Radiation
efficiency of horizontal VLF antennas connected to ground
Radial field dependence: Transmitting dipole moment current . length = 1 Am Background noise level above ground: 5 dBuV/m red: vertical E-field in air, black: horizontal E-field in the ground, blue: H-field ( . 377 ohm)
Horizontal wire connected to average ground:
Horizontal wire connected to very dry ground:
Geometry of an earth-antenna:
View from side Equations: Complex wavenumber k in lossy medium:
(applicable if antenna length l > d and l > d) In the air above the surface, the vertical (E-field) polarisation is doubled by the image antenna, whereas the horizontal polarization is short-circuited. Beneath the surface, the air
acts as a magnetic wall, suppressing vertical E-fields and currents.
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