User's Manual

Silicon Laboratories Finland Oy
Page 24 of 51
Figure 16: Recommended metal keep put area for WT11u
Figure 17: Effect of FR4 under the antenna to the resonant frequency
Use good layout practices to avoid excessive noise coupling to supply voltage traces or sensitive analog signal
traces, such as analog audio signals. If using overlapping ground planes use stitching vias separated by max 3
mm to avoid emission from the edges of the PCB. Connect all the GND pins directly to a solid GND plane and
make sure that there is a low impedance path for the return current following the signal and supply traces all
the way from start to the end.
Edge of the PCB
Do not place
copper or any
metal within
the area
marked with
cross lines
GND area with
stitching vias
Effect of PCB thickness to the antenna impedance matching
-40
-35
-30
-25
-20
-15
-10
-5
0
2300 2350 2400 2450 2500 2550 2600
Freq (MHz)
S11 (dB)
1 mm
2 mm
3 mm
BT Band