Concept

Umbrella antenna

Résumé
An umbrella antenna is a capacitively top-loaded wire monopole antenna, consisting in most cases of a mast fed at the ground end, to which a number of radial wires are connected at the top, sloping downwards. They are used as transmitting antennas below 1 MHz, in the MF, LF and particularly the VLF bands, at frequencies sufficiently low that it is impractical or infeasible to build a full size quarter-wave monopole antenna. The outer end of each radial wire, sloping down from the top of the antenna, is connected by an insulator to a supporting rope or (usually) insulated cable anchored to the ground; the radial wires can also support the mast as guy wires. The radial wires make the antenna look like the wire frame of a giant umbrella (without the cloth) hence the name. Design The antenna is supported by a central steel tubular or lattice mast. The top of the mast is attached to a ring of equally spaced radial wires extending diagonally to near the ground, where each i
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