26 . Electromagnetic Wave Theory and Applications

We have derived the electromagnetic fields for dipole antennas embedded in a two-layer dissipative medium by using the following techniques: (1) the brute-force numerical-integration method, (2) the modal approach by finding the residues for the integrals, (3) the image-source approach in conjunction with the steepest descent method, (4) and the hybrid technique with the combination of the two latter approaches. It is noted that the quasistatic, near field approximation is valid for frequencies less than 100 KHz, and for measurement distances of less than 1/30 of the free space wavelength. For high frequencies or large layer thickness, the multi-image method gives accurate results in an efficient way, while for low frequencies or small layer thickness, the normal mode approach is more attractive. In the intermediate range, the hybrid image-mode approach is useful.