Study On Multi-mode Imaging Techniques For FMCW SAR

The combination of synthetic aperture radar(SAR)and Frequency Modulation Continuous Wave(FMCW)technique leads to the rapid development of FMCW SAR.FMCW SAR not only has the advantages such as small size,light weight,low cost and good concealment,but also has the ability to obtain high precision images all-day and all-weather,it feasible can mount on a small unmanned aerial vehicle,thus it plays a very important role in the military and civil fields.Multi-mode imaging can play the advantages of each mode fully and realize the combination of imaging scene census and the detailed investigation,lead to a comprehensive grasp of the battlefield situation.Squint SAR can carry out high-resolution imaging without leaping directly to a certain area,improving the security of the aircraft platform.Spotlight SAR is a very important high resolution working mode.It can overcome the azimuth resolution restriction in strip mode and has important application value for high resolution battlefield detection.According to the signal characteristics of FMCW SAR,this paper makes a deep research on Squint mode and Spotlight mode.Based on Frequency Scaling(FS)algorithm,the flow of the multi-mode integrated imaging is designed in this paper.The main work and achievements are summarized as follows:1?The time-domain and frequency-domain characteristics of chirp signals are analyzed in detail.The matched filtering and Dechirp-on-receive technology of the Linear Frequency Modulated Signal are discussed.Then,by analyzing the characteristics of De-chirped signal,the elimimation method of Residual Video Phase(RVP)is deduced.Finally,the calculation method of range resolution for FMCW SAR is given.2?The signal model of squint FMCW SAR is established,Based on this model,the Doppler feature,azimuth resolution,azimuth spectrum and range migration of squint SAR are analyzed.Then,according to the characteristics of high range walk and small range curvature in squint SAR,an Rang-Doppler(RD)imaging algorithm and an FS imaging algorithm which is suitable for squint imaging are proposed.The feasibility and efficiency of the proposed modified methods are validated by the simulation results of point targets and the vehicle-based experiment results.3?The signal model of spotlight FMCW SAR is established,According to this model,the Doppler feature,azimuth resolution,azimuth spectrum and range migration of spotlight SAR are analyzed.Then,based on the characteristics of spotlight SAR,an RM imaging algorithm and an FS imaging algorithm which are suitable for spotlight imaging are proposed.The feasibility and efficiency of the proposed modified methods are calidated by the simulation experiment and the airbirne-based experiment.4?This chapter present a comprehensive and systematic study for the differences among broadside stripmap mode,squint stripmap mode and spotlight mode in imaging geometry,Doppler feature,azimuth resolution,range migration and echo equation.According to the differences among the three modes,the multi-mode integrated imaging flow with FS algorithm as the core is designed.