A New Resonance Phenomenon Observed in UWB 14–50 GHz SAR and Its Application to the Retrieval of Thickness and Dielectric Properties of Scene Features

Abstract

We describe the observation of a previously unreported resonance phenomenon in UWB SAR imaging and its application in a novel scheme for the retrieval of thickness and dielectric properties of scene features. The resonance was observed in a 14–50\xa0GHz laboratory study of very high resolution SAR imagery. It presented as a periodic fluctuation in the backscatter of a scene feature in response to changes in the radar measurement frequency. The complimentary static reflectivity measurements of a range of dielectric materials showed the phenomenon could be understood as a material behaving as a resonant microwave cavity. Modeling simulations were able to accurately reproduce the observed nulling characteristics for visually homogeneous materials (acrylic, MDF, and plasterboard) and which displayed a regular frequency spacing between nulls. Those with inhomogeneous structures (chipboard and plywood) showed much more irregular nulling patterns. The spacing of the backscatter nulls is set by the product of the permittivity and thickness of the material. By exploiting diversity in viewing geometry, the two terms can be separated and measured. The scheme offers a new opportunity in the SAR surveillance and monitoring of man-made structures.