On Mar 17, 12:41*pm, Owen Duffy wrote:
"Tom Donaly" wrote :

...

Why would NEC reduce a TL two-port to a lumped load? Two-port
parameters can handle transmission line problems quite well without
the simplifying assumption that all components are of zero length.

Hi Tom,

I expect that NEC does model the propagation delay from end to end on a
transmission line. My comment was that NEC reduces a s/c TL stub to a
lumped load for the stub input end which is inserted in the vertical.

The problem here perhaps is our viewing the phasing section as a s/c stub
of two wire line, when perhaps is it better described as a single wire TL
of a half wave length.

....

I'm not sure why you want to reduce it to something less complex than
it is. Transmission lines like this support both even and odd mode
propagation, I guess what we'd normally call "transmission line
currents" and "antenna currents." It seems perfectly OK to me to let
both exist on the line at the same time. It also seems to me there is
value in doing that, because I believe there's insight to be gained
from understanding how each of those currents contributes to the net
performance of the antenna. It's important that the stub be in the
field of the antenna so that antenna current is excited on it, and
it's also important that the stub be shorted a quarter wave away from
where it attaches to the collinear elements, so that the differential
transmission line currents do the right thing.

On the other hand, you may well discover some insights looking at it
in a different way, so I hope my comments won't discourage you from
doing that!

Cheers,
Tom