Application Of FPGA In SAR Real-time Imaging System

Synthetic Apture Radar (SAR) is high in resolution and far in distance. However, there are two major problems to be considered about how to realize it in practice. One aspect requires to deal with large amount and high speed data. The other aspect demands high real-time control. The above two problems become a great challenge to the engineering realization. Thus, it is important to choose and plan hardware system.Generally, DSP chip is always chosen to process the radar signal. With the high requirement for SAR's performance, it is difficult for the DSP to deal with the signal processing alone. At the same time, the FPGA is playing a more and more important role in signal processing.And it also has more application in SAR imaging. So this thesis will give a brief introduction to the application of FPGA in SAR imaging.The flow of SAR algorithm can be described as follows. At first, the original data need to be preprocessed, then matched by the matched filter and processed by some more complicate algorithm. The preprocessing algorithm always includes range preprocessing and azimuth preprocessing: range preprocessing is composed of DDC and LPF in which the former is multiplication operation and the latter is convolution operation; the azimuth preprocessing is similar. There are many algorithms to realize pulse-compression. This thesis will introduce the generally structure to realize it, which is FFT, complex multiplication and IFFT where FFT and IFFT can be implemented in FPGA. And also, we can use the parallel and flexibility advantage of FPGA to take the place of DSP.As mentioned above, the pulse-compression is sorted into range pulse-compression and azimuth pulse-compression. In SAR imaging, if two kinds of pulse-compressions are needed, transposition is indispensable. However, the RAM resource in FPGA can not satisfy the requirement for dealing with large amount of data. So, DDRII SDRAM is properly chosen to accomplish this task.