nRF54L15 PCB Antenna Design

[JonCoombs]

Hi! I started designing a PCB for the nRF54L15 radio chip, which I intend to use for ESB communication between two relatively close-together (<10 meters) devices. I've been working with the example QFN layout, but wasn't sure how to handle the antenna.

Is the example QFN layout intended to connect to an external antenna? If so, what resources could I use to learn how to design a simple PCB antenna for this purpose (or preferably, what existing PCB antenna designs could I use for my PCB)?

Thanks!

[Asbjørn]

Hello Jon,

Reference layout: https://www.nordicsemi.com/Products/nRF54L15/Reference-layout

The reference schematic and layout is product and package specific. So there's a schematic and layout for the QFN variant of the nRF54L15. This provides filtering and attenuation of the radio output and a 50Ohm point for you to connect any 50Ohm antenna for the 2.4GHz band at the right end of the reference layout. The guide here might also be useful: https://devzone.nordicsemi.com/guides/hardware-design-test-and-measuring/b/nrf5x/posts/general-pcb-design-guidelines-for-nrf52-series

Antenna design guidelines: I'd recommend you to have a search around DevZone and see, there are lots of antenna options and implementations, like for example this one here:

https://devzone.nordicsemi.com/f/nordic-q-a/104586/nrf52840-pcb-antenna-design. Some use chip antenna for space, others use PCB trace antenna and a few use SMA/connector based antenna. It's up to the application to select.

DK have various antenna, but we often go for PCB trace antenna, like on the nRF54L15 DK: https://www.nordicsemi.com/Products/Development-hardware/nRF54L15-DK/Hardware-files?lang=en#infotabs 

We go for PCB traces as they are easy to tune, they are cheap, flexible and have good performance. There are other DKs and kits that have smaller antenna implementations, such as the nRF52840 Dongle design.

These are just suggestions for you to start with. Once you have a design in the works, send it over to us through a ticket here on DevZone and we'll review it for you and recommend changes and possible improvements.

Best regards

Asbjørn

[JonCoombs]

Hi Asbjørn,

Thanks for the advice! I'm interested in making a meander trace antenna, similar to the one on the nRF52840 dongle.

Would the shape and size of the meander trace be the same as in the nRF52840, or do I need to modify it?

Also, what components do I need to connect to the nRF pad for a meander trace antenna?

Do I just need the R1 resistor and the 1.5 pF capacitor (as seen on the top image in the nRF52840 dongle schematic), or do I need the J1 SWF coaxial connector (as seen on the bottom image in the nRF54L15 DK schematic)? If I don't need the J1 SWF port, should I use a 50 ohm resistor and a 1.4 pF capacitor (like in the nRF54L15 DK) or a 0 ohm resistor and 1.5 pF cap (like in the nRF52840 dongle)?

Thanks again for your help!

[Asbjørn]

Hello Jon,

You can use the shape and form as it is on the nRF52840 dongle. The components R1 and C26 needs to be determined with measurements on the actual board. This is what we call tuning the input impedance of the antenna. An antenna on one board might be close to 50Ohm input impedance, but it will not be the same on a different board. Might not be far off, but usually there's a bit of improvement to be gained from tuning on the actual board as well. It will work perfectly fine without the tuning (15-20 meters range, typically), but if you are trying to maximise the performance (beyond 20 meter), antenna tuning is recommended. 

I'd start with the R1 and C26 values from the dongle design. They will work fine. Add them after the C61 component of the nRF54L15 RF match. The C38 component on the nRF54L15 DK is to tune the antenna on the specific board. They're close in value to C26 on the dongle board, but slightly different as they are different antenna on different boards

Best regards

Asbjørn