Broken RF ground plane

Hi all,

I'm designing PCB and I have 2 SMA connectors - in, out. Unfortunately, I have to route 3 signals for LEDs under (bottom layer) the coplanar waveguide which providing path to the RF signal (top layer).

Do you have any tips to do it most "correctly"?. Should the LEDs signal be placed together, should be some bigger space between them?

I'm telling myself, that when using coplanar waveguide, broken RF ground plane in bottom layer will not cause so much trouble, because I still have "top ground".



Thank you for the answer

milansedlak said:

I'm telling myself, that when using coplanar waveguide, broken RF ground plane in bottom layer will not cause so much trouble, because I still have "top ground".

Click to expand...

Sounds reasonable, just connect top and bottom near the gap. Another option would be to place a capacitor with suitable SRF across the slot, or a 0R resistor, so that RF can pass.

Don't cut the GND plane, connect the LEDs' wires by jumpers over CPWG in air..( put at least 5mm or more height and use rigid jumper wires.)

0R resistors is the answer..choosing their optimum size allow routing an RF signal between terminal pads without problems.

I would think your idea is correct. A small gap in the bottom plane should not change the impedance significantly since there is still a solid plane in the top layer. 1mm gap should be wide enough to let three 0.07mm tracks to go through.
Of course you should use enough GND vias to connect the planes in top and bottom layer together, especially along the both sides of the gap.

In addition you have an IMN there, the little distortion caused by the gap could be easily remedied by the IMN. If you are really worried, Vfone's method is a very good solution. Use big 0R resistors as bridges for the LED signals. Place a wide enough GND track in the bottom layer underneath the RF track to function as the reference plane. Three~five times of the dielectric material height is sufficient.

Thank you very much for the answers. I will pick one of the method you've mentioned.