What are some Sterling-lWB PCB design considerations?

Question: We had a question regarding adjusting the thickness of the PCB from an RF perspective. I understand that adjusting the layerstack would change those traces that are sized and impedance matched to the current stackup, specifically the SDIO between the MCU and the LWB. But besides those, what impact say would the antenna area be if we adjusted the stackup for a thicker board? We could also add FR4 stiffener bonded to the bottom side in sections, would that affect the RF performance at all?

Answer: Per the FCC, the RF portion must match exactly, if a change in thickness between the top layer (SIP) and the GND layer (layer 2) occur, the RF traces would have to change widths which will not match the reference design and void the certification. I recommend not changing this thickness at all.  The dielectric thickness between Layer 2 to 3 and layer 3 to bottom could be change, but the SDIO lines impedance must account for the changes. I think adding a stiffener would be a better option, it shouldn't affect the RF performance if added under the module because of using the external antenna. The antenna performance could be affected by the stiffener, but the distance to the GND plane has the biggest effect to the antenna performance. So the antenna spacer thickness could be adjusted to maximize the Antenna performance.