[en] For ITER, an ECRH upper port launching system is being developed [A.G.A.Verhoeven et al, '' Design and Test of the Remote-steering ITER ECRH Upper-port Launcher '', this conference]. This system will consist of 24 beam lines (divided over 4 upper ports), each capable of delivering up to 2 MW of 170 GHz ECW (Electron Cyclotron Wave) power to the plasma. This power is used primarily for the stabilization of NTM's (Neoclassical Tearing Modes), for which the launcher requires beams that can be steered over a range of ∼ 30 ^o. In order to achieve steering capability of the mm-wave beams, two design philosophies are being investigated; front steering (FS) and remote steering (RS). The FS design uses the more conventional approach of a plasma facing steerable mirror in the front of the upper port plug, while the RS design uses corrugated square waveguides (one for each of the 24 lines) within the upper port plugs through which the beams can be steered under an angle of up to ± 12 ^o. The steerable mirrors of this design are placed at the entrances of the square waveguides, outside of the first confinement boundary (provided by water-cooled diamond windows) of the vacuum vessel. At the exit of each square waveguide, a set of two focusing mirrors is placed in a dogleg configuration to guide the beam towards the required locations inside the ITER-plasma and to ' blow up' the steering range to conform to the requirements. With the use of Catia, a 3D model has been developed which is capable of accurate visualization of the mm-wave beam along the entire transmission line. Because this model uses parameterized equations to calculate the quasi optical beam propagation, it can show the effects of a change of the locations or of the optical properties of any of the transmission line components. Furthermore it also accurately calculates the effects the square waveguide has on the propagating beams as a function of its steered angle. Measurement in the 3D model of the beam size at its target inside the ITER plasma has proven to give a good indication of the launcher's performance. It has also become clear that the 3D visualisation of the beam propagation in the structural design can result in a much more efficient use of the confined space inside each upper port plug - space that is also needed to locate sufficient neutron shielding and cooling structures, as well as to allow access for remote-handling tools. (author)