Abstract: A system and method is provided for transmitting input energy in an electromagnetic field test chamber having a predetermined fundamental frequency f.sub.0 determined by the dimensions of the chamber. The test chamber has an electromagnetic shield for preventing external electromagnetic fields from being applied to the interior of the chamber. A tuner is provided for modifying the impedance of the chamber and a rod is provided for establishing new boundary conditions for the electromagnetic energy. Energy is applied to the chamber at a frequency equal to a subharmonic frequency f.sub.S wherein f.sub.S <f.sub.0 and a gain is applied to the input energy by the test chamber. The resonance of the chamber is tuned by adjusting the rod. Energy may be applied to the test chamber at a plurality of frequencies in the vicinity of the subharmonic frequency, creating a corresponding plurality of gains. A peak gain is provided at the subharmonic frequency.