ZyXEL N4100 Guia Do Utilizador

 Appendix D Wireless LANs

N4100 User’s Guide

An antenna couples RF signals onto air. A transmitter within a wireless device 
sends an RF signal to the antenna, which propagates the signal through the air. 
The antenna also operates in reverse by capturing RF signals from the air. 

Positioning the antennas properly increases the range and coverage area of a 
wireless LAN. 

An antenna in the frequency of 2.4GHz (IEEE 802.11b and IEEE 802.11g) or 5GHz 
(IEEE 802.11a) is needed to communicate efficiently in a wireless LAN

A radiation pattern is a diagram that allows you to visualize the shape of the 
antenna’s coverage area. 

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.   

There are two types of antennas used for wireless LAN applications.