| Synthetic aperture radar(SAR)imaging system has the characteristics of all-weather operation,long-distance high-resolution imaging,strong anti-jamming ability and so on.It provides the advantages that can not be replaced by other guidance modes for the precise guidance of missiles.In recent years,with the development of radar imaging technology,microwave antenna technology and hardware platforms,the adaptability and autonomy of the complex battlefield environment of the missile platforms equipped with SAR have been greatly improved.However,there is still a certain gap from the capabilities of rapid combat,stealth combat,collaborative combat and precision combat required by the future war.Starting from the demand of the development trend of precision guided weapons for missile-borne SAR,and combining with the characteristics of missile platforms,such as small space size,fast flight speed,high real-time requirements,high dive-angle and high squint-angle/forward-looking imaging,this dissertation carries out relevant theoretical research and simulation verification around the key problems of monostatic/bistatic SAR systems design and imaging algorithm of missile platforms.It lays a theoretical foundation for promoting the engineering application of missile-borne SAR.The specific research content of this paper mainly includes the following parts:(1)Aiming at the design contradictions between the system parameters and imaging indexes caused by the constraints of mission planning,image performance indexes,spatial structure,low cost and real-time processing of missile-borne SAR system,a parameter optimization design method of missile-borne SAR system based on genetic algorithm is proposed.Based on the traditional parameter design method,four key parameters to be designed that affect the imaging indexes are sorted out and solved by genetic algorithm;In order to further improve the solution efficiency,an idea of step-by-step element reduction is proposed.Taking the maximum average power as the optimization criterion,an optimization mathematical model is established to reduce the iteration times of optimization variables and effectively improve the efficiency of system parameter design.The proposed method solves the problem of system parameter optimization search for missile-borne SAR under multiple constraints.It can not only quickly obtain the system parameters that optimize the image performance,but also apply to the parameter optimization design that requires multiple beam positions in the azimuth direction.(2)Aiming at the inherent azimuth spatial variation of radar echo caused by the characteristics of missile-borne SAR dive curve trajectory,and the serious range azimuth coupling and spectrum folding of echo data caused by high squint-angle observation mode,an accelerated factorized backprojection imaging algorithm suitable for missile platforms with high squint-angle and high dive-angle is proposed.On the basis of the traditional accelerated factorized back projection algorithm,aiming at the nonlinear motion trajectory,the wavenumber spectrum fusion accelerated factorized back projection imaging algorithm with high squint-angle and high dive-angle is derived.An accurate sub-aperture spectrum fusion method is proposed.By constructing an accurate spectrum shift function to eliminate spectrum folding,the problem of focusing quality degradation caused by spatial variation of the central position of the sub-aperture spectrum is solved.The proposed method can break through the limitation of time domain imaging algorithm in the application of missile platforms,and provide a feasible solution for the engineering implementation of real-time imaging system of missile platforms.(3)Aiming at the problem that the traditional airborne/spaceborne bistatic configuration design method is inapplicable to the missile platforms due to the high-mobility,a configuration design method of parameter dimensionality reduction for missile-borne bistatic forward-looking SAR system is proposed.Firstly,on the basis of calculating the two-dimensional resolution and the resolution angle based on the gradient theory,the key parameters that have a great impact on the resolution index are sorted out;Then,taking the shortest imaging time as the objective function,an optimization mathematical model is established to reduce the dimension of parameters to be designed and improve the efficiency of configuration design.Finally,the effectiveness of the proposed method is verified by simulation experiments,which lays a foundation for the subsequent engineering application of trajectory optimization design.(4)Aiming at the missile-borne bistatic forward looking SAR imaging model,a new polar format imaging algorithm processing flow is proposed.Based on the basic focusing algorithm,the analytical expression of wavefront curvature error of polar format algorithm is derived;A two-dimensional spatial-variant filtering method is used to correct the wavefront curvature error of the focused image,and the refocused image is re-interpolated to obtain the geometric distortion corrected image;The problem of non convergence of the coordinates of the central pixel in the iterative solution of the two-dimensional space-variant filter module in the traditional algorithm processing flow is improved.Compared with the traditional algorithm processing flow,the improved algorithm processing flow improves the robustness of the algorithm without increasing the complexity of the algorithm. |
