Trace Antenna Simulation 4 Layer Pcb

[AmaanSingh]

So I’m trying figure out when simulating a trace antenna for 4 layer pcb. Do I just simulate the top 2 layers or all 4 layers? I was looking at the Silicon labs 4 layer pcb antenna which shows the stack up and dimensions and results. https://www.silabs.com/documents/public/application-notes/an1088-designing-with-pcb-antenna.pdf. So I copied it and used it in the freecad export macro that includes openems. So when I simulate 4 layers I get something very far off from 2.4ghz while when I simulate 2 layers I get something very close to the results. I simulated the 0.8mm model. My stack up for 2 layers was the antenna on first layer and a copper plane. Port touching the feed trace to copper plane on first layer. And for second layer just a copper plane and no copper under the antenna part. So for the 4 layers, same thing and copper plane on layer 3 and 4 as well. So my question is did I do something wrong or do I just simulate the first two layers when it comes to 4 layer pcb? I didn't know the length of the board so I made the board 25.4 mm x 50 mm and they didn't state substrate so I guessed 4.3. There is no copper on layer 3 because they said no ground on layer 3. The main reason I'm doing this is I am trying to copy the setup from the silicon labs with the same stackup. I just want to see if the way I'm doing it is right so I can replicate it and tune it for another stackup. But I wanted to see if I can replicate my results by copying their dimensions and stackup.

[AmaanSingh]

Made the boxes smaller and moved the port so I can get the original dimensions of the antenna.