Re: NEC-LIST: Re: resonance and Q of an antenna and scattering system

There is not a simple way to compute the stored energy needed for this
computation. It has been the subject of work for several years and led
about a half-century ago to the "fundamental limits" of antennas. The
limits computed are based on lower bounds of the stored energy and thus
give a lower bound on the Q. To get a smaller Q, you have to add loss,
that of course cuts into the efficiency and results in a false measure of
performance.

At resonance, the stored energy acts much like a tuned circuit where the
energy simply varies between the field components in time and maintains
the stored energy as constant. About the only way to get at the Q for a
specific situation is to compute the energy in a CAD package or to
estimate it by a measure of the impedance bandwidth.

Bill Davis

> Happy new year, everyone.
>
> A dicussion of the definition of Q for an antenna is helpful to us. The
> conpect of the ratio of energy stored to the energy dissipated per cycle is
> according to the definition of the circuit theory. John B. Wood pointed out
> that in the case of an antenna, the energy "dissipated" consists of that
> dissipated as heat in the antenna structure and radiated into the medium, and
> the stored energy is that contained in the reactive near field of the antenna.
> The other important problems are what is the definition of resonance of an
> antenna or an antenna array, and how to determine the stored energy contained
> in the reactive near field of the antennas. Thank you for you kind attention.
>
> Sincerely
>
> Long Li

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