In common with all oscillators, the Gunn diode oscillators have both AM and FM noise which vary with frequency from the carrier. The noise arises from random nucleation of domains. Closer to the carrier both the AM and the FM noise vary inversely with frequency off the carrier. Some diodes exhibit this aperiodic noise quite often. In others, the frequency of appearance is rather low.
External circuitry including the cavity and the power supplies influence the noise behavior.
The power output and the frequency of the oscillator depend on the bias supply. The second term is due to the power supply ripple. The figures above show typical AM and FM noise spectra of X band Gunn diodes. Frequency of operation for the GUNN diode must be specified with the order. Minimum specified power is measured in a critically coupled high Q cavity.