The generation and recording of electromagnetic waves by ground-penetrating
radar (GPR) systems are complex phenomena. To investigate the characteristics
of typical surface GPR antennae 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 3D Cartesian
coordinates. The accuracy of the algorithm is validated with respect
to laboratory measurements for comparable antenna systems. Numerically
efficient and accurate modelling of small antenna structures and
high permittivity materials is achieved through a grid-refinement
procedure. We simulate the radiation characteristics of a wide range
of common surface GPR antenna types ranging from thin-wire antennae
to bow-tie antennae with arbitrary flare angles based on the assumption
of perfect electrical conductivity (PEC) of the metal parts. 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. To enhance the damping effects,
this metal box can be filled with a dielectric absorber and/or connected
to the antenna panels through discrete resistors. Finally, we also
consider the effects of continuous resistive loading of the antenna
panels using a sub-cell algorithm. We find that GPR antennae with
Wu?King-type resistivity profiles radiate compact, broadband pulses
and, as opposed to PEC antennae, are largely insensitive to their
operating environment. Unfortunately, these favourable radiation
characteristics are accompanied by a dramatic loss in radiation efficiency
compared to the corresponding PEC antennae.