Typical ground?penetrating radar (GPR) transmitters and receivers
are dipole antennas. These antennas have pronounced directivity properties
and exhibit strong coupling to interfaces across which there are
changes in electric material properties. Antenna coupling to the
surface of idealized half?space models has been the subject of intense
research for several decades. In contrast, the behavior of antennas
in the vicinity of interfaces with realistic topographic fluctuations
and/or subsurface heterogeneities has been largely unexplored. To
explore this issue, we simulate the responses of a typical surface
GPR antenna system located on a suite of realistic fractal earth
models using the finite?difference time?domain (FDTD) method. The
models are characterized by topographic roughness of the air?soil
interface and small?scale heterogeneous distributions of permittivity
and conductivity in the subsurface. Synthetic radiation patterns
and input impedance values of the simulated GPR antenna system demonstrate
that topographic roughness significantly affects the coupling of
the antenna to the ground, whereas heterogeneities in the subsurface
predominantly influence the antenna radiation through scattering
and absorption along the propagation path.