Abstract
In the current scenario of high-range resolution radar and noncooperative target, the rotational motion parameters of the target are unknown and migration through resolution cells (MTRC) is apparent in the obtained inverse synthetic aperture radar (ISAR)images, in both slant-range and cross-range directions. In the case of the high-speed maneuvering target with a small value of rotation, the phase retrieval algorithm can be applied to compensate for the translational motion to form an autofocusing image. However, when the target has a relatively large rotation angle during the coherent integration time, phase retrieval method cannot get an acceptable image for viewing and analysis as the location of the scatterer will not be true due to the Doppler shift imposed by the target’s rotational motion. In this paper, a novel ISAR imaging method for maneuvering targets based on phase retrieval and keystone transform is proposed, which can effectively solve the above problems. First, the keystone transform is used to solve the MTRC effects caused by the rotation component. Next, phase errors caused by the remaining translational motion will be removed by employing phase retrieval algorithm, allowing the scatterers are always kept in their range cells. Finally, the Doppler frequency shifts of scatterers will be time invariant in the phase of the received signal. Furthermore, this approach does not need to estimate the motion parameters of the target, which simplifies the processing steps. The simulated results demonstrate the validity of this method.
Highlights
Inverse synthetic aperture radar imaging is a radar technique to obtain a high-resolution image of moving targets [1,2,3,4,5,6]
Shi et al [19, 20] believe that the inverse synthetic aperture radar (ISAR) echo module of the maneuvering target is not affected by its radial motion, that is, phase retrieval can be applied to compensate for translational motion
When the radial velocity becomes larger, by utilizing keystone transform, the ISAR image is still smearing in Figure 6(b), which is induced by larger carrier phase changes with respect to Figure 4(b) imposed by the Doppler effect
Summary
Inverse synthetic aperture radar imaging is a radar technique to obtain a high-resolution image of moving targets [1,2,3,4,5,6]. Shi et al [19, 20] believe that the ISAR echo module of the maneuvering target is not affected by its radial motion, that is, phase retrieval can be applied to compensate for translational motion (radial velocity and radial acceleration). The unfavorable effect induced by the rotational motion is less severe than that induced by translational motion In this way, keystone transform can be first applied for removing the range cell migration due to the target’s rotation. To make the Doppler frequency shifts constant among the range cells in radar signal processing, it is necessary to combine the keystone transform and phase retrieval. Based on the above analysis, a novel ISAR imaging algorithm for maneuvering targets based on phase retrieval and keystone transform is proposed. The target’s translational range distance, R tm , can be modelled in terms of motion parameters:
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