Efficient Image Generation For Ultra-Wide Band Synthetic Aperture Radar

Ultra WindBand Synthetic Aperture Radar(UWB-SAR) has a broad applications because it can produce fine images of concealed targets with the capabilty of penetrating the foliage and the surface of the earth.lt has been an important sign for acquiring high-resolution images of UWB-SAR for real time processing, and the efficient imaging algorithm is the pivotal and the fundation.Firstly,in this paper, the basic principles of SAR imaging are exploited following the analysis of SAR imaging process; It is shown that the imaging algorithm of traditional SAR can be used effectively only on the condition of narrow relative bandwidth signals, narrow azimuthed processing angle and narrow swath width. Large range migration has brought many new features and difficulties. After comparing many imaging algorithms, we find out the direction research of the UWB-SAR imaging algorithm. A Chirp-Z Transform (CZT) algorithm on the which is similar to Range-Doppler algorithm is studied, and the effective swath width is analyzed. Secondly, a modified block CZT algorithm is presented, which improvs the computational efficiency of the high-resolution SAR imaging with wide swath. Thirdly,a modified Extended Chirp Scaling (ECS) algorithm is presented,which solves the problem of producding fine focused images in the class of Chirp Scaling (CS) algorithm.lt can be used for UWB-SAR imaging effectively. The phase error produced by CS operation are analyzed.A windowed process in two dimension frequency domain before CS operation are proposed. It can improve the quality of image and widen the effectively swath and increase the Peak to SideLobe Ratio(PSLR). Fourthly,a Fast Back Projection (FBP) algorithm is presented.It sloves the problem of large computational load of BP algorithm and the condition of dividing the subapterture is presented. Finally,a modified Planar SubArray Processing (PSAP) algorithm is presented.It improves the computation efficiency by solving the problem of large data overlapped ratio of PSAP algorithm in UWB-SAR imaging. The quality of imaging is enhanced by change the keystone formatin and using the whole energy of the signal. The method of designing and implementing the window is given. Combining the CZT with FFT,we implement the scaled transform and use it to realize the interpolation and improves the computation efficiency. All algorithms in this thesis are verified by computer simulation, we also use UWB-SAR raw data and obtain satisfactory images.