High-resolution SAR imaging system using tapered slot antenna with orthogonally anisotropic directivity

We have developed a synthetic aperture radar (SAR) imaging system using an ultra-short pulse for the nondestructive evaluation of reinforced concrete structures. A Vivaldi tapered slot antenna is designed to have the 10-dB bandwidth from 3.2 to 11.3 GHz. In the system, a monocycle pulse wave with the duration shorter than 200 ps is propagated in free space. Two-dimensional imaging in a reinforced concrete sample demonstrated that the system can estimate the positions of reinforcing bars with a depth resolution of less than 2 mm which is a tenth that of a conventional system. To increase radiation efficiency for SAR, the antenna directivity is designed to be orthogonally anisotropic with radiation angles in the azimuth and elevation directions of 120 and 60 degrees, respectively. Synthesizing an image along the azimuth direction enables the shapes of the reinforcing bars to be restored with high spatial resolution and contrast from radar echoes.