Research On Multi-Channel SAR Imaging Processing Technology

Synthetic aperture radar ?SAR? is a kind of high resolution imaging radar, whose principle is that using the matching filter by pulse compression technology achieves high range resolution, and using large aperture antenna through the radar carrier motion to simulate the equivalent by synthetic aperture technology reaches high azimuth resolution.Compared to the single-channel SAR systems, the multi-channel systems' echo data have redundancy, which increases the degree of freedom of the system due to much more receive channels. As a result, we can get the rich details of the targets, and precisely distinguish the target from the background clutter and noise, which can apply to the high-resolution imaging and target detection technology. Multi-channel systems have many advantages such as high data availability, low system cost, flexibility and so on. Against this background of this thesis, sub-band splicing technology and sidelobe suppression technology were applied to multi-channel SAR system, and the sub-band splicing methods based on IEEE₈02.11 protocol and the sidelobe suppression method via dual-delta factorization were studied. In the thesis, the main work and innovation are as follows:1. The basic theory of SAR imaging and the principles of BP imaging algorithm are given. Firstly, the thesis analyzed the two-dimensional resolution of SAR, and defined the improvement of LFM signal bandwidth is the key to achieve SAR range high resolution; Secondly, the thesis introduced the echo model of SAR imaging and the theories of fuzzy functions; the principles and steps of back projection algorithm was analyzed. Finally, compared with other frequency domain algorithm, the main advantages of the BP algorithm were described.2. Two kinds of multi-channel sub-band splicing methods are studied. The thesis found that the baseband structure of IEEE₈02.11ac is similar to that of the SAR system,and its frequency range is so wide that it can meet the requirement of high resolution SAR Imaging. After splicing all bands together, to obtain a higher range resolution, the thesis proposed sub-band splicing method based on IEEE₈02.11ac Protocol for multi-channel SAR systems. First, the relationship between the Wi-Fi protocol and the SAR system, and two kinds of signals for the sub-band splicing technique were summarized. Secondly, the multi-channel sub-band splicing methods in the signal domain were studied, and the steps of the method were deduced. The simulation results show that the method can effectively improve the range resolution,and reach about 0.5 meters. Then, the image domain sub-band splicing method was introduced, and we briefly described the steps and existing problems of the method. Finally, the effects of channel delay error and channel amplitude error on the system were analyzed empirically in the two sub-band splicing methods.3. A method of sidelobe suppression based on dual-delta factorization was proposed. In the multi-channel sub-band splicing method based on the IEEE₈02.11ac protocol, compared with the traditional SAR system the splicing results result in higher sidelobes due to the existence of the spectral gap. Therefore, we used the sidelobe suppression technique to deal with it, and introduced the classic method of windowing.However, due to the presence of system distortion and phase noise, the actual sidelobe of the system's point spread function ?PSF? is irregular and even indivisible,which may severely degrade the performance of windowing processing based on sinc functions.Aiming at the limitation of windowing methods, a sidelobe suppression method based on dual-delta factorization was proposed to deal with many indivisible problems.Compared with other methods, the exact expression of PSF is not necessary before iteration, and it is continually updated by greedy strategy. In addition, its implementation is fairly simple and it is compatible to the high-dimensional and non-separable cases.