平流层太阳能无人机双基合成孔径雷达 (Synthetic Aperture Radar，SAR) 系统依托其 独特的工作空域，可突破气候条件的限制，具有侦察视野广阔、续航时间长、生存能力 强等优势。但同时太阳能无人机双基 SAR 平台体积大、动能低、扰动强，其轨迹呈现 为复杂的低速曲线运动状态，导致成像过程中存在二维耦合及空变问题，因此，本文从 平流层曲线轨迹双基 SAR 的系统特性入手，围绕其回波信号模型、二维频谱、成像算 法等方面展开了研究，主要研究内容如下：

(1) 平流层曲线轨迹双基 SAR 相比常规条件下的双基 SAR 其空间几何成像模型与 成像特性发生了变化。导致现有的双基 SAR 成像模型存在模型失配问题。针对上述问题，本文构建了适用于曲线轨迹双基 SAR 的空间几何成像模型。对收发平台进行矢量描述，得到了目标的距离历程以及回波信号模型。并推导了曲线轨迹下双基 SAR 空间分辨率的计算公式，同时对三维加速度带来的回波信号的耦合特性和空变特性进行了分析，为后续的成像算法设计提供了理论基础。

(2) 曲线轨迹双基 SAR 系统的聚焦成像处理在极为复杂的条件下进行，传统 SAR成像方法已难以满足要求。考虑到曲线轨迹带来的二维耦合空变性，本文提出了两种不同的成像算法，首先在分析了广义 Keystone 变换方法的基础上，提出了一种基于频域Keystone 变换的双基 SAR 成像算法，该算法通过对频谱系数的二维泰勒级数展开，获得两维 Keystone 变换的插值映射关系，从而消除耦合性及空变性问题。

(3) 同时，针对任意构型双基 SAR 配置，提出了另一种成像处理方法——改进的方位扩展 NLCS 成像算法，该算法首先在距离向进行线性距离徙动矫正，接着在方位向通过多相滤波与方位变标相结合的方式有效的去除了方位向的空变性，并通过最终的仿真结果验证了所提方法的有效性。

The stratospheric solar UAV bistatic Synthetic Aperture Radar (SAR) system, relying on its unique working airspace, can break through the restrictions of climatic conditions, and has the advantages of broad reconnaissance field of view, long endurance and strong survivability. However, at the same time, the bistatic SAR platform of solar UAV has large volume, low kinetic energy and strong disturbance, and its trajectory presents a complex low-speed curve motion state, resulting in two-dimensional coupling and space-time problems in the imaging process. Therefore, this paper starts with the system characteristics of the stratospheric curve-track bistatic SAR, focusing on its echo signal model, two-dimensional spectrum, imaging algorithm and other aspects. The main research contents are as follows:

(1) The spatial geometric imaging model and imaging characteristics of stratospheric curlily-trajectory bistatic SAR have changed compared with the conventional bistatic SAR. This results in the problem of model mismatch in existing bistatic SAR imaging models. The existing bistatic SAR imaging models have the problem of model mismatch. To solve these problems, this paper constructs a spatial geometric imaging model suitable for curvilinear trajectory bistatic SAR. The range history and echo signal model of the target are obtained by vector description of the transceiver platform. The calculation formula of the spatial resolution of bistatic SAR under curved trajectory is derived, and the coupling and space-time characteristics of the echo signal caused by three-dimensional acceleration are analyzed, which provides a theoretical basis for the subsequent imaging algorithm design.

(2) The focus imaging processing of curve-trajectory bistatic SAR system is carried out under extremely complex conditions, and the traditional SAR imaging methods are difficult to meet the requirements. Considering the two-dimensional coupled space-time brought about by the curve trajectory, two different imaging algorithms are proposed in this paper. First, based on the analysis of the generalized Keystone transform method, a dual-base SAR imaging algorithm based on the frequency domain Keystone transform is proposed. The interpolation mapping of the two-dimensional Keystone transformation is obtained, and the coupling and cavitation problems are eliminated.

(3) Simultaneously, for arbitrary configuration bistatic SAR systems, another imaging processing method is proposed-an improved azimuthal extended NLCS imaging algorithm. This algorithm first performs linear range migration correction in the range direction, then effectively removes azimuthal space-variant properties through a combination of multi-phase filtering and azimuth variable transformation in the azimuth direction. The effectiveness of the proposed methods is verified through final simulation results.

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