Research On Imaging Algorithm Of Frequency Modulation Continuous Wave Synthetic Aperture Radar

Synthetic Aperture Radar(SAR)imaging technology is a kind of imaging technology developed on the basis of radar system,the purpose of which is to solve the problem of low imaging resolution caused by the limited aperture size of antenna.With the development of radar theory and the increasing requirements of airborne radar system weight,volume and resolution of small flight platforms such as UAV,imaging radar based on signal processing technology and broadband millimeter wave technology has been born.Combining synthetic aperture radar(SAR)with frequency modulation continuous wave system,frequency modulation continuous wave synthetic aperture radar(FMCW SAR),FMCW SAR has a series of advantages,such as light weight,small volume,low energy consumption and high imaging resolution.It meets the requirements of airborne radar for small flight platforms such as UAV,and has been widely concerned by various industries because of its various working modes and high imaging resolution,and different applications have different requirements.Different imaging algorithms are needed to realize their own functions.In this paper,the frequency modulation continuous wave(FMCW)signal and synthetic aperture imaging technology are studied,and the range migration problem caused by the continuous flight of radar carrier is analyzed.Because the period of FMCW SAR transmitted signal is 1ms to 10 ms,and the period of pulse synthetic aperture radar is 1?s to 10?s,FMCW SAR is compared with pulse synthetic aperture radar.frequency modulation continuous wave synthetic aperture radar FMCW SAR can not ignore the influence of range migration on imaging,so the "stop-walk-stop" mode used in pulse synthetic aperture radar is not suitable for FMCW SAR,.With the increase of oblique angle of radar transmitted signal beam,the continuous motion of radar carrier has greater influence on imaging,so it is necessary to study the algorithm suitable for FMCW SAR imaging.At the same time,after the frequency modulation of the FMCW signal is removed,the frequency is constant and the frequency is constant,which will greatly simplify the matching filtering process in the range direction.The echo signal of FMCW SAR is analyzed by constructing the imaging geometry of FMCW SAR.Through the research of the classical range Doppler(RD)imaging algorithm,the range Doppler imaging algorithm suitable for FMCW SAR is deduced,and then the matlab simulation results show that the improved RD imaging algorithm can be applied to FMCW SAR system.At the same time,a well-focused point target image is obtained.Because RD algorithm uses interpolation method to realize range migration correction,which leads to the problem of excessive calculation of imaging processing,FS algorithm uses phase multiplication to correct range migration,which reduces the computational complexity of the algorithm.Therefore,this paper also studies the frequency variant(FS)algorithm suitable for FMCW SAR.The process of frequency modulation and the expression of frequency variation function are derived in detail,and the errors introduced in the process of frequency variation and their influence on the imaging results are studied,and an improved frequency variable scale(FS)imaging algorithm is proposed.Finally,the improved FS is used to simulate the point target imaging.The experimental results show that the improved FS imaging algorithm can eliminate the spectrum aliasing and obtain a well-focused point target image.