Abstract: An apparatus is disclosed for testing the immunity of an electronic device to interfering electromagnetic radiation. The apparatus includes a room enclosing a bounded space for containing the electronic device to be tested and a plurality of radiating elements disposed on the interior surfaces of the room for generating an electromagnetic field in the room. Each of the radiating elements includes a controllable phase shifter, a controllable amplifier, and antenna. The circuits of the phase shifter and amplifier are connected by a common signal bus to a radio-frequency signal source and by a common control bus to a controller for individually adjusting the phase and amplitude of the radiated signal to create an electromagnetic field within the room having a predetermined strength and distribution.