Looking for a very precise tx/rx circuit module to calculate distance
Gosh, so does every other RTLS system. (/humor)

Research UWB (ultra wideband) ranging if you want off the shelf modules. That's probably going to be your best bet for millimeter grade accuracy.

There are of course other systems such as laser TOF/interforemetry, however they are line of sight (unless you use mirrors) and don't go through most objects.

Using RF triangulation techniques can be done, however multipath issues are problematic (hence the UWB push).

It all depends on your environment (which you say very little about).