Interfacial Dipoles and Radiated Energy

Electric dipoles radiate an electromagnetic field into their surroundings. The electric and magnetic fields from a point source or from linear dipoles have components parallel to a spherical surface but also a radial component. In most investigations on radiated fields, only the part of the electric field that is parallel to a spherical surface is taken into account. The argument is that only that component contributes to the radiated energy. Here we show that the phase front in the lower half space is not a spherical surface and hence, the radial components contribute to radiated energy. We show differences in radiation patterns for point electric dipoles and linear dipoles, either modeled as perfectly conducting wires or as resistively loaded wires. Our primary interest lies with improving image resolution through processing of Ground-Penetrating Radar data. Here the emphasis lies with understanding the radiation characteristics of linear dipoles that can be incorporated with image processing algorithms. The model uses a thin-wire approximation for the transmitter antenna. The solution to the discrete system of equations is solved, incorporating interaction between the interface, using a CGFFT scheme including symmetrization and a newly developed preconditioning operator. We look at the electric and magnetic fields as well as the time-averaged Poynting vector radiation patterns in the E-plane and H-plane of the transmitting antenna. The results show that the radial component of the radiated electric and magnetic field is not negligible, even at distances more than seven wavelengths away from the antennas.