Modeling of resistively loaded surface GPR antennas

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.