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For inversed synthetic aperture radar (ISAR) imaging of remote manoeuvring targets via linearly stepped-frequency modulated waveform, a digital stretch technique and a phase coherence compensation method are proposed to achieve high-resolution range profile (HRRP) synthesis. By using this digital stretch technique, the sampling rate can be dramatically reduced and thus the data amount can be significantly decreased. Since the motion estimation error is inevitable for conventional parameters estimation methods, the residual Doppler will give rise to the phase discontinuity at the juncture between the neighbouring sub-pulses, which may blur the HRRP to some extent. A phase coherence compensation method is proposed to further eliminate the phase difference. Owing to the adaptively and convenience for residual Doppler compensation of the proposed method, a good HRRP can be obtained by means of time-domain sub-pulses synthesis technique. Finally, a well-focused ISAR image can be achieved after the conventional range alignment and autofocusing. Experimental results confirm the effectiveness of the proposed methods.