A sweep frequency generator is a type of signal generator that generates a sinusoidal output signal whose frequency is automatically varied or swept between two selected frequencies. It uses two oscillators - a master oscillator that produces a constant frequency and a voltage-controlled oscillator whose frequency varies. A mixer combines the outputs of the two oscillators to produce a sinusoidal output whose frequency is swept between the frequencies of the two oscillators. Sweep frequency generators are primarily used to measure the responses of amplifiers, filters, and other electrical components over various frequency bands.