nRF52 antenna design review

[oneguy]

Hi,

we are now in the second round of prototyping - we'd like to move away from the chip-antenna based design to a PCB antenna. We have come up with two different ideas (see images enclosed).

Would anyone at Nordic comment on our ideas? Merits of each design? Once we know which way to proceed can we ask Nordic to do some antenna calcs?

Thank you for your support (... I'm a software guy and have no idea about antennas)

[FormerMember]

For proper design of a PCB antenna, I would recommend you to take a look at the whitepaper "quarter-wavelength monopole for 2.45 GHz", it explains how to design a PCB antenna. Important keypoints are the following:

• The length of the antenna should be approximately 25 mm
• For best performance, the distance from ground to the antenna should be a long as possible. Typically, there has to be a compromise between the optimal antenna and the space on the PCB (distance to ground). A distance of approximately 5mm works fine. That's what we have on the nRF51/52-DK.
• Avoid 90 degree corners: the antenna will radiate from corners. If a corner is needed, use two 45 degrees instead. Radiation from corners will disturb radiation pattern.
• Ground: The impedance of the antenna is important, and the reference of the impedance of the antenna is ground. Therefore, to get a stable impedance of the antenna, it is important to have a much ground as possible.

If there is not enough space for a monopole antenna, it is possible to use a meander antenna. The nRF51-Dongle has a such antenna. Meander antennas are quite tricky to design because they radiate from the corners, rather than from the sides, and we therefore recommend you to copy the antenna on the nRF51-Dongle. Copy the the antenna means to use the same dimensions on the antenna as on the nRF51-dongle.

For layout in general, I would recommend you to take a look at this tutorial and these design guidelines on the infocenter.