I am using the nRF24L01 + circuit on a PCB made according to reference design.
Can I use a 0.5 or 0.6 mm thick PCB? Reference design is made on 1.6mm PCB thick.
1.6mm is by far recommended for nRF24 and nRF51, thinner substrates tend to raise harmonic emissions. You will have to measure this (you should either way) tune the matching network, but even then it might be hard to bring the harmonics below required levels. In this case you will have to turn down the TX power, which in the end reduces your max wireless range.
Thank you for the quick reasponse :). Do you have test results on how the harmonic level for different PCB thicknesses increases?
No, this hugely varies between every design, based on differences in layout, PCB and components.