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Random wire antenna. A wire antenna kit, with a coil of wire, strain insulators and a balun. When installed the wire is supported by buildings or trees using the insulators to prevent a short circuit to ground. A random wire antenna is a radio antenna consisting of a long wire suspended above the ground, whose length does not bear a particular ...
The J-pole antenna is an end-fed omnidirectional half-wave antenna that is matched to the feedline by a shorted quarter-wave parallel transmission line stub. [5] [1] [6] For a transmitting antenna to operate efficiently, absorbing all the power provided by its feedline, the antenna must be impedance matched to the line; it must have a resistance equal to the feedline's characteristic impedance.
Massive. v. t. e. In electrical engineering, electrical length is a dimensionless parameter equal to the physical length of an electrical conductor such as a cable or wire, divided by the wavelength of alternating current at a given frequency traveling through the conductor. [ 1 ][ 2 ][ 3 ] In other words, it is the length of the conductor ...
v. t. e. Radiation resistance is that part of an antenna 's feedpoint electrical resistance caused by the emission of radio waves from the antenna. [a][1][2] A radio transmitter applies a radio frequency alternating current to an antenna, which radiates the energy of the current as radio waves. Because the antenna is absorbing the energy it is ...
The antenna feedpoint is usually high in the air (for example, a dipole antenna) or far away (for example, an end-fed random wire antenna). A transmission line, or feedline, must carry the signal between the transmitter and the antenna. The ATU can be placed anywhere along the feedline: at the transmitter, at the antenna, or somewhere in between.
In electromagnetics, an antenna's gain is a key performance parameter which combines the antenna 's directivity and radiation efficiency. The term power gain has been deprecated by IEEE. [1] In a transmitting antenna, the gain describes how well the antenna converts input power into radio waves headed in a specified direction. In a receiving ...
German physicist Heinrich Hertz first demonstrated the existence of radio waves in 1887 using what we now know as a dipole antenna (with capacitative end-loading). On the other hand, Guglielmo Marconi empirically found that he could just ground the transmitter (or one side of a transmission line, if used) dispensing with one half of the antenna, thus realizing the vertical or monopole antenna.
For such an antenna, the near field is the region within a radius r ≪ λ, while the far-field is the region for which r ≫ 2 λ. The transition zone is the region between r = λ and r = 2 λ . The length of the antenna, D, is not important, and the approximation is the same for all shorter antennas (sometimes idealized as so-called point ...