Applications of the Theory of the Horizontal Dipole Near the Boundary Between Air and Earth or Sea

Abstract

In Chapter 4, applications of the vertical electric dipole to communication with submarines and to geophysical measurements on the sea floor are described. The horizontal electric dipole can be used for similar purposes. It has also been used for remote sensing from the surface of the earth. For these applications the radial component of the electric field is generally the most useful and its properties in the direction ø = 0 of its maximum are essentially the same for the horizontal as for the vertical dipole. However, the relative magnitudes of the field for unit dipoles are quite different. In the intermediate 1/ρ range, the ratios of the fields for dipoles at the boundary in Regions 1 and 2 (wave numbers k₁ and k₂ with |k₁| ≥ 3|k₂|) are

$$ {\text{[Vertical in 2 : Horizontal in 1 or 2 : Vertical in 1]}} = \left[ {1:\frac{{k{}_2}}{{k{}_1}}:\frac{{k_2^2}}{{k{}_1}}} \right] $$

((7.1.1))

For communication with submarines, the unit vertical dipole on the boundary in air (Region 2) is to be preferred; for transmission along the sea floor with the source in the sea (Region 1), the unit horizontal dipole gives the larger field. But actual antennas are not unit dipoles. At low frequencies—which must usually be used for these applications—electrically long antennas are possible with horizontal elements and generally physically impractical with vertical antennas.