NEC-LIST: Patches versus Wire mesh

Hello all,

Been doing some validation modeling using patch commands and wire
gridding, and comparing results. Seems that in doing nearfield electric
(NE) on patches give very large E-Fields at the surfaces versus wire
grid models. For example, take the boxes below, using patch commands and
another model using wire grid, with a dipole radiating some 10 meters
distance at 30MHz. Doing a NE calculation cutting through X, Y, Z axis's
you can visualize the fields and compare. The Major differences are in
the XY plane, slicing through the middle of the boxes. The wire grid
shows very small fields, while the Surface Patch model shows HUGE
fields.

Can anyone explain why the differences, and which one of the models is
valid? Could it be that Patches are not to be used in near fields
calculations? And if so, what rules (besides 6 sided boxes) are patches
be used for?

Thanks for any help.

CM Comparison of surface patch and Wire Grid box, free space. Near
Fields.
CM Wire Box
GW 1 4 .8 -.3 0 .8 -.3 .4
.001
GM 1 6 0 0 0 0 .1 0
1
GW 10 4 .4 -.3 0 .4 -.3 .4
.001
GM 1 6 0 0 0 0 .1 0
10
GW 20 6 .8 -.3 0 .8 .3 0
.001
GM 1 4 0 0 0 0 0 .1
20
GW 30 6 .4 -.3 0 .4 .3 0
.001
GM 1 4 0 0 0 0 0 .1
30
GW 40 4 .4 -.3 .4 .8 -.3 .4
.001
GM 1 6 0 0 0 0 .1 0
40
GW 50 4 .4 -.3 0 .8 -.3 0
.001
GM 1 6 0 0 0 0 .1 0
50
GW 60 6 .5 -.3 .4 .5 .3 .4
.001
GW 61 6 .6 -.3 .4 .6 .3 .4
.001
GW 62 6 .7 -.3 .4 .7 .3 .4
.001
GW 63 6 .5 -.3 0 .5 .3 0
.001
GW 64 6 .6 -.3 0 .6 .3 0
.001
GW 65 6 .7 -.3 0 .7 .3 0
.001
GW 70 4 .4 -.3 .1 .8 -.3 .1
.001
GM 1 2 0 0 0 0 0 .1
70
GW 75 4 .5 -.3 0 .5 -.3 .4
.001
GM 1 2 0 0 0 .1 0 0
75
GW 80 4 .4 .3 .1 .8 .3 .1
.001
GM 1 2 0 0 0 0 0 .1
80
GW 85 4 .5 .3 0 .5 .3 .4
.001
GM 1 2 0 0 0 .1 0 0
85
CM Surface Patch Box
SM 4 6 .4 1 .4 .8 1 .4
'Top
SC 0 0 .8 1.6 .4
SM 4 4 .4 1 .4 .4 1 0
'Left Side
SC 0 0 .8 1 0
SM 4 4 .4 1.6 .4 .8 1.6 .4
'right Side
SC 0 0 .8 1.6 0
SM 6 4 .8 1.6 .4 .8 1 .4
'front edge
SC 0 0 .8 1 0
SM 3 2 .8 1 0 .4 1 0
'under
SC 0 0 .4 1.6 0
SM 4 6 .4 1 0 .4 1 .4
'back
SC 0 0 .4 1.6 .4
CM Dipole Antennna - 10 meters out.
GW 800 11 10 .9 -1.0 10 .9 1.0
.005
GE 0
GN -1 'free space
LD 4 800 6 6 50 '50 Ohm load
FR 0 0 0 00 30 'MHz
EX 0 800 6 00 100
NE 0 6 25 8 .2 -.5 -.2 .2
.1 .1
EN

v/r
Ken Carrigan

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