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5.3 Without Line-of-Sight
When line-of-sight is not possible, signal penetrates and is reflected by different objects
to reach the destination. Therefore, it is important to learn about how these materials
would affect signal propagation.
Depending on the thickness, moisture content and angle of incidence, a wall may allow
between 1% and 25% of the radio power to pass through.
Metal panel or metalized glass window will not allow much radio power to pass through.
Signal will be reflected if the panel is a mirror.
Some radio power may propagate through small holes in the panel or around metal
edges through the process of diffraction.
Material Type
Wood, Plaster, Sheetrock, Fiberglass
Uncoated Glass w/out Metal
Brick, Pressboard
Reinforced Concrete
Metal Walls, Metal Doors, Elevators, Metal Piping,
Metal Stair Cases, Metal Mesh, Metal Screening
In a non-line-of-sight situation at 2.45 GHz, it is possible to move the receive antenna
only 1 to 1 1/2" (3 to 4 cm) and see signal strength varies from 6 dB to -20 dB due to
multiple signal reflection path. Therefore, there should be about 20 dB path loss margin
to take signal fading into account.
5.4 Casing and Closure Around the Antenna
1.
Metallic structure should be kept at least 0.8" (2 cm), although 2.4" (6 cm) is
recommended away from the antenna.
2.
Any casing that encloses the antenna should be plastic. In addition, it is also wise
to avoid plastic case with dark fillers or colorants.
Figure 5.3 Materials in Buildings
42
Possible Signal Reduction
0 to 10%
5 to 35%
10 to 90%
90 to 100%
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