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1、国防科学技术大学硕士学位论文多通道SAR回波信号模拟器幅相误差校正研究姓名：陈镜申请学位级别：硕士专业：信息与通信工程指导教师：董臻2010-11国防科学技术大学研究生院工学硕士学位论文 第 i 页 摘 要 合成孔径雷达(SAR)半实物仿真是仿真技术和 SAR 技术相结合的产物， 它通过全数字仿真和 SAR 回波信号模拟器相结合的方式灵活地产生包含空间几何、场景和各种误差特性的射频回波信号，在 SAR 系统设计、硬件调试、性能指标测试、系统集成维护和任务规划等 SAR 研制和应用全生命周期内发挥着重要作用。 多通道 SAR 回波信号模拟器是在地面构建 SAR 半实物仿真系统， 进行地面测试以及
2、半实物仿真试验的重要地检设备，其通道误差决定着测试和试验的有效性。由于模拟器件的非理想特性等实际限制，多通道 SAR 回波信号模拟器不可避免的存在通道幅相误差，会影响对雷达成像性能及 InSAR 性能的准确评估，因此对模拟器幅相误差校正具有重要意义。 传统的预失真校正技术不能满足模拟器在实时模拟模式下幅相误差的校正， 需要采用实时 FIR 滤波的方法实时校正模拟器幅相特性， 由于模拟器系统传递函数不具有共轭对称性， 问题转化为复系数 FIR 校正滤波器系数的设计问题。 本文首先对多通道 SAR 回波信号模拟器进行建模，通过理论与仿真相结合的方式分析了模拟器通道幅相误差对 SAR 聚焦性能和 S
3、AR 图像相位的影响， 以及幅相不一致性误差对干涉 InSAR 性能的影响。 其次，给出了两种提取通道特性的方法：频谱比对法和匹配滤波加窗法，对这两种方法进行仿真验证。根据提取得到的通道补偿特性，分别采用预失真技术和设计实时校正复系数 FIR 滤波器的方法来实现模拟器通道幅相误差的校正。 再次，根据设计的复 FIR 滤波器系数，利用 FPGA 芯片内嵌 RAM 配置成异步FIFO，采用乒乓模式实时实现高数据率 FIR 滤波器。采用该滤波器对模拟器进行幅相误差校正，实现了模拟器通道特性的校正和优化。 最后，通过分布式卫星 SAR 通道一致性半实物仿真试验，得到分布式卫星 SAR实际载荷通道一致性
4、误差对 InSAR 干涉测高的影响，表明采用复系数 FIR 实时滤波器的方法实现多通道 SAR 回波信号模拟器通道幅相误差校正的有效性。 关键词：幅相误差校正；预失真；复系数 FIR 滤波器；SAR 信号模拟器。 国防科学技术大学研究生院工学硕士学位论文 第 ii 页 ABSTRACT SAR hardware-in-loop simulation is the combination of simulation technology and SAR technology, which generate RF SAR echo containing space geometry, scene
5、and kinds of error characteristics by combining digital simulation and SAR echo signal simulator, and have played important role in the SAR system design, hardware debugging, performance testing, systems integration and mission planning, the development and application of SAR during its life cycle.
6、Multi-channel SAR echo signal simulator is an important ground auxiliary equipment to construct SAR hardware-in-loop simulation system on the ground for the groundbased testing and hardware-in-loop simulation. The validation of the experiment results was main determined by the channel amplitude and
7、the phase error of the SAR echo signal simulator. However, due to the practical constraints such as the non-ideal characteristics of analog, its unavoidable that the amplitude and phase errors existed in multi-channel SAR echo signal simulator affect the performance evaluation of radar imaging respo
8、nse and InSAR. Thus its important to correct the amplitude and phase errors of simulator in real time. The traditional pre-distortion technology cannot meet the demands of correcting of amplitude and phase errors in real-time simulation, so there is need to get a method of FIR filter with real time
9、to correct the amplitude and phase errors of simulator in real time. As the simulator system transfer function does not have conjugate symmetry, the problem transforms to coefficient designing of complex coefficient FIR correcting filters At first, the multi-channel SAR echo simulator is modeled. Ba
10、sed on combination of theory and simulation, all the effects on the SAR image focusing performance and SAR imaging phase caused by simulator channel amplitude and phase errors is analyzed in detail, and the mismatch errors of amplitude and phase effects on the interference InSAR performance is also
11、analyzed. Then，two methods of channel characteristics extraction are proposed:the spectral contrast method and the matching filter method, and then these two methods are compared 国防科学技术大学研究生院工学硕士学位论文 第 iii 页 and verified. Based on the obtained channel characteristics, the simulator channel amplitude
12、 and phase error is corrected by pre-distortion technology and FIR filters with correcting complex coefficient in real-time. Then， based on the designed FIR filter complex coefficients, utilize FPGA chip within embedded RAM configured as an asynchronous FIFO, and the FIR filter with high real-time d
13、ata rate which worked in ping-pong model was constructed. As the proposed methods application, the amplitude and phase error of simulator is corrected, and the results indicate the corrected and optimized performance of simulator channel is obviously. At last，the influence of channel amplitude and p
14、hase mismatch on InSAR height measurement for the distributed SAR system by the hardware-in-loop simulation method, verified that the designed complex coefficient FIR filters can correct the amplitude and phase error of multi-channel SAR echo efficient in real-time. Key Words：Correcting Amplitude and Phase； Pre-distortion； Complex FIR Filters； SAR Signal Simulator. 国防科学技术大学研究生院工学硕士学位论文 第 I 页 表目录 表 2.1 幅相不一致性误差单独对 InSAR 干涉相位的影响 . 22 表 2.2 幅相不一致性误差同时存在对 InSAR 干涉相位的影响 . 23 表 3.1 校正前后幅相误差对比 . 37 表 3.2 校正前后幅相误差对比 . 40 表 4.1 模拟器幅相误差校正前后通道特性对比 . 50 表 5.1 通道一致性误差指标 . 56 表 5.2 半实物试验通道特性引起的相位偏差 .
