Ground Planes and BLE Performance

General Electronics
21

Technically, no - the dev board has copper floods on the outer layers, not planes; they are different.

Depends on how much contiguous area the top flood has, but yes, vias add impedance and this is a valid point for ground pads on the rim of the module (many ground pads are inside the pad array and so vias are unavoidable, but each pad has its own via).

22

So it turns out that the client was hiding information from me. They sent me a photo of their range test rig with the unit positioned such that the module antenna was butted right up against the metal enclosure wall. When I told them that was a Bad Idea, they finally admitted ā€œYeah, when we moved the unit away from the enclosure wall the range improved a lotā€.

image

So now Iā€™m less concerned. Will go to 1mm PCB and outer layer floods in the next spin.

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23

You just gave me chillsā€¦ back when I was working a government project using some newly developed handheld transceivers, one piece of hardware consistently fell far short of the advertised capabilityā€¦ When we drilled down to the details, their test team was using near ideal conditions, RF transparent test fixture, transmitter/antenna on a test fixture perfectly positioned relative to the groundā€¦ turns out their test team never tested the ā€œhandheldā€ transceiver while ā€œheld in a handā€ā€¦

SMH

24

Great that you got to the bottom of it. I wish I had better tools for detecting hidden information the client has that I donā€™t have.

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25

Sorry for missing this one: some weeks are heavy.

  • If you have multiple ground planes on different layers, itā€™s really important to have good via fills.
  • In any case, itā€™s important for the perimeter of the board to be nothing but ground, whether itā€™s just on one layer or multiple layers. Letā€™s say the outer 1mm from the edge of the copper.
  • If you have a power plane, or other planes, donā€™t bring them to the edges of the board.

Hereā€™s a quick and dirty trick: solder a long wire to ground on your board, and just leave it hanging. If you get much better results than without the wire, then your ground is a problem.

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26

Thanks, @jpnorair!

27

I re-spun the board

  • Adding grounded copper flood on both outer layers (in addition to the inner plane already there), with stitching vias on a 5mm grid.
  • Changing to 1mm laminate instead of 1.6mm, per the module manufacturer Lairdā€™s recommendations.

Client tested yesterday and reports a 10% improvement in range. If the improvement is real and not the result of some measurement uncertainty, itā€™s significant, given the target range of 50-100m.

Unfortunately I didnā€™t have the luxury of changing variables one at a time, so canā€™t say how much each change contributed.

In any case, the client is delighted, and I suppose Iā€™ve learned something :slight_smile:

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