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

New generation of precision guided weapons not only demanded to identify and destroy the high-value military targets quickly and accurately, but also demanded to work in all-weather, all-time and long-range conditions. Therefore, the pattern that synthetic aperture radar used in missile platform for two-dimensional imaging guidance has received increasing attention. Compared with airborne and space-borne platforms, missile-borne platforms have the characteristics of high-speed, high squint and non-uniform straight. Missile-borne SAR needs to resolve a series of key technical issues, including mainly high squint SAR imaging methods and non-uniform direct trajectory SAR Imaging methods. Meanwhile, the new missile-borne SAR systems are also an important part of the future development of precision guided weapons, among those, synthetic bandwidth SAR system and the biostatic SAR system are the most promising directions. On the one hand, universality of the key technologies on missile-borne SAR need to be resolved , on the other hand, particularity of the key issues on new SAR system need to be studied. In response to these the four specific issues of two aspects, the following researches focusing on Missile-borne SAR imaging technology are carried out in this paper.1. High squint missile-borne SAR imaging methods are studied. At first, taylor approximation formulas of instantaneous slant range equation and two-dimensional spectrum are analyzed. And the relationship of the coupling phase correction is obtained. From this, Range Doppler algorithm and Chirp Scaling algorithm on missile-borne SAR are derived. Then, The Chirp Scaling algorithm based on range walk correction in time domain is presented. To adapt for higher squint imaging, redundant design strategies are proposed, and the algorithm with third-order phase correction from the offset is improved. At last, parameter estimation method based on fractional fourier transform is improved to obtain the more accurate imaging parameters, and the simulation experiments show its effectiveness.2. Missile borne SAR imaging method of non-uniform direct trajectory is studied. At first, through analysis of non-uniform linear trajectory, the velocity decomposition model in range and azimuth direction is constructed. The principle of restructure method from non-uniform sampling data to virtual uniform sampling data to resolve the SAR imaging with variable motion is expounded. And proceeding from this idea, missile-borne SAR imaging for variable motion based on interpolated array transformation is studied. The principle of equivalent method from the uniform sampling data with variable motion to the non-uniform sampling data with uniform motion is expounded, and from this, the SAR imaging for variable motion based on non-uniform discrete fourier transform is studied. Second, Movement offset equations in range direction with diving motion and yaw motion is analyzed, and the motion compensation function is obtained. Non-uniform motion SAR imaging program is constructed—motion compensation in range direction and non-uniform treatment in azimuth direction. Then, Taking into account the measurement error factors in engineering practice, the method for ballistic parameters method based on trajectory fitting is expounded, and simulation results verify the effectiveness of the method for trajectory fitting and the SAR imaging program for non-uniform linear motion. At last, the spotlight SAR imaging method based on PFA algorithm in the stage of homing terminal guidance is discussed.3. The imaging method based on synthetic bandwidth technology is studied. At first, the SAR imaging method with synthetic bandwidth technology based on multi-band sub-pulse signal is presented. To resolve the synthetic bandwidth under different parameters, synthesized signal model of non-uniform sampling are constructed, and the SINC interpolation is used to complete the signal reconstruction. The problem about bandwidth synthesis processing before and after imaging is discussed. Pre-treatment is considered to suit for the circumstances under sub-pulse of different parameters, and the re-treatment parameters and imaging process are proposed. Then, the imaging method of random stepped frequency radar in the terminal guidance tracking segment is studied, moreover, the problems about frequency matching and motion compensation are resolved under the high repetition frequency condition. The determination method whether the echo is mixed correctly is presented, which uses the properties that the good adjacent range profiles have strong coefficient correlation, and the Algorithm process based on contraction-type frequency matching search strategy is designed.4. The missile-borne bistatic SAR method is studied. At first, starting from the use of motion feature and combat style of missile platform, the feasibility of various bistatic SAR combinations of patterns and geometrical on missile platform is discussed, and the imaging algorithm on geometric scenes of parallel mode, one fixed platform mode, and slanting flight mode is studied. Slanting flight bistatic SAR model is especially built up, the air variable error in the range direction is analyzed, and the motion compensation methods of first order approximation method and the model approximation are designed. An equivalent method from asynchronous bistatic model to monostatic variable velocity motion model is proposed, and with the non-uniform discrete Fourier transform, it resolves the non-uniform sample problems raised by variable velocity motion.Finally, the research is summarized in this paper. The summary and outlook about development tendency and application prospects in the subject research direction are given, and the problems about further study and solution are pointed out.