[antennaware] Convergence problem with EZNEC

L. B. Cebik cebik@utkux.utcc.utk.edu
Wed, 19 Apr 2000 06:52:10 -0400 (EDT)


Although there might be a number of reasons for the lack of convergence,
let me suggest a few checks.

1.  When using the tapered-diameter schedule for the elements, only the
elements within 15% of 1/2 wl will be corrected when the correction factor
is on.  The elements for the other bands will be uncorrected.  Depending
on antenna design, this can throw off the gain figures.  Almost all of
the elements have some significant current on all bands, and the
uncorrected elements will thus not behave correctly.  In some multi-band
designs, this can be critical; in others it may not be critical.

2.  In NEC-2 it is best if the segments meet two criteria, especially when
elements are closely spaced:  a. The segment lengths should be about the
same throughout the model, and b. The segment junctions should line up
with each other from element to element to the degree possible.  Achieving
these goals often requires the use of more segments than even the
conservative minumum.  Minimum conservative segmentation is fine for
simple antennas.  But even on a dipole, where 5 is the absolute minimum
and 9 or 11 is conservative, the report curves smooth out with about 21
segments.  The diffrerences are tiny in a single elements, but add up in a
many-element array.  So I tend to use higher levels of segmentation to
ensure that errors do not add up in large arrays.

I do not know if either of these possible concerns is applicable to your
models, but thought I'd toss the note into the pot, just in case.



L. B. Cebik, W4RNL         /\  /\     *   /  /    /    Tel: (865) 938-6335
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