基于星载辐射源的被动SAR频率同步:误差分析与同步方法

Frequency Synchronization of The Passive SAR Based on Spaceborne Transmitters:Errors Analysis and Synchronization Approach

基于星载辐射源的被动SAR的收、发系统采用各自独立的频率源,因此,其收、发系统本振信号存在着频率同步误差。在接收端解调过程中,该频率同步误差会引入一定的相位误差,进而影响下一步的成像处理。本文针对基于星载辐射源、采用地面固定接收机的被动SAR系统,分析了不同类型的频率同步误差对其方位向相位的影响,提出了一种利用直达波信号提取相位误差的频率同步方法。在利用直达波信号提取相位误差时,零多普勒时间的精确估计是关键问题。文章改进了零多普勒时间的估计方法,提高了其估计精度,从而较好地实现了频率同步。最后仿真分析了研究结论的有效性。

The frequency synchronization errors exist in the Local Oscillating Signals of the transmitters and receivers of the passive SAR based on spaceborne transmitters because the transmitters and receivers are mounted on separated platforms. Phase errors is introduced in echo demodulation process because of the frequency synchronization error, and then, the final focus result will be deteriorated. This paper focus on the passive fixed-receiver SAR based on spaceborne transmitters. First, this paper discusses the influence of various frequency synchronization errors on azimuth phase. And then, a frequency synchronization approach of using direct-path echo is presented, in which we obtain the phase error from direct-path. In the process of obtaining the phase error, the Zero Doppler Time is the key. A more precise estimation method of the Zero Doppler Time has been improved, and the frequency synchronization is achieved. Finally, simulations are carried out to prove the validity of the research result.