Microwave oscillator stability

By considering an oscillator as a regenerative noise amplifier, one can define an output half-power noise bandwidth. This quantity, which can be calculated from the physical constants of the oscillator, is an exact measure of the purity of the oscillator output. A small noise bandwidth indicates a relatively constant output frequency. Calculations show that three general types of circuits have sufficiently narrow noise bandwidths to be useful in highly critical applications. These circuits are (1) a simple regenerative oscillator, (2) frequency-stabilized oscillator, and (3) crystal oscillator-frequency multiplier chain. These systems are compared on the basis of simplicity and reliability, ease of constructions, and stability.