Realistic modeling of surface ground-penetrating radar antenna systems: where do we stand?

The generation and recording of electromagnetic waves by ground-penetrating radar (GPR) systems are complex phenomena. To investigate the characteristics of typical surface GPR antennas operating in realistic environments, we have developed an antenna simulation tool based on a finite-difference time-domain (FDTD) approximation of Maxwell's equations in 3-D Cartesian coordinates. The accuracy of the algorithm is validated with respect to laboratory measurements for comparable antenna systems. Numerically efficient and accurate modeling of small antenna structures and high permittivity materials is achieved via subgridding. We simulate the radiation characteristics of a wide range of common surface GPR antenna types ranging from thin-wire antennas to bow tie antennas with arbitrary flare angles. Due to the modular structure of the algorithm, additional planar antenna designs can readily be added. Shielding is achieved by placing a metal box immediately above the antenna. Damping is accounted for by filling the shield with absorbing material, by connecting the antenna to the shield with resistors or by continuous resistive loading of the antenna panels. The effects that these features have on the radiative properties of the tested GPR systems and thus on the illumination of the subsurface are investigated for various half-space models.