Get your wireless donut right

Did you ever experience that your brand new wireless Access Point (AP) does not deliver as strong signal in your house as you expected? I did. Short investigations revealed details useful not only for fixing your home wireless network, but also for designing stable enterprise wireless environments. Putting configuration issues aside, one of the reasons for bad signal can be improper positioning of your wireless AP antennas.

The thing is that the coverage zone around your Access Point is not a sphere, but a donut. Wireless donut, so to say. And the orientation of this donut is dependent on the orientation of the antenna. If your access point has visible external antennas, they must be put in a vertical position. The “wireless donut” will be laying horizontally, providing maximum coverage in horizontal plane.

What happens to the wireless coverage field if the access point is not mounted like it is supposed to?

a) The wireless field is extended vertically. You will have much less coverage, and the neighbours above and below you – much more noise in wireless spectrum.

b) The wireless field is wrongly polarized: antenna position also defines the polarity of the emitted wave. If you want to have good reception, both sender and receiver’s antennas must be identically polarized.

Blind spot

There is one curious consequence. If your access point is more than, let’s say, 10 meters right above or below you, you may be in its blind spot. That’s why one AP might not be sufficient to cover the whole house.

Internals

Things get more complicated if your Access Point has internal antennas. They hardly ever mention in the manual what wireless field it has. Sometimes it is good for home use (the field looks almost like a ball), but sometimes not. Check few examples below.

Elevation plane:

Azimuth plane:

So for access point with internal antenna, check the manual: it must be mounted like supposed to. If they say it should lay on the floor, never attach it to the wall: it will put its wireless donut on its side.


Alex Mavrin, CCIE #7846

Visit http://www.apteriks.com and use FREE ONLINE tools for network professionals.

Advertisements

6 comments

  1. paul snoep · · Reply

    Good stuff, however……
    Coverage of the signal in your own place – or the work area – suffers from whatever objects interfere. Concrete, metal plating in doors etc. Also in an urban area, your signal might suffer from wifi-radio’s nearby transmiiting at the same frequency – as the 2.4 Ghz is subdivided in channels.
    Simple tools as the wifi analyser (Android) show whatever other signals are in plac, which might help you select the proper location of your antenna.

    1. Thanks, Paul. I do agree. Next to wireless coverage, there are many other influencing factors. However in this post I was only looking at the emission pattern.

  2. paul snoep · · Reply

    The comment field does not expand when entering text. More than 4 lines are not visible anymore. Can you fix that?

    1. Nope, this seems to be fixed in the theme design.

  3. Alex,

    Thank you for your article.

    Most of the WiFi antenna I have seen are monopole/whip designs.
    Usually they have no ground plane… So they are not true/good monopoles…

    As monopoles, the radiation pattern should differ from the picture you indicated at the top of the article. The radiation pattern is more like a sliced bagel than a donut.
    With a good monopole, no radiation is “wasted” going below the antenna’s horizon, which would typically be into the ground – if the antenna were at the ground.
    (The fact that they don’t radiate “downward” makes the half bagel slightly larger in diameter than the donut. Hence a ~2-3dBi gain.)

    The reason I bring this up is that because monopoles don’t radiate “down”, I have found that placing a WiFi AP in the second story of a house (common with cable management boxes usually placed in the master bedroom closet) you can get lousy performance on the first floor!

    For that reason, it would be best to place the AP on the first floor (though as you note, directly above it would be a hole).

    A second alternative that I’ve had surprising success with – if the AP must be on the second floor – is turning the AP (or its antennas) upside down.

    With it upside down, its (horizon) is in the attic, and you should have coverage on the first floor.

    Both my ATT and Cox routers (both were on the second floor) gave much better overall coverage in my home upside down.

    Give it a try!

    1. Hi, Rick, thanks for sharing your experience, very useful indeed!

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: