telecommunication Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that ...

s, a collinear antenna array (sometimes colinear antenna array) is an

array An array is a systematic arrangement of similar objects, usually in rows and columns. Things called an array include: {{TOC right Music * In twelve-tone and serial composition, the presentation of simultaneous twelve-tone sets such that the ...

dipole In physics, a dipole () is an electromagnetic phenomenon which occurs in two ways: *An electric dipole deals with the separation of the positive and negative electric charges found in any electromagnetic system. A simple example of this system ...

or quarter-wave antennas mounted in such a manner that the corresponding elements of each

antenna Antenna ( antennas or antennae) may refer to: Science and engineering * Antenna (radio), also known as an aerial, a transducer designed to transmit or receive electromagnetic (e.g., TV or radio) waves * Antennae Galaxies, the name of two collid ...

are parallel and

collinear In geometry, collinearity of a set of points is the property of their lying on a single line. A set of points with this property is said to be collinear (sometimes spelled as colinear). In greater generality, the term has been used for aligned o ...

; that is, they are located along a common axis. Collinear arrays are high gain

omnidirectional antenna In radio communication, an omnidirectional antenna is a class of antenna which radiates equal radio power in all directions perpendicular to an axis (azimuthal directions), with power varying with angle to the axis ( elevation angle), declining ...

s. Both dipoles and quarter-wavelength monopoles have an omnidirectional

radiation pattern In the field of antenna design the term radiation pattern (or antenna pattern or far-field pattern) refers to the ''directional'' (angular) dependence of the strength of the radio waves from the antenna or other source.Constantine A. Balanis: “A ...

in free space when oriented vertically; they radiate equal radio power in all

azimuth An azimuth (; from ar, اَلسُّمُوت, as-sumūt, the directions) is an angular measurement in a spherical coordinate system. More specifically, it is the horizontal angle from a cardinal direction, most commonly north. Mathematical ...

al directions perpendicular to the antenna, with the signal strength dropping to zero on the antenna axis. The purpose of stacking multiple antennas in a vertical collinear array is to increase the power radiated in horizontal directions and reduce the power radiated into the sky or down toward the earth, where it is wasted. They radiate vertically polarized radio waves. Theoretically, when stacking idealized lossless antennas in such a fashion, doubling their number will produce double the gain, with an increase of 3.01 dB. In practice, the gain realized will be below this due to imperfect radiation spread and losses. Collinear arrays are frequently constructed as a stack of dipoles, but can also be constructed as a stack of phased quarter-wave antennas. In this configuration, the individual radiators within the array are often constructed of coaxial feedlines with the center conductor of one element being connected electrically to the shield of the one above, and so on in alternating phase for as many elements are specified by gain or overall length requirements. The final or 'top' element in the stack is a quarter-wave radiator connected directly to the center conductor of the element below it. This style of collinear antenna is usually housed in a

fiberglass Fiberglass ( American English) or fibreglass (Commonwealth English) is a common type of fiber-reinforced plastic using glass fiber. The fibers may be randomly arranged, flattened into a sheet called a chopped strand mat, or woven into glass cl ...

radome A radome (a portmanteau of radar and dome) is a structural, weatherproof enclosure that protects a radar antenna. The radome is constructed of material transparent to radio waves. Radomes protect the antenna from weather and conceal antenna e ...

, to provide both support and environmental protection to the relatively fragile coaxial elements. A third type of collinear array, rarely seen outside of amateur radio VHF/UHF applications, uses half-wavelength monopole elements with phasing coils between each consecutive pair of elements to achieve the necessary phase shift. This style tends to be less efficient due to coil losses, but has the advantage that it can be constructed with the elements supporting themselves, doing away with the need for a protective radome. Collinear arrays are often used as the antennas for base stations for

land mobile radio system A land mobile radio system (LMRS) is a person-to-person voice communication system consisting of two-way radio transceivers (an audio transmitter and receiver in one unit) which can be stationary ( base station units), mobile (installed in veh ...

s that communicate with mobile

two-way radio A two-way radio is a radio that can both transmit and receive radio waves (a transceiver), unlike a radio broadcasting, broadcast receiver which only receives content. It is an audio (sound) transceiver, a transmitter and radio receiver, receive ...

s in vehicles, such as police, fire, ambulance, and taxi dispatchers. They are also sometimes used for

broadcasting Broadcasting is the distribution of audio or video content to a dispersed audience via any electronic mass communications medium, but typically one using the electromagnetic spectrum (radio waves), in a one-to-many model. Broadcasting began wi ...

References

Radio frequency antenna types Antennas (radio) {{radio-comm-stub