The excitation of lateral waves along the boundary between two electrically different media like air and earth or sea or the oceanic crust and the sea is effectively achieved with horizontal antennas in the earth or sea close to the boundary with the air or the sea floor. These are usually insulated terminated antennas, often of the traveling-wave type, such as described in Chapter 17. An alternative to the antenna in the sea or earth is the antenna in the air—it is clearly impractical to insert an antenna in the rock of the sea floor. An example described in Chapter 4 is the vertical monopole erected on the surface of the earth for AM radio broadcasting (Section 4.2) or for communicating with submarines (Section 4.5). Although the vertical dipole is an effective generator of lateral waves, it is difficult at low frequencies to construct one that is not electrically very short and requires very large currents to provide an adequate electric moment. An alternative is the horizontal antenna discussed in Chapter 17 for subsurface use.
KeywordsAttenuation Radar Assure Posite Itan
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