Re: NEC-LIST: Negative driving point impedances in phased arrays

"Peter Excell" <P.S.Excell_at_Bradford.ac.uk> writes:
> > -----Original Message-----
> > From: nec-list-bounces+p.s.excell=bradford.ac.uk_at_robomod.net
> > [mailto:nec-list-bounces+p.s.excell=bradford.ac.uk_at_robomod.net
> > ] On Behalf Of Jim Lux
> > Sent: 03 January 2005 16:17
> > To: nec-list_at_robomod.net
> > Subject: NEC-LIST: Negative driving point impedances in phased arrays
> >
> >
> > I'm looking for good conceptual explanations (potentially backed up by
> > models) for when negative driving point impedances (or
> > negative power) occurs in a phased array.

> > IMO this is only like an electric-field version of a traditional
> transformer: that is an EM-coupled device which has -ve impedance (i.e.
> a power source) at one port.

Interesting conceptual model.. A very lossy transformer, though, because,
after all, it does radiate (hopefully) a signfiicant fraction of the power.

 I would expect such a situation to occur
> routinely in most arrays, unless very widely spaced.

I don't know that "routinely" is the case (in fact, that's what I'm trying
to get a handle on). Consider that a Yagi-Uda has closely spaced elements,
but doesn't extract significant power from any of the elements. Likewise, I
think a broadside linear array with uniform excitation probably has no
negative elements, even if it's scanned somewhat off-broadside.

>
> Fritz Landstorfer (Stuttgart Univ.) did some plots of power flow around
> array elements some years ago that might give the insight you're
> seeking: they were mostly in the Archiv fuer Electronik und
> Uebertragungstechnik.

I'll take a look for this.. sounds like it might be what I'm looking for.

Jim Lux

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