Steve N. wrote:
. . .

Side bar:
For some situations, the resistive part of this new impedance can even go
negative. This means that this antenna is absorbing power, not radiating
it. This can happen in phased, directive arrays used in broadcast. A
friend of mine described such a situation that vexed him for a while until
he improved his calculations to be more general to be applicable to this
situation (to get the correct result).
Don't ask me how to match to a negative resistance. All I know is that
given some certain directional pattern that is desired, this happens and
with the proper math you can design a matching network that works and
restores order to the universe and keeps the big bang happy (:-)

Negative feedpoint resistances in phased arrays have of course been
known for a very long time. One of the example files (4Square.EZ) which
comes with EZNEC shows an element with a slightly negative feedpoint
resistance. The accompanying "antenna notes" file includes a brief
explanation of the phenomenon.

You can't "match to" a negative resistance, because matching
requirements are determined by the load, not source, impedance, and an
element with a negative resistance is a source rather than a load. But
there's no necessity to match individual elements and, in fact,
attempting to do so complicates the problem of achieving the desired
element current ratios. One thing you can count on, though -- the
resistance of the whole array will be positive. And that's what needs
matching.

Roy Lewallen, W7EL