Sparse SAR imaging for a stepped-frequency harmonic radar

The U.S. Army Research Laboratory is studying the feasibility of using stepped-frequency, ultra-wideband (UWB) synthetic aperture radar (SAR) for the detection of nonlinear targets with harmonic frequency responses. The approach would filter out all natural clutter and manmade objects in the scene that do not have responses in the harmonic frequency bands. In this paper, we show the formulation of SAR imaging using harmonic responses from nonlinear targets. We also show the degradation in SAR image quality when the radar operates in a restricted and congested frequency spectrum where a significant percentage of the spectrum is either reserved or used by other systems. Fortunately, due to the sparse nature of the nonlinear objects in a typical scene, information in the missing frequency bands can be recovered to reduce the artifacts in SAR imagery. In this paper, we apply our sparse recovery technique to estimate the information in the missing frequency bands. Recovery performance in both raw data and SAR image domain is demonstrated using simulation and measured data from experiment.