Whip antenna
Encyclopedia
A whip antenna is an antenna consisting of a single straight flexible wire or rod, often mounted above some type of conducting surface called a ground plane
. The bottom end of the whip is connected to the radio receiver or transmitter
. They are designed to be flexible so that they won't break off, and the name is derived from their whip-like motion when disturbed. Often whip antennas for portable radios are made of a series of interlocking telescoping metal tubes, so they can be retracted when not in use. They 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, Wifi
enabled devices, and GPS receivers, and also attached to vehicles as the antennas for car radio
s and two way radios for police, fire and aircraft.
, 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. 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-talkie
s, and two-way radio
s 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.
antennas. Therefore the length of the whip antenna is determined by the wavelength
of the radio waves used. The most common length is one-quarter of the wavelength, called a quarter-wave whip (although this type of antenna is often shortened by the use of a loading coil; see Electrically short whips below). For example, the common quarter-wave whip antennas used on FM radios in the USA are approximately 75 cm long, which is roughly one-quarter the length of radio waves in the FM radio band, which are 2.78 to 3.41 meters long. Half-wave whip antennas are also common.
twice (3 dB greater than) that of a half wave dipole, or 5.19 dBi
, and a radiation resistance
of 36.8 ohms. However without a ground plane the gain is reduced and the radiation resistance increased. 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. In stationary whip antennas, a "ground plane" consisting of several rods a quarter-wavelength long radiating horizontally from the base of the whip is often used. This type of antenna is called a ground plane antenna.
To reduce the length of a whip antenna to make it less cumbersome, an inductor
(loading coil
) is often added in series with it. This allows the antenna to be made much shorter than the normal length of a quarter-wavelength, and still be resonant
. The coil is added at the base of the whip (called base-loaded) or occasionally in the middle (center-loaded). In the most widely-used form, the Rubber Ducky antenna
, the loading coil is integrated with the antenna itself by making the whip out of a narrow helix
of springy wire. The helix distributes the inductance along the antenna's length, improving the radiation pattern, and also makes it more flexible. Another alternative to shorten the antenna is to add a "capacity hat", a metal plate or screen, at the end. However all these electrically short
whips have lower gain
than a full length quarter-wave whip.
Multi-band operation is possible with coils at about one-half or one-third and two-thirds that do not affect the aerial much at the lowest band but create the effect of stacked dipoles at a higher band (usually x2 or x3 frequency).
At higher frequencies (2.4 GHz, but Military whips for 50 MHz to 80 MHz band exist, and are standard issue for the SINCGARS
radio in the 30-88 MHz range), the feed coax can go up the centre of a tube. The insulated junction of the tube and whip is fed from the coax and the lower tube end where coax cable enters has an insulated mount. This kind of vertical whip is a full dipole and thus needs no ground plane. It generally works better several wavelengths above ground, hence the limitation normally to microwave bands.
Ground plane
In electrical engineering, a ground plane is an electrically conductive surface.-Radio antenna theory :In telecommunication, a ground plane structure or relationship exists between the antenna and another object, where the only structure of the object is a structure which permits the antenna to...
. The bottom end of the whip is connected to the radio receiver or transmitter
Transmitter
In electronics and telecommunications a transmitter or radio transmitter is an electronic device which, with the aid of an antenna, produces radio waves. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. When excited by this alternating...
. They are designed to be flexible so that they won't break off, and the name is derived from their whip-like motion when disturbed. Often whip antennas for portable radios are made of a series of interlocking telescoping metal tubes, so they can be retracted when not in use. They are the most common type of monopole antenna
Monopole antenna
A monopole antenna is a class of radio antenna consisting of a straight rod-shaped conductor, often mounted perpendicularly over some type of conductive surface, called a ground plane. The driving signal from the transmitter is applied, or for receiving antennas the output voltage is taken,...
. These antennas are widely used for hand-held radios such as cell phones, cordless phones, walkie-talkies, FM radios, boom boxes, Wifi
WIFI
WIFI is a radio station broadcasting a brokered format. Licensed to Florence, New Jersey, USA, the station is currently operated by Florence Broadcasting Partners, LLC.This station was previously owned by Real Life Broadcasting...
enabled devices, and GPS receivers, and also attached to vehicles as the antennas for car radio
Car radio
Car radio may refer to:*a radio in a car. See car audio and in car entertainment*"Car Radio", a song by Spoon from their 1998 album A Series of Sneaks...
s and two way radios for police, fire and aircraft.
Radiation pattern
The whip antenna can be considered half of a dipole antennaDipole antenna
A dipole antenna is a radio antenna that can be made of a simple wire, with a center-fed driven element. It consists of two metal conductors of rod or wire, oriented parallel and collinear with each other , with a small space between them. The radio frequency voltage is applied to the antenna at...
, and like a vertical dipole has an omnidirectional
Omnidirectional antenna
In radio communication, an omnidirectional antenna is an antenna which radiates radio wave power uniformly in all directions in one plane, with the radiated power decreasing with elevation angle above or below the plane, dropping to zero on the antenna's axis. This radiation pattern is often...
radiation pattern
Radiation pattern
In the field of antenna design the term radiation pattern most commonly refers to the directional dependence of the strength of the radio waves from the antenna or other source ....
, 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. 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-talkie
Walkie-talkie
A walkie-talkie is a hand-held, portable, two-way radio transceiver. Its development during the Second World War has been variously credited to Donald L. Hings, radio engineer Alfred J. Gross, and engineering teams at Motorola...
s, and two-way radio
Two-way radio
A two-way radio is a radio that can both transmit and receive , unlike a broadcast receiver which only receives content. The term refers to a personal radio transceiver that allows the operator to have a two-way conversation with other similar radios operating on the same radio frequency...
s 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.
Length
Whip antennas are normally designed as resonantResonance
In physics, resonance is the tendency of a system to oscillate at a greater amplitude at some frequencies than at others. These are known as the system's resonant frequencies...
antennas. Therefore the length of the whip antenna is determined by the wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
of the radio waves used. The most common length is one-quarter of the wavelength, called a quarter-wave whip (although this type of antenna is often shortened by the use of a loading coil; see Electrically short whips below). For example, the common quarter-wave whip antennas used on FM radios in the USA are approximately 75 cm long, which is roughly one-quarter the length of radio waves in the FM radio band, which are 2.78 to 3.41 meters long. Half-wave whip antennas are also common.
Gain and radiation resistance
If mounted above a perfect ground plane, a quarter wave whip has a gainAntenna gain
In electromagnetics, an antenna's power gain or simply gain is a key performance figure which combines the antenna's directivity and electrical efficiency. As a transmitting antenna, the figure describes how well the antenna converts input power into radio waves headed in a specified direction...
twice (3 dB greater than) that of a half wave dipole, or 5.19 dBi
Decibel
The decibel is a logarithmic unit that indicates the ratio of a physical quantity relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power quantities...
, and a radiation resistance
Radiation resistance
Radiation resistance is that part of an antenna's feedpoint resistance that is caused by the radiation of electromagnetic waves from the antenna. The radiation resistance is determined by the geometry of the antenna, not by the materials of which it is made...
of 36.8 ohms. However without a ground plane the gain is reduced and the radiation resistance increased. 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
Feed line
In a radio antenna, the feed line is the cable or other transmission line that connects the antenna with the radio transmitter or receiver. In a transmitter, it feeds the radio frequency current from the transmitter to the antenna, where it is radiated as radio waves. In a receiver it transfers...
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
Dipole antenna
A dipole antenna is a radio antenna that can be made of a simple wire, with a center-fed driven element. It consists of two metal conductors of rod or wire, oriented parallel and collinear with each other , with a small space between them. The radio frequency voltage is applied to the antenna at...
than as a monopole. In stationary whip antennas, a "ground plane" consisting of several rods a quarter-wavelength long radiating horizontally from the base of the whip is often used. This type of antenna is called a ground plane antenna.
Electrically short whips
Inductor
An inductor is a passive two-terminal electrical component used to store energy in a magnetic field. An inductor's ability to store magnetic energy is measured by its inductance, in units of henries...
(loading coil
Loading coil
In electronics, a loading coil or load coil is a coil that does not provide coupling to any other circuit, but is inserted in a circuit to increase its inductance. The need was discovered by Oliver Heaviside in studying the disappointing slow speed of the Transatlantic telegraph cable...
) is often added in series with it. This allows the antenna to be made much shorter than the normal length of a quarter-wavelength, and still be resonant
Resonance
In physics, resonance is the tendency of a system to oscillate at a greater amplitude at some frequencies than at others. These are known as the system's resonant frequencies...
. The coil is added at the base of the whip (called base-loaded) or occasionally in the middle (center-loaded). In the most widely-used form, the Rubber Ducky antenna
Rubber Ducky antenna
The Rubber Ducky antenna is an electrically short monopole antenna which functions somewhat like a base-loaded whip antenna and is sealed in a rubber or plastic jacket to protect the antenna...
, the loading coil is integrated with the antenna itself by making the whip out of a narrow helix
Helix
A helix is a type of smooth space curve, i.e. a curve in three-dimensional space. It has the property that the tangent line at any point makes a constant angle with a fixed line called the axis. Examples of helixes are coil springs and the handrails of spiral staircases. A "filled-in" helix – for...
of springy wire. The helix distributes the inductance along the antenna's length, improving the radiation pattern, and also makes it more flexible. Another alternative to shorten the antenna is to add a "capacity hat", a metal plate or screen, at the end. However all these electrically short
Electrically short
An electrically short antenna is an antenna of length 2h, such that2 \pi h\over\lambda \scriptstyle\ll 1.An electrically short transmission line is a transmission line in which all of its effects will complete within one cycle of an impressed alternating current....
whips have lower gain
Antenna gain
In electromagnetics, an antenna's power gain or simply gain is a key performance figure which combines the antenna's directivity and electrical efficiency. As a transmitting antenna, the figure describes how well the antenna converts input power into radio waves headed in a specified direction...
than a full length quarter-wave whip.
Multi-band operation is possible with coils at about one-half or one-third and two-thirds that do not affect the aerial much at the lowest band but create the effect of stacked dipoles at a higher band (usually x2 or x3 frequency).
At higher frequencies (2.4 GHz, but Military whips for 50 MHz to 80 MHz band exist, and are standard issue for the SINCGARS
SINCGARS
SINCGARS is a Combat Net Radio currently used by U.S. and allied military forces. The radios, which handle voice and data communications, are designed to be reliable, secure and easily maintained...
radio in the 30-88 MHz range), the feed coax can go up the centre of a tube. The insulated junction of the tube and whip is fed from the coax and the lower tube end where coax cable enters has an insulated mount. This kind of vertical whip is a full dipole and thus needs no ground plane. It generally works better several wavelengths above ground, hence the limitation normally to microwave bands.