RF PCB - Design Guidline

Hi,

I already made a couple of PCBs operating at lower frequencies. Currently I'm planing to realize a project operating in the sub - GHz range. I have seen a lot of pictures of realized RF projects. Most times the PCBs does not have a ground plane at the top layer. Is there a reason for that, beside the PCBs most times look like the are etched at home ;-). I found the following document https://www.ti.com/lit/an/swra367a/swra367a.pdf, on page 5 a top layer GND plane is recommended.

I know I should avoid a GND plane below a signal path due to due stray capacitances, as for low frequencies. Are there any other recommentations?


BR

Microwave engineering is its own field of study. Various PCB features can act as resonators and/or antennas, the choice of dielectric itself can have a large impact on performance, and characteristic impedance becomes a critical concept.

So long as you can keep all of your trace lengths electrically short (smaller than one fifth of a wavelength), you should be OK with basic rules of thumb. Otherwise... you'll need to to quite a bit of study first!

The no ground plane on top is one type of waveguide, with a ground plane on top it becomes another, and removing the bottom ground plane gives yet another type. You'll need to know what these are -- check out the terminology for microstripline, coplanar waveguide, and conductor-backed coplanar waveguide.

I've laid out many an RF PCB for both military and commercial applications and each and every one of them had a ground plane on the top layer. I use Co-Panar Waveguide for the PCB topology.