EMI Shielding on Custom Devices

Wireless Connectivity Ultra-Wideband
1

Hi all,

I have some custom PCBs, and wanted to ask about EMI shielding. How critical is it to have an EMI shield on my devices or not? Will this be application specific? I don’t seem to be having a problem without one. Will the device experience interference from its own antenna, or is this to protect it from other UWB devices and other random devices.

Thanks!

2

Hi @bstarbuck
the EMI shielding is there to avoid EMI issues (outcoming and incoming). I thing that for FCC it is mandatory to have it there.

Cheers
JK

3

From what I can tell as long as you pass all the required tests it’s not required that you have a shield can internally. But it may be required for a pre-certified modules.

But even if you plan on testing without one it’s prudent to at least allow provision for one just in case. Not fitting a part is a lot easier than trying to add a shield later.

Also take care on the size of the shield, you want to avoid anything that is matches the wavelength of your signal or it can become a resonant chamber. I’ve seen a GPS system completely killed by having a large shield over the board that happened to be exactly 1/2 of the wavelength.

4

Thank you both, this is very good insight.

5

One other note - at one point in my testing the antenna was on a 1 meter cable and we had the transmit power turned up fairly high. Everything worked fine most of the time but when the range went under about 4 meters the range would jump around, sometimes correct, sometimes 25, 50, 75 or 100 cm short.
UWB will pick the first signal not the strongest. The signal was getting picked up by the cable and antenna traces rather than the actual antenna and so skipping the 1m cable. This was DS-TWR where 4 measurements are used, depending on whether 1,2 ,3 or 4 packets skipped the cable the range would work out as one of those shorter distances.

As long as your antenna traces are short in comparison to a wavelength this isn’t an issue. If that isn’t the case then shielding is your friend.

6

Okay good to know, my transmission line is as short as possible so I think I will skip the shielding for now unless I need it for some certification as you mentioned. Thanks!