A bounded wave transmission line ENP simulator which achieves a very good confinement of the field inside its volume is described. Results of field mapping in free space and inside a shielded room are presented. These measurements have shown that the field decays very rapidly outside the structure, making it possible to use the antenna without disturbing its environment. It was also shown that when the simulator is used inside a Faraday cage, the reflections from the walls of the room do not produce significant field distortions within the working volume