FMCW SAR Imaging Algorithm Research

The combination of FMCW method and SAR method has developed a highresolution radar system with the name of FMCW SAR. FMCW is the abbreviation ofFrequency Modulated Continuous Wave, and SAR is the abbreviation of SyntheticAperture Radar. Compared with conventional pulsed SAR, FMCW SAR has manyadvantages, such as simple structure, light weight and cost effective. In the meanwhile,FMCW SAR also has the advantages that conventional SAR possesses, like highresolution under all weather environment days and nights. Thus FMCW SAR has agreat market value. Depending on the advantage of a very small size, FMCW SAR canbe applied to small the platform like Unmanned Aerial Vehicle. So it can be used in thecomplicated environment that could not easily be done. Because of the great researchvalue and market prospects, FMCW SAR has been the focus of several countries. It hasa broad application prospects in the national economy and military fields.FMCW SAR is continuously transmitting signal during the sweep period.Compared with the pulsed SAR that the signal duration time is usually1~10s, FMCWSAR has a much longer signal duration time that lasts1~10ms.Therefore, the distancevariation that the relative motion between the platform and the target brings aboutduring sweep period could not be ignored. The “stop-go-stop” model assumption thatwidely used in conventional pulsed SAR could not be applied to FMCW SAR systemanymore, resulting in the differences between the two different radar systems. And it ismainly focused on the echo model and signal processing algorithm. So the pulsed SARimaging algorithm should be improved to get the appropriate imaging algorithm forFMCW SAR system combining the characteristics of FMCW SAR signal.The basic principle of FMCW SAR has been detailed analyzed in this dissertation.At first, the Dechirp principle has been elaborated, understanding that the sampling rateof FMCW SAR system is very low, thus reducing the system requirements, such as A/Dsampling rate, data storage capacity and real-time processing rate. The principle ofrange high-resolution that FMCW SAR system possesses is explained from the point ofview using FMCW method to get the distance information. Then the principle of azimuth high-resolution that FMCW SAR system possesses is explained through thepoint of view using SAR method. The point target echo model which can be applied tothis new system then has been derived on the basis of the above two principles.According to the echo model and classic SAR imaging algorithm, imagingalgorithm that could be applied to FMCW SAR system thus has been proposed.The Range Doppler (RD) imaging algorithm suitable for FMCW SAR system hasbeen derived according to the dechirped echo model and classic RD imaging algorithm.And then the simulation experimental results of point target and plane target have alsobeen provided. Next, The Frequency Scaling (FS) imaging algorithm suitable forFMCW SAR system has been proposed, and an improved FS imaging algorithm toeliminate frequency aliasing has also been proposed. At last the simulation experimentalresults of point target and plane target about the two FS imaging algorithm have alsobeen provided.Finally, a detailed analysis of the differences about the two systems between theconventional pulsed SAR and FMCW SAR has been elaborated from the aspects ofsystem structure, the form of transmitting signal and the mode of range processing. Theadvantages and disadvantages of both systems have been concluded and analyzedthrough the imaging about one same point target. In the end, the aspects needed to beimproved have been proposed.