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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