NEC-LIST: Modeling annulus surface on NEC-2?

Can anyone on this list with decent experience in modeling an annulus
(disk with concentric hole) give me some indication on how accurate
the model (centroid and area of the surface patches, SP) needs to be?

If you look at the exmple in the NEC-2 Manual (by the way, the online
OCR version of the manual has a lot of missing "minus" signs), I
believe the end caps of the cylinder are modeled as two anulii with
each of the centers filled with extra patches.

Essentially, an annulus is model with a smaller surface that is
rotated, e.g.,

SP 0 0 6.89 0.0 11.0 90.0 0.0 38.4
GR 0 6

The radius of the annulus is 10 units. And, from the area, the size
of the hole can be surmised to having a radius of 3.78 units.

Notice that the NEC2 example gave the centroid as 6.89.

The actual centroid of a segment the annulus, of inner radius of 3.78
and outer radius of 10.0, should be about 7.36.

How significant is this type of deviation in modeling surfaces?

Regards,
Kok Chen
Received on Tue Mar 02 1999 - 05:50:33 EST