Use an Antenna with Wi-Fi

Antennas are used with Wi-Fi cards to give them a better connection to the access point broadcasting a signal.

Antennas are used with access points to add power (and range) to the access point’s radio broadcast. They are also an integral part of a Wi-Fi network that covers a substantial area. The use of antennas with your access points can greatly reduce costs in deploying a wireless local area network because you can use fewer access points than you would need without the antennas.

If you are planning to use antennas as part of your Wi-Fi network deployment, it’s important to understand the different kinds of antennas that are available.

When you are buying antennas, you need to consider the following characteristics:

Frequency

Antennas used with Wi-Fi need to be tuned to 2.4GHz (802.11b or 802.11g) or 5GHz (802.11a). The frequency of the antenna needs to match the frequency of the radio transmitter.

Power

Antennas are rated to handle a specific amount of power put out by a radio transmitter. In the case of Wi-Fi, this is not a great issue because most antennas are capable of handling the one-watt maximum transmission allowed by the FCC.

Radiation Pattern

The radiation pattern of an antenna defines the shape of the radio wave that the antenna propagates, or sends into the air. The radiation pattern that all other radiation patterns are compared to is called isotropic. In an isotropic radiation pattern, the antenna transmits radio waves in all three dimensions equally, so that the pattern represents a ball, or globe, with the antenna at its center.

Gain

The amount of gain an antenna provides means how much it increases the power of signals passed to it by the radio transmitter. The amount of gain is measured in decibels (dB), and bears a logarithmic relationship to the power input to the antenna. What you should keep in mind is that an antenna with a 3dB gain outputs double the power input to it, and an antenna with 6dB gain quadruples the power.

If you look at the specifications provided by antenna manufacturers, you will find gain measured in dBi, or gain in decibels relative to an isotropic radiation pattern. So dBi measures how much “better” a particular antenna is than if using a fictitious antenna with an isotropic radiation pattern, and it is a good measure of how effective an antenna is.