Wideband multi-frequency chirp waveforms combined with stretch processing on receive provides a way to obtain linear projection of range profiles at sub-Nyquist sampling rates. Stable recovery of high resolution range profiles from these projections is guaranteed only if the mutual coherence between the columns of the sensing matrix is sufficiently small. In this note, we derive the sensing matrix for the compressive radar sensor with multi-frequency chirp waveforms and analyze its coherence structure. We show that for suitable choice of system parameters the inter-column coherence of unstructured random sensing matrices is achieved.