Study On Real-time Signal Processing For ISAR Imaging Of Space Targets

The radar can obtain the high resolution one-dimensional image of the target by transmitting the broadband signal.However,the one-dimensional distance image is essentially the projection distribution of the target scattering point on the radar’s line of sight.Therefore,the information of the one-dimensional distance image is insufficient and sensitive to change in the attitude of the target.However,the inverse synthetic aperture radar(ISAR)uses the relative motion between the target and the radar to improve the cross-range resolution,thus separating the target distance from the coincident points,greatly improving the target information,and then can get the size,shape,posture and other details of the target.Therefore,ISAR imaging technology has always been a hot spot for people to study.This paper mainly studies the real-time signal processing technology of ISAR imaging based on space target.Aiming at the complex and real-time requirement of ISAR imaging process,this thesis mainly from the algorithm and engineering realization to solve the problem.In the aspect of algorithm,The velocity of air targets is too high,which results in excessive tilt of echo envelope after pulse pressure,and thus lead to the problem of low efficiency of engineering treatment.In this thesis,we propose a rough compensation method based on narrowband information.The compensation function is constructed by using the speed and acceleration provided by the narrowband information.The phase compensation of the echo is carried out and then the data is intercepted along the distance.This method reduces the amount of data and improves the engineering efficiency.In addition,The traditional method of cross-range scaling for ISAR image is very complex.In this thesis,we propose a method of cross-range scaling based on single image.By extracting the scattering point phase information,the rotational angular velocity of the target is calculated according to the phase slope relation of different time periods,and the azimuth size of the target is obtained.In the concrete project realization aspect,from three angles to meet the system real-time request.The first angle is the chip selection.We select XC7VX690 T and TMS320C6678.These two chips are high performance chips.While improving the quality of imaging,they greatly improve the speed of signal processing.The second angle is signal processing flow.This thesis uses 4 DSP as the core of the signal processing scheme.FPGA is for RVP correction and distance pulse pressure algorithm preprocessing,DSP is for follow-up imaging algorithm.At the same time we use water structure in DSP1,DSP2 and DSP3.We use ping-pong structure between the DSP3 and DSP4.This scheme makes good use of hardware resources and improves the efficiency of signal processing.The third angle is algorithm processing.In this thesis,we make full use of TMS320C6678 chip 8 cores advantages in the method of allocating reasonable tasks to each piece of DSP’s core.So that each algorithm module can be parallel processing,greatly reducing the system’s imaging time.Finally,through the imaging of point targets and surface targets,the reliability and real-time performance of the ISAR imaging system are verified.