nRF52 Antenna Design Questions

[billt79]

Hi,

I need to design a small nRF52 board, with a 3cm by 3cm size. I am very new to antenna design, so i have some questions, in order to avoid ruining it. The reference PCB antenna on the nRF52 dev kit will be too big, so i was wondering if i could modify it, or move to a chip antenna. I would rather use the PCB antenna than a chip if it can be helped due to costs. Firstly i was wondering if the lobe itself could be mirrored so it faces in the other direction, which will save some space, and also i was wondering about the rf connecter aswell, and how to remove it, without changing the impedance or resonance. It also has a ground plane underneath the connector on the top layer, so i would like to know how to remove the plane and the connector. Will it just be ok to bridge it with the same size of track and remove the plane? Also i was wondering about the size of the keepout layer, if the PCB is going to be smaller than the width of the keepout, will it matter as long as the width is the same size? My main worry is that the ground plane will be too small. Also for extra info, i am looking for a range of around 10 metres, ideally with a low transmit power. The device will be worn around the wrist, which may also be a factor. Thanks in advance for your help and time.

[Anders Strand]

C15 is there for tuning purposes. Have you read the White Paper about antenna tuning? It might help.

PS. Note the small path to ground in the picture below. This becomes a small inductor, making a filter which removes some harmonic frequencies.

[billt79]

After a brief read of the white paper on tuning, i can see that it is somewhat impractical just just put a meander trace onto the pi network of the nRF52, my original plan was to do that an just mess around with the capacitance and inductance values, but the chances of me getting this even close look pretty minimal. Given any values that can be extracted from the altium design, such as size of the ground plane, antenna trace length and resistance, do you think it is possible to work out some rough values for the components in the pi network? As i have mentioned before, then antenna does not need to be perfect, just functional. There is no possible way i could afford the rental or equipment described in the white paper. We have been using the 'cut and paste' approach on all of our nRF51 antennas, and we get some good range from them, even with large variations in the application.