This work presents a study about a analytical technique used to model the wave coupling from a coaxial line fed probe to a waveguide device with promising applications in the Additive Manufacturing (AM). The analytical technique estimates the input impedance of the probe based in dyadic Greens functions. This technique allows to obtain the appropriate parameters, height and position, of the probe in a closed form and ensure a good impedance matching. In order to validate the electrical response of the device, the estimated parameters were used to build the geometrical model using COMSOL software and determine the return loss to the coaxial probe-to-rectangular waveguide transition. The simulation results showed a good impedance matching to the operating frequency 2.41 GHz. Finally, a fine-tuning was applied in the waveguide device to maximize the power transfer.