Joint Design of SAR Waveform and Imaging Filter Based on the Signal-to-Clutter-Plus-Noise Ratio Criterion
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摘要: 针对合成孔径雷达(SAR)在弱目标成像时目标回波信号易被背景杂波淹没的问题,该文提出了一种基于信杂噪比准则的SAR波形与成像滤波器联合设计方法。该方法首先建立以信杂噪比为目标函数的联合优化模型,综合考虑了恒模、主瓣峰值、旁瓣电平及目标散射不确定性等约束条件,形成了具有极大极小结构的非凸多约束优化问题。为求解该复杂非凸恒模问题,该文发展了一种序贯交替迭代框架,将原问题分解为波形与滤波器两个子问题,采用上镜图变换与MM算法相结合的策略,实现分式目标函数解耦和非凸约束条件转化;通过引入辅助变量以扩展可行域,保证初始迭代时的可行性,再添加随迭代次数递增的惩罚项,最终迫使辅助变量趋于零,实现原始问题的求解,并从理论上分析了算法的收敛性和计算复杂度。实验结果表明:与同参数的线性调频信号相比,联合设计方案在仿真、半物理及外场真实试验中均表现出显著的杂波抑制能力,SAR图像的信杂比可提升3.2 dB以上,为改善SAR系统对弱目标的探测与成像性能提供了工程可行的技术途径。Abstract: To address the critical issue of weak-target imaging performance in synthetic aperture radar (SAR), this paper proposes a method for jointly designing the SAR waveform and imaging filter based on the signal-to-clutter-plus-noise ratio (SCNR) criterion. The method first establishes a joint optimization model aimed at maximizing the SCNR. This model comprehensively considers constant modulus constraints, mainlobe peak constraints, sidelobe levels, and target scattering uncertainty, resulting in a nonconvex, multiconstrained optimization problem with a max– min structure. To solve this problem, this paper develops a sequential alternating optimization framework that decomposes the original problem into two subproblems: waveform design and filter design. A strategy combining the epigraph transformation with the majorization–minimization algorithm is employed to handle the nonconvex fractional objective function and constraints. Auxiliary variables are introduced to extend the feasible region, thereby guaranteeing feasibility at the initial iteration. A penalty term that increases progressively with the number of iterations is then incorporated, ultimately forcing the auxiliary variables to approach zero and thereby enabling the solution of the original problem. The convergence and computational complexity of the proposed algorithm are also analyzed. Experimental results demonstrate that, compared with traditional linear frequency-modulated signals with identical parameters, the joint design scheme exhibits pronounced performance advantages in simulated, semi-physical, and field scenarios. The proposed method improves the SCNR of SAR images by more than 3.2 dB, providing an engineering-feasible approach for enhancing the detection and imaging performance of SAR systems for weak targets.
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1 联合优化算法
1. Joint optimization algorithm
设置参数:$ {E}_{0} $,$ \delta $,e,$ {e}^{\prime} $,$ \varepsilon $,$ {\tau }_{0} $,$ {\lambda }^{(0)} $和$ \omega $。 1:初始化$ {\boldsymbol{x}}_{(0)} $和$ {\boldsymbol{w}}_{(0)} $,设置迭代索引$ k=1 $,开启外层迭代$ {\mathcal{L}}_{1} $。 2:repeat固定$ \boldsymbol{w}={\boldsymbol{w}}^{\left(k-1\right)} $,构造$ {\mathcal{P}}_{2} $。 3: 令$ m=0 $,开启迭代循环$ {\mathcal{L}}_{2} $,$ {\lambda }^{(m)}={\lambda }^{(0)} $,
$ {\boldsymbol{x}}_{(m)}={\boldsymbol{x}}^{(k-1)} $,$ {\tau }_{(m)}={\tau }_{0} $。4: repeat引入松弛变量$ \boldsymbol{u} $,构造$ {\mathcal{P}}_{4} $,求解得到$ {\boldsymbol{x}}^{*} $。 5: 更新$ {\lambda }^{(m)} $,$ {\boldsymbol{x}}_{(m)} $,$ {\tau }_{(m)} $,$ m=m+1 $。 6: until$ ||\boldsymbol{u}|{|}_{1}\leq e $触发停止条件。 7: 更新波形$ {\boldsymbol{x}}^{\left(k\right)}={\boldsymbol{x}}^{\ast } $。 8: 固定$ \boldsymbol{x}={\boldsymbol{x}}^{\left(k\right)} $,构造$ {\mathcal{P}}_{5} $。 9: 令$ n=0 $,开启迭代$ {\mathcal{L}}_{3} $,$ {\boldsymbol{w}}_{(n)}={\boldsymbol{w}}^{(k-1)} $,
$ {\tau }_{(n)}={\tau }_{(m)} $。10: repeat构造$ {\mathcal{P}}_{6} $,求解得到$ {\boldsymbol{w}}^{\ast } $。 11: 更新$ {\boldsymbol{w}}_{(n)} $,$ {\tau }_{(n)} $,$ n=n+1 $。 12: until$ {\tau }_{(n)}-{\tau }_{(n-1)}\leq {e}^{\prime} $触发停止条件。 13: 更新滤波器$ {\boldsymbol{w}}^{\left(k\right)}={\boldsymbol{w}}^{\ast } $,$ {\tau }_{0}={\tau }_{(n)} $。 14:until $ f({\boldsymbol{x}}^{(k)},{\boldsymbol{w}}^{(k)})-f({\boldsymbol{x}}^{(k-1)},{\boldsymbol{w}}^{(k-1)})\leq \varepsilon $触发$ {\mathcal{L}}_{1} $的停
止条件。15:输出优化波形与滤波器解对$ ({\boldsymbol{x}}^{\left(k\right)},{\boldsymbol{w}}^{\left(k\right)}) $ 表 1 SAR系统参数
Table 1. List of SAR parameters
参 数 取 值 平台高度 H0 6 km 天线长度 D 2 m 有效雷达速率 v 150 m/s 视角 $ \theta $ 30° 斜视角 $ \phi $ 0° 中心频率 $ {f}_{0} $ 5.3 GHz 脉冲持续时间 T 1 μs 距离带宽 $ {B}_{\text{r}} $ 100 MHz 距离采样率 $ {F}_{\text{r}} $ 120 MHz 方位采样率 $ {F}_{\text{a}} $ 180 Hz 距离线数量 $ {N}_{\mathrm{a}} $ 256 每个距离线的采样点数 $ {N}_{\text{r}} $ 256 表 2 外场试验参数
Table 2. List of field experiment parameters
参数 数值 平台高度 1.5 m 场景中心距 20 m 载波频率 5.5 G 信号带宽 100 MHz 脉冲时宽 2 us 采样率 122882080 Hz方位向步长 0.05 m 合成孔径长度 11 m 天线物理口径 0.15 m -
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