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5 Keys to Selecting the Best Antenna for Wi-Fi Applications

Friday, August 15, 2014

There are times when a customer may ask, “What kind of antenna will work in my wireless system?” Let’s take a look at the principal kinds of antennas for WIFI applications.

Choosing the Right Type of Antenna

When looking for the right antenna, there are some categories to consider. We will touch on 5 different types specifically designed for Wi-Fi and look at their applications.


1. Omni-Directional Antennas
This is the common “base” antenna used for Point-to-Multi-Point, or it can be an Omni-Directional antenna for your car. 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 two 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 it to going from point A to point B. For this type of system, please refer to Directional antennas below.

Typical Omni-Directional Wi-Fi antennas consist of Vertical Omnis, Ceiling Domes, Rubber Ducks, Small Desktops, and Mobile Vertical antennas.

2. Directional Antennas
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 include Backfires, Yagi, and Dish type antennas.

3. Yagi Antennas
Yagi antennas were the design of two Japanese people, Hidetsugu Yagi and Shintaro Uda, and are sometimes referred to as Yagi-Uda antennas. They were originally designed for radio, but are now also used for 802.11 systems. These antennas are typically very directional and are used for point to point, or to extend the range of a point to multi-point system. They have excellent signal strength and in the right circumstances can communicate for miles!

4. Backfire Antennas - The backfire is a small directional antenna with excellent gain. They look similar to a parabolic dish, but the gain isn't as high. Backfire antennas are recommended for point to point or point to multipoint systems because of the excellent gain and the good noise figures. A backfire antenna with 15 dBi of Gain is an excellent parameter for decent range.

5. Parabolic or Dish Antennas
This is where the real power is! Parabolic dish antennas put out tremendous gain but are a little hard to point and make a connection with. As the gain of an antenna increases, the antenna’s radiation pattern decreases until you have a very small window to point or aim your dish correctly. Dish antennas are almost always used as point to point for long haul systems. Parabolic dish antennas work by focusing the power to a central point and beaming the radio’s signal to a specific area, kind of like the adjustable reflector on a flashlight. These antennas are highly focused and are the perfect tool if you want to send your signal a very long distance.

5 Important Characteristics When Making a Selection

 

1. Point-to-Point Antennas

Point-to-Point systems usually involve two different wireless points, or building to building wireless connections, but there are exceptions to every rule. If the access point is across a long valley and the owner of the system wishes to share the connection with multiple users on the other side of the valley, this would demonstrate a Point to Multi-Point system, but using directional antennas.
 

2. Point to Multi-Point Antennas

Point to Multi-Point systems are usually for sharing a WLAN (Wireless Local Area Network) or a high-speed internet connection inside of your home or with neighbors (oops, we didn't say that). They can also be for WAP (Wireless Access Points) such as those found at local coffee shops, truck stops, airports, RV parks, and the ever expanding list of WAPs becoming available. These make traveling with a notebook computer extremely fun and can be a great business tool for the frequent traveler.

 
3. Range and Power

The range of the signal will depend on several factors, including power output of your wireless card or router, receive strength of the wireless card or cards you are transmitting to, and obstructions, including buildings, walls, or trees, etc., which may be in the way of your transmitting path. Since there are so many factors that can determine the overall range of your wireless system, it is impossible to cover it in this simple article. A rule of thumb, however, is to always choose an antenna which you think may be overkill. Why? Because when the power output is extremely small it is necessary to have as much gain as possible. Most wireless cards have a power output of 32 milliwatts (+15dBm), which is roughly the same amount of power it takes to light a high power LED (Light Emitting Diode). LEDs are bright, but imaging trying to see one at a large distance or through a building or trees. This is why the antenna is critical for amplifying that signal so it is as strong as possible. Why is the power output so small? Because 802.11 works at the same frequency as a microwave oven (2.4 GHz).

 
4. Gain Considerations

The gain you will require for each individual Wi-Fi antenna system will be dependent on any direct objects in your path, the distance you must cover, and the individual Wi-Fi cards or modules. These all must be taken into consideration before choosing the proper antenna system.

 
5. Interference

As with all radio systems, interference is always a problem. If you are listening to a radio and you hear static, this is interference. The same thing applies to Wi-Fi systems, however not to such a large degree. Things that cause interference with Wi-Fi systems are microwave ovens, certain lighting systems, other 802.11 access points or systems, microwave transmitters, or even high speed processors for computers. All these problems must be isolated before you can expect any significant range out of your system.

If you need help determining the correct antenna for your wireless application, please don't be afraid to ask us. After all, at Symmetry Electronics, wireless is our business! Call us at (310) 536-6190, or contact us online.

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Why partner with Symmetry Electronics? Symmetry's technical staff is specially trained by our suppliers to provide a comprehensive level of technical support. Our in-house Applications Engineers provide free design services to help customers early in the design cycle, providing solutions to save them time, money and frustration. Contact Symmetry for more information.

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