The state of the art in NTM control involves electromagnetic wave beams as primary actuator. These are generated by gyrotron sources and injected into the plasma via the steerable mirrors of controlled electromechanical launchers. In connection to the control design for the overall process, a theoretical model of the ECRH system should include, among others, the gyrotron operation, the launcher mirror dynamics, the motion transmission to the mirror by the associated servomotors, and the beam propagation in the transmission lines and the plasma. In this work, we present fragments of the physics-based modelling which is involved in the control system design.