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whip antenna
A whip antenna is an antenna consisting of a single straight flexible wire or rod. The bottom end of the whip is connected to the radio receiver or transmitter. They are designed to be flexible so that they do not easily break, and the name is derived from their whip-like motion when disturbed. Whip antennas for portable radios are often made of a series of interlocking telescoping metal tubes, so they can be retracted when not in use. Longer ones made for mounting on vehicles or structures are made of a flexible fiberglass rod surrounding a wire core, and can be up to 35 ft (10 m) long. Whips are the most common type of monopole antenna. These antennas are widely used for hand-held radios such as cell phones, cordless phones, walkie-talkies, FM radios, boom boxes, Wi-Fi enabled devices, and GPS receivers, and also attached to vehicles as the antennas for car radios, as well as two way radios for police, firefighting and aircraft. Larger versions mounted on roofs or radio masts are used as base station antennas for police, fire, ambulance, taxi and other vehicle dispatchers.
==Radiation pattern==
The whip antenna can be considered half of a dipole antenna, and like a vertical dipole has an omnidirectional radiation pattern, radiating equal radio power in all azimuthal directions (perpendicular to the antenna's axis), with the radiated power falling off with elevation angle to zero on the antenna's axis. Whip antennas 1/4 wavelength long or less (the most common type) have a single main lobe, with field strength maximum in horizontal directions, falling monotonically to zero on the axis. Antennas longer than a quarter wavelength have patterns consisting of several conical "lobes"; with radiation maxima at several elevation angles; the longer the electrical length of the antenna, the more lobes the pattern has.
Vertical whip antennas are widely used for nondirectional radio communication on the surface of the Earth, where the direction to the transmitter (or the receiver) is unknown or constantly changing, for example in portable FM radio receivers, walkie-talkies, and two-way radios in vehicles. This is because they transmit (or receive) equally well in all horizontal directions, while radiating little radio energy up into the sky where it is wasted.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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