Radiation characteristics of a high-frequency antenna in different dielectric environments

This paper presents an investigation of the radiation characteristics and sensitivity of a high-frequency Ground-Penetrating Radar (GPR) antenna using radiation patterns obtained from both physical measurements and a three-dimensional (3D) Finite-Difference Time-Domain (FDTD) numerical model. The aim was to develop an understanding of how electromagnetic energy is radiated and received by a real GPR antenna in lossy dielectric environments. The radiation patterns were obtained by measuring responses from a target positioned at a series of intervals on the circumference of a circle surrounding the antenna in the H-plane. We believe this approach offers a more realistic characterisation of antenna behaviour and is therefore a useful addition to the traditional transmitted field pattern. Measured patterns came from a 1.5 GHz commercial antenna. A series of oil-in-water emulsions were used to simulate homogeneous materials with different permittivities (ε_r = 5, 10, 30, 72) and with frequency-dependent conductivities. The measured patterns were compared with modelled ones obtained from a 3D FDTD model which included a description of the antenna. Good correllation was shown between the experimental results and modelled data with respect to the strength of the main lobe within the critical angle window. However, there are discrepancies in the strength of main lobe at shallow angles. In all the dielectrics the main lobes are generally broad due to the near-field observation distance but, as expected, become narrower with increasing permittivity. Using the FDTD model, further research is planned to compare these received energy patterns with transmitted field ones.