Research On High-resolution Imaging Technology For Ship Target With Missile-borne Radar

The major challenges about imaging ship targets at sea with high-resolution that missile-borne radar facing are the high speed and maneuvering of radar platform,non-cooperation of ship targets,imaging requirements of front-squint and real-time and so on.In order to solve the above practical engineering application problems,this paper analyzes and simulates the work process of missile-borne radar low-resolution searching and high-resolution imaging,and mainly focuses on the high-resolution imaging technology of missile-borne radar for the very large ship at sea.Firstly,this paper simulates the process of low-resolution searching for ship target,and implements the targets separation in the same wave beam simultaneously.Using traditional linear searching mode with wave beams scanning,the radar antenna scans from left limit to right limit with several wave beam positions and each position stays 0.2 second to cover the region to be detected which varies from-20° to 20°.The radar antenna keeps scanning until the target is searched,and then use Doppler analysis to determine the azimuth of targets.Using the differences of range or azimuth between different targets,the targets can be separated and their echoes can be extracted respectively.In addition,aiming at imaging for non-uniform trajectory and considering that the missile-borne radar platform has characteristic of satisfying uniform acceleration motion model during short time,this paper establishes echo model of SAR imaging under uniform acceleration motion state on the basis of above conditions.The analysis of slant distance function error in different situations is done and the imaging algorithm is inferred based on the fourth order approximate formula.The imaging process includes range pulse compression,range migration correction,high-order Doppler frequency elimination and azimuthal Dechirping.Aiming at imaging non-cooperation ship targets,this paper analyses the influence of ship translation and shaking for imaging result in detail.The simulation results show that the ship translation has a greater influence and the ship shaking has little influence on imaging for the very large ship.During the imaging process,the main consideration is the estimation and compensation of ship translation.Considering imaging for non-uniform trajectory and imaging non-cooperation ship targets,a method of combining target Doppler parameters estimation based on Fractional Fourier Transform and real-time motion compensation based on INS data is proposed.The problem of moving platform imaging moving target is converted into problem of moving platform imaging stationary target.The high-resolution imaging of moving ship target under high dynamic condition is realized.The simulation results show that the imaging results resolutions of range and azimuth can less than 1.3m and 5m under plane front bevel 10 on different sea levels.Using ISAR imaging algorithm,the resolutions of range and azimuth can less than 1.4m and 4m in the same situation with SAR.Finally,this paper proposes an improved hybrid SAR and ISAR method to improve the azimuth resolution.Firstly,the motion estimation is combined with the range-cell migration correction to complete the roughly e alignment of the echo envelopes,and at the same time,the phase modulation is eliminated by phase in Range-Doppler domain.Then the accurate envelop alignment is achieved by correlation alignment to compensate the errors caused by the motion estimation inaccuracy,the model mismatch and the inertial measurement.Finally,the residual non-space-variant phase term is uniformly corrected by the weighted multi-special-points autofocus method.The simulation results show that the proposed algorithm can effectively improve the imaging effect and obtain a well-focused target image.In the same situation as before,the resolutions of range and azimuth can less than 1.5m and 3m.