Make Wi-Fi Visible S02E01 – Omnidirectionnal Antennas

January 19, 2015

Welcome to season 2 of “Make Wi-Fi Visible”!
Previously in season 1, we presented radio frequency features using light analogies. In this new season, we are going to focus on antennas.

As we know, RF signal is invisible. So how do we know how RF will radiate out of an antenna? We used what is called an azimuth and elevation chart. These charts represent how the signal will radiate on a 360° round chart so potential buyers can easily compare several antennas.
The Azimut represent the top-down view and the Elevation represent the side view.

Reading Azimut and Elevation planes patterns can be a little bit tricky at first. It is not always easy to visualized how the signal will be transmitted.
To help you in this process, we will help you compare different type of antennas using the light analogy, once again!

EPISODE #1 - OMNIDIRECTIONNAL ANTENNAS

In terms of gain pattern, an omnidirectional antenna has:
– An Horizontal Beamwidth of 360°
– A Vertical Beamwidth between 7° and 80°

The chart bellow illustrate the RF antenna gain pattern of a 2.4 GHz omnidirectional antenna with a gain of 4dBi:

In Wi-Fi, omnidirectional antennas can come in different form factors:

The most common form factor is the embedded antenna. In fact, it is now very common to have multiple omnidirectional antennas embedded in a single access point (AP). For instance, the AP M32 from Meraki has 2 omnidirectional antennas for each frequency band (2 antennas for 2.4 GHz and 2 antennas for 5 GHz). Let’s have a look at its gain pattern in the 2.4 GHz frequency band:

As you can see, the azimut plane looks quite like the one of the chart shown earlier. However, on the elevation plane, the Meraki antennas look like they are radiating the signal in a more even direction (as equally as possible).
This is the results of having multiple omnidirectional antennas within the AP. Where there is more than 1 antenna next to each other, the radiating elements interact slightly with each other. Moreover, the higher gain you have on these antennas, the higher the elevation plane will change.

Omnidirectional antennas radiate RF in a fashion similar to the way a light bulb radiates light. They are designed to provide general coverage in all directions:

So when and where do we use omnidirectional antennas in Wi-Fi networks?
Omnidirectional antennas are use in most Wi-Fi deployments. They are often used indoor in offices, warehouses, restaurants, hotels, schools… They can also be used outdoor for point-to-multiple Wi-Fi networks.
This is also the type of antenna used in the SOHO routers most of us have at home!

Source:
– Meraki blog article on antennas : Link
– Cisco Antenna Portfolio : Link