Folded Clutter Suppression for Pulse-Doppler Radar Based on Pulse-Agile Waveforms

Pulse-Doppler radar systems with medium/high pulse repetition frequencies (PRFs) usually produce severe range ambiguities, and strong nearby ground/sea clutter will then fold into a single range interval with weak remote target echoes, further limiting the dynamic range of radar. The existing methods for modeling or estimating clutter spectra are usually not applicable to the case of folded clutter. In recent years, pulse-agile waveforms have attracted an increasing amount of attention for resolving range ambiguities. However, cross-correlations among pulse-agile waveforms with the same frequency band, usually required for pulse-Doppler radar to coherently measure the Doppler shift, are not satisfactory for suppressing folded clutter since clutter echoes are much stronger than those of targets. In this paper, two algorithms based on the method of alternating projection (MAP) in the range-Doppler domain (RD-MAP) and the space-Doppler domain (SD-MAP) are proposed to suppress folded clutter and resolve range ambiguities for pulse-Doppler radar based on different types of pulse-agile waveforms. The effectiveness of these algorithms is verified based on several realistic simulations and a ground-based experiment. Iterative solutions and closed-form solutions are both provided for different computational complexity and accuracy requirements in certain application scenarios. Moreover, algorithm analysis, including algorithm boundary analysis, signal-to-noise ratio (SNR) loss, computational complexity and factor selection, is performed to provide an estimation of the applicable conditions and assess the performance of the proposed algorithms.