Can you tell me, please, why didn't you cover the transmission lines in the CN0369 reference design (those, which are connected to the HMC512, for example) with a solder mask? What was the reason for not doing it?
Thanks in advance!
I didn't write this circuit note so I can't speak for the author. I can tell you that while we typically do use solder mask on our board assemblies, soldermask is hydroscopic and as such can affect performance. Translation loops are typically used for high performance applications such as test and measurement where repeat-ability, exceptionally low phase noise, low spurious and fast tuning are required. Variation due to humidity levels would be a valid concern so perhaps this is why it was left off (probably still has OSB though).