RE: Required help to design very small PCB based on nRF51822

Kaja — Thu, 27 May 2021 12:10:20 GMT

Hi,

the reference design can be found under the product page on our website.
General design guidelines for the nRF51 series can be found on DevZone.

An alternative is to look at the 52 series, where the radio needs fewer external components, to make it more suitable for a smaller design.
General design guidelines for the nRF52 series

nRF52 dongle

Antenna choice is complex and depends on many factors including technical and commercial considerations. But here are some info:

Monopole, printed PCB antenna: This is easy to make and easy to tune, you also only need one impedance matching component, so it’s cost effective. Here the spacing is the issues, you need to make it about 23 mm long needs a minimum of 5 mm clearance to the ground plane. High bandwidth, making it fairly resistant to detuning. Link to our whitepaper: https://infocenter.nordicsemi.com/pdf/nwp_008.pdf?cp=12_18

Meander antenna, printed PCB antenna, ex. our dongle antenna design: Requires a smaller area than the monopole antenna, but usually requires a pi-network for tuning in addition to length. Lower bandwidth than a quarter wave monopole antenna. Here is a link to our nRF52840 Dongal design files as an example of this: https://www.nordicsemi.com/Software-and-Tools/Development-Kits/nRF52840-Dongle/Download#infotabs

Chip antenna: Higher BOM, but the antenna is small. The downside is that it usually has less gain. It requires a matching network, based on the vendors recommendations. It has a lower bandwidth than a quarter wave monopole antenna so it can be sensitive to detuning.

Considering your target of a very small form factor a chip Antenna makes sense but reducing antenna size most often results in reduced performance. Some of the parameters that suffer are:

Reduced efficiency (or gain)
Shorter range
Smaller bandwidth
Distorted radiation pattern
More critical tuning
Increased sensitivity to component and PCB spread
Increased sensitivity to external factors (“body” effect, ground plane etc.)

It is often better not to reduce antenna size too much, if you can avoid it.

As a rule we do not usually recommend specific chip antennas. The selection will depend very much on the end application design, the antenna vendors can assist on choosing the right antenna for a specific design, for example Johanson has a useful tool that helps with this selection: https://www.johansontechnology.com/chip-antenna-selection

Best regards,
Kaja

RE: Required help to design very small PCB based on nRF51822

AnupBalharpure — Tue, 25 May 2021 13:04:56 GMT

Thanks for your reply, I had gone through both the module details but again my required PCB size is smaller than that. And if possible kindly share the PCB design guide. And also suggest a selection of Antenna as size point of view, i.e. shall I use chip antenna or PCB antenna.

Thanks for your support.

RE: Required help to design very small PCB based on nRF51822

Kaja — Tue, 25 May 2021 10:45:40 GMT

Hi,

our smallest design with nRF51 series is our Smarte beacon and dongle.

Best regards,
Kaja