Design
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.
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 signal strength at the ±33° directions is half (3 dB down) from its peak value at the center. 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 broadcasting - 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.
Read more about this topic: Sector Antenna
Famous quotes containing the word design:
“With wonderful art he grinds into paint for his picture all his moods and experiences, so that all his forces may be brought to the encounter. Apparently writing without a particular design or responsibility, setting down his soliloquies from time to time, taking advantage of all his humors, when at length the hour comes to declare himself, he puts down in plain English, without quotation marks, what he, Thomas Carlyle, is ready to defend in the face of the world.”
—Henry David Thoreau (1817–1862)
“We find that Good and Evil happen alike to all Men on this Side of the Grave; and as the principle Design of Tragedy is to raise Commiseration and Terror in the Minds of the Audience, we shall defeat this great End, if we always make Virtue and Innocence happy and successful.”
—Joseph Addison (1672–1719)
“You can make as good a design out of an American turkey as a Japanese out of his native stork.”
—For the State of Illinois, U.S. public relief program (1935-1943)