Study Of ISAR Imaging In Complicated Environments

ISAR imaging is a high resolution radar imaging technique in the small segment of viewing angle. The resolution in range is obtained by use of relatively large bandwidth waveforms, and in cross-range by coherent integration of the return signals. In the recent two decades, ISAR theory and technique have got great development and, furthermore, it is gradually applied to practical system. We set off our discussion and research work to the problem in ISAR imaging in complicated environments.In the process of the ISAR data with low input SNR when the target is flying smoothly, the conventional motion compensation method is no longer valid. In this dissertation, a new motion compensation method based on Keystone transformation is proposed to deal with the data with low input SNR. The Keystone transformation is used to eliminate the effects of linear range alignment caused by the radial velocity of the target. By coherently accumulating the adjacent range profiles, the SNR is increased so that the envelope correlation and PGA algorithms can be applied to compensate the high order radial motion. The simulation results show that, for the process of the data with low input SNR, the performance of the method proposed in this paper is better than that of the classical method , thus it is possible to increase the radar range at which targets can be imaged. Multi-target imaging is a new field in ISAR. After describing the basic theories of multi-target imaging, a new multi-target imaging technique based on motion parameter estimation and Keystone transformation is proposed in this dissertation. By use of Keystone transformation to eliminate the effects of linear range alignment, the echoes of low resolution radar are coherently processed to generate accurate target motion parameter estimates. Through a motion compensation process and Keystone transformation at a proper time when the signals of each object can be separated in slant range, it is easy to separate the signals of one object from others in the two-dimensional range-Doppler image. The high order radial motion compensation of each target signature is done separately using the envelope correlation and PGA algorithms. An image is obtained for each target by applying a two-dimensional Fourier transform to its compensated signature. Compute simulation results is given to show the efficiency of the method.