Research On FMCW Micro SAR Real-time Imaging Technology

With the in-depth research of Synthetic Aperture Radar(SAR),a new type of system radar that combines Frequency Modulated Continuous Wave(FMCW)technology and SAR technology has become a new research hotspot.FMCW SAR system has a simple structure,miniaturization,low power consumption,and low cost,which is very suitable for being mounted on a micro-unmanned device platform.And it has the high-resolution capability of imaging.It plays an important role and is a key research area at home and abroad.Among them,high-efficiency real-time imaging processing under the condition of meeting the resolution requirements is a key problem that the FMCW SAR system needs to solve.Therefore,this topic discusses and studies the signal characteristics and miniaturization requirements of the FMCW SAR based on the pulse SAR.SAR real-time imaging processing technology has been researched in depth,this paper mainly completes the following work:1.analyze the basic principles of continuous wave imaging and discuss the dechirp processing method of the chirp signal in detail.The de-frequency processing not only simplifies the compression processing in the distance direction,but reduces the system's requirement of sampling rate.Then,we analyze the time-domain and frequency-domain characteristics of the chirp signal in detail.Based on the established FMCW SAR imaging geometric model,we derive the echo signal model in detail.2.Based on the analysis of the traditional pulsed SAR range doppler(RD)imaging algorithm,according to the characteristics of the echo signal in the FMCW SAR squint mode,a solution to the RD algorithm calculation in strabismus mode is given.An improved range Doppler algorithm suitable for FMCW SAR is analyzed for its efficiency,and the improved algorithm is verified by simulation data.The results show that:(1)The effect of Doppler frequency shift on imaging quality can be eliminated by correcting the linear movement in the strabismus mode effectively.(2)The peak sidelobe ratio(PSLR)and integrated sidelobe ratio(ISLR)of the imaging index of the improved algorithm are close to the theoretical values.(3)By optimizing the imaging distance Doppler algorithm,its operation efficiency is higher than that of the classical distance Doppler algorithm.The improved algorithm is more suitable for real-time imaging of continuous wave SAR.3.Through the analysis of the traditional Frequency Scaling(FS)imaging algorithm,according to the effects of range migration correction and frequency scaling function on imaging,aiming at the frequency scaling processing in the FMCW SAR front view and squint mode.The large-bandwidth problem gives an improved frequency scaling algorithm suitable for FMCW SAR,and analyzes the operation efficiency of the improved algorithm.The improved algorithm is verified by simulation data.The results show that:(1)the improved algorithm can eliminate the impact of large bandwidth on imaging quality.(2)The peak sidelobe ratio(PSLR)and integrated sidelobe ratio(ISLR)of the imaging index of the improved algorithm are close to the theoretical values.(3)The improved algorithm does not increase the system load significantly,and is suitable for real-time imaging of continuous wave SAR.This paper discuss and study the signal echo model,give an improved range Doppler algorithm and an improved frequency scaling algorithm,and provides an effective and feasible solution for the efficient real-time imaging of micro SAR systems.