Dipole antenna
A dipole antenna is an Antenna (electronics) with two driven elements. These antennas are the simplest antennas from a theoretical point of view, though the whip antenna is probably the most common, and simplest looking antenna.The two driven elements in a dipole antenna are arranged end to end, along a line. The two elements are separate, and fed at the center. The length of the two elements is the same, and their overall length determines the antenna's wavelength. The two elements are fed the same signal 180 degrees out of phase.
The most common dipole antenna is the kind used with televisions called "rabbit ears". While theoretically the dipole elements should be along the same line "rabbit ears" are adjustable in length and angle. Larger dipoles are sometimes hung in a V shape with the center near the radio equipment on the ground.
Dipoles are more efficient than whip antennas. Dipoles have a toroidal radiation pattern where the axis of the toroid centers about he dipole.
Antenna Gain is commonly measured as "X db above a dipole", which means that the antenna in question is being compared to a dipole, and has X db more gain (is more efficient) than the dipole tuned to the same operating frequency.
Related concepts: Antenna theory