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expression of Q of an antenna with very low values

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Vineeth m p

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Hi all,

I am having a doubt regarding finding Q of antenna.
The classical expression on antenna Q, as the ratio of resonant frequency and band width is based upon, viewing antenna as a resonant circuit. But in a paper I read, 'Fundamental limitation of antennas' by RC Hansen, it says, this expression is holds good for high values of Q, but when the Q value comes down to 2 or lower, it becomes inaccurate. I am working with the problem of antenna miniaturization, and hence am supposed to deal with Q values lower that 2 quite often. Is there any (approximately correct at least) expression which can be used in this situation?

Thank you, regards MP.
 

A previous thread that discusses different definitions of quality factor Q and their relation https://www.edaboard.com/threads/128004/

Related to antennas, this expression is often used
Q = antenna reactance / antenna resistance

Generally, "miniaturized" (electrical small) antennas are expected to have high Q rather than low Q. Reason is the decreasing radiation resistance. Adding artificial losses will decrease Q, but is usually unwanted, for obvious reasons.

You'll find a lot of literature about this topic, e.g. this paper analyzing the theoretical achievable minimal Q of electrical small antennas
J.S.McLean: A re-examination of the fundamental limits on the radiation Q of electrically small antennas, IEEE Trans Antennas Propagat, vol 44, pp672-675, May 1996
 

low q antennas are hard to deal with. very hard to measure too! good luck
 

From frequency response find complex nature frequency f and Q = Re(f)/Im(f)/2
 

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