The datasheet for DWM1000 mentions 10mm keepouts to copper on the PCB. Is it safe to assume the same applies to any metallic surface the product containing this module is mounted on? I.e does the case need to enforce 10mm distance between antenna and outside world in the Z dimension?
Yes, for sure. It is always best to keep all metal parts (PCB tracks etc.) as far away from the antenna.
I assume that you mean the z-dimension is with the module laid flat in the y-x plane, if so, then yes, if there are metal parts it could create an RF ‘shadow’.
The application information section in the DWM1000 datasheet is really stating that there shouldn’t be anything metallic at all in the antenna’s main radiating plane. The distance ‘d’ of 10 mm is a separate recommendation to limit the carrier PCB dimension so that there’s more vertically polarised gain.
In terms of the housing that the module and carrier PCB fit in, this can be close to the antenna (the ‘d’ dimension of 10 mm doesn’t apply), but it can’t be made from metal (as electromagnetic energy can’t penetrate metal). Usually people choose a polymer with a low dielectric constant such as ABS. By doing this, attenuation is minimised, link budget maximised, etc.
Let me know if you have further questions.
I guess my question is more about usage. These units may be installed on metallic surfaces surfaces, and the only way to control it somewhat (in the Z dimension) is to design enclosure with enough separation between the antenna and the “back wall”. So is there an acceptable number that could be put on that separation distance so that the rest of the radiation pattern is affected less? I do realize the wall/metal object will create a shadow.
If the wall is very dense, the recommended distance is not less than 15 cm. This is to ensure that the wall is outside the near field of the anchor’s antenna, so you avoid de-tuning it. It’s also to avoid corruption of the channel impulse response due to the reflection from the wall that the anchor is mounted on.
We usually try and avoid mounting on metallic surfaces but you may find it’s alright. It can be desirable to use directional antennas on the wall-mounted anchors, with the directional beam pointing away from the wall.
It’s worth experimenting - you may even find that putting the anchor closer to the metallic surface causes the surface to act as a reflector - thereby creating the effect of having a directional antenna.