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用多个分布式小卫星构成星座.可以完成多项雷达探测任务,如地面动目标检测(GMTI)、地面高程测量等。其探测性能可比单个卫星明显提高。分布式小卫星也可用来提高SAR的横向分辨率,主要是解决高横向分辨率与宽测绘带的矛盾。小卫星用横向孔径小的天线(为提高横向分辨率)和较低的重复频率(为加宽测绘带),其回波信号会产生多普勒模糊,但多个小卫星的空间自由度可用来解模糊,从而可以实现宽域(宽观测条带)和高方位分辨率SAR成像。本文对分布式卫星解多普勒模糊的方法进行了讨论,并提出了对卫星星座构形的要求。如果星座构形已定,则应微调脉冲重复频率以满足解多普勒模糊的要求。 相似文献
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针对寄生式星载SAR系统抗干扰时编队构形的限制,研究了优化阵列在超稀疏构形抗干扰中的应用。使用优化阵列确定编队小卫星的相对位置,可以提高方向分辨率,减小达到相同波束形成性能所需要的孔径长度,减小所需小卫星数目,降低硬件开销。仿真证明,优化阵列可以使寄生式星载SAR系统获得良好抗干扰性能。 相似文献
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采用地球同步轨道(GEO)卫星作为双基合成孔径雷达(SAR)的发射站,可为低轨(LEO)接收站提供大范围、持续的波束覆盖。同时,由于收发分置的系统形态,LEO接收站可以实现下视、前视、后视等多视区成像,因此,GEO-LEO双基SAR在地球测绘、侦察监视等领域具有广阔的应用前景。为实现大幅宽成像,GEO SAR发射站的脉冲重复频率较低,而LEO SAR接收站会引入大的多普勒带宽,造成GEO-LEO双基SAR方位欠采样。通过在接收站引入多通道技术虽可抑制模糊,但是面临GEO-LEO双基SAR的严重欠采样问题,多通道无模糊重建方法所需通道数过多,不利于接收系统小型化。针对方位严重欠采样条件下的复杂观测场景无模糊成像问题,该文提出了序贯多帧-多接收通道联合重建无模糊成像方法,通过利用序贯观测场景多帧图像的相关性和多接收通道的采样信息进行联合重建,实现无模糊成像。首先将GEO-LEO双基SAR无模糊成像问题建模为张量联合低秩与稀疏优化问题,然后在交替方向乘子法迭代求解中利用多接收通道信息,实现了GEO-LEO双基SAR对复杂观测场景的无模糊成像。相比于基于传统多通道重构的成像方法,该方法可显著减少无模糊成像所需的接收通道数,仿真实验验证了该方法的有效性。 相似文献
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天基GMTI(Ground Moving Target Indication)稀疏阵雷达的模糊性问题受到广泛关注。针对角度模糊、多普勒模糊导致的动目标检测盲区问题,本文将最小冗余思想应用于雷达阵列设计,在子阵列数目受限的情况下,给出两种最小冗余阵列配置,能够解决无模糊测速范围和速度分辨率之间的矛盾,改善稀疏导致的角度模糊问题。在存在多普勒模糊的情况下,结合多载频技术,建立了多载频最小冗余阵雷达系统模型。通过仿真证明空 时 频三维自适应处理比单频STAP(Space-Time Adaptive Processing)性能明显提高,能够有效消除多普勒模糊和提高动目标检测性能。 相似文献
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为减轻主从模式编队卫星SAR对稀疏目标场景回波信号的采集与传输负担,提出了编队卫星SAR的回波信号稀疏方法。在研究编队卫星SAR回波信号特征的基础上,构建了编队卫星SAR距离向和方位向的稀疏基、测量矩阵和重构矩阵。针对主从模式编队卫星SAR与地面的数据传输特点,提出了低传输负荷下的主从模式编队卫星SAR压缩感知成像方法,并借助于正交匹配追踪算法 (Orthogonal Matching Pursuit,OMP) 对稀疏后的回波信号进行了恢复重构,获得了高质量的编队卫星SAR图像。仿真结果表明,针对稀疏目标场景,本文提出的压缩感知成像方法利用较少的回波数据便能重构出原始目标场景,实现了低负荷下的编队卫星SAR成像。 相似文献
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Conventional Synthetic Aperture Radar (SAR) systems cannot obtain high-resolution and wide-swath illumination area due to the well-known minimum antenna area constraint. Single Phase Center MultiBeam (SPCMB) technique can overcome this limitation by adding spatial sampling through multiple receivers in azimuth direction. Unfortunately, this approach will lead to an increase of azimuth ambiguities (interbeam ambiguities), because each receive beam's mainlobe overlaps with the other ones' sidelobes. This paper proves that the front part of SPCMB SAR systems can be considered to be a hybrid filterbank. Therefore, the azimuth signal can be reconstructed and the interbeam ambiguities can be effectively suppressed by a well-designed hybrid filterbank. 相似文献
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We consider the problem of estimating the parameters of multiple wideband polynomial-phase signal (PPS) sources in sensor arrays. A new maximum likelihood (ML) direction-of-arrival (DOA) estimator is introduced, and the exact Cramer-Rao bound (CRB) is derived for the general case of multiple constant-amplitude polynomial-phase sources. Since the proposed exact ML estimator is computationally intensive, an approximate solution is proposed, originating from the analysis of the log-likelihood (LL) function in the single chirp signal case. As a result, a new form of spatio-temporal matched filter (referred to as the chirp beamformer) is derived, which is applicable to "well-separated" sources that have distinct time-frequency or/and spatial signatures. This beamforming approach requires solving a three-dimensional (3-D) optimization problem and, therefore, enjoys essentially simpler implementation than that entailed by the exact ML. Simulation results are presented, illustrating the performance of the estimators and validating our theoretical CRB analysis 相似文献
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提出组合多决策准则的稀疏表示分类(Sparse Representation-based Classification,SRC)并在合成孔径雷达(Synthetic Aperture Radar,SAR)目标识别中进行应用。传统SRC通常在全局字典上对测试样本进行重构,分别计算不同训练类别对于测试样本的重构误差,最终根据最小重构误差的原则进行分类决策。然而,由于SAR目标识别问题的复杂性,单一决策准则往往对扩展操作条件的适应性不强,导致整体性能下降。为此,文中基于稀疏表示求解的系数矢量,分别采用最小重构误差原则、最大系数能量原则以及局部最小重构误差原则分别进行分类。最小重构误差准则直接采用传统算法。最大系数能量准则分别计算不同训练类别系数能量,按照能量最大的原则进行判决。局部最小重构误差原则在局部字典上对测试样本进行表征和分析,充分体现SAR图像的视角敏感性。对于三个准则获取的决策变量,通过适当转换统一采用概率分布形式进行表达。最终,基于线性加权融合对三个准则的结果进行分析,判决测试样本所属目标类别。基于MSTAR数据集对方法进行测试,分别验证了提出方法在标准操作条件、俯仰角差异、噪声干扰及目标遮挡等情形的性能。实验结果表明:所提方法通过结合多决策准则能够有效提升SAR目标识别性能。 相似文献
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A fast algorithm for computing the coarray of sparse linear arrays is presented. Deriving linear minimum redundancy arrays or linear minimum hole arrays involves huge searches over candidate arrays to determine which arrays have the desired coarray characteristics. Since the number of candidate arrays grows very large with increasing numbers of sensors, it is important to be able to check each array's coarray quickly so that the search does not take too long. The method presented for computing coarrays is considerably faster than existing methods. This algorithm is well suited to implementation on a digital computer-it exploits the fact that integer multiplication is equivalent to convolution of the integer's representations 相似文献
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Ravandran Muttiah 《International Journal of Satellite Communications and Networking》2023,41(5):441-459
Satellite constellation design plays an important role in satellite networks. Network constellation system design can affect the effectiveness of current improvements of the communications link and the management of the entire network. The power requirement of the mobile stations and ground stations is very high in a geostationary Earth orbit communication system, which means the terrestrial terminal is hard to be made handheld for fifth generation mobile communications. The emergence of nongeostationary orbit satellites such as low Earth orbit satellites greatly compensates for the disadvantage of geostationary Earth orbit satellites. Based on the classical constellation design method, the orthogonal circular orbit constellation is proposed. The design objectives considered here are the following: global Earth coverage by low Earth orbit satellites, the duration of continuously covering one mobile station by one satellite is more than 9.57 min, the access satellite link duration time of the mobile station is more than 4.79 min, and the number of satellites and orbits is to be minimum. 相似文献
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