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In telecommunications, a collinear antenna array is an array of dipole or quarter-wave antennas mounted in such a manner that the corresponding elements of each antenna are parallel and collinear; that is, they are located along a common axis.
A loading coil or load coil is an inductor that is inserted into an electronic circuit to increase its inductance. The term originated in the 19th century for inductors used to prevent signal distortion in long-distance telegraph transmission cables. The term is also used for inductors in radio antennas, or between the antenna and its feedline, to make an electrically short antenna resonant at its operating frequency.
Coaxial cable, or coax, is a type of electrical cable consisting of an inner conductor surrounded by a concentric conducting shield, with the two separated by a dielectric ; many coaxial cables also have a protective outer sheath or jacket. The term coaxial refers to the inner conductor and the outer shield sharing a geometric axis.
In radio engineering, an antenna or aerial is the interface between radio waves propagating through space and electric currents moving in metal conductors, used with a transmitter or receiver. In transmission, a radio transmitter supplies an electric current to the antenna's terminals, and the antenna radiates the energy from the current as electromagnetic waves. In reception, an antenna intercepts some of the power of a radio wave in order to produce an electric current at its terminals, that is applied to a receiver to be amplified. Antennas are essential components of all radio equipment.
In radio communication, an omnidirectional antenna is a class of antenna which radiates equal radio power in all directions perpendicular to an axis, with power varying with angle to the axis, declining to zero on the axis. When graphed in three dimensions (see graph) this radiation pattern is often described as doughnut-shaped. This is different from an isotropic antenna, which radiates equal power in all directions, having a spherical radiation pattern. Omnidirectional antennas oriented vertically are widely used for nondirectional antennas on the surface of the Earth because they radiate equally in all horizontal directions, while the power radiated drops off with elevation angle so little radio energy is aimed into the sky or down toward the earth and wasted. Omnidirectional antennas are widely used for radio broadcasting antennas, and in mobile devices that use radio such as cell phones, FM radios, walkie-talkies, wireless computer networks, cordless phones, GPS, as well as for base stations that communicate with mobile radios, such as police and taxi dispatchers and aircraft communications.
In radio and telecommunications a dipole antenna or doublet is the simplest and most widely used class of antenna. The dipole is any one of a class of antennas producing a radiation pattern approximating that of an elementary electric dipole with a radiating structure supporting a line current so energized that the current has only one node at each end. A dipole antenna commonly consists of two identical conductive elements such as metal wires or rods. The driving current from the transmitter is applied, or for receiving antennas the output signal to the receiver is taken, between the two halves of the antenna. Each side of the feedline to the transmitter or receiver is connected to one of the conductors. This contrasts with a monopole antenna, which consists of a single rod or conductor with one side of the feedline connected to it, and the other side connected to some type of ground. A common example of a dipole is the "rabbit ears" television antenna found on broadcast television sets.
A whip antenna is an antenna consisting of a straight flexible wire or rod. The bottom end of the whip is connected to the radio receiver or transmitter. A whip antenna is a form of monopole antenna. The antenna 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. 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 whips, made for mounting on vehicles and structures, are made of a flexible fiberglass rod around a wire core and can be up to 11 m long.
A mast radiator is a radio mast or tower in which the metal structure itself is energized and functions as an antenna. This design, first used widely in the 1930s, is commonly used for transmitting antennas operating at low frequencies, in the LF and MF bands, in particular those used for AM radio broadcasting stations. The conductive steel mast is electrically connected to the transmitter. Its base is usually mounted on a nonconductive support to insulate it from the ground. A mast radiator is a form of monopole antenna.
A discone antenna is a version of a biconical antenna in which one of the cones is replaced by a disc. It is usually mounted vertically, with the disc at the top and the cone beneath.
The J-pole antenna, more properly known as the J antenna, is a vertical omnidirectional transmitting antenna used in the shortwave frequency bands. It was invented by Hans Beggerow in 1909 for use in Zeppelin airships. Trailed behind the airship, it consisted of a single one half wavelength long wire radiator, in series with a quarter-wave parallel transmission line tuning stub that matches the antenna impedance to the feedline. By 1936 this antenna began to be used for land-based transmitters with the radiating element and the matching section mounted vertically, giving it the shape of the letter "J", and by 1943 it was named the J antenna. When the radiating half-wave section is mounted horizontally, at right-angles to the quarter-wave matching stub, the variation is usually called a Zepp antenna.
A television antenna is an antenna specifically designed for use with a television receiver (TV) to receive over-the-air broadcast television signals from a television station. Television reception is dependent upon the antenna as well as the transmitter. Terrestrial television is broadcast on frequencies from about 47 to 250 MHz in the very high frequency (VHF) band, and 470 to 960 MHz in the ultra high frequency (UHF) band in different countries. Television antennas are manufactured in two different types: "indoor" antennas, to be located on top of or next to the television set, and "outdoor" antennas, mounted on a mast on top of the owner's house. They can also be mounted in a loft or attic, where the dry conditions and increased elevation are advantageous for reception and antenna longevity. Outdoor antennas are more expensive and difficult to install, but are necessary for adequate reception in fringe areas far from television stations. The most common types of indoor antennas are the dipole and loop antennas, and for outdoor antennas the Yagi, log periodic, and for UHF channels the multi-bay reflective array 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 signal to the receiver is taken, between the lower end of the monopole and the ground plane. One side of the antenna feedline is attached to the lower end of the monopole, and the other side is attached to the ground plane, which is often the Earth. This contrasts with a dipole antenna which consists of two identical rod conductors, with the signal from the transmitter applied between the two halves of the antenna.
A short backfire antenna is a type of a directional antenna, characterized by high gain, relatively small size, and narrow band. It has a shape of a disc with a straight edge, with a vertical pillar with a dipole acting as the driven element in roughly the middle and a conductive disc at the top acting as a sub-reflector. The bottom disc has the diameter of two wavelengths, and its collar (edge) is quarter the wavelength tall. The center pillar consists of two coaxial tubes, with a quarter-wavelength slot cut into the outer tube
A radio transmitter or receiver is connected to an antenna which emits or receives the radio waves. The antenna feed system or antenna feed is the cable or conductor, and other associated equipment, which connects the transmitter or receiver with the antenna and makes the two devices compatible. In a radio transmitter, the transmitter generates an alternating current of radio frequency, and the feed system feeds the current to the antenna, which converts the power in the current to radio waves. In a radio receiver, the incoming radio waves excite tiny alternating currents in the antenna, and the feed system delivers this current to the receiver, which processes the signal.
The folded unipole antenna is a type of monopole mast radiator antenna used as a transmitting antenna mainly in the medium wave band for AM radio broadcasting stations. It consists of a vertical metal rod or mast mounted over and connected at its base to a grounding system consisting of buried wires. The mast is surrounded by a "skirt" of vertical wires electrically attached at or near the top of the mast. The skirt wires are connected by a metal ring near the mast base, and the feedline feeding power from the transmitter is connected between the ring and the ground.
A sheath current is a form of charge transfer in wires. Sheath currents can run along the outer sheath of a coaxial cable. This can be caused by a geographically proximate or remote ground potential.
Nominal impedance in electrical engineering and audio engineering refers to the approximate designed impedance of an electrical circuit or device. The term is applied in a number of different fields, most often being encountered in respect of:
A halo antenna, or halo, is a center-fed 1 /2 wavelength dipole antenna, which has been bent into a circle, with a break directly opposite the feed point. The dipole's ends are close, but do not touch, and their crossections may be broadened to form an air capacitor, whose spacing is used to adjust the antenna's resonant frequency. Most often mounted horizontally, this antenna's radiation is then approximately omnidirectional and horizontally polarized.
Curtain arrays are a class of large multielement directional radio transmitting wire antennas, used in the shortwave radio bands. They are a type of reflective array antenna, consisting of multiple wire dipole antennas, suspended in a vertical plane, often in front of a "curtain" reflector made of a flat vertical screen of many long parallel wires. These are suspended by support wires strung between pairs of tall steel towers, up to 90 m high. They are used for long-distance skywave transmission; they transmit a beam of radio waves at a shallow angle into the sky just above the horizon, which is reflected by the ionosphere back to Earth beyond the horizon. Curtain antennas are mostly used by international short wave radio stations to broadcast to large areas at transcontinental distances.
In radio systems, many different antenna types are used whose properties are especially crafted for particular applications. Antennas can be classified in various ways. The list below groups together antennas under common operating principles, following the way antennas are classified in many engineering textbooks.
