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Forward-looking Imaging via Doppler Estimates of Sum-difference Measurements in Scanning Monopulse Radar（in English）
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摘要: 单脉冲测角技术用于扫描雷达前视成像可有效提高图像的清晰度，但单个脉冲对同分辨单元多目标测角时会发生角闪烁现象，造成图像模糊。该文提出了一种基于单脉冲雷达和差通道多普勒估计的前视成像算法，利用目标和平台之间相对运动引起的多普勒梯度差异实现同分辨单元内不同方向目标的分离，然后在多普勒域采用和差比幅测角(SDAC)技术测量目标的方位角，完成能量投影。为提高测角精度，进一步提出了采用调频Z变换(CZT)重建和差多普勒估计并进行比幅测角的算法。点目标仿真实验结果表明，所提出的算法在前斜视方向具有分离多目标的能力，对实测数据成像结果验证了基于CZT的成像算法相比传统算法能显著提高对场景成像的轮廓清晰度。Abstract: Monopulse technique is used in scanning radar systems to improve image quality in the forward-looking area. However, monopulse measurements fail to resolve multiple targets in the same resolution cell because of angular glint which often results to image blurring. In response to this, we propose a monopulse forward-looking imaging method utilizing Doppler estimates of sum-difference measurements. First, target multiplicity is resolved by exploiting the different Doppler shifts caused by the relative motion between the platform and the targets at different directions. High azimuthal angle measurement accuracy of the Doppler estimates is then obtained using the Sum-Difference Amplitude-Comparison (SDAC) monopulse technique. Subsequently, the intensity of the sum channel estimates is projected onto the image plane according to the range and angle measurements. To further improve the precision of angle measurements, a Chirp-Z Transform (CZT)-based algorithm is proposed for the reconstruction of the Doppler estimates of the sum-difference channels. Simulation results demonstrate the capability of the proposed methods in resolving multiple targets at high squint angles in a large scanning field. Real data experiments show significant improvement of image profiles using the CZT-based algorithm compared to that of the conventional monopulse imaging method.
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图 1 雷达扫描前视成像几何关系示意图
Figure 1. Geometry for forward-looking imaging of a scanning radar
图 2 基于多普勒估计的单脉冲前视成像流程
Figure 2. Flowchart of mono pulse forward-looking imagination based on Doppler estimates
图 3 基于重建多普勒估计的单脉冲前视成像流程
Figure 3. Flowchart of monopulse forward-looking imaging based on the reconstructed Doppler estimates
图 4 点阵目标单脉冲前视成像效果对比(SNR=20 dB)
Figure 4. Comparison of forward-looking imaging performance (SNR=20 dB)
图 5 距离1730 m处目标的方位向剖面图(SNR=20 dB)
Figure 5. Azimuthal contour plots for point targets at the range cell 1730 m (SNR=20 dB)
图 6 仿真场景前视成像效果对比
Figure 6. Comparison of experimental results in forward looking imaging
图 3 Flowchart of monopulse forward-looking imaging based on the reconstructed Doppler estimates
表 1 波束扫描前视成像实验仿真参数
Table 1. Simulation parameters of a forward-looking scanning radar
参数 取值 参数 取值 场景中心地距 1700 m 平台飞行速度 100 m/s 雷达中心频率 18 GHz 距离×方位分辨单元 3 m×3 m 信号带宽 50 MHz 信号脉宽 1 μs 和通道3 dB波束宽度 5° 波束扫描范围 –15°～15° 脉冲重复频率PRF 2000 Hz 天线扫描速度 30°/s 
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表 1 Simulation parameters of a forward-looking scanning radar
Parameters Value Parameters Value Center ground range 1700 m Platform velocity 100 m/s Center frequency 18 GHz Pixel resolution 3 m × 3 m Bandwidth 50 MHz Pulse width 1 μs 3 dB beamwidth of the sum channel 5° Antenna scanning area –15°–15° Pulse repeat frequency 2000 Hz Scanning rate 30°/s
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