Re: NEC-LIST: Wire proximity in NEC

With regard to junctions in wires in MoM calculations, junction have to be
handled specially.
There are 2 ways to handle them: 1) force the sum of the current to be
zero, or impose a Gaussian surface around the junction and account for the
junction as a conservation of charge constraint. Both are equivalent but
the Green's functions must be modified appropriately for the junction
sub-section.

ed sayre
====================================

At 12:14 PM 1/12/2004 -0800, EVonvaltie_at_aol.com wrote:
>With regard to the issue of crossing wires, the problem runs even deeper. The
>NEC approximation method uses the free-space Green's function (exp(ikR)/R)
>for the coupling beyween ANY pair of segments. This function is highly
>divergent
>as R->0 so there are going to be gross errors (i.e. singularities) whenever
>this happens, regardless of the angle between the current vector of the two
>segments. There is simply no a priori way of estimating the amount of error.
>Conceivably the one element (or two) of the Z matrix in such a case could
>easily
>overwhelm the entire calculation (the matrix is inverted by use of row/column
>pivoting which will go crazy when the divergent matrix element is reached.)
>
>The only foolproof conditions for successful solutions with NEC are cases
>using thin wire segments, relatively far spaced (compared to lambda), in free
>space or half-space with perfect ground. Anything else is a crap-shoot.
>
>Eric von Valtier K8LV
>
>--
>The NEC-List mailing list <nec-list_at_gweep.ca>
>http://www.gweep.ca/mailman/listinfo.cgi/nec-list
>
>
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