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I have been studying about embedded low power RF system on chips. I understand how different antennas, baluns and filters affect the quality and power drain of RF communications.

In all RF documentation there are plane polarization graphs that I do not understand.

enter image description here

Can somebody explain it in layman's terms.

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I believe this means, if you place the source (what the datasheet is describing) at x=0 z=0, and you stand far enough away on the xz plane to be in the far field, and you measure its output with a horizontally-polarized antenna, you will measure a certain received power. This power will depend on your angular location relative to the x-axis(?), and the chart shows how it will vary. – The Photon Jul 30 '12 at 20:59
I know that makes sense .. somehow- I just do not know how to imagine it. Does it mean something specific in any sense. That data sheet if a RF module btw, using an Inverted-F anteanna- if that makes any more sense. – ppumkin Jul 30 '12 at 22:07
For example, with the chart you posted, if you put your receiving antenna directly in front of it (the direction shown as 90 degrees on the chart), you measure a certain amount of power. If you move around to be off to the side (at the same distance away), you'll measure about the same power. In between, the power will vary by about +3/-6 dB. If you move around directly behind it, the power will drop to almost 12 dB lower. – The Photon Jul 30 '12 at 23:09

1 Answer

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It's a measure of how efficient the antenna is depending on the angle of the transmission/reception.

The reference is often an ideal isotropic antenna and values given in dBi, but it can be dBm (relative to 1 milliwatt), dBd (relative to a dipole), etc. As it's a 3D object, you need plots for both horizontal and vertical planes (or a 3D plot) to get the "full picture".
Microphones have similar graphs that display the same information. but for sensitivity to the SPL (sound pressure level) Here's a polar plot for a typical cardoid mic:

enter image description here

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Thanks Oli, so based on that graph the microphone has very little reception behind it self? The problem is I cannot visualise this what is being represented. – ppumkin Jul 30 '12 at 22:04
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Yes, exactly right - the microphone will not respond well at all to sound coming from the rear. If you imagine a typical directional microphone this makes sense. – Oli Glaser Jul 30 '12 at 22:38
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@ppumkin, polar plots take a bit of getting used to. On a rectangular plot, you might plot, say, signal level versus distance from source. Now, imagine that the horizontal axis is angle instead of distance. Now, imagine that you wrap the horizontal axis around a circle to better depict the angular direction. That's essentially what you see above. – Alfred Centauri Jul 30 '12 at 22:51
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@ppumkin - have a look at figures 1 and 2 of this link to see an example of what Alfred mentions. They are both from the same antenna, just with the information displayed in rectangular and polar plots. – Oli Glaser Jul 30 '12 at 22:57

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