大卫星平台速度,使得多普勒域也存在模糊。簇内小卫星之间间距远大于半波长,空间的欠采样使接收天线方向图中存在栅瓣。最后,在分析分布式星载雷达地杂波协方差阵、功率谱、杂波迹的基础上,研究了在分布式星载雷达中地杂波的空时二维特性。理论和仿真结果表明:地球的自转会产生仅与轨道倾角和星下点纬度相关的偏航角和偏航幅度,同时地球自转使得角度-多普勒迹发生弯曲。距离模糊时不同距离环上的散射单元相互叠加,使地杂波距离-多普勒谱展宽。多普勒模糊使地杂波的角度-多普勒分散开来。栅瓣的存在使分布式星载雷达地杂波中产生受天线方向图调制的主杂波分布。更多还原

【Abstract】 Distributed Spacborne Radar is a sparse array radar formed by a cluster of microsatellites flying in formation, Those microsatellites through collaborative work form a larger and more complex dummy satellite radar. With the advantage of single satellite radar, such as covering large scope, working all-weather and all-time and so on, Distributed Spacborne Radar can detect low speed ground target, because of its multi-aperture and longer base-line. Unfortunately, using Distributed Spacborne Radar to detect moving target faces many difficulties made by the higher orbit altitude, larger microsatellite speed, and gratinglobes coming with sparse antenna aperture.To suppress ground clutter and detect low speed moving target, the main issue of ground clutter and the ground clutter space-time characteristics in Distributed Spacborne Radar is studied in this dissertation, the main contents are as follows.In terms of the observation geometry of Distributed Spacborne Radar, five coordinate systems involving in the observation geometry are established first, and their mutual transformational relation are analyzed. Then the partition of range bins in observation region is studied, and establish the observation geometry model of Distributed Spacborne Radar finally, the established model is examined correct through simulations and analysis. The model is a foundation of studying the space-time characteristics of ground clutter and detecting of low speed moving target in Distributed Spacborne Radar.After the introduction of originates of common radar ground clutter, the main issues of the ground clutter in Distributed Spacborne Radar are studied. The earth is rotating all the time according to microsatellites, crab angle and crab magnitude come with the earth’s rotation in the Doppler frequency of the return signals. Because of the larger observation region of the Distributed Spacborne Radar and the higher altitude of the microsatellite orbit, range ambiguities occur in the ground clutter. Also, the larger speed of microsatellite platform result in Doppler ambiguities in Distributed Spacborne Radar. The length between microsatellites is much bigger than half of wavelength, the low sample frequency in space results in gratinglobes in receiving antenna. Finally, on the foundation of the analysis of the clutter covariance matrix, power spectrum, clutter ridges of Distributed Spacborne Radar, the space-time characteristics of the ground clutter in Distributed Spacborne Radar are studied in detail. Theoretical analysis and simulation results show that: the clutter rank becomes bigger along with the crab angle brought by the earth’s rotation, and the angle-doppler trace is changed a curve from a straight by earth’s rotation. When range ambiguities happen, return signals from different range bins add together, and the width of ground clutter spectrum is made larger by range ambiguities. The clutter rank is made lager by the doppler ambiguities, also doppler ambiguities cause the clutter spectrum dispersed. Gratinglobes bring gratinglobes clutter modulated by the receive antenna.更多还原