Proper Antenna Mounting
Antennas come in many different styles and form factors, and
you have even more choices with mounting brackets. Some antennas are designed to
be mounted to a mast, others to a drop ceiling, and others to a custom bracket.
Most antenna manufacturers provide some type of mounting for the antennas.
However, not all "standard" mounting solutions will work in all situations. A
number of companies offer a wide variety of accessories for mounting antennas.
Most of these are designed for outdoor applications, but work just fine for the
indoor WLANs. However, some antennas are not sealed for outdoor use. Prior to
using any antenna outdoors, verify that the antenna is rated for outdoor
exposure. Also verify that any outdoor antenna is mounted properly to prevent
water from entering any vent holes that might exist. Another concern with
antenna mounting is to be certain they are positioned properly and they are
secure in that position. Failure to secure an antenna properly can result in
poor performance, or even the possibility of falling and causing damage or
injury.
At some sites, installation will be easy. In Figure 12-12, the Yagi antenna, the AP, and all
connections are mounted to a single piece of plywood, which in turn is mounted
to the wall. This particular installation is located at a large home-improvement
store.
Likewise, not all sites require a large number of APs and
antennas. If the application bandwidth requirement is minimal, user density is
low, and minimum bandwidth is fine, you can use a minimum number of APs to
provide adequate coverage. In Figure
12-13, the installation for a retail appliance store uses a single AP with a
single patch antenna mounted on the front wall.
Although the
previous two installations do not offer a very aesthetically pleasing system,
the location of the APs and antennas is about 25 feet off the floor and most
customers never know the devices are there.
Inexperienced survey engineers and installation teams commonly
use conventional omni-directional antennas. The antennas works well for some
sites, but as explained in Chapter 8,
these antennas tend to attract attention in sites where the public is present.
Antennas that can be either hidden well (behind the ceiling or wall) or blend
into the environment (low-profile, ceiling-mount antennas) are better suited for
this scenario.
One simple installation example is to take an AP, poke a hole
in the ceiling tile, and stick the dipole through the tile. The AP sits on top
of the tile, and the antenna hangs down as shown in Figure 12-14a. However, this method is not recommended
unless the AP is secured above the ceiling in some fashion to prevent it from
falling through the ceiling tile. A better solution is to use a conventional
omni antenna and drop-ceiling mount, as shown in Figure 12-14b.
Both of the omnidirectional antennas might entice a passer-by
to grab, pull, or otherwise disturb the antenna. Other antennas are designed to
be "stealthy" and blend in; such antennas are designed to create minimum
disturbance to the surroundings while still providing the level of performance
of a dipole antenna. Figure 12-15 shows a
profile antenna designed to clip to the grids of a drop ceiling.
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