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16th June 2019, 07:31 #1
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Antenna efficiency from S11
Hi,
how to i calculate the antenna efficiency from the antenna s11 return loss i measured from VNA.
thanks.

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16th June 2019, 09:49 #2
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19th June 2019, 07:44 #3
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23rd June 2019, 06:26 #4
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23rd June 2019, 09:31 #5
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Re: Antenna efficiency from S11
Actually, that antenna efficiency (percentage of power that is actually radiated) is a useful number and we use it in many projects. It's easy to obtain from simulation, not so easy from measurement because you need to measure the pattern over all directions.
So I don't agree with vfone: it's nothing theoretical, it's a practical and useful figure of merit for antenna performance.
What you call "terminal efficiency" is trivial: Sparameters are voltage ratio, so normalized reflected power is S11^{2} and your requested efficiency is 1S11^{2}
But as mentioned, that has nothing to do with antenna efficiency, which is defined differently.

23rd June 2019, 13:17 #6
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23rd June 2019, 13:31 #7
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Re: Antenna efficiency from S11
Reasonable matching of the antenna to your source is a requirement, so that you get your transmitter power into the antenna, at your frequency of interest.
This doesn't tell anything about radiation efficiency. There are some nicely matched wideband antennas which radiate poorly, and most of the input power is lost (heat the antenna). Antenna efficiency depends on antenna structure and sometimes on materials. For example, the popular cheap FR4 PCB material is very lossy at RF, so you can build antennas with FR4 that look fine in S11 but have poor radiation efficiency > poor performance. You can get an idea about radiation efficiency if you look at antenna gain and pattern, and compare to similar antennas.

23rd June 2019, 13:35 #8
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Re: Antenna efficiency from S11
S11 tells you how to perform optimal antenna impedance matching. This also assures maximal efficiency with a given antenna. You still don't know which part of the input power is radiated respectively dissipated.
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