NEC-LIST: Negative resistance

I have a problem that relates to the following question answer on the
Nittany Scientific NecWinPro technical FAQ page.

  "This part was submitted by L.B. Cebik."

  "The above section on negative input impedances is only correct for
   single source models that give this result. There are instances of
   using multiple sources where one or more may correctly show a
   negative resistance. These values occur in cases where
   parasitically induced currents are greater than source currents. In
   those instances where multiple sources are used in advance of tying
   sources together via transmission lines or networks, inclusion of
   those features and specification of a single source will normally
   return a correct value for the new feed point resistance."

I am doing a NEC2 simulation feeding 46 identical 2.8 m long dipoles
(28 segments each) at equal heights (8 feet) above real ground with 46
separate sources (equal voltage). They are spread out but fairly
close together (no closer than 4 feet). Some of the sources show a
negative resistance portion of impedance. I assume this is for the
reason stated in the above FAQ answer. But is this really "correct"?
The simulation was done at 30MHz, although I have seen this happen at
other frequencies. In real life each of these antennas has its own
matching network and is fed by its own 50W transmitter. With that
kind of variation in feed point impedance, is there a possibility that
the matching networks will not work as they do with a single isolated
antenna? Can I expect anything unusual in my measurements?

Thanks,

John Yorko
Received on Fri Mar 06 1998 - 08:56:16 EST