A dipole antenna is the simplest type of radio antenna, consisting of a conductive wire rod that is half the length of the maximum wavelength the antenna is to generate. This wire rod is split in the middle, and the two sections are separated by an insulator. Each rod is connected to a coaxial cable at the end closest to the middle of the antenna.
Radio frequency voltages are applied to dipole antennas at the center, between the two conductors. They are used alone as antennas, especially in rabbit-ear television antennas and as the driven elements in other types of antennas.
Dipole means "two poles."
Dipole provides the best performance if it is more than a half-wavelength above the ground, surface of a body of water or horizontal conducting medium such as sheet-metal roofing. The element should also be a certain wavelength away from electrically conducting obstructions such as supporting towers, utility wires and other antennas.
Dipole antennas are oriented vertically, horizontally or in slants. Polarization of electromagnetic fields radiated by dipole-transmitting antennas correspond to element orientation. Radio frequency (RF) current in dipoles is at its maximum at the centers of the dipole and at its minimum at ends of the element, and vice versa for RF voltages.
Dipole antennas were invented in 1886 by a German physicist named Heinrich Hertz. These antennas are also referred to as a doublet and make up the main RF radiating and receiving element in different sophisticated type of antennas. Dipole antennas are balanced in that they are bilaterally symmetrical, and they are fed with balanced, parallel wire RF transmission lines.
There are three types of dipoles:
- Ideal half-wavelength dipole
- Folded dipole
- Hertzian dipole
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