If reading the Fancom blog hasn’t already made you a master of Wi-Fi design, (Wireless or Fibre Optic?, Wi-Fi Detection and Design), then hopefully this post will help you achieve this much sought-after goal.
During the design phase of one of our projects, we had to make the decision whether to employ omnidirectional or unidirectional wireless access point antennas. Before we reveal our consultant’s choice, let’s discuss the advantages and disadvantages of each type:
An omnidirectional antenna is able to radiate or receive equally well in all directions. From the locus, the signal is emitted in the 360 degree plane to cover a certain area. Because the signal is not focused, the distance that it reaches is generally small relative to that of a unidirectional antenna. For example, a 9dBi (decibel isotropic) antenna can reach up to 360m in all directions. However, due to the emission patterns, there is often an area of poor coverage right underneath the antenna itself. Typical applications of these antennas include the generation of hotspots for Wi-Fi either indoors or outdoors where multipath environments exist.
A unidirectional antenna focuses the radiofrequency (RF) energy in one or two directions which lowers the beamwidth and overall area covered, but increases the strength of the signal and distance covered in that direction. In fact, an indoor 14dBi directional antenna can reach up to 3.2km indoors and 6.4km outdoors! However, for these antennas to work optimally they have to be pointed directly at the receivers so that the signal can be detected – this can make installation a difficult process.
Image courtesy of http://www.brck.com/.
If this description isn’t clear, try imagining the utility of a light bulb and a flashlight. A light bulb would be best to light a dark room, as it emits light in all directions (similar to an omnidirectional antenna). A flashlight, however, would be more useful for walking around outside at night due to the focused, increased range of the light (like a unidirectional antenna). Contrarily, you wouldn’t try to light a room by hanging a flashlight…and walking around at night carrying a lightbulb would not be the the most optimal choice either.
One other consideration to make when choosing between these antennas is interference. Because 802.11 operates in an unlicensed band, any other device that releases RF waves, like microwave ovens, cordless phones, radar signals from a nearby airport, or Bluetooth devices, can interfere with those from the antenna and cause signal attenuation.
Because our project involved an indoor environment, our consultants opted for omnidirectional transmitters. If you are unsure whether omni- or uni- directional antennas are the best choice for your project, feel free to give us a call!