[antennaware] A look at the commercial present and ham future

L. B. Cebik cebik@utkux.utcc.utk.edu
Tue, 5 Jan 1999 08:50:45 -0500 (EST)

Ken Hirschberg, K6HPX, informed me of some software relevant to full
situational modeling.  It is presently not affordable by hams ($30K +) and
may best run on large UNIX stations, but there is a site which may whet
your appetite (and possibly make you forever dissatisfied with any current
NEC package).


Follow the links to the products page, select the Microstripe Full 3-D HF
EM Field Solutions product, and then go to applications.  Two
applications--1 involving a Humber + 3 element 125 MHz Yagi, and the other
involving a 9.8 MHz descending vertical from a helicoipter--will give you
an idea of what full 3-D field analysis can yield by way of analyzing
structure interactions with antennas.

Unlike NEC structures, the Sonnet products build models from solid
"primitives" (not wire grids).  The approach of the software is not that
of NEC, which uses wires and their mutual impedances as the basis for
calculating performance.  Hence, the site may introduce you to an entirely
new language for electromagnetic analysis, if you have only NEC/MININEC as
your EM foundation.

However, the site has some extensive materials that form a background.  It
is not an introduction to the field, but reading through the material may
acquaint you with some of the operative terminology.  At the site, there
is also an on-line copy of a late 19th century biography of James C.

Back to the software.  It appears to be eminently suited to aircraft and
other relatively isolated systems.  I did not see (but may have missed in
my early AM speed reading) a ground module.  I can understand this by
taking the view that the software was originally developed for microwave
analysis and has since proven useful at VHF and HF.  Hence, even this
package needs development.

In any event, my purpose is not to get anyone to sell his or her home and
buy the software.  Instead, I just want to pass along a little info on
what is possible in the EM modeling field from a direction other than
NEC-based products.

Although not publicized, likely due to funding source restrictions, work
goes on even within method-of-moments techniques to overcome some of the
shortcomings of NEC (even through version 4) by using different
formulations/algorithms than the ones so painstakingly developed by Jerry
Burke and company at LLNL over the years.  Consequently, I suspect that we
can look forward to better cores within the next 5 years or so.  At the
same time, a lot of work is going on in the development of more powerful
interfaces so that you can more easily enter more data to form a model and
receive more output in more forms in return.

However, in my estimation, core development--whether the NEC-type or
alternatives--remains the key to perfecting situational modeling of
complex structures in interrelationship with each other.  NEC-2 was nearly
a decade old when it became generally available.  NEC-4 is approaching the
same age but remains proprietary (meaning expensive--but cheap compared to
the commercial product noted above).  So it is unclear to me just how
accessible the items under current development will be once they appear.
It may yet come to pass that those among us interested in any number of
facets of antenna performance, including detailed situational analysis
(interactions, grounds, etc.) may have to pool resources to form a "lab"
with the best extant software and do the job for a sustaining fee or
membership subscription.  Unlike NEC-2 and MININEC products, the next
generations of software may not be affordable to individuals, despite the
prospect that they may well be able to integrate all of the functions that
folks on this list have put into the wish book.  The alternative will be
to judge the present system of moving from one piece of software to
another to provide sufficiently accurate results for our ham
purposes--trading time and some uncertainty of result for the high price
of programs designed to be sold to industry at commercial prices.

I hope this note is useful to those who want a peek down the pike of
antenna modeling.



L. B. Cebik, W4RNL         /\  /\     *   /  /    /    (Off)(423) 974-7215
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