Airborne Bistatic SAR Synchronization Technology And Imaging Studies

Since the 1980 s, Bistatic Synthetic Aperture Radar(BiSAR) is always the focus of the technology of radar imaging all over the world. Compared to the traditional monostatic Synthetic Aperture Radar(SAR), the bistatic characteristics of BiSAR make it collect rich information, perform well in anti-stealth and has a better behaviour of anti-interference. However, BiSAR is faced with some new technological problems because of its structure of the bistatic part. One of the most complicated problems is the technology of the synchronization of the system, including the space synchronization, time synchronization and frequency synchronization. This thesis will focus on the issues of the space synchronization, and the main works are as following:1. Based on the analysis of the modes of parallel flight and squint flight of the airborne BiSAR, the imaging parameters, such as the Doppler parameter, the length of synthetic aperture and the azimuth resolution are discussed in respective mode. Based on the radar equation of the airborne BiSAR, the model of antenna direction error is proposed and the simulation about how can antenna direction error affect Antenna Pattern is fulfilled.2. With ignoring the antenna direction error in range direction, the derivation of how can the antenna direction error in azimuth direction affect echo amplitude is done, and the the simulation of how can the antenna direction error in azimuth direction can affect the result of imaging is completed.3. The algorithm of space synchronization based on the estimation of Sub-Aperture Doppler Center is proposed, with the equation of the Doppler Center and the antenna direction error. This algorithm can obtain the antenna direction error with estimating the echo of Doppler Center, and then the real time revision of the antenna direction error can be realized. Considering the actual conditions, the central Doppler frequency must be estimated with the echo of the Sub-Aperture. Then the length of the Sub-Aperture is discussed. Under homogeneous scene, 0.3 Ls can satisfy the requirement of the estimation precision. However, under non-homogeneous scene, the data must be handled to approximately homogeneous. What’s more, the length of the data should be increased to 0.5 Ls, otherwise, the estimation precision can not be achieved. Simulation verified the correction of the algorithm.4. The Back-projection(BP) algorithm is proposed based on the compensation to antenna direction error. With segmented estimation of the Doppler Center form the echo, the function of the antenna direction error can be obtained, therefore, the function of amplitude compensation can be derived. BP imaging process, in a coherent superposition of the cumulative curve signal amplitudes corresponding compensation process of adding value to compensate for antenna pointing errors caused by echo amplitude decrease, thereby improving image quality.