Millimeter-Wave SAR Imaging of Composites Using Rectangular Aperture Probe

In this paper, a rectangular aperture probe operating in the Q-band (33-50 GHz) frequency range is utilized for imaging multilayer fiberglass and honeycomb composite samples of different thicknesses. A synthetic aperture radar (SAR) focusing algorithm is also applied to the images to enhance the image quality and focus at desired depths to obtain better indications of sub-surface defects. It has been demonstrated that industry relevant and practical defects encompassing disbond, delamination, crushed core, moisture intrusion, etc. can reliably be detected, even when scanning from a higher standoff distance (SOD). The advantage of applying focusing at desired depths is illustrated through images that are higher in quality when compared to the raw images and provide clearer and relatively accurate depictions of defects.