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Appendix B Wireless LANs
VMG5313-B10A/-B30A Series User’s Guide
373
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.
Types of Antennas for WLAN
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.
Positioning Antennas
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.