nRF52840-CKAA ANT Port Impedance

[johnny89]

Is the nRF52840-CKAA port impedance for the various transmit power settings (or at least for 8dBm) available?

Alternatively, is the expected port impedance, when viewed from the antenna side into the end of the recommended matching network, roughly 50 ohms (see "Circuit configuration no. 1 for CKAA WLCSP" in nRF52840_PS_v1.7)?

[johnny89]

mathiaso said:

Yes, that is the way to do it. Look at how the output power of the fundamental frequency and the harmonic frequency change depending on the matching network.

I tweaked the network until I got > 7dBm fundamental power out and the harmonics where I'm comfortable with them. Tweaking the matching circuit to get an optimal output impedance of 50 ohms (via an S11) would not provide any good insight into harmonic performance, so looking at the output power of the fundamental and harmonics seems to be the best approach, thank you for confirming it.

What helped guide me was reverse-engineering a theoretical RF port impedance value from the proposed matching network, assuming it tweaks it exactly to 50-ohm real impedance - this landed at approximately 84+j16.5. I used this value in my simulations, and it reflected my practical observations quite well.