[nRF52840] Poor RF Performance on Custom PCB with Chip Antenna

RE: [nRF52840] Poor RF Performance on Custom PCB with Chip Antenna

ketiljo — Fri, 11 Sep 2020 13:52:11 GMT

Yes, C16 and L7, sorry.

It's preferable to have a ground plane instead of a power plane. From a AC point of view, they are the same, but you can't connect the power plane to the ground plane the same way you could do with an inner ground plane. It's important to use plenty of vias to connect the different ground planes together for a low impedance ground connection.

RE: [nRF52840] Poor RF Performance on Custom PCB with Chip Antenna

mkimhj — Wed, 09 Sep 2020 17:04:03 GMT

Hey ketiljo,

Thanks for the tips. When you say C1 and C7, you're referring to C16 and L7 on my schematic, correct?

TP19 was placed down so that the chip antenna could be reworked with a UFL connector for test and debug purposes. Plan on removing this for future iterations.

The bottom side is actually a 1v8 power plane instead of a ground plane... Do you think this is what's causing the lackluster performance?

RE: [nRF52840] Poor RF Performance on Custom PCB with Chip Antenna

ketiljo — Wed, 09 Sep 2020 13:20:54 GMT

Routing ground like this doesn't work well. The inductance in the tracks are too high. You need to connect the components C1 and C7 directly to the ground plane

Remove TP19 as it will affect the antenna.

The bottom side, under the RF section should be solid ground. No tracks or components here.

You also need plenty of vias to connect the top and bottom ground planes together.

When it comes to the antenna tuning components, they strongly depend on the layout, PCB size, proximity to metal and plastic etc. So mostly likely, the values from the antenna's datasheet doesn't apply to your board. Take a look at this whitepaper: https://infocenter.nordicsemi.com/pdf/nwp_017.pdf

RE: [nRF52840] Poor RF Performance on Custom PCB with Chip Antenna

mkimhj — Wed, 09 Sep 2020 07:25:27 GMT

The values for C24, L6, and L7 were taken from the Johanson datasheet:

www.johansontechnology.com/.../2450AT18A100.pdf

Below are screenshots from the layout:

RE: [nRF52840] Poor RF Performance on Custom PCB with Chip Antenna

ketiljo — Wed, 09 Sep 2020 07:22:35 GMT

The schematic is correct. But the layout plays a major role as well, how does that look like? How have you gotten the value of the antenna tuning components, C24, L6 and L7?