An Antenna Stick is an antenna consisting of a straight flexible wire or rod. The bottom end of the Antenna Stick is connected to the radio receiver or transmitter. The Antenna Stick is designed to be flexible so that it does not break easily, and the name is derived from the whip-like motion that it exhibits when disturbed.
Antenna Sticks 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 and structures, are made of a flexible fiberglass rod around a wire core and can be up to 35 ft (10 m) long. The length of the Antenna Stick is determined by the wavelength of the radio waves it is used with. The most common type is the quarter-wave whip, which is approximately one-quarter of a wavelength long.
Antenna Sticks are the most common type of monopole antenna, and are used in the higher frequency HF, VHF and UHF radio bands. They are widely used as the antennas for hand-held radios, cordless phones, walkie-talkies, FM radios, boom boxes, and Wi-Fi enabled devices, and are attached to vehicles as the antennas for car radios and two-way radios for wheeled vehicles and for aircraft. Larger versions mounted on roofs, balconies and radio masts are used as base station antennas for amateur radio and police, fire, ambulance, taxi, and other vehicle dispatchers.
The Antenna Stick is a monopole 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.
Antenna Sticks less than one-half wavelength long, including the common quarter wave whip, have a single main lobe, and with a perfectly conducting ground plane under it maximum field strength is in horizontal directions, falling monotonically to zero on the axis. With a small or imperfectly conducting ground plane or no ground plane under it, the general result is to tilt the main lobe up so maximum power is no longer radiated horizontally but at an angle into the sky.
Antenna Sticks longer than a half-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 Antenna Sticks 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.
A quarter wave vertical antenna working against a perfect infinite ground will have a gain of 5.19 dBi and a radiation resistance of about 36.8 ohms. Whips mounted on vehicles use the metal skin of the vehicle as a ground plane. In hand-held devices usually no explicit ground plane is provided, and the ground side of the antenna’s feed line is just connected to the ground on the device’s circuit board.
Therefore, the radio itself, and possibly the user’s hand, serves as a rudimentary ground plane. Since these are no larger than the size of the antenna itself, the combination of whip and radio often functions more as an asymmetrical dipole antenna than as a monopole antenna. The gain will suffer somewhat compared to a half wave metallic dipole or a whip with a well defined ground plane.
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