RE: NEC-LIST: Q of multiply-resonant antenna structures.

Doug,

I think your algebra might need checking:

Q = 2*pi*(stored energy)/(energy lost per cycle)

which can be restated as:

Q = 2*pi*(stored energy)/(energy lost per 2*pi radians)

or

Q = (stored energy)/(energy lost per radian)

is this right? it seems to work for a series RLC circuit
where the power lost per radian is RI^2/(2.pi.f) and the
peak stored energy is LI^2 (I being the rms current),
hence Q = 2.pi.f.L/R = X/R, a well known result.

All the best

Alan

-----Original Message-----
From: D. B. Miron [mailto:dbmiron_at_paulbunyan.net]
Sent: 05 January 2003 15:08
To: NEC-LIST
Subject: Re: NEC-LIST: Q of multiply-resonant antenna structures.

Good day,

I'd like to remind everybody that the energy-based definition is

Q=2*pi*(stored energy)/(energy lost per cycle)

which can be restated as

Q=(stored energy)/(energy lost per (2*pi radians)),

not (stored energy)/(energy lost per radian).

Even for simple elements or circuits, Q is a function of frequency. I agree
with Lux and Simpson that it is not very useful for complex wideband
circuits or assemblies. If, however, an antenna system has a number of
sharp resonances, Q can be found at each of these, and is meaningful
(useful).

Doug Miron

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