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.