Re: NEC-LIST: MININEC Shows Standing Waves at Resonance on Twinline

Dr Ian David Flintoft:
At 09:05 AM 6/11/98 +0000, you wrote:
>
>[From Chuck Counselman] Here's your problem, I believe. MININEC can not
> accurately model a
> parallel-wire transmission line, or "twinline," with such close
> spacing between the wires. It's been five years since I used MININEC,
> but I think I recall that the practical lower limit for the
> center-to-center spacing is about three times the wire diameter.
> (Perhaps someone can refine this estimate.)
>
...
>
>I have done a lot of work with parallel wire lines using NEC2 and
>agree with the above. The smallest centre-to-centre spacing to
>diameter ratio (s/d) which I have found to give an acceptable model is
>about 1.5, corresponding to a 115 Ohm line. Even this requires very
>careful segmentation of the load and feed points and probably use of
>GC cards to give varying segmentation along the line. I think the best
>VSWR I achieved for a matched line at 115 ohms was about 1.13 (~6%
>reflection) and for a 220 ohm line (s/d = 3) about 1.08 (~4%
>reflection).

Ian,

Thanks for your reply. I have sent a reply to Chuck Counselman
indicating that I tried a spacing to diameter ratio (I called it D/d)
of up to 20 with no basic change in the results. Hence, I'm still
puzzled.

(-: Jerry R. Ehman :-)
Received on Wed Jun 17 1998 - 09:41:13 EDT