A Wireless Antenna is a device for transmitting an receiving radio waves over a range of radio frequencies. The greater the range of frequencies over which the antenna operates, the more broadband the antenna is said to be in its operation. Another common name for an Antenna is an Aerial.
Wi-Fi signals operate over a number of frequency bands, with the most common being the 2.4Ghz and the 5Ghz ranges. IEEE 802.11b and 802.11g standards use the 2.4 Ghz ISM (Industrial, Scientific and Medical) band and IEEE 802.11a uses the 5 Ghz Band. Radio signals in the 2.4 Ghz band travel further for a given amount of power and are less absorbed by obstacles such as walls than signals in the 5Ghz band, although the effective range of 5 Ghz signals is significantly less.
Wireless Antennas fall into 2 general categories of Omni-Directional and Directional.
Omni-Directional Antennas – These Antennas distribute the signal evenly throughout 360 degrees, thus making it ideal to reach computer devices located in any direction. A home Broadband Wireless router, for example will normally be seen with a small stick type aerial attached, which serves as an omni-directional antenna. It is normally adjustable so that it can be rotated from the vertical plane to the horizontal plane to achieve the best results. These days, in modern notebooks, the antenna will be integrated and not visible externally.
Directional Antennas – This type of aerial is designed to concentrate the radio signal strength in a single direction, and the narrower the beamwidth of the antenna, generally speaking the greater the gain. High-Gain aerials with tend to have a narrow beamwidth. Examples of directional antennas are Yagi, Dish, Horn and Patch.
The range of a wireless antenna will be dependent upon a number of factors including the power output, the receive qualities of the devices that will receive the signal and the makeup of any obstructions between say the Wireless Access Point and the receiving device. The amount of power that can radiated by a wireless device is regulated, least because we are operating in the microwave range of frequencies and too much power could be harmful. Secondly, these frequency bands are used by many different devices and interference could be a big issue.
Choosing the most suitable antenna will depend on the environment you intend to operate in. Most home and office type environment will predominately use omni-directional, ceiling-mounted antennas to ensure the greatest all round coverage. In large areas, multiple Wireless Access Points may be used and depending on the physical layout of the building, some form of directional antennas may be needed in certain areas of the building.
We will now include a brief description of some common directional antennas:
A Yagi antenna was named after the main Japanese inventor, but its full name is Yagi-Uda. It is essentially a dipole antenna with additional elements known as parasitic elements. Only the main dipole element is driven and the parasitic elements merely re-radiate the signal helping to concentrate the signal power in one direction.
These antennas can be extremely directional and can be very powerful high-gain devices that have narrow beamwidths. They are very well suited to point-to-point connection rather than point-to-multipoint. Alignment of the two dishes is critical to ensure they are propagating the radio signal towards each other. A small physical movement of one antenna or other can have a dramatic effect on received signal strength, or none at all.
Patch Antennas are normally used in small to medium office environment and are usually wall or ceiling mounted. Coverage is typically over around 50-100 degrees from where the device has been mounted but can be designed to radiate over a 180 degrees if necessary. Other names for this type of antenna are microstrip or flat panel due to the fact that they are normally constructed of a pair of metallic plates which are the antenna elements. steve stratis