@theatrus - Thanks again for the feedback and have updated the project with your recommended changes. For the protection circuit would I use two LM5050 and MOSFET in each of the power rails. I think I get the concept where when power is detected by the LM5050 it then flip the MOSFET but I'm having trouble visualizing how I would build the circuit. A little more detail would be great. Could you also recommend a MOSFET that would be good for this application.
Ok, can you help me understand your comments about the ground a little more. I'm using a ground copper polyfill on the bottom and top of the board. This way I don't have to put copper traces all over the place. I was under the impression this is the better way to do it. Is this not the case? Or do I just have to isolate/clean up some other ground? I want to get it right but I'm not sure what to clean up.
@ziggyfish - I also made the changes to account for an active antenna like this. However, I'm not so sure I understand your comments about the 50-ohm impedance. Would I just start with the 10-ohm that the datasheet suggests and then test the impedance once I get my first board and adjust R11.
I have uploaded new images with the pollyfil turned off so you can see the traces better.
Page 15 of the LM5050 datasheet describes the selection process: N-channel, logic level, meeting continuous current and voltage ratings for the circuit, with a low but not the lowest Rds(on). However, I realized you were discussing both the Pi and the board being powered, so ORing rails doesn't buy you much since the Pi will always be powered - at best you'd isolate the supply to just the hat board and prevent powering the Pi from the HAT - not sure it's worth it.
Re: grounding. Planes are best, but you have two and very few points (1? 2?) connecting them. Ideally, the ground plane is unbroken (no or minimum number of tracks interrupting it). This is especially critical around the RF section. My suggestion would be to move as many traces to one layer as possible, and sink one or more vias directly adjacent to any ground pin to the ground plane. You can also do via stapling of the planes (unsure if the free Altiums have this as an automatic tool).
Re: RF: this looks far worse than before from what I expect. N
When they say "50 ohms" they mean impedance and 1.5GHz, not at DC. Tuning this ideally uses a VNA, which is not likely something you have kicking around. However, manufacturers generally offer reference designs which includes board layouts - follow these exactly (spacing, dimensions, component size, widths, angles, etc) if they meet the board stackup you are using (0.062 two layer).