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Appendix B Wireless LANs
V660 User’s Guide
177
Positioning the antennas properly increases the range and coverage area of a wireless LAN.
Antenna Characteristics
Frequency
An antenna in the frequency of 2.4GHz (IEEE 802.11b) or 5GHz(IEEE 802.11a) is needed to
communicate efficiently in a wireless LAN.
Radiation Pattern
A radiation pattern is a diagram that allows you to visualize the shape of the antenna’s
coverage area.
Antenna Gain
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.
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.