Re: NEC-LIST: Modelling thick wires in NEC-2

Roland,

Sounds like you're on the right track. Just make sure to feed it
symmetrically, possibly with one source per wire. You could also
connect all the wires to another set of horizontal wires that meet in
the center of the bottom of the cylinder at a point, and then another
short, one segment vertical wire going downward from that. The short
vertical wire would contain your source. This would be preferred
because then you will have a better idea of what the impedance looks
like.

You should absolutely follow all the dimensioning and spacing rules
contained in the NEC manual. It also has some rules for wire grid
models that you must adhere to. With wire grids, you have to be very
careful in your segmentation near junctions. For wires that meet at
angles less than 90 degrees (or any angle - it just becomes more
likely that you'll encounter this problem with angles less than 90
degrees), you have to make sure the center of end segment on one wire
is at least about 0.5 radii away from the surface of any other wire.
There are a number of useful rules for wire grids in a paper called
"Verifying Wire-Grid Model Integrity with Program "Check"", by
C.W. Trueman and S.J. Kubina, published in the Winter 1990 edition of
the ACES (Applied Computational Electromagnetic Society) Journal.

John Yorko

_________________________ Reply Separator _________________________________
Subject: NEC-LIST: Modelling thick wires in NEC-2
Author: Roland Mueller <rmueller_at_rami.com> at INTERNET
Date: 8/11/98 5:31 PM

Hi,
     
I have a basic question regarding the modelling of thick antenna
elements in NEC-2.
     
I am trying to model a octave bandwidth cylindrical dipole with two
wires, 12 segments each, that have a segment length to diameter ratio
(l/d) of 0.6. I have read that for accurate calculations l/d should
be > 4. What is normally done to get around this problem?
     
I am thinking about possibly using several parallel thin wires
positioned on the surface of cylinder to model the wires.
     
Sincerely,
     
Roland Mueller
     
     
     
     
Received on Wed Aug 19 1998 - 10:28:55 EDT