Yesterday my boards arrived and first task of designing any RF circuit board is making sure that all the lines are 50ohm(or thereabout) at the intended frequency (868MHz and 917MHz in my case), so few boards had to be sacrificed to determine the values of components for antenna matching.

Because of stability only NP0 capacitors were used.

For testing I used a PCB with only RF line and DC feed components mounted and a semi-rigid coaxial cable with SMA connector soldered where RF pin of the LoRa module will be.

As load I was switching between direct 50ohm termination and a stub SMA monopole antenna.

Beside the main board, the solar power supply circuit also needed to be tested, but luckily the already planed ferrite bead for power injection was all it was necessary to get 50ohms

Final results of S11 parameter were around:

-30dB to -40dB on power supply + antenna

-25dB for the sensor board

-12db for the ESP compatible PCB module (worse results were expected since PCB antennas always have lower performance than proper ones)