Antenna Characteristics - ZyXEL Communications ZyAIR G-5100 User Manual

ZyAIR G-5100 User's Guide
Effects within the system or outside the system can cause interference. Good planning for
frequencies and antennas can overcome most interference challenges.
Co-Channel and Adjacent Channel Interference
Co-channel interference results when another RF link is using the same channel frequency.
Adjacent-channel interference results when another RF link is using an adjacent channel
frequency.
A spectrum analyzer can be used to determine if there is any strong signals present at the site
and determine how close they are to the desired frequency. The further away from your
proposed frequency, the less likely they are to cause a problem.
Antenna placement and polarization, is the most effective method of reducing this type of
interference.
Antennas
Antennas play a key role in reducing the potential for interference. They come in a variety of
configurations that have different performance characteristics in the areas of gain and
direction. Antennas that transmit/receive in all directions are known as omni-directional, while
those that transmit/receive in one specific direction are categorized as directional.
Antennas are tuned to operate on a specific group of frequencies. The manufacturer also fixes
other specific attributes such as beam width and gain. Antennas should be selected and placed
according to your site and your application.

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.
238 Appendix G Outdoor Site Planning