ZyXEL WAP3205 Manuel d'utilisateur télécharger pdf (Page 179)

Appendix D Wireless LANs

WAP3205 v2 User’s Guide

179

Antenna Characteristics

Frequency

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

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.

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ZyXEL WAP3205 Manuel d'utilisateur Page 179