I finished laying out HACK, my first RF (2.45 GHz) layout. The sensitive part is the connection between the IC (Atmel SAM R21G18A), the balun (Johanson 2450BM15A0015), and the PCB antenna (copied from a TI app note, thank you Texas Instruments!).
I followed the suggested schematic for the SAM R21 XPlained pro with regards to the connection from chip to balun and from balun to antenna. The schematic part is here:
Before laying out, I used an edge-coupled microstrip differential impedance calculator to find a width of the two traces from IC to balun that was near 100 Ohms, while I used a coplanar waveguide calculator to find a width of the trace from balun to PCB antenna that was near 50 Ohms. My values are:
- Er:4.5 (FR4 PCB)
- PCB width: 1 mm
- Copper (trace) thickness: 1 oz/ft^2
- Traces distance or ground plane distance: 7 mils
And I got 24 mils for the 100 Ohms differential traces from IC to balun, and 55 mils for the 50 Ohms trace from balun to antenna. The layout is here: I also placed vias to ground near the 50 Ohms trace at 1/20th of the wavelength, then I also stitched the ground planes.
Before I send this out for the first run of prototypes (low budget, so the less revisions the better), can you please tell me if the math I did is correct (did I use the correct formulas?), and if this layout would perform well?