Sector antenna
Encyclopedia
A sector antenna is a type of directional
microwave
antenna
with a sector
-shaped radiation pattern
. The word "sector" is used in the geometric sense; some portion of the circumference of a circle measured in degrees of arc. 60°, 90° and 120° designs are typical, often with a few degrees 'extra' to ensure overlap and mounted in multiples when wider or full-circle coverage is required (see photos below). The largest use of these antennas is as antennas for cell phone base-station sites
. They are also used for other types of mobile communications, for example in WiFi
networks. They are used for limited-range distances of around 4 to 5 km.
s for coaxial cable
(feedline), and adjustment mechanisms. For its outdoor placement, the main reflector screen
is produced from aluminum, and all internal parts are housed into a fiberglass
radome
enclosure to keep its operation stable regardless of weather conditions (see detuning
).
Grounding
is very important for an outdoor antenna so all metal parts are DC
-grounded.
The antenna's long narrow form gives it a fan-shaped radiation pattern
, wide in the horizontal direction and relatively narrow in the vertical direction. According to the radiation patterns depicted, typical antennas used in a three-sector base station
has 66° of horizontal beamwidth
. This means that the maximum gain
is achieved at 0° and its value is slightly low at the ±33° directions. At the ±60° directions, it is suggested to be a border of a sector and antenna gain is negligible there.
Vertical beamwidth is not wider than 15°, meaning 7.5° in each direction. Unlike antennas for commercial broadcast station
s - AM, FM and Television for example - which must achieve line-of-sight
over many miles or kilometers, there is usually a downward beam tilt
or downtilt so that the base station can more effectively cover its immediate area and not cause RF interference to distant cells.
The coverage area which is equal to the square of the sector's projection to the ground can be adjusted by changing electrical or mechanical downtilts. Electrical tilt is set by using a special control unit which usually is built into the antenna case, though different remote control
devices are widely produced. Mechanical downtilt is set manually by adjusting an antenna fastener
.
.
Such a construction is often called a sectorized antenna, though sometimes for brevity "sector antenna" is used as well. It has several angularly-separated sector antennas as shown on the figures at right.
Once the antenna unit is attached to a supporting structure, it has to be positioned. Positioning means not only setting a correct direction or azimuth, but setting a correct downtilt as well. By restricting emitted energy to a sub-circular arc and narrow vertical coverage the design makes efficient use of relatively low power transmitter equipment. Though absolute range is limited, this configuration allows for good data rate
s (digital information transfer measured in bits/second, sometimes given as total minus error-correction overhead), and good signal consistency within the coverage area.
Prior to positioning, grounding and lightning protection are required. As seen in the pictures, all supporting constructions have lightning rod
s.
A well-chosen downtilt setting strategy can lower the overall interference in the network. A too-aggressive downtilting strategy will however lead to an overall loss of coverage due to cells not overlapping. Downtilting can be used to solve specific problems, for example local interference problems or cells that are too large. Electrical tilting slightly reduces beam width.
In a picture on the right, there are two sector antennas with different mechanical downtilts. Note that a more vertical antenna is less visible than a mechanically tilted one - the use of purely electrical tilt with no mechanical tilt is therefore an attractive choice for aesthetic reasons which are very important for operators seeking acceptance of integrated antennas in visible locations.
Directional antenna
A directional antenna or beam antenna is an antenna which radiates greater power in one or more directions allowing for increased performance on transmit and receive and reduced interference from unwanted sources....
microwave
Microwave
Microwaves, a subset of radio waves, have wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. This broad definition includes both UHF and EHF , and various sources use different boundaries...
antenna
Antenna (radio)
An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...
with a sector
Sector
- Places :* Sector, Devon, a location in the county of Devon in south-western England* Sector, West Virginia, an unincorporated community in Hampshire County, West Virginia, United States of America- In computing :...
-shaped 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 ....
. The word "sector" is used in the geometric sense; some portion of the circumference of a circle measured in degrees of arc. 60°, 90° and 120° designs are typical, often with a few degrees 'extra' to ensure overlap and mounted in multiples when wider or full-circle coverage is required (see photos below). The largest use of these antennas is as antennas for cell phone base-station sites
Cell site
A cell site is a term used to describe a site where antennas and electronic communications equipment are placed, usually on a radio mast, tower or other high place, to create a cell in a cellular network...
. They are also used for other types of mobile communications, for example in 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...
networks. They are used for limited-range distances of around 4 to 5 km.
Design
A typical sector antenna is depicted in the figure on the right. At the bottom, there are RF connectorRF connector
A coaxial RF connector is an electrical connector designed to work at radio frequencies in the multi-megahertz range.RF connectors are typically used with coaxial cables and are designed to maintain the shielding that the coaxial design offers. Better models also minimize the change in transmission...
s for coaxial cable
Coaxial cable
Coaxial cable, or coax, has an inner conductor surrounded by a flexible, tubular insulating layer, surrounded by a tubular conducting shield. The term coaxial comes from the inner conductor and the outer shield sharing the same geometric axis...
(feedline), and adjustment mechanisms. For its outdoor placement, the main reflector screen
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...
is produced from aluminum, and all internal parts are housed into a fiberglass
Fiberglass
Glass fiber is a material consisting of numerous extremely fine fibers of glass.Glassmakers throughout history have experimented with glass fibers, but mass manufacture of glass fiber was only made possible with the invention of finer machine tooling...
radome
Radome
A radome is a structural, weatherproof enclosure that protects a microwave or radar antenna. The radome is constructed of material that minimally attenuates the electromagnetic signal transmitted or received by the antenna. In other words, the radome is transparent to radar or radio waves...
enclosure to keep its operation stable regardless of weather conditions (see detuning
Detuning
Detuning can refer to:*Musical tuning, the act of tuning an instrument or voice.*Laser detuning, the difference between an laser frequency and a resonant frequency....
).
Grounding
Ground (electricity)
In electrical engineering, ground or earth may be the reference point in an electrical circuit from which other voltages are measured, or a common return path for electric current, or a direct physical connection to the Earth....
is very important for an outdoor antenna so all metal parts are DC
Direct current
Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...
-grounded.
The antenna's long narrow form gives it a fan-shaped 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 ....
, wide in the horizontal direction and relatively narrow in the vertical direction. According to the radiation patterns depicted, typical antennas used in a three-sector base station
Cell site
A cell site is a term used to describe a site where antennas and electronic communications equipment are placed, usually on a radio mast, tower or other high place, to create a cell in a cellular network...
has 66° of horizontal beamwidth
Beamwidth
In telecommunication, the term beamwidth has the following meanings:1. In the radio regime, of an antenna pattern, the angle between the half-power points of the main lobe, when referenced to the peak effective radiated power of the main lobe....
. This means that the maximum gain
Gain
In electronics, gain is a measure of the ability of a circuit to increase the power or amplitude of a signal from the input to the output. It is usually defined as the mean ratio of the signal output of a system to the signal input of the same system. It may also be defined on a logarithmic scale,...
is achieved at 0° and its value is slightly low at the ±33° directions. At the ±60° directions, it is suggested to be a border of a sector and antenna gain is negligible there.
Vertical beamwidth is not wider than 15°, meaning 7.5° in each direction. Unlike antennas for commercial broadcast station
Broadcast station
A broadcast station may be:*a radio station*a television stationIt does not include radio networks or television networks.-See also:*Broadcasting*Broadcast network*Station...
s - AM, FM and Television for example - which must achieve line-of-sight
Line-of-sight propagation
Line-of-sight propagation refers to electro-magnetic radiation or acoustic wave propagation. Electromagnetic transmission includes light emissions traveling in a straight line...
over many miles or kilometers, there is usually a downward beam tilt
Beam tilt
Beam tilt is used in radio to aim the main lobe of the vertical plane radiation pattern of an antenna below the horizontal plane.The simplest way is mechanical beam tilt, where the antenna is physically mounted in such a manner as to lower the angle of the signal on one side...
or downtilt so that the base station can more effectively cover its immediate area and not cause RF interference to distant cells.
The coverage area which is equal to the square of the sector's projection to the ground can be adjusted by changing electrical or mechanical downtilts. Electrical tilt is set by using a special control unit which usually is built into the antenna case, though different remote control
Remote control
A remote control is a component of an electronics device, most commonly a television set, used for operating the television device wirelessly from a short line-of-sight distance.The remote control is usually contracted to remote...
devices are widely produced. Mechanical downtilt is set manually by adjusting an antenna fastener
Fastener
A fastener is a hardware device that mechanically joins or affixes two or more objects together.Fasteners can also be used to close a container such as a bag, a box, or an envelope; or they may involve keeping together the sides of an opening of flexible material, attaching a lid to a container,...
.
Use
To increase or widen the coverage area, and thus the number of served clients, several sector antennas are installed on the same supporting structure, e.g. tower or mastRadio masts and towers
Radio masts and towers are, typically, tall structures designed to support antennas for telecommunications and broadcasting, including television. They are among the tallest man-made structures...
.
Such a construction is often called a sectorized antenna, though sometimes for brevity "sector antenna" is used as well. It has several angularly-separated sector antennas as shown on the figures at right.
Once the antenna unit is attached to a supporting structure, it has to be positioned. Positioning means not only setting a correct direction or azimuth, but setting a correct downtilt as well. By restricting emitted energy to a sub-circular arc and narrow vertical coverage the design makes efficient use of relatively low power transmitter equipment. Though absolute range is limited, this configuration allows for good data rate
Data rate
Data rate can refer to:* Bit rate, or data transfer rate* Data signaling rate* Data rate units-See also:* Baud rate* Channel capacity* Throughput* Bandwidth everything in this page is falsified...
s (digital information transfer measured in bits/second, sometimes given as total minus error-correction overhead), and good signal consistency within the coverage area.
Prior to positioning, grounding and lightning protection are required. As seen in the pictures, all supporting constructions have lightning rod
Lightning rod
A lightning rod or lightning conductor is a metal rod or conductor mounted on top of a building and electrically connected to the ground through a wire, to protect the building in the event of lightning...
s.
A well-chosen downtilt setting strategy can lower the overall interference in the network. A too-aggressive downtilting strategy will however lead to an overall loss of coverage due to cells not overlapping. Downtilting can be used to solve specific problems, for example local interference problems or cells that are too large. Electrical tilting slightly reduces beam width.
In a picture on the right, there are two sector antennas with different mechanical downtilts. Note that a more vertical antenna is less visible than a mechanically tilted one - the use of purely electrical tilt with no mechanical tilt is therefore an attractive choice for aesthetic reasons which are very important for operators seeking acceptance of integrated antennas in visible locations.
See also
- AntennaAntenna (radio)An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...
- Radio frequencyRadio frequencyRadio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...
- panel antenna, a similar type used in broadcast engineeringBroadcast engineeringBroadcast engineering is the field of electrical engineering, and now to some extent computer engineering and information technology, which deals with radio and television broadcasting...