Sub-band mutual-coherence compensation in multiband fusion ISAR imaging

Phase-coherence of signals in different sub-bands is a prerequisite for multiband fusion radar imaging. Here, a mutual-coherence compensation method based on valid dominant poles and phase autofocusing is proposed to compensate for the incoherent phases (ICPs) between sub-bands in multiband fusion inverse synthetic aperture radar (ISAR) imaging. In the proposed method, the linear ICP compensation and fixed ICP compensation are decoupled rather than the ICPs being compensated pulse by pulse as in traditional methods. In this method, the valid dominant poles that correspond to strong scatterers in the estimated poles of each sub-band are first extracted to estimate the linear ICP. Then, phase autofocusing technology based on the same rotation centre is applied to multiple pulses in each sub-band in the ISAR coherently processing time to jointly compensate for all the fixed ICPs at once. Furthermore, a unitary estimation of signal parameters via the rotational invariance techniques (U-ESPRIT) method, which can exploit considerable information from the measured data, is utilised to estimate the poles of the sub-bands to improve the accuracy of the estimation of the linear ICP between sub-bands. The effectiveness and robustness of the method were verified experimentally based on both numerical simulations and real data.