Sectorized Panel Antenna
Sectorized Panel Antenna
Although there are many different style of antennas possible
for WLANs and wireless bridging, one specific antenna is particularly well
suited for local outdoor coverage: a sectorized panel antenna (see Figure C-2). Many of the cellular telephone
base-station sites use a type of sectorized antenna.
Wall-mounted omnidirectional antennas can suffer from multipath
components created by the wall itself. Covering a large area for local coverage,
such as a parking area, neighborhood, or educational or industrial campuses, can
also be a challenge for an omnidirectional antenna placed on a building.
Sectorized antennas, although similar in nature to omni antennas, offer a
solution for these situations. These antennas use a wide horizontal coverage
angle with ranges from as little as 60 degrees to as much as 180 degrees. Figure C-3 shows how using three 120-degree
sectorized antennas can provide a 360-degree range of coverage providing higher
gain than possible from an single omni, while having a very broad vertical
radiation angle.
Figure C-4 depicts the
use of three sector antennas on a single
mounting mast. Notice that you can angle the antennas slightly downward with the
mounting brackets to obtain down tilt (discussed in Chapter 2).
Notice also the possibility of physical space between the
antennas; this space helps to eliminate the receiver de-sense issues discussed
in Chapter 5, "Selecting the WLAN
Architecture and Hardware." An alternative method is to mount these at some
greater physical distance apart, such as at the edges of a building, or separate
them using longer horizontal support arms similar to those found on cellular
phone towers.
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