An Electron-Cyclotron Resonance Heating (ECRH) system has been designed for JET in the framework of the JET-Enhanced Performance project (JET-EP) under the European Fusion Development Agreement (EFDA). Due to financial constraints it has recently been decided not to implement this project. Nevertheless the design work conducted from April 2000 to January 2002 shows a number of features which can be relevant in preparation of future ECRH systems such as the ITER one. The system was foreseen to comprise 6 gyrotrons, 1 MW each, in order to deliver 5 MW of mm-wave power into the tokamak plasma [1]