Getting Started with EZ-BT WICED Modules
Document Number: 002-23400 Rev. **
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Figure 33. EZ-BT WICED Module Inside of a Plastic Mouse Enclosure
8 . 3 . 3
E f f e c t o f M e t a l l i c O b j e c t s
An antenna is sensitive to the presence of metallic objects in its vicinity. A metallic object shorts the electric field and
thus changes the radiation field. Depending on the size of the obstruction, electromagnetic waves go through different
diffraction patterns or may be completely shielded by the metallic object.
Metallic objects in the near-field can have a drastic impact on the radiation pattern. The thickness of the
CYBT-343026-00 module is 2.25 mm (including the shield) and the near field of this module extends up to 4 mm from
the antenna. Therefore, it is recommended that any metallic obstruction be at least 6.2 mm away from the PCB plane
to avoid negative effects to the RF performance. Cypress recommends an 8-mm gap from the module PCB plane to
any metallic enclosure.
details the required clearance from the EZ-BT WICED Module to small metal
obstructions.
Figure 34. Clearance from Small Metal Obstructions
8 . 3 . 4
R e c o m m e n d a t i o n s f o r P l a c e m e n t o ve r a L a r g e M e t a l P l a n e
The other effect of metal is the formation of an image antenna. The best practice in this case is to orient the metal
orthogonal to the antenna to ensure minimum effects. If the length or width of the plane approaches the size of the
module, it is considered a large metal object near the antenna.
details two placement options for this scenario.
Of these two placement options, option “1” should be avoided.
It is recommended to not have any large metallic objects parallel to the antenna. This has a drastic effect because the
image antenna is of opposite polarity. The interference caused by such an antenna is destructive to RF radiation.
If it is not possible to avoid a large metallic object running parallel to the module plane, you should maintain a distance
(h) of at least 30 mm. This will ensure that the interference caused by the image antenna will not be completely
destructive. The radiation will be strongly directional below the 30-mm distance; the efficiency will dramatically drop at
a distance (h) below 8 mm. At a distance (h) of around 2 mm, the radiation efficiency can go below 20%.
5 mm
Module
8 mm
6.2 mm
