User's Manual

Silicon Laboratories Finland Oy
Page 23 of 51
5 Layout Guidelines
WT11u is pin compatible with WT11i and WT11, despite slightly different external dimensions compared to
WT11. For a new design it recommended to follow the land pattern shown in the figure below.
Figure 15: Recommended PCB land pattern for WT11u
Do not place any copper under the antenna. The minimum recommended keep out area is shown in the Figure
16. Any dielectric material in close proximity to the antenna will effect on the impedance matching of the antenna
by lowering the resonance frequency. Figure 17 shows how different FR4 thickness under the antenna effect on
the resonance frequency. Recommended PCB thickness for the PCB is 1.6 mm – 2.8 mm. Avoid placing plastic
cover closer than 3 mm from the antenna as this will also tune the resonance frequency downwards.