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I have a Fortigate AP, and need to understand its radio pattern for optimal positioning.

I've already understood the E-plane and H-plane representations and also that number on the circumference of the circles are radiuses.

But what are the values listed vertically down to the center of the circle and what do they mean, how can I equate that to any distance(in meters).

- enter image description here

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  • $\begingroup$ The E-plane patterns look completely wrong to me. They should show two bubbles, no radiation above and below the transmitter. $\endgroup$
    – tomnexus
    Jul 22, 2019 at 21:39
  • $\begingroup$ Agreed - this AP seems to have an almost perfect isotropic antenna, something which we all know is basically impossible $\endgroup$
    – Scott Earle ♦
    Jul 23, 2019 at 6:41

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The numbers arranged vertically are decibels. They tell you the relative radiant intensity in each direction. For example if in one particular direction you read 0 on that scale, and in another direction you read -3, then the power in the latter direction is half what it is in the first direction.

Translating this into a range in meters depends on the link budget, which would have to include things like additional attenuation due to walls and floors, and some margin for interference.

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  • $\begingroup$ Thanks a lot for the link on link budget ^^, however i didn't really understand this statement if in one particular direction you read 0 on that scale, and in another direction you read -3, then the power in the latter direction is half what it is in the first direction I I also wish to know why are the values negative when closer to the antenna. $\endgroup$
    – Xsmael
    Jul 22, 2019 at 18:47
  • $\begingroup$ They are not closer to the antenna. Those two circles are graphs, showing the strength of the radiated signal for 360° around the AP. The closer to the centre of the circle the lines are, the lower the radiated signal is in that direction. If you were to 'straighten' the circles out, so the zero point becomes a line at the bottom (forming an X axis) you might visualise it more easily, but showing it as a circle helps visualise it as how strong the signal will be around the antenna in all directions. $\endgroup$
    – Scott Earle ♦
    Jul 23, 2019 at 6:44

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