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Monopole antenna
A monopole antenna is a class of radio antenna consisting of a straight rod-shaped conductor, often mounted perpendicularly over some type of conductive surface, called a ''ground plane''. The driving signal from the transmitter is applied, or for receiving antennas the output signal to the receiver is taken, between the lower end of the monopole and the ground plane. One side of the antenna feedline is attached to the lower end of the monopole, and the other side is attached to the ground plane, which is often the Earth. This contrasts with a dipole antenna which consists of two identical rod conductors, with the signal from the transmitter applied between the two halves of the antenna.
The monopole is a resonant antenna; the rod functions as an open resonator for radio waves, oscillating with standing waves of voltage and current along its length. Therefore the length of the antenna is determined by the wavelength of the radio waves it is used with. The most common or fundamental form is the ''quarter-wave monopole'', in which the antenna is approximately 1/4 of a wavelength of the radio waves. The monopole antenna was invented in 1895 by radio pioneer Guglielmo Marconi, for this reason it is sometimes called a ''Marconi antenna''. Common types of monopole antenna are the whip, rubber ducky, helical, random wire, umbrella, inverted-L and T-antenna, inverted-F, mast radiator, and ground plane antennas.
==History==
The monopole antenna was invented in 1895 by radio pioneer Guglielmo Marconi during his historic first experiments in radio communication. He began by using Hertzian dipole antennas consisting of two identical horizontal wires ending in metal plates. He found by experiment that if instead of the dipole, one side of the transmitter was connected to a wire suspended overhead, and the other side was connected to the Earth, he could transmit for longer distances. For this reason the monopole is also called a ''Marconi antenna'', although Alexander Popov independently invented it at about the same time. Common types of monopole antenna are the whip, rubber ducky, helical, random wire, umbrella, inverted-L and T-antenna, mast radiator, and ground plane antennas.
A definition of a Marconi antenna is an antenna which uses a ground plane as part of its resonant circuit. A ''Hertzian antenna'' is one that does not require a ground to oscillate, such as a half-wave.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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