Re: NEC-LIST: Shorted Stub Modeling

John,

I have modelled transmission lines and short circuited transmission
lines as a part of antenna systems [1]. It is common to use a short
circuited stub as a part of a 2-element quad beam, to tune and phase
the reflector element. I used MININEC to model such an antenna
system.

The reflector element needs to be about 5-percent larger than the
perimeter of the driven element. One way of doing this is to make the
reflector element physically larger. Another method is to employ a
reflector element the same size as the driven element, and to lengthen
its perimeter with the shorted transmission line stub.

Since both methods, when the reflector element is tuned for maximum
forward gain, give the same pattern and gain, MININEC/NEC model the
shorted stub correctly.

To do this merely include the wires in the model, the parallel
conductors and the shorting wire. Do not space the wires too closely.
NEC works great for 450 - 600 ohm transmission lines.

73, Jack, VE2CV

[1] J.S. Belrose, "Modeling HF Antennas with MININEC --- Guidelines
and Tips from a Code User's Notebook", The ARRL Antenna Compendium,
Volume 3, 1992, pp. 156-164.

>Has anyone on the list ever modeled a shorted stub transmission line
>in NEC2? I would like to use a shorted stub to load a segment, but it
>doesn't appear that NEC2 will let me merely short the other end of the
>transmission line using the TL card. Is there a way to do this by
>properly setting the shunt admittance parameters?
>
>Thanks,
>
>John Yorko
>ITT Defense

_____________________________________________
John S. (Jack) Belrose, PhD Cantab, VE2CV
Senior Radioscientist
Radio Sciences Branch
Communications Research Centre
PO Box 11490 Stn. H
OTTAWA ON K2H 8S2
CANADA
TEL 613-998-2779
FAX 613-998-4077
e-mail <john.belrose_at_crc.ca>
_____________________________________________
Received on Wed Feb 16 2000 - 17:47:17 EST