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Antenna efficiency

 
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winson
Antenna Theory Regular


Joined: 12 Jul 2009
Posts: 16

PostPosted: Thu Dec 09, 2010 4:42 am    Post subject: Antenna efficiency Reply with quote

Hi friends,

What is efficiency of antenna?

I have simulate some antennas in CST and i saw the results for radiation efficiency and total efficiency, so what are the difference between this two efficiency?

Thanks a lot.
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Schubert
Antenna Wizard


Joined: 08 Apr 2009
Posts: 161

PostPosted: Thu Dec 09, 2010 5:46 am    Post subject: Efficiency Reply with quote

Antenna efficiency can be defined in a couple of ways:

(1) Radiation Efficiency

Rad Eff = (Power_Radiated)/(Power delivered to antenna )

(2) Total Efficiency

Total Eff = (Power_Radiated)/(Power The Transmitting Radio Outputs)

The difference has to do with mismatch loss. The first, radiation efficiency, ignores antenna mismatch loss, and only looks at the power delivered to the antenna.

The second, total efficiency, is technically a function of the impedance of the radio and transmission line (typically 50 Ohms). Then the mismatch loss is calculated (see gamma, the reflection coefficient or
<a href="http://www.antenna-theory.com/definitions/vswr.php">VSWR</a>. The total efficiency can be increased with an impedance matching network, the radiation efficiency cannot.

If the antenna is exactly matched to the transmission line/radio, then
the two efficiencies are the same.

Hope this clears things up
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winson
Antenna Theory Regular


Joined: 12 Jul 2009
Posts: 16

PostPosted: Sun Dec 12, 2010 6:10 am    Post subject: Reply with quote

Hi Schubert,

Thanks for the clear and detail explanation. Very Happy

After reading your comment, now i understand why the total efficiency is always lower than the radiation efficiency.

Winson
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