Whip antenna
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A whip antenna is an antenna with a single driven element and a ground plane. These antennas are very common, especially for mobile applications and hand held radios. These antennas are usually attached to a vehicle and designed to be flexible, so that they don't break when struck. These antennas derive their name from the whip-like motion they exibit during transit.
A whip antenna is a stiff, yet flexible, wire (almost always) mounted vertically, and attached at one end to a ground plane. The whip antenna can also be called a half-dipole antenna, and as such, has a toroidal radiation pattern where the axis of the toroid centers about the whip. The length of the whip determines its wavelength, although it may be shortened with a loading coil anywhere along the antenna. Whips are generally a fraction of their actual operating wavelength, half-wave, and quarter-wave whips are very common.
Being vertically mounted causes the whip antenna to have vertical polarization. Whips are thought of as omni-directional, because they radiate equally in all directions when viewed from above, however whips are less receptive to signals directly above them.