ZyXEL Communications Corporation NBG418NV2 Manual De Usuario

 Appendix D Wireless LANs

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

An antenna in the frequency of 2.4GHz or 5GHz 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.

• 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.

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.