Silicon Labs' A variant of modules typically require copper clearance area on the carrier board (together with a minimum size of suggested GND plane in order to achieve the possible best antenna performance). The recommended keep-out area dimensions and location for the on-module antenna are documented in the module's datasheet. Also, the A variant modules typically require to be placed at the edge of the carrier PCB.
However, there is an option to use these modules with external antennas as well. For this purpose the E variant of modules are also available.
Below are the layout recommendations in the case of using E module variants:
- There is no need for copper clearance area for the module on the carrier board.
- It is still recommended to ensure big enough continuous ground plane on the carrier board for the external monopole-type antenna. The minimum recommended GND plane size is quater-wavelength.
- 50 ohms RF port is typically accessible through an u.FL connector or a pad of the module. Via one of these connections a 50-ohm antenna can be attached, however it can also be suggested to place some placeholders for the external antenna matching components on the carrier board to be able to fine-tune the external antenna impedance to 50 ohms. A 3-element PI network can be suggested here.
- Connect the GND pads of the module directly to a well-stitched GND plane on the carrier board.
- In order to achieve the possible best antenna performance and avoid EMC immunity failures, it is also suggested to ensure continuous and large (and well-stitched) GND planes across the whole carrier board design. High density of GND via stitching is especially recommended around the RF sections and the carrier board edges.
- Also, try to get as many traces as possible buried between the top and bottom layers of the carrier board.