Inverse Synthetic Aperture Radar Target Imaging-based On Frequency Diversity And Its Technical Application

Inverse synthetic aperture radar(ISAR)has been widely used in many fields because it is not affected by the environment and can image long-range targets with high resolution.ISAR is a two-dimensional radar imaging technology that obtains range resolution by transmitting wideband signal and uses the relative movement of the target and the radar to obtain azimuth resolution.However,there is a high requirement for system hardware to transmit wideband signal.Combined with frequency diversity technology,single frequency signals with different frequencies can be transmitted at different times to synthesize wideband signals,so as to reduce the complexity of imaging system hardware.According to the characteristics of the ISAR imaging system,this paper studies the ISAR imaging model based on frequency diversity and its application in frequency scanning array.The main work is summarized as follows:1.Based on the research of the ISAR system structure,we introduce the ISAR imaging turntable model and deduce the resolution formula.At the same time,several methods of translational compensation are introduced.The simulation experiments are carried out on the linear frequency modulation signal and stepped frequency signal commonly used in ISAR system.The influence of several radar system resources on imaging performance is analyzed.2.A frequency diversity ISAR imaging system model is established by combining with frequency diversity technology.By transmitting a single frequency signal to synthesize a wideband signal,the performance of wideband detection can be achieved,and the problem of complex hardware for transmitting and receiving wideband signals can be alleviated.The effectiveness of the system is verified by the simulation experiment with back projection(BP)algorithm.At the same time,to resolve the problem of high sidelobes caused by frequency sparseness,a frequency diversity ISAR target imaging algorithm based on multiple signal classification(Music)is further proposed.The algorithm performs eigenvalue decomposition on the echo signal covariance matrix to obtain the signal subspace and the noise subspace,and then construct a spectral function based on the orthogonality of the two to estimate the target position.Simulation results show that the application of this algorithm can effectively solve the problem of high sidelobes under sparse frequency conditions.3.Application of the frequency diversity ISAR imaging joint frequency scanning array.Because the phase difference generated by the feeder between elements of the frequency scanning array cannot match the change of the transmitted or received signal frequency,this system has certain constraints on the instantaneous bandwidth of the signal when performing ISAR imaging.In response to the above problems,frequency diversity technology is applied to the ISAR imaging radar using frequency scanning array.By transmitting multiple single frequency signals and combining with frequency synthesis technology,the ISAR target imaging method for frequency scanning array is realized.The system can not only form a beam to point at the target,but also overcome the limitations of the frequency scanning array using wideband signals,and realize the two-dimensional imaging of moving target.The simulation results verify that the system is effective.Finally,the influence of array parameters and target flight parameters on the system performance is analyzed.