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post #7 of (permalink) Old 2010-07-19, 01:14 PM
firimari
 
Join Date: Feb 2009
Location: Upstate NY
Posts: 180
Quote:
It would be interesting if someone models this, to see how it performs in theory.
This seems to be my current procrastination method of choice. Unfortunately these wire mesh models chew up computational resources like nobody's business.

Here's a model for an antenna that's an even increment of the mesh size, so 32"x14", with a 4"x12" hole cut out of the center. I'll work up a model that works for odd heights like the above later. Unfortunately, NEC says that this while this model has decent SWR over UHF, it's not blessed with positive gain. People with more computational patience may find variations on the antenna with this template, though. I release it to the public domain.

First the 4NEC2 template ( I have autosegmentation on, so the segment numbers are wrong here)
Code:
CM Slot Antenna
CE
SY mesh_radius=0.81407e-3
SY mesh_horz_space=0.0254
SY mesh_vert_space=0.0254
SY outer_height=14
SY inner_height=(outer_height-2)
SY outer_width=32
SY inner_width=4
CM Inner driving gap
GW 1 11 -mesh_horz_space*(inner_width/2) 0 0 mesh_horz_space*(inner_width/2) 0 0 mesh_radius
CM Top mesh
GW 2 5 0 0 0 mesh_horz_space 0 0 mesh_radius
GW 3 5 0 0 0 0 0 mesh_vert_space mesh_radius
GW 4 5 0 0 mesh_vert_space mesh_horz_space 0 mesh_vert_space mesh_radius
GM 3 outer_width-1 0 0 0 mesh_horz_space 0 0 2
GW (2+3*outer_width) 5 mesh_horz_space*outer_width 0 0 mesh_horz_space*outer_width 0 mesh_vert_space mesh_radius
GM 0 0 -45 0 0 -mesh_horz_space*outer_width/2 0 mesh_vert_space*inner_height/2 2
CM Bottom mesh
GW (3+3*outer_width) 5 0 0 0 mesh_horz_space 0 0 mesh_radius
GW (4+3*outer_width) 5 0 0 0 0 0 -mesh_vert_space mesh_radius
GW (5+3*outer_width) 5 0 0 -mesh_vert_space mesh_horz_space 0 -mesh_vert_space mesh_radius
GM 3 outer_width-1 0 0 0 mesh_horz_space 0 0 (3+3*outer_width)
GW (3+6*outer_width) 5 mesh_horz_space*outer_width 0 0 mesh_horz_space*outer_width 0 -mesh_vert_space mesh_radius
GM 0 0 45 0 0 -mesh_horz_space*outer_width/2 0 -mesh_vert_space*inner_height/2 (3+3*outer_width)
CM Flat Mesh with Hole
GW (4+6*outer_width) 5 0 0 -mesh_vert_space mesh_horz_space 0 -mesh_vert_space mesh_radius
GW (5+6*outer_width) 5 0 0 0 0 0 -mesh_vert_space mesh_radius
GM 2 inner_height-2 0 0 0 0 0 -mesh_vert_space (4+6*outer_width)
GW (2+6*outer_width+2*inner_height) 5 0 0 -mesh_vert_space*(inner_height-1) 0 0 -mesh_vert_space*inner_height mesh_radius
GM (2*inner_height-1) (outer_width-inner_width)/2-1 0 0 0 mesh_horz_space 0 0 (4+6*outer_width)
GW 4+6*outer_width+(2*inner_height-1)*(outer_width-inner_width)/2 5 (outer_width-inner_width)/2*mesh_horz_space 0 0 (outer_width-inner_width)/2*mesh_horz_space 0 -mesh_vert_space mesh_radius
GM 1 inner_height-1 0 0 0 0 0 -mesh_vert_space 4+6*outer_width+(2*inner_height-1)*(outer_width-inner_width)/2
GM 0 0 0 0 0 -mesh_horz_space*outer_width/2 0 mesh_vert_space*inner_height/2 (4+6*outer_width)
GM 2*inner_height*(outer_width-inner_width)/2 1 0 0 180 0 0 0 (4+6*outer_width)
GE	0
GN	-1
EK
EX	0	1	6	0	1	0		
FR	0	39	0	0	470	6
RP 0 1 73 1000 90 0 0 5
EN
And the actual NEC file that NEC2 computes on...
Code:
CM 
CM forw: 90, 90 ; back: 90, 270
CE
GW 1 9 -0.0508 0 0 0.0508 0 0 8.1407e-4
GW 2 3 0 0 0 0.0254 0 0 8.1407e-4
GW 3 3 0 0 0 0 0 0.0254 8.1407e-4
GW 4 3 0 0 0.0254 0.0254 0 0.0254 8.1407e-4
GM 3 31 0 0 0 0.0254 0 0 2
GW 98 3 0.8128 0 0 0.8128 0 0.0254 8.1407e-4
GM 0 0 -45 0 0 -0.4064 0 0.1524 2
GW 99 3 0 0 0 0.0254 0 0 8.1407e-4
GW 100 3 0 0 0 0 0 -0.0254 8.1407e-4
GW 101 3 0 0 -0.0254 0.0254 0 -0.0254 8.1407e-4
GM 3 31 0 0 0 0.0254 0 0 99
GW 195 3 0.8128 0 0 0.8128 0 -0.0254 8.1407e-4
GM 0 0 45 0 0 -0.4064 0 -0.1524 99
GW 196 3 0 0 -0.0254 0.0254 0 -0.0254 8.1407e-4
GW 197 3 0 0 0 0 0 -0.0254 8.1407e-4
GM 2 10 0 0 0 0 0 -0.0254 196
GW 218 3 0 0 -0.2794 0 0 -0.3048 8.1407e-4
GM 23 13 0 0 0 0.0254 0 0 196
GW 518 3 0.3556 0 0 0.3556 0 -0.0254 8.1407e-4
GM 1 11 0 0 0 0 0 -0.0254 518
GM 0 0 0 0 0 -0.4064 0 0.1524 196
GM 336 1 0 0 180 0 0 0 196
GE 0
GN -1
EK
EX 0 1 5 0 1 0
FR 0 39 0 0 470 6
RP 0 1 73 1000 90 0 0 5
XQ
PQ -1
PT -1
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