Imaging radars employ wideband linear frequency modulation (LFM) waveforms to achieve high resolution while maintaining moderate sampling rates through restricting the target support to a known range interval and using stretch (deramp) processing. In recent work motivated by compressive sensing principles, multi-frequency extensions of the chirp waveforms were proposed to obtain randomized projections of range profiles. This paper considers the sparse target recovery problem with chirp transmit waveforms and their multi-frequency extensions. We derive the sensing matrix for multi-frequency chirp waveforms and study its coherence properties. We show that multi-frequency chirp waveforms result in sensing matrices with lower coherence between the columns resulting in improved target estimation performance compared to the standard LFM waveform.
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