Most of the people I have spoken to lately have had a minor misunderstanding about how their wireless antennas actually work. Everyone gets the part about “extending the range of the signal” correct but it is usually incorrectly attributed to active gain instead of passive gain. In the picture, below, you can see a flashlight bulb, and a flashlight. These two items can serve as pretty decent analogies for how your standard omni-directional and directional antennas work.
This is the type of antenna that will usually come on your access points by default. The purpose of the omni-directional antenna is to radiate the signal at equal strength in all directions. No man-made object will actually be able to do this perfectly since the signal will obviously be obstructed by the connector. Also, variations in the manufacturing process of the antenna elements can cause slight deviations in the coverage pattern which means the signal will never truly provide perfect 360 degree signal coverage.
A few things to remember about omni-directional antennas:
- They are designed to radiate the signal in all directions but can never do this perfectly.
- They are an example of passive gain. This means that they do not add any additional power to the signal. Instead, they focus the existing power. In this case, they usually sacrifice vertical range in order to extend the signal horizontally.
You would use this type of antenna when you wanted to direct your signal coverage into a specific area but not into others, or for point-to-point communications. Some examples of directional antenna uses would be: providing outdoor coverage and mounting the antenna on the side of the building, in warehouses to focus the signal down the isles between metal shelves, and long distance point-to-point communications.
The directional antenna can be thought of like the flashlight in the picture. If we take the omni-directional bulb and place a reflective dish around the base, we focus the light in a given direction. The same amount of energy is still being used to power the bulb but the reflective dish focuses it in one direction. Since the energy is more focused, the usable signal travels further than the original omni-directional signal does.
A few things to remember about directional antennas:
- They are designed to radiate the signal in a specific direction and can vary in beam width. Some will radiate a signal in a 120 degree coverage pattern and other can have a 45 degree beam width. The beam width you choose should depend on your specific purposes.
- They are also an example of passive gain.
So there you have the quick and dirty explanation for how your wireless antennas work. They do not add any power into the system (active gain), instead they focus the existing power to shape the signal for specific purposes. I’ve tried to remove as much technical jargon and communicate this in relatively plain English. If you would like a more technical explanation I would highly recommend checking out The Sybex Official CWNA Study Guide. It’s an amazingly comprehensive book and can be purchased in both paperback and Kindle formats.
If you found this article interesting, or would like further clarification, please leave a comment.