Are you an RF n00b? Maybe you know enough so that it’s not a complete blind spot in your work- enough that you ask a relative expert, like Greg Peek of Silicon Farmers when you need to lay out some high frequency traces.
Greg took a look at my initial design around connecting an SMA connector to the Cellular Module board I banged out for testing real time telemetry for RaceCapture/Pro. He quickly pointed out how I had started designing a Coplanar Wave Guide – but kind of a crappy one.
Greg provided some simple guidelines: extend out the ground plane as far as possible, and run the numbers through this calculator (one of many). The goal was to get the impedance as close as possible to 50 ohms at 900MHz.
Using the:
- Dialectric Constant (er) of 4.7 for standard FR4 circuit board
- Standard PCB Thickness of 1.575mm (.062″)
- 1oz copper thickness of 35um
I played around with difference signal trace thicknesses and spacing to ground plane:
…and came up with a combination that yielded impedance of 50.3 ohms. Close Enough!
There we go! Hope this helps you when treading into the RF waters.