Theoretical and experimental evaluation of the gain of log-periodic dipole antenna placed over ground plane

The log-periodic dipole (LPD) is one of the most useful antenna among the frequency independent antennas. It has been successfully used in many applications, ranging from HF to microwaves because of their intrinsically large bandwidths and rather high gain. The main reason for such a success has certainly been the straightforward design procedure introduced by Carrel (1961). The nonideal terrain around the antenna gives a strong modification of the radiation pattern and a degradation of the gain. For this reason, theoretical and experimental studies for log-periodic dipole antennas radiating over an imperfectly conducting ground plane, have been carried out in order to estimate the gain. To achieve this objective we have applied the moment method so as to solve the electric field integral equation of a thin wire in order to determine a more accurate dipole current distribution. After validation, the method was extended to the log-periodic dipole antenna in free space. Combining this method with the approximation reflection coefficient method, an approach taking into account the degradation due to the presence of the ground is established. This allows us to calculate the antenna characteristics in near-field and far-field, and then to check the theoretical gain. Experimentation has been set up in order to make this theory valid. Emission antennas were placed at different heights over various natural grounds. A budget link over short distance permits us to study the ground effect on the power gain. Finally a comparison between our theory and experimental results is made