RE: nRF52840 Meandering Antenna Placement & Layout Questions

AmbystomaLabs — Thu, 20 Apr 2017 18:11:58 GMT

For starters just lose the provision for the sma connector. Any data derived from it will be useless since it will be so far out of phase of the real circuit and will have it's own set of parasitics to deal with. The correct way to tune something like this is with an .047 semi rigid pigtail. You cut the microstip in half then use the pigtail to look at the antenna with a vna and then switch it around to look at the output of the nRF and finally come up with a match for the two.

The switch over the meander will significantly detune it and will ruin the radiation pattern. Also, you could get false switch triggering due to all the RF that will be injected into the gpio. If you truly don't care about range, this can work. But, place a shunt 10pF or so on the gpio that will get coupled to the antenna.

As far as the via feed for the antenna, you will already have made a mess out of the antenna tuning with the switch so the via will just add to the mess you have to tune.

You might want to look into other antennae topologies some are better suited to this style of device. There are smd patch antennae that will have a ground plane underneath, monopoles always sit very close to a ground plane. The meander needs a pretty large area away from a ground plane to work correctly. Another thought could be just a short terminated leaky microstrip.

I'm sure if you google a bit you can probably find half a dozen different antenna designs that would help you out.