The design of surface ground-penetrating radar (GPR) antennas is inherently
difficult, primarily because the presence of the air-soil interface
greatly complicates both analytic and laboratory-based approaches
aimed at characterizing the antennas. Versatile numerical simulation
techniques capable of describing the key physical principles governing
GPR antenna radiation offer new solutions to this problem. We use
a finite-difference time-domain (FDTD) solution of Maxwell's equations
in 3-D Cartesian coordinates to explore the radiation characteristics
of various antennas operating in different environments. The antenna
panels are either modeled as perfect electrical conductors (PEC)
or as having a Wu-King-type conductivity profile. Input impedances,
radiated waveforms, and energy radiation patterns of antennas with
Wu-King conductivity profiles are largely invariant when placed in
free space or above half-space earth models. By comparison, antennas
with PEC panels have variable characteristics that depend on their
design and operating environment. Antennas with resistively loaded
panels are considerably less sensitive to their environment than
their PEC analogs, because the loss resistance is increased and the
effective electrical length of the antenna becomes shorter when the
antenna panels are resistively loaded. For Wu-King conductivity profiles,
the current in the antenna panels approaches that of a quasi-infinitesimal
electric dipole. Unfortunately, the favorable characteristics of
the Wu-King-type antennas are counter-balanced by markedly lower
radiation efficiency. We found that the peak energy radiated into
realistic earth models from antennas with Wu-King conductivity profiles
is about one order-of-magnitude lower than for PEC antennas.