RF PCB - Design Guidline

[stenzer]

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 http://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

[PlanarMetamaterials]

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.

[SLK001]

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.