A new broadband ECRH (Electron Cyclotron Resonance Heating) system is currently under construction at the ASDEX Upgrade tokamak. This system will employ multi-frequency gyrotrons step-tunable in the range 105–140 GHz. In its final stage the system will consist of 4 gyrotrons with a total power of 4 MW and a pulse length of 10 s. It employs a fast steerable launcher for feedback controlled deposition that allows for poloidal steering of 10° within 100 ms. Transmission line elements, such as corrugated waveguides, polarizer mirrors and vacuum windows, are designed to cope for this frequency band.