Research On Missile-borne Spotlight Mode SAR Imaging

Synthetic Aperture Radar (SAR) is an imaging radar,expanding the original conception of radar. SAR has the imaging ability to moving targets and regional targets,and which is an important aspect of ATR.Missile-borne SAR has three important characteristics including the high flight speed,the movement with non-constant speed and the big squint angle.The complexity of missle's movement increases the difficulty of imaging processing, and which also brings forward crucial requirement for performance of real time and the precision of motion compensation of imaging algorithm.In this paper,the imaging processing of missile-borne spotlight mode SAR is mainly investigated based on the peculiarity of missile flight.Firstly, the paper founds the diving model of high speed based on the missile-borne SAR movement mode and analyzes the peculiarity of the phase error.This work is the foundation of the following research.Then the paper studies the autofocus algorithm.Movement compensation is one of the key steps in achieving high resolution SAR images.Due to the movement with non-constant speed of the missile,the rotation of the radar to the target is non-uniform after translational motion compensation.The common method is to do two-dimentional nonlinear interpolation,but this method would increase the complexity of the algorithm and cannot meet the requirement of real-time processing. An autofocus algorithm based on Spectral-fit method is established and the simulation results prove its effectivity.The rotation angle of missile-borne radar cannot be too large. To solve the problem of achieving higher resolution with small rotation angles, the paper studies several common super-resolution imaging algorithms, and simulation results are gived. At last, to solve the problem of imaging of missile-borne spotlight SAR in high squint mode,an imaging algorithm based on the fractional Fourier transform(FrFT) is proposed. Experiment results prove its effectivity.