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).

Figure C-4. Mounting Sectorized Antennas

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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.