Re: NEC-LIST: 4nec2 LATEST. Patches

Paul Thanks,
I've read about the same things somewhere on the Web, but still foreign
to me. If only the center is used and its normal vector, sounds more
like either a point source, or infinite spance in perpendicular
coordinates from the vector. It would seem like the patch represents a
perfect magnetic & electric field plate, which reflects all energy. I'm
not seeing what the use for Patch (SP) command would apply to?
I know in the 4NEC2 there are patch examples, like Coffee, which is just
a coffee can patch model with a dipole inside as radiator. Are we saying
that each patch coordinate is a perpendicular vector (normal) with a
center vector? I'm not seeing each vector/patch coordinate as a 'box'.

Can someone explain this a bit better on the used for, and against a
Patch?

I'm using it to model a Table (patched) with equipment and radiators on
it, and the legs of the table are modeled as 'wires' to the ground
plane. If I model the table with wires, are we saving that the results I
am getting using patches will be different then modeling with wires?
There are examples in 4NEC2 which use Patches for modeling 3 dimensional
structures which have radiating elements mounted on them.

Any thoughts?
v/r
Ken Carrigan

>-----Original Message-----
>From: nec-list-bounces+kcarrigan=anteon.com_at_robomod.net
>[mailto:nec-list-bounces+kcarrigan=anteon.com_at_robomod.net] On
>Behalf Of Paul Carlier
>Sent: Sunday, April 17, 2005 10:56 AM
>To: nec-list_at_robomod.net
>Subject: Re: NEC-LIST: 4nec2 LATEST. Patches
>
>Ken,
>
>Apologies if I have sent this twice, but I don't think it went
>first time!
>
>A surface patch is indeed a patch, but NEC uses the Magnetic
>Field Integral Equation for them and they can only be used to
>model completely closed structures with non-vanishing volume.
>NEC patches model only the side of the surface from which
>their normals are directed outwards and are not valid for a
>conducting plate. MFIE does not allow anything that results
>in a field inside the structure (e.g. gaps or non-perfect
>conductors). Incidentally, NEC takes no account of the shape
>of the patch even though the SP command does allow you to
>specify a shape and the co-ordinates of its corners. NEC uses
>these just to determine the co-ordinates of the patch's centre
>and its normal.
>
>For wires NEC use the Electric Field Integral Equation and
>these can, with care, be used to model thin plates and open structures.
>
>Paul Carlier
>FanField Ltd
>
>Miron,
>In nec, a surface patch is a patch, not a box. You can make it
>a box with 6 patches. Not sure though, how patches are treated
>in nec. They don't show currents as in wires, but it does seem
>to reflect EM waves. Have not tried to place a 1/4 wave wire
>inside a Patch Box to see if fields outside the box couple to
>it. Would be a neat example to try.
>How are dielectrics, other then ground plane, specified in
>nec? Or maybe they can not be?
>Thanks!
>Ken Carrigan
>
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