In this paper we compare current implementations of commonly used numerical techniques-the Finite-Difference Time-Domain (FDTD) method, the Finite-Integration Technique (FIT), and Time-Domain Integral Equations (TDIE)-to solve the canonical problem of a horizontal dipole antenna radiating over lossless and lossy half-spaces. These types of environment are important starting points for simulating many Ground Penetrating Radar (GPR) applications which operate in the nearfield of the antenna, where the interaction among the antenna, the ground, and targets is important. We analysed the simulated current at the centre of the dipole antenna, as well as the electric field at different distances from the centre of the antenna inside the half-space. We observed that the results from the simulations using the FDTD and FIT methods agreed well with each other in all of the environments. Comparisons of the electric field showed that the TDIE technique agreed with the FDTD and FIT methods when observation distances were towards the far-field of the antenna but degraded closer to the antenna. These results provide evidence necessary to develop a hybridisation of current implementations of the FDTD and TDIE methods to capitalise on the strengths of each technique.
Abstract-The development of accurate and realistic models of Ground Penetrating Radar (GPR) antennas is being driven by research into quantitative amplitude information from GPR, improved GPR antenna designs, and better-performing forward simulations that can feed into inversion algorithms. The FiniteDifference Time-Domain (FDTD) method and Finite-Integration technique (FIT) are popular numerical mehtods for simulating electromagnetic wave propagation. Time-Domain methods are particularly well-suited to modelling ultra-wideband GPR antennas as a broad range of frequencies can be modelled with a single simulation. We present comparisons using experimental and simulated data from a Geophysical Survey Systems 1.5 GHz antenna and a MALÅ Geoscience 1.2 GHz antenna. The antennas were investigated in free space and over a lossy dielectric environment with a target. For the simulations we used a commercial solver -Computer Simulation Technology Microwave Studio (CST) -and a free open-source FDTD solver -gprMax. For each test scenario, phase and amplitude information from the antenna responses were compared. Generally, we found very good agreement between the experimental data and the two simulations.
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