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Planar
Near Field Chamber for Antenna Measurements |
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12.65m
X 10m X 11.5m(L X W X H) |
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Quiet
Zone Volume and Location: 9m X 6m X 3m (LXHXW) located
in
the center both at length (12.65 m) and height (11.5m)
wise and starts from
4.5m to 7.5m from wall behind the Scanner width
(10m) wise.
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Quiet Zone
Performance: Better than –40 dB throughout the
quiet zone.
Minimum Frequency of operation: 2.0 GHz. |
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Make:
M/S Orbit /FR, Israel
Type: A-1-4953-1-9m-6m-V
Scan Area: 9m X 6m scan area
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Includes
Mounting Bracket, Metal Tower,
Azimuth Positioner and Z Axis Slide.
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Design Considerations. |
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The
Specular regions are decided from the shadow region
of
the quiet zone volume and the Planar Scanner Structures
on the
front and back Walls (of the AUT/Scanner), both
side walls,
Ceiling and Floor by considering ray –tracing
approach.
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In
addition to ray-tracing the size and shape of the
specular areas on each walls be determined in terms
of Fresnel Zones. It is recommended that at least first
three Fresnel Zones be considered as specular regions
and be covered by premier absorbers. |
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Non-specular
scattering of pyramidal and wedge type absorbers
has also been considered. By considering the tips
of pyramids as regular array of point scatterers
interaction of the plane and spherical waves was
evaluated were Pyramidal absorbers used at near
normal incidences (<45°) while wedge absorbers
are used at near grazing incidence ( > 45°). |
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18”, 12”
and 8” thick absorbers of following specs
were chosen covering most
important, less important, and least important areas,
respectively.Minimum Performance
(down in dBs) of Pyramided (FU) absorbers at near normal
incidence
w.r.t. metal
plate is as under at various
frequencies |
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| Type |
Thickness
( inches ) |
Frequency |
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2.0 GHZ |
5.0 GHZ |
18.0 GHZ |
| FU-18 Pyramidal(A) |
18 |
40 dB |
40 dB |
40 dB |
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| FU-12 Pyramidal(B) |
12 |
25 dB |
40 dB |
40 dB |
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| FU-8 Pyramidal(C) |
8 |
15 dB |
25 dB |
40 dB |
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| FU-FL-24 Walk-on |
24 |
30 dB |
30 dB |
30 dB |
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| FW-18 ( 18
Inch thick wedge ), FW-12 (12 inch thick wedge) absorbers
are also used giving better performance at near grazing
incidences w.r.t. Pyramidal absorber. Special corner blocks
were used corresponding to (C) type absorbers. Special open
cell (10 pores per inch polyurethane foam based) absorbers
with very high air permeability were used on conditioned
air dispensers. |
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