Abstract
The imaging issue of a rotating maneuvering target with a large angle and a high translational speed has been a challenging problem in the area of inverse synthetic aperture radar (ISAR) autofocus imaging, in particular when the target has both radial and angular accelerations. In this paper, on the basis of the phase retrieval algorithm and the Gabor wavelet transform (GWT), we propose a new method for phase error correction. The approach first performs the range compression on ISAR raw data to obtain range profiles, and then carries out the GWT transform as the time-frequency analysis tool for the rotational motion compensation (RMC) requirement. The time-varying terms, caused by rotational motion in the Doppler frequency shift, are able to be eliminated at the selected time frame. Furthermore, the processed backscattered signal is transformed to the one in the frequency domain while applying the phase retrieval to run the translational motion compensation (TMC). Phase retrieval plays an important role in range tracking, because the ISAR echo module is not affected by both radial velocity and the acceleration of the target. Finally, after the removal of both the rotational and translational motion errors, the time-invariant Doppler shift is generated, and radar returned signals from the same scatterer are always kept in the same range cell. Therefore, the unwanted motion effects can be removed by applying this approach to have an autofocused ISAR image of the maneuvering target. Furthermore, the method does not need to estimate any motion parameters of the maneuvering target, which has proven to be very effective for an ideal range–Doppler processing. Experimental and simulation results verify the feasibility of this approach.
Highlights
Inverse synthetic aperture radar (ISAR) imaging has been attracting a lot of attention from many radar researchers in recent years [1,2,3]
inverse synthetic aperture radar (ISAR) imaging technology provides a new way of thinking in automatic aircraft models classification, which is the classification of small boats in littoral environments via polarimetric ISAR and automatic target recognition (ATR) for multiple targets flying in formation [4,5,6]
The uncertainty of the maneuvering target increases the difficulty of ISAR imaging, for the aerial targets
Summary
Inverse synthetic aperture radar (ISAR) imaging has been attracting a lot of attention from many radar researchers in recent years [1,2,3]. It should be pointed out that the phase retrieval method has some difficulties of removing the rotational motion effects from the ISAR image. Autofocused images can be obtained only under the condition that the rotation of the target is small for the coherent integration time of the radar; once the rotation angle becomes larger, the phase retrieval algorithm cannot solve the unfavorable effect caused by the rotational motion. In some works [24,25], the authors have carefully chosen a short coherent processing interval using the time-frequency analysis This technique can achieve good imaging results, it has a low utilization rate of radar signals, resulting in the decreasing of the cross-range resolution.
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