Zyxel NBG-418N v2 - Инструкция по эксплуатации - Страница 217

 Appendix E Wireless LANs

NBG-418N v2 User’s Guide

217

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An antenna in the frequency of 2.4GHz or 5GHz is needed to communicate efficiently in a wireless LAN

Ra d ia tio n Pa tte rn

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

A nte nna  G a in

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.   

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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.

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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.