Re: NEC-LIST:Proper Antenna Patterns

I agree entirely with what Prof. Giuseppe Mazzarella has posted. In our research, we also confirmed that a single feed point or load point will not change the antenna current distribution by changing the source impedance, so the pattern unchanged. In the case of the single feed, if we analyse the antenna pattern, a model of the ideal excitation source is ture.
But if more than one feed point, due to mode coupling, a change of the source impedance will change the current and therefore pattern.

Sincerely

Li Long
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----- Original Message -----
From: Giuseppe Mazzarella <mazzarella_at_diee.unica.it>
To: <nec-list_at_gweep.ca>
Sent: Friday, October 12, 2001 12:24 AM
Subject: RE: NEC-LIST:Proper Antenna Patterns

> I think that the problem shuld be posed in a slightly different way:
>
> Every antenna has one or more characteristic modes [see a paper by
> Harrington ], i.e., different current distributions, which gives
> different patterns as well. The problem is whether only a single mode can
> be excited or not. In the former case the pattern does not depend on the
> feeding structure, in the latter it could.
>
> A transmitting dipole antenna is monomode, so that you cannot modify the
> pattern by simply changing the feeding. You have to modify the antenna.
>
> On the other hand, every array is multimode, and you can change the
> pattern by changing the feeding. If the array is fed by voltage sources
> (as allowed by NEC), a change of the source impedance will change the
> current and therefore the pattern.
>
> I'm not sure of what antenna Dr. Lysiak is interested in, but it seems to
> me that, as long as you have an antenna (not necessarily modelable by
> NEC) with a single input point, this antenna is necessarily single
> mode. So that you cannot change the pattern of that antenna by changing
> only the source impedance. This impedance chance is completely
> equivalent to a change in the source current.
>
> A multimode antenna must have either more than one feed point (array) or
> a distributed input section. Of course, in the latter case, the input
> impedance concept has no more meaning.
>
> Sincerely
>
> Giuseppe Mazzarella
>
> -*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*-Prof. Giuseppe
> MAZZARELLA, Ph. D. Senior Member, IEEE
> Dip. Ing. Elettrica Elettronica Univ. di CagliariPiazza
> d'Armi 09123 CAGLIARI ITALY
> Ph. + 39 070 675 5884 Fax + 39 070 675 5900
> E-mail mazzarella_at_diee.unica.it
> --
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>

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