The generation and recording of electromagnetic waves by typical ground-penetrating
radar (GPR) systems are complex phenomena. To investigate the characteristics
of typical GPR antennas operating in diverse environments, we have
developed a versatile and efficient simulation tool. It is based
on a finite-difference time-domain (FDTD) approximation of Maxwell's
equations that lets one simulate the radiation characteristics of
a wide variety of typical surface GPR antenna systems. The accuracy
of the algorithm is benchmarked and validated with respect to laboratory
measurements for comparable antenna systems. Computed radiation patterns
demonstrate that the illumination of the subsurface in the near-to
intermediate-field range varies significantly according to how the
antenna is designed. Our models show the effects of varying the shapes
of the antennas, adding shielding (metal box with and without absorbing
material and with and without resistive loading), adding a receiver
antenna, and changing the soil conditions. Given the flexibility
of this modeling software, we anticipate that it will be helpful
in designing GPR surveys and new GPR systems with arbitrary planar
structures. It will also be useful in interpreting certain GPR data
sets.