Reference design for a nRF52 + onboard NFC?

[Gordon]

Hi,

I'm interested in making a beacon-style device with nRF52, an NFC aerial printed around the perimeter, and a CR2032 on the back. Is there a reference design for such a thing (like your nRF51 smart beacon).

Failing that, are there any design issues to be aware of (like whether the BLE aerial should be inside or outside the NRF aerial?).

Thanks!

[Øyvind Karlsen]

Hi,

First off, we don't have any direct experience with this, however here are a couple of notes I think you will find useful. The reference layout for the nRF52 can be found here, we do not have a beacon reference like the one you are describing for the nRF52. You might find the solar powered sensor beacon with reference design interesting.

If you want the 2.4 GHz antenna on the outside you will end up with a larger PCB, you might also have to use a 4 layer PCB. Having the 2.4 GHz printed antenna on the outside will mean that it will not be impacted as much by the NFC antenna.

Since the two antennas are far apart in frequency they will not couple that badly, in order to make your PCB as small as possible you will want to have the NFC antenna on the outside, and the 2.4 GHz antenna inside. There are a couple of design choices you can make.

1. Use a printed quarterwave monopole: The monopole will be impacted by the NFC antenna and radiation pattern will be affected. This is a cheap option that is likely to work, but range will probably be impacted. Be sure to leave as much space between the NFC antenna and 2.4 GHz antenna as possible.

2. Chip antenna designed for placement on a groundplane: If you purchase a chip antenna for 2.4 GHz you won't have to worry about the NFC antenna around the perimeter, however you will add to your bill of materials (BoM). This is probably the option that will give the best performance in your case.

3. If you have a lot of vertical space available you can make a quarter wave vertical antenna. This will be close to the chip antenna in performance, however it has a higher BoM.

Best regards,

Øyvind

[Øyvind Karlsen]

Well, parallel or perpendicular should probably not matter, but you will have to consult the specific antenna datasheet on this. The antenna will have a few additional components to match it to 50 ohms, this is called a pi network. For more information please see the general PCB design guidelines for nRF52.