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Typical GSM sector antenna outdoor unit

A sector antenna is a kind of directional antenna with a sector-shaped radiation pattern. In mobile communications, these antennas are typically installed in base-station sites for point-to-multipoint connections used in mobile communications. In WiFi, it is used for limited-range distances, around 4 to 5 km in practical use.



Horizontal and vertical radiation patterns, the latter with a pronounced downward beam tilt

A typical sector antenna is depicted in the figure on the right. At the bottom, there are RF connectors 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 directivity is basically achieved by antenna's narrow shape. According to radiation patterns depicted, typical antenna used in three-sector base station has 66° of horizontal beam width. 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 broadcast stations which must cover tens of 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 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.


Sector antennas installed on a short mast
Alternative installation

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 mast.

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. Even though it is for limited distance, at these limited distances it will serve clients with a high data rate.

Prior to positioning, grounding and lightning protection are performed. As seen in the pictures, all supporting constructions have lightning rods.

An antenna at bottom has bigger mechanical downtilt

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. In addition to a general downtilt strategy, applied in all cells, downtilt can be used to solve specific problems, for example local interference problems or cells that are too large.

In a picture on the right, there are two sector antennas with different mechanical downtilts.


All major telecommunication equipment manufactures have their own antennas, including:

and many others. There are lot of "antennas only" vendors, the major of them are:

and others.

See also

External links



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