NEC-LIST: Q of small antennas.

Good day,

Several times over the last few years, antenna Q has been a
hot topic on NEC-LIST. Recently, in an effort to be less
behind on my reading, I found several articles on the
subject in this year's IEEE Trans. A&P, and went back to a
referenced paper from 2000, all listed below. [1] and [3]
give different methods of calculating Q from the numerical
solution of the antenna's current and radiation. [1] argues
that the traditional expressions for minimum Q give values
that are too small, and discusses some factors that affect Q
for small antennas. [2] and [4] are re-examina;tions of
minimum Q and maximum gain/Q. For NEC users, [4] gives a
circuit-based expression for Q that I like (eq. (55))

Q=0.5[w dX/dw + |X|)/R, w=2 pi frequency.

I've left off the sub and super scripts. Be wary of typos
in [2-4]. I think, but I'm not certain, they are all
obvious.

Doug Miron

[1] Thiele, Detweiler, and Penno, "On the Lower Bound of the
Radiation Q for Electrically Small Antennas", IEEE Trans.
A&P, vol. 54, no. 6, pp1263-1269, June, 2003.
[2] W. Geyi, "Physical Limitations of Antennas", IEEE Trans.
A&P, vol. 54, no. 8, pp2116-2123, August, 2003.
[3] W. Geyi, "A Method for the Evaluation of Small Antenna
Q", IEEE Trans. A&P, vol. 54, no. 8, pp2124-2129, August,
2003.
[4] Geyi, Jarmuszewski, and Qi, "The Foster Reactance
Theorem for Antennas and Radiation Q", IEEE Trans. A&P, vol.
48, no. 3, pp401-408, March, 2000.

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