Re: NEC-LIST:Proper Antenna Patterns

I agree entirely with what Chuck Counselman has posted. I also would be
very interested in seeing an antenna having a single source in which the
transmit pattern varies with source impedance. When multiple sources are
used, of course, the pattern does vary with source impedance because of
the interaction among sources due to mutual coupling. But I wanted to
add that NEC doesn't use a conjugate matched source on transmit. It uses
voltage sources, which have zero internal impedance. You can verify this
by noting that the source current, but not its voltage, changes as the
feedpoint impedance changes. You can simulate the effect of any source
impedance you'd like by placing a load of that impedance on the same
segment as the source. NEC will connect the load in series with the
source.

Roy Lewallen

KLysiak wrote:
>
> Colleagues,
> The complex (real and imaginary parts or amplitude and phase) antenna
> patterns for transmit and receive antennas change with termination
> impedance. Normally NEC uses an ideal conjugate matched source on transmit
> antennas. If the antenna is fed with something other than an ideal conjugate
> load (i.e. 50 ohm coax) its pattern will change.
> How can this be properly modeled in NEC? In particular, if we want to model
> a LPDA that has internal transmission lines which we want to feed with a 50
> ohm source. How do we a 50 ohm source to a segment that has an internal
> transmission line on it?
>
> Keith A. Lysiak, Ph.D.
> Southwest Research Institute
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> http://www.gweep.ca/mailman/listinfo.cgi/nec-list

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