Research On Multimode Imaging Technologies Of Missile-borne Synthetic Aperture Radar

Synthetic aperture radar(SAR) is an active microwave remote sensor, which use pulse compression technique and the aperture radar theory to obtain high resolution 2-D images. The SAR technology used in missile seeker can not only improve their all-weather, all-time detection capability, but also can enhance the precision-guided seekers’ autonomy and anti-jamming capability around the complex electromagnetic environment. Compared with conventional airborne and space-borne platforms, motion process of missile-borne platforms is more complicated, which both have a certain speed and acceleration in horizontal and vertical directions to attack targets and evade enemy anti-aircraft fire. Therefore, missile-borne SAR is faced with a few problems induced by its characteristics of high-speed, high squint and non-uniform straight. This dissertation focusing on these problems of missile-borne SAR imaging technology respectively studies imaging methods in strip, circle-scan and spotlight these three modes of missile-borne SAR. The main researches include the following aspects:Firstly, missile-borne SAR echo computer simulation methods are studied. A series of missile-borne SAR spatial geometry model, platform model, load model and scenes with the electromagnetic model are established. And methods of occlusion calculation in 3-D scenes are also analyzed. A rapid calculation method based on range dimensional Fourier transform is given to solve the problems of heavy computation load for large scene echoes, which make a firm foundation for subsequent imaging algorithms simulation.Then A three-dimensional space geometry model for missile-borne SAR imaging is established, the signal model of echoes in strip mode is obtained. And then the two-dimensional spectral of echoes is deduced. Considering the complex motion of missile platforms, the method of compensation for velocities and accelerations of missiles in three directions in two-dimensional frequency-domain is studied. On this basis, a RD algorithm for missile-borne SAR worked in strip mode is given. And a location method which use the Doppler equation to complete geometric correction of images is proposed. Simulation results show that the algorithm can compensate the complex motion of missile platforms well.The traditional DBS algorithm in missile-borne SAR circle-scan mode. In order to break the azimuth resolution limitations by azimuth in traditional DBS algorithms, an improved focusing DBS algorithm is proposed in this dissertation, which increases azimuth focusing and motion compensation compared with the traditional ones. While for the problems of heavy computation load in large scene location calculation, a rapid location method is proposed based on two stage Taylor series of the Doppler equation, replacing complex trigonometric calculations by the basic operations. The simulation results show that the improved algorithm can effectively improve the image resolution while greatly reducing the calculation time.At last, the spectral characteristics of the echo signal in missile-borne SAR spotlight mode is analyzed. The key to spotlight SAR image is pointed out: solving the azimuth spectrum aliasing. For this purpose, the two-step spotlight SAR imaging algorithm used on airborne and space-borne platforms is introduced to missile-borne SAR, using azimuth coarse focusing to solve the azimuth spectrum aliasing. Simulation results show that the algorithm can effectively solve the problem of the azimuth spectrum aliasing and obtain high-resolution images.