Research On Wide-angle Isar Imaging Using Frame Theory And Cross-range Scaling

Inverse Synthetic Aperture Radar(ISAR) is one of the most important radar at present, it has a high resolution in both range a nd cross-range dimension. The range resolution of ISAR image will be decided by the radar signal bandwidth, and the cross-range resolution is decided by the total rotation angle of the target relative to radar line of sight(RLOS) during the imaging time. To obtain high cross-range resolution in the inverse synthetic aperture radar(ISAR) image, it is necessary to increase the rotation angle of the target with respect to radar line of sight during the coherent integration interval. This paper has carried out the research on wide-angle ISAR imaging, mainly discussed the ISAR imaging algorithm based on frame processing structure and the problem of cross-range scaling based on the parameter estimation. The main contents are listed as follows:1. Described some problems when increase the rotation angle of the target with respect to radar line of sight during the coherent integration interval to obtain high cross-range resolution in the inverse synthetic aperture radar image, then, analysis of range-Doppler FFT algorithm’s imaging results by using the experiments with simulated data when changing the angle of target rotation. And lay theoretical foundation for further detailed analysis.2. Provided an overview the relevant knowledge about frame theory, and introduced the frame theory to ISAR imaging, application the frame theory on the target imaging. In this algorithm, we putted the radar echo signal expressed in the form of a linear combination of a set of frames in the vector space. The target is imaged by projecting the radar echo signal into the dual frames of the above frames. Then, we analyzed the performance of this algorithm and suitable for wide-angle target imaging algorithm(Polar Format Algorithm) by using the experiments with simulation and real data, and using the ISAR image quality evaluation index to qualitative evaluation.3. Researched two cross-range scaling based on the parameter estimation, they are: the cross-range scaling based on Fr FT and the cross-range scaling based on the phase frequency modulation parameter estimation. In the first algorithm, radar echo signal is dechirped by using the constructed reference signal. And then the fast Fourier transform applied to the dechirped signal. After that, we searched for the energy distribution of this signal, when we found the maximum value, then we found the corresponding chirp rate. Through the calculation we can estimated the target rotation speed. And then we completed the cross-range scaling. In the second algorithm, Fr FT is used to detect the LFM signal to estimate the chirp rate and obtain the rotation angular velocity during imaging, then the total rotation angle can be calculated, and cross-range scaling can be carried out. We verified the performance of the two algorithms above mentioned by using experiments with simulated data, and comparative analysis of anti-noise performance of the two algorithms above mentioned. Finally, through two sets of real data experiments to verify the validity of the two algorithms.