Near-field modeling of radar antennas: An intrinsic approach

Full-wave inversion of near-field radar data for nondestructive characterization of material properties requires an accurate electromagnetic model, which in particular accounts for complex antenna-medium interactions. We present an intrinsic way for modeling radar antennas for the particular case of planar layered media. Fundamental antenna features consist of an equivalent set of infinitesimal electric dipoles, field points and associated frequency-dependent, global reflection and transmission coefficients. These antenna characteristic functions permit to describe wave propagation between the radar reference plane and the equivalent source dipoles and field points. Near-field antenna-medium coupling is thereby inherently accounted for. Hence, the antenna characteristic functions do not depend on the medium. We show an example of application in which the dielectric permittivity of a sand subject to a range of water contents is estimated from measurements collected with a vector network analyzer and a 0.8-4 GHz Vivaldi antenna.