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Novel Forward-looking Three-Dimensional Imaging Based on Vortex Electromagnetic Wave Radar
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摘要: 涡旋电磁波具有独特的波前相位调制特性，其作为一种新的雷达发射端分集模式，可实现目标雷达截面积 (RCS)分集、提升信号与信息处理维度和性能，其探测与成像性能在多种雷达体制中得到了验证。该文针对前视雷达成像的应用背景，基于均匀圆阵发射与圆阵中心单天线接收的收发体制，在建立了电磁涡旋前视雷达信号模型与成像模型的基础上，提出了一种分时多模态扫描的成像方法，利用多模态涡旋电磁波在不同俯仰角的幅度差异性和在不同方位角的相位差异性，以及雷达与目标相对运动产生的多普勒效应，提出了改进的后向投影-距离多普勒算法，实现了目标三维成像。由于涡旋电磁波的能量发散特点，随着俯仰角增大，高模态方向图增益急剧下降，该文所提方法通过对多个模态在空域能量分布的有效利用，在较大视场角下具有较高的稳定性。基于点目标成像结果，验证了在多模态涡旋波覆盖的较大视场范围内，目标成像结果的归一化等效增益在低俯仰角与高俯仰角处基本相当。所提方法通过对飞机目标的实验验证，根据成像结果可较为准确地重构目标的三维结构。Abstract: Vortex Electromagnetic Waves (VEMWs) have unique wavefront phase modulation characteristics. As a new degree of freedom in the diversity of radar transmitters, the VEMW Radar (VEMWR) provides radar cross-section diversity and improves signal and information processing dimensions and performances. The detection and imaging performances of VEMWR have been verified in various radar systems. This article focuses on the applying background of forward-looking radar imaging and proposes a time-division multiple-mode scanning imaging method based on a Uniform Circular Array (UCA) system with multiple transmitters and a single receiver at the UCA center. First, we establish the forward-looking VEMWR imaging mode and corresponding signal mode. Next, an improved three-Dimensional (3D) back-projection and range-Doppler algorithm is proposed, which utilizes the magnitude difference at various elevation angles of multimode VEMW, phase difference at different azimuth angles, and Doppler effect resulting from the relative motion of the radar and target to achieve 3D imaging of the target. As the elevation angle increases, the beam pattern gain of the high-mode VEMW decreases sharply due to the energy divergence of the VEMW. The proposed method can maintain stability at low or high elevation angles using the energy distribution of multiple modes in the spatial domain. Imaging results of point targets revealed that the normalized gain of target-imaging results is equivalent either at low or high elevation angles within the multimode VEMW field of view. The proposed method is validated through experiments with an aircraft target. Based on the imaging results, it is verified that the proposed method can accurately reconstruct the 3D structure of complex targets.
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图 2 涡旋雷达前视成像坐标系
Figure 2. The coordinate system of vortex radar forward-looking imaging
图 9 归一化信号处理增益变化图(以俯仰角θ=0为参考点进行归一化)
Figure 9. Signal processing gain curves with different elevation (based on zero angle, normalized signal processing gain )
图 13 目标2不同维度的成像结果($ \theta =0.15\mathrm{\pi } $)
Figure 13. Point target2 imaging results in different dimensions ($ \theta =0.15\mathrm{\pi } $)
图 12 目标1不同维度的成像结果($ \theta =0.1\mathrm{\pi } $)
Figure 12. Point target 1 imaging results in different dimensions ($ \theta =0.1\mathrm{\pi } $)
图 16 实测数据在不同模态下的脉压结果
Figure 16. Pulse pressure results of measured data with different modes
图 18 飞机目标三维成像的二维切面图
Figure 18. Aircraft target imaging results in different dimensions
表 1 不同俯仰位置下信号处理增益变化
Table 1. Signal processing gain of different elevation
俯仰角θ
(rad)有效模态 输入信
噪比(dB)输出信
噪比(dB)归一化信号处理
增益 (dB)0.00$\pi $ [0] 12.4140 52.3270 39.9130 0.01$\pi $ [–2,2] 12.4140 52.3231 39.9091 0.02$\pi $ [–4,4] 12.4140 52.3115 39.8975 0.03$\pi $ [–6,6] 12.4140 52.2922 39.8782 0.04$\pi $ [–8,8] 12.4140 52.2653 39.8513 0.05$\pi $ [–10,10] 12.4140 52.2307 39.8167 0.06$\pi $ [–12,12] 12.4140 52.1887 39.7747 0.07$\pi $ [–14,14] 12.4140 52.1393 39.7253 0.08$\pi $ [–16,16] 12.4140 52.0826 39.6686 0.09$\pi $ [–18,18] 12.4140 52.0188 39.6048 0.10$\pi $ [–20,20] 12.4140 51.9482 39.5342 0.11$\pi $ [–23,23] 12.4133 51.8693 51.4341 0.12$\pi $ [–25,25] 12.4010 51.7580 39.3570 0.13$\pi $ [–27, 27] 12.2969 51.4341 39.1372 0.14$\pi $ [–28, 28] 11.9384 50.5159 38.5775 0.15$\pi $ [–30, 30] 11.7014 49.8458 38.1444 0.16$\pi $ [–32, 32] 12.2512 51.0137 38.7625 0.17$\pi $ [–34, 34] 12.2907 50.9907 38.7001 
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表 2 仿真参数
Table 2. Simulation parameters
参数 值 目标1的$R - \theta - \varphi $坐标(m, rad, rad) (300, 0.10$\pi $, 0.055$\pi $) 目标2的$R - \theta - \varphi $坐标(m, rad, rad) (300, 0.15$\pi $, 0.055$\pi $) 雷达UCA阵元数量N(个) 64 UCA半径${r_a}$(m) 0.09 信号载频${f_c}$(GHz) 35 信号脉冲周期${T_p}$($ \text{μ}\text{s} $) 0.54 带宽B (MHz) 300 OAM范围 [–30, 30]
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表 3 实测参数
Table 3. Experimental parameters
参数 值 飞机模型中心位置(m) 4.5 飞机模型在XYZ上的跨度(m) (1.5, 0.08, 1.15) 阵元数量N(个) 16 UCA半径${r_a}$(m) 0.0615 信号载频${f_c}$(GHz) 35.025 信号脉冲周期${T_p}$($ \text{μ}\text{s} $) 0.54 带宽B(MHz) 300 OAM范围 [-7,7]
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