We present a 3-D finite-difference time domain (FDTD) solution of
Maxwell's equations for modeling the near-field radiation of dipole
antennas in ground-penetrating radar surveys. The antenna is represented
as a conducting wire with a narrow gap in the middle. The electromagnetic
field in the immediate vicinity of the wire is evaluated by numerical
solution of an integral representation of Maxwell's equations. Integration
contours and surfaces are defined by the finite-difference cells
surrounding the wire. Everywhere else the electromagnetic wavefield
is calculated using conventional FDTD approximations of Maxwell's
equations. The accuracy of the algorithm has been tested by comparing
the simulated near-field radiation of a dipole antenna between two
dielectric media with corresponding experimental observations.