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

I'm not sure that Q (or damping ratio, etc.) is even an appropriate measure
for something that isn't really a RLC circuit (for which the concept of Q is
well defined).

Consider:
1) Multiple resonances
2) Energy Loss (due to resistive loss and radiation) varies as a function of
frequency

I think Q (as in short for "quality") is really something that applies to
lumped components like capacitors and inductors, or to singly resonant
devices (i.e. cavities), where it is a measure of the resistive losses in
the component (and has, in the case of lumped components, really been
replaced by more meaningful things like ESR).

Consider also something like a multi section filter, where each section may
have a different Q, deliberately, to shape the filter characteristic. What
about something like a single section (2nd order) active filter, where the
energy out could be greater than the energy in, but could still have a 3dB
bandwidth and a corresponding Q.

I think that you are either looking at something like "bandwidth(s) over
which the match/reflected power is acceptable" or some measure like
"bandwidth over which resistive losses are acceptable"

----- Original Message -----
From: "David Jefferies" <dj_at_eryptick.net>
To: <nec-list_at_gweep.ca>
Sent: Friday, January 03, 2003 12:32 PM
Subject: NEC-LIST: Q of multiply-resonant antenna structures.

> Dear List,
>
> The definition of Q factor as stored e-m energy divided by
> dissipated plus radiated energy per radian of oscillation
> seems to me to be appropriate only to singly resonant structures.
> In the case where there are overlapping resonances of multiple
> resonators, the whole concept of Q (in the sense of centre frequency
> divided by half power bandwidth) needs revisiting.
>
> Regards
>
>
> --
> David Jefferies
> http://www.ee.surrey.ac.uk/Personal/D.Jefferies/
> http://www.eryptick.net/
> fax +44 (0)1483 534139 attn D.Jefferies
> --
> The NEC-List mailing list <nec-list_at_gweep.ca>
> http://www.gweep.ca/mailman/listinfo.cgi/nec-list

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