2.
DESIGN RECOMMENDATIONS
2.1
PCB material
A multilayer (for example 4-layer) PCB is recommended. A good grounding is always
available in a multilayer design. You can also hide signals traces and supply lines inside
the PCB. By doing that they are safe from a radiating antenna and do not pick up RF so
easily.
However, if 2-layer PCB is chosen for cost effective reasons take special care of grounding,
filtering etc. A design should be small and simple with the 2-layer PCB.
Never use 1-layer PCB. It won’t work.
2.2
Grounding
•
Do not remove copper from the PCB more than needed. Use ground filling as much
as possible. However remove small floating islands after copper pour.
•
Do not place a ground plane underneath the antenna. The grounding areas under
the module should be designed as shown in Figure 1.
•
Use conductive vias separated max. 3 mm apart at the edge of the ground areas.
This prevents RF to penetrate inside the PCB. Use ground vias extensively all over
the PCB. If you allow RF freely inside the PCB, you have a potential resonator in
your hand. All the traces in (and on) the PCB are potential antennas.
•
Avoid loops.
•
Ensure that signal lines have return paths as short as possible. For example if a
signal goes to an inner layer through a via, always use ground vias around it.
Locate them tightly and symmetrically around the signal vias.
Figure 1:
Ground areas under the WT11 module
(Green color is layer 1 copper and light blue is layer 2 copper)
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