RF energy is one form of electromagnetic energy that is a component of the electromagnetic spectrum, which covers microwaves, visible light and X-rays, as well as many more kinds of energy emissions. RF energy, sometimes called "RF emissions," "RF waves" or "RF fields," is generated when a source current, such as a transmitter, is fed to an antenna. This current excites electrons within the antenna and the energy moves outward in the form of an electromagnetic wave.