Wi-Fi Antenna Basic Concept and Common Implementation
Wi-Fi Antenna that part of a transmitting or receiving system which is designed to radiate or to receive electromagnetic waves wirelessly. An antenna can also be viewed as a transitional structure (transducer) between free-space and a transmission line (such as a coaxial line). An important property of an antenna is the ability to focus and shape the radiated power in space e.g.: it enhances the power in some wanted directions and suppresses the power in other directions.
Below is an example of a roof-mounted wi-fi antenna:
Wireless or Wifi antennas are separated into two main types, directional and omnidirectional. For long distance work there is no substitute for a good directional antenna. While focusing the transmitted signal to cover greater distance, the receive performance is also greatly enhanced. By listening in one direction only, a significant amount of ‘noise’ from other directions is eliminated, providing a better ‘signal to noise ratio‘.
Directional antennas are used for Point-to-Point or sometimes for Multi-Point systems depending on the setup. If you are trying to go from one location (say for instance your router), to another location, this is the type of antenna we recommend. Directional antennas are Backfires, Yagi, Panel and dish type antennas.
An Omni-Directional antenna would serve as your main antenna to distribute the signal to other computers or devices (such as wireless printers, PDAs, etc) in your workgroup. You can use 2 Omni-Directional antennas for a point to point system, but this is usually not recommended because there is no real point to distributing your signal all over the place when you only want to going from point A to point B. Typical Omni-Directional Wi-Fi antennas consist of Vertical Omnis, Ceiling Domes, Rubber ducks, Small Desktops and Mobile vertical antennas.
Moreover, nowadays most people try to construct homemade antennas to boost their Wi-Fi range. Below is a video of an example of it:
The performance of an antenna is measured in dB. For every 3db of gain the power is doubled. Most manufactures specify gain as dBi (dB gain over an isotropic or fictitious antenna radiating equally in all directions).
When using an antenna to increase the range of your wireless network, be careful not to violate any local laws governing output power. Because the signal is magnified in one direction the EIRP (Equivalent Isotropically radiated Power) is increased.
Basically, 2400 to 2463 MHz (channels 1-9) maximum EIRP of 4W (36dBm) and 2463 to 2483 MHz (channels 9-13) maximum EIRP of 200mW (23dBm).
As you can see, this grid or parabolic directional antenna (above) is designed to reflect the signal into a focal point. This is similar to how a magnifying glass works with light. This type of antenna usually provides the best gain and thus the longest link distance. It can focus the signal into a very fine point.
Directional antenna, yagi with bigger elements also serves to reflect signal back to the main element, thus focusing the signal from one direction.
Even though omnidirectional antennas do radiate in all directions, they too can be made to perform better by improving their gain. In this case the sphere pattern that would surround an antenna with no gain, is squashed flatter to provide better coverage out to the sides instead of wasting energy transmitting up and down.
In addition, here is a video of an advanced omnidirectional antenna with amazing features but has not been that much known.
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