Inverse synthetic aperture radar (ISAR) is very useful in radar signature applications. In ISAR imaging of nonuniformly rotating target, the radar echo signal in a range cell can be modeled as multicomponent quadratic frequencymodulated (QFM) signals. The high-quality radar images can be obtained by the parameters estimation of QFM signals combined with the range-instantaneous-Doppler technique. In this paper, a novel algorithm for the parameters estimation of QFM signal via the modified cubic phase function (MCPF) is presented. This algorithm estimates the quadratic phase coefficient at first, and the other parameters can be estimated by the traditional CPF and the fast Fourier transform. The implementation of MCPF algorithm requires only 1-D maximizations, and the comparison with some existing algorithms is discussed. The ISAR imaging results of simulated and raw data validate the effectiveness of the novel algorithm proposed in this paper.
Index Terms-ISAR, QFM signals, MCPF.1530-437X
High resolution inverse synthetic aperture radar (ISAR) imaging of targets with complex motion is a main topic in the radar imaging domain. In fact, the traditional range-Doppler algorithm is not appropriate to generate a focused ISAR images because of the time-varying Doppler shifts caused by the target's complex motion. In this study, the azimuth received signal is modelled as multi-component amplitude-modulated and frequency-modulated (AM-FM) signal, and a novel algorithm for the cubic Chirplet decomposition based on generalised cubic phase function is proposed to investigate the AM-FM signal analytically. Then, the corresponding ISAR imaging algorithm associated with the rangeinstantaneous-Doppler technique is proposed. Results of simulated and real data demonstrate the effectiveness of the presented algorithm.
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