I am designing a compact custom BLE board with the MKW41Z controller for wearable application. I have some recommendations from the antenna datasheet on the RF matching circuit and also the 50 Ohm transmission line impedance matching from the NXP FRDM-KW41Z schematic.
Of course I have replaced the "J5 and ANT1" part of the circuit from the FRDM-KW41Z schematic with the Molex MID SMT antenna [with its recommended 1.3pF and 1.8nH RF matching circuit].
And routed the PCB as close as possible to the recommended working layout in the application notes:
My problem is I cannot figure out a specific trace width to use on the RF trace from the MCU ANT pad to the antenna
If I was to pick a PCB manufacturer who makes PCBs using FR4 boards of a specific dielectric constant, board thickness and top copper thickness, like OSHPark 2oz Copper with 0.8mm FR4, how do I figure out the width of the trace required and distance between the trace and the top ground plane. I need to fix this final part in order to do via stitching and make prototypes. Any assistance will be greatly appreciated.
By any chance have you checked the Hardware Design Considerations for MKW41Z/31Z/21Z BLE and IEEE 802.15.4 Device? I believe you will find a lot of useful information regarding our recommendations in the design for the KW products.
For some reason I had access to some older version of that document. That one is more updated and precise. I will do further tweaking. I also found a formula I can use to calculate the exact transmission line dimesions on top copper given the FR-4 material properties. I did that but it's amazing how the manufacturers cannot provide precise information for the properties of the FR-4 like dielectric constant like it's given in that document. I emailed OSHPark.com and they are yet to get back. I will check other manufacturers probably using better materials for high frequency RF, but FR-4 is more affordable and is worth prototyping for now as well. I will post some notes here when am done. Thanks.