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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.
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 ...
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 ...
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.
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. [1][2][3] 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 ...
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 ...
A dipole can be fed from very near its end (needing to be only about 1 / 20 th of the dipole length from the actual end) but the end impedances are exceedingly high – a few thousands of ohms, depending on the average height of the antenna and thickness of its wire. The end location has an inconveniently high impedance, but 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.