In this assignment the source of microwave power power will be an oscillator based on a field-effect transistor ( FET ). It frequency of oscillation is determined by the resonance of the waveguide cavity in which it is mounted. This cavity is coupled to the external waveguide by a narrow slit to reduce the influence the external load has on the oscillator"s built-in resonance.
Other form of negative-resistance device, can be used at low powers. For higher powers, vacuum tubes ,such as klystrons and magnetrons can be used. These use the finite speed of electrons travelling in vacuum.