You can doubt all you want, but you can't use different type of radar on a different launcher. especially when band are incompatible like in this case when S-300Pn (the one Ukrainian uses) are semi-active homing with Passive Array and S-400 is active homing with quad band solution.
It's like you try to plug a PAC-3 Radar into a PAC-1 system, it wouldn't work because the comm are different. Radar system is not exactly a Plug-n-Play system where you can just plug any system with any launcher.....
I was trained with Radar system as part of my TOC controller training and have gone thru the same class Anti-Aircraft artillerymen in Air Defence Artillery School with their PAC course (don't ask me why I have to do this course)