Antenna modeling programs available for hams (that is, the low end
versions) are limited to two calculating cores: MININEC and NEC-2. Each
has advantages and limitations. These are spelled out in a pair of
articles accessible from my site in the Antenna Modeling series for
AntenneX. You do not need to be a subscriber to access these columns,
even though they are stored at that site.
I recommend reading these two articles so that you can compare features
and limitations of the cores relative to the range of antenna types you
anticipate using. For example, NEC-2 is better than MININEC for low wire
antennas and arrays because the S-N ground system in NEC-2 permits
accurate results down to almost ground level, whereas MININEC accuracy
goes bad below 0.2 wl. On the other hand, for complex geometries
involving wires of different diameters--either at corners or closely
spaced--MININEC is superior and NEC-2 results can often be misleading.
Once you have at least halfway decided which core you think you want to
use, then explore magazine ads and web sites to look at program features.
The first entry under antenna modeling at my site links to known web sites
for implementations of both NEC-2 and MININEC.
MININEC: the present chief versions are AO by K6STI, ELNEC by W7EL, and
NEC4WIN by Orion. AO and ELNEC are DOS programs, NEC4WIN is a Windows
program--and is in v.2 for Windows 95/98. All three programs have
different styles as well as different features. So look not only at the
question of which program has which features, but also ask yourself which
program style will be most comfortable for you to use, both now and in the
long term. (If you do not ask this last question, you will end up like
me, with copies of all of them and using each for special purposes.)
NEC-2: the present chief versions ar NEC-Win and EZNEC. EZNEC is DOS,
while NEC-Win is Windows. EZNEC has the Leeson corrections, NEC-Win Basic
does not, relative to tapered diameter elements as used on Yagis and such.
However, reports are that EZNEC will have a windows version early in 1999
and NEC-Win Basic will be replaced by NEC-Win Plus in the same time frame.
EZNEC will try to retain much of the same feel as the DOS version, while
adding some facilities. NEC-Win Plus will have a redesigned antenna
geometry page, with symbolic capability (like AO), Leeson correctives for
tapered diameter elements, and some rectangular graphing capabilities
(like SWR sweeps). There will also be available next Spring a basic
modeling text/workbook/tutorial with over 100 models and variants on disk
available for NEC-Win, although the models can be rewritten for any
version of NEC-2. I should mention that NEC-Wires is a version of NEC-2
by K6STI, but most users of this DOS program appear to use it as an
extension of AO. Nonetheless, its results and features are extensive.
Other software exists for the MININEC-NEC core systems, some of which can
cost up to $10,000 and require that you have MATHCAD as well.
I am not trying to sell any package. I have all of them in the public
domain MININEC and NEC versions up to NEC-4. They all serve me within
their limitations. In the next couple of months, there should be a 2-part
article in CQ on getting the most out of antenna patterns that uses
graphics taken from EZ/ELNEC, AO, NEC-Win, and NEC4WIN--hand counted to
try to be fair to all the software makers.
I am also not trying to make anyone wait until 1999 to purchase software,
since most software makers provide some sort of upgrading deal. However,
I thought that a review of what may be coming might be useful.
I trust these notes will be useful to anyone contemplating modeling
software. Whichever package you obtain, please run all of the tutorial or
sample models and study them, modify them, and make all of the mistakes as
soon as you can. Getting used to the programs and discovering what sorts
of output reports are sensible and which indicate a need for model or
paramerter revision are crucial steps in getting the most out of your
selection. Once past the major blunder period (which is actually rather
short if you play with the program intensively), you will be surprised
by what the program can teach you about antennas.
At the other end of the line, once you have thoroughly mastered the
program so that you design antennas with ease, you will still discover
new things about antennas from your work.
-73-
LB, W4RNL
L. B. Cebik, W4RNL /\ /\ * / / / (Off)(423) 974-7215
1434 High Mesa Drive / \/ \/\ ----/\--- (Hm) (423) 938-6335
Knoxville, Tennessee /\ \ \ \ / / || / (FAX)(423) 974-3509
37938-4443 USA / \ \ \ \ || cebik@utk.edu
URL: http://web.utk.edu/~cebik/radio.html
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