Modified frequency domain backprojection autofocus: Experimental assessment using millimeter wave radar

Recently, drone-borne synthetic aperture radar (SAR) imaging has attracted increasing attention owing to miniaturization of millimeter wave (MMW) radars. Most studies have attempted to reconstruct SAR images of the ground observed from the sky in a simplified manner. Some of these have applied autofocus techniques to reconstruct SAR images in limited geometrical conditions. In this study, a modified frequency domain backprojection autofocus (FDBP-AF) technique is developed to generate well-focused SAR images without any geometrical limitation. The modified FDBP-AF method is precisely formulated. Its validity is confirmed by experiments in which a MMW radar is operated in a near-field radar geometry.