Study On Ground Moving Target Indication Technology Based On Hypersonic Platform Forward Squint Synthetic Aperture Radar

Hypersonic vehicle(HSV)generally flies in the height of 20~100km at a speed of more than 5 Mach,with the “high altitude and high speed” dual-high characteristics and high maneuverability.However,it might be confronted with many problems when HSV detects ground targets in the mode of forward squint,such as serious Doppler broadening,great range walk and Doppler center shift,serious range-azimuth coupling and Doppler spectrum ambiguity et.al.According to HSV borne radar platform,clutter characteristics,synthetic aperture radar(SAR)forward squint imaging and ground moving target indication(GMTI)are studied.Firstly,this paper analyzes the clutter characteristics of hypersonic platform.(1)Analyze the clutter range Doppler characteristic and the influences of range ambiguity and Doppler ambiguity on it.(2)Analyze the clutter space time spectrum characteristic,points out the clutter non-uniformity under non-side-looking arrays,and analyze the influences of platform height and platform speed on it.(3)Analyze the clutter range walk characteristic and the reason of range walk,and calculate clutter range walk of hypersonic platform quantificationally.Secondly,the precious model of the echo signal based on the hypersonic platform is established,and influences of platform velocity and acceleration on matched filtering are analyzed.Next,this paper proposes a precise large scene imaging algorithm based on the hypersonic vehicle cruise forward squint SAR.First,it corrects range walk precisely to decouple two-dimensional frequency.Then,the echo signal is matched filtered precisely in range domain and secondary range compressed in two-dimensional frequency domain.Next,the echo signal is processed by chirp scaling(CS)operation to unify range curve of different distances and the range curve is compensated.Finally,by three-order phase compensating,azimuth compressing and residual phase compensating,a good focused image is obtained.Finally,according to HSV forward squint SAR-GMTI,this paper proposes improved dual-channel displaced phase center antenna(DPCA)clutter suppression method and multi-channel ambiguous clutter suppression method successively.In the former method, range walk of the echo signal is corrected firstly in range time domain to decoupled two-dimensional frequency.Then,the echo signal bandwidth is fully compressed by three-order chirp Fourier transform(CFT)operation to avoid Doppler spectrum folding.Next,range envelope and azimuth envelope of the echo signals from different channels are aligned by compensating a fixed phase.Finally,by the DPCA method in range compression-azimuth CFT domain,the stationary clutter is suppressed and the moving target is kept.This method can reduce minimum detectable velocity of the moving target by half.Using DBF technology to null in the directions of clutter and its ambiguous components in range compression-azimuth CFT domain,the latter method can achieve clutter suppression by space-time adaptive processing(STAP).It can effectively suppress the stationary clutter and its ambiguous components,and extract the echo signal of the moving target without ambiguity.This method can reduce the number of spatial freedom.