A novel range-instantaneous-Doppler (RID) algorithm of inverse synthetic aperture radar (ISAR) imaging based on adaptive Doppler spectrum extraction is proposed in this paper. Regarding maneuvering targets, such as military aircraft, the ISAR image is blurred on cross-range domain when the range-Doppler (RD) algorithm is applied. The RID imaging method is often used to resolve the Doppler ambiguity, but there are some scatterers that could be lost because the sliced time is fixed in traditional RID imaging. To the method proposed in this paper, the optimal Doppler spectrum of each range bin is extracted by gradient energy function (GEF) after time-frequency (TF) analysis, and then all of the optimal Doppler spectrums are combined to obtain a final 2-D RID image of the target. Compared with the traditional RID method, the novel algorithm can obtain image with better focused quality. The results obtained from simulated and field-measured data verify the superiority of the proposed algorithm.
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