antenna q factor losses efficiency
How to measure Efficiency of an antenna.
Can we use Network analyser or spectrum analyzer and do the same. Do we need chamber for this measurement.
Please let me know if anyone has got anyapplication note on this.
Thanks
GVVIN
Have to use a Network Analyzer because you need S11 and S21 measurements, and for accurate measurements you need an anechoic chamber.
Antenna efficiency is: the ratio of the total radiated power [W] to the total input power [W].
Total input power is: total radiated power [W] minus power loss due to resistive loss [W]
S21 means we need a ideal antenna connected to one port and test antenna to other port, Right.
Will this hold true if the antenna is non isotropi. If antenna has some directivity.
I did some googling and found that 2 common methods used are wheeler cap method and Q factor method but the setup is not simple. any comments ?
You can only use S11 measurement. I think Balanis book has a nice and
simple but still accurate way to calculate antenna efficiency through
measurement.
Assuming that your antenna is small enough (say biggest dimension
not more than 10 cm or so) idea goes like this: In open space Q factor
includes radiation, resistance, dielectric losses. When you cover(!) the
antenna completely within a shielded metallic box, then radiation losses
dissapear and Q factor increases. There is a formula that connects Q factor
with S11 parameter. So, it's possible to relate power in open and shilded
enviroinment and hence extract radiation efficiency.
I've seen several researchers using the above procedure to get approximate
but quick results on antenna efficiency! Nice...
Hi,
book : Antenna.Theory-Balanis
http://www.amazon.com/Antenna-Theory.../dp/0471592684
page 722
may be can help you
or but the best is use simulator, CST Microwave studio fo example :)
ML