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Firstly, the above picture is the layout recommendation of the 20737S SiP module. This module has packaged the IC, filter, crystal, EEPROM and antenna altogether under one roof.
Side A can be near to the edge of the motherboard.
The purpose of the L-shaped ground plane is to maximize the antenna efficiency (up to 40% with a maximum usable range of 50m) of the embedded antenna. Deviations will result in the reduction of range, but it may be acceptable to some as they need probably only 10m. It can sit on the top layer or underneath. Below is a picture of a top-only layout and do take note there are no component on the ground plane.
Otherwise, you may lay the ground in a two-layer arrangement as shown below. The picture were extracted from an actual layout and I think it offered a better view.
(1) Top layer (in blue)
(2) Second layer (in purple)
More details at here:
On the top layer in blue there is a trace coming out from the corner (it is a GND trace) but the datasheet clearly states
- Connect to system ground from side D of the module (pins 13–22).
- Route signal traces out of the module from side C (between pins 27 and 30) or side D (between pins 16 and 19) of the module. Traces can be overlapped to avoid routing through the keep-out area.
In our previous designs we implemented the layout exactly as descried by you plus we respected the above two points but we never get more than 10m. Is there a more detailed description on how to do the layout? The information given on the documentation is not clear for such an important aspect of the design witch is the RF requirements.