Appendix D Wireless LANs
WAP3205 v3 User’s Guide
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A nte nna C ha ra c te ristic s
Fre q ue nc y
An antenna in the frequency of 2.4GHz or 5GHz is needed to communicate efficiently in a wireless LAN
Ra d ia tio n Pa tte rn
A radiation pattern is a diagram that allows you to visualize the shape of the antenna’s coverage area.
A nte nna G a in
Antenna gain, measured in dB (decibel), is the increase in coverage within the RF beam width. Higher
antenna gain improves the range of the signal for better communications.
For an indoor site, each 1 dB increase in antenna gain results in a range increase of approximately 2.5%.
For an unobstructed outdoor site, each 1dB increase in gain results in a range increase of approximately
5%. Actual results may vary depending on the network environment.
Antenna gain is sometimes specified in dBi, which is how much the antenna increases the signal power
compared to using an isotropic antenna. An isotropic antenna is a theoretical perfect antenna that
sends out radio signals equally well in all directions. dBi represents the true gain that the antenna
provides.
Typ e s o f A nte nna s fo r WLA N
There are two types of antennas used for wireless LAN applications.
• Omni-directional antennas send the RF signal out in all directions on a horizontal plane. The coverage
area is torus-shaped (like a donut) which makes these antennas ideal for a room environment. With a
wide coverage area, it is possible to make circular overlapping coverage areas with multiple access
points.
• Directional antennas concentrate the RF signal in a beam, like a flashlight does with the light from its
bulb. The angle of the beam determines the width of the coverage pattern. Angles typically range
from 20 degrees (very directional) to 120 degrees (less directional). Directional antennas are ideal for
hallways and outdoor point-to-point applications.
Po sitio ning A nte nna s
In general, antennas should be mounted as high as practically possible and free of obstructions. In
point-to–point application, position both antennas at the same height and in a direct line of sight to
each other to attain the best performance.
For omni-directional antennas mounted on a table, desk, and so on, point the antenna up. For omni-
directional antennas mounted on a wall or ceiling, point the antenna down. For a single AP application,
place omni-directional antennas as close to the center of the coverage area as possible.
For directional antennas, point the antenna in the direction of the desired coverage area.
