Types Of Antennas For Wlan; Positioning Antennas - ZyXEL Communications ZyWALL USG 300 User Manual

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Appendix F Wireless LANs

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.

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

For directional antennas, point the antenna in the direction of the desired coverage area.

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