Basic RF Antenna Concepts - 3

WLAN Antenna Types

Three common types of antennas for use with wireless LANs are:

• Omnidirectional / Dipole antennas
• Semi-directional antennas 
• Highly directrional antennas

Omnidirectional Antennas

Omnidirectional antennas are very common on most access points. An omnidirectional antenna has a horizontal beamwidth of 360. The vertical beamwidth will vary depending on the antenna's gain. As the gain of the antenna increases, the horizontal radiation pattern will increase, providing more horizontal coverage. However, the vertical radiation pattern will decreases, therefore providing less vertical coverage.

The shape of the radiation pattern from an omnidirectional antenna looks like a donut, as shown in the following picture.

 

Above picture from CWAP

Omnidirectional antennas are one of the most common type of antennas for indoor wireless LAN deployments. Most of this type antenna typically has a low gain of 2 dBi or 3 dBi and connects directly to an access point. 

Azimuth and elevation charts are usually available to allow  visualization of the RF radiation pattern emitted from the antenna, as shown in the following picture. 

Semidirectional Antennas

Semidirectional antennas take power from the transmitting system and focus it into more specific pattern than an omnidirectional antenna offers. Semidirectional antennas are available in various types, including patch, panel, sector and Yagi. 

Patch/Panel

In the wireless LAN world, the terms patch and panel are commonly used to describe the same type of antenna. A patch/panel antenna can have a horizaontal beamwidth of as high as 180, but usually the horizontal beamwidth is between 50 and 80. The following picture shows a 2.4Ghz flat patch antenna. 

above picture from CWAP

Azimuth and elevation charts are available for patch/panel antennas, as shown in the following picture. 

Sector

Sector antennas are often used for base station connectivity for point-to-multipoint connectivity. Sector antennas have an azimuth that varies from 90 from 180. The following are pictures for sector antennas.

above pictures from CWAP.

Yagi 

Yagi antennas are designed to be used indoors in long hallways and corridors, or outdoors for short-range bridging. Yagi antennas have vertical and horizontal beamwidths range from 25 to 65. The following are pictures for Yagi antennas.

Highly Directional Antennas

Highly directional antennas are typically parabolic dish antennas used for long-range point-to-point bridging links. Some manufacturers of parabolic dish antennas advertise ranges of 25 miles or more. Parabolic dish antennas have very narrow horizontal and vertical beamwidths. This beamwidth can range from 3 to 15. The following are pictures for Highly directional antennas.