RF multipliers, also known as RF frequency multipliers, are devices that generate an output signal that is a harmonic product of the input frequency. They are used to up-convert RF signals to microwave or millimeter bands for transmission. This is achieved by non-linear devices distorting the input signal so as to emphasize a particular harmonic product. RF multipliers are available in 2, 3, 4 and 8x configurations. They are used in applications that include microwave radio, VSAT, military radios, radar, electronics countermeasures (ECM) and for test instrumentation.

RF multipliers are only appropriate for use in communication systems with modulation schemes that are carrier amplitude independent. This is due to the non-linear amplitude distortion that occurs in harmonic generation. They are suitable for frequency modulation (FM) transmission. Non-linear characteristics are chosen to emphasize the particular harmonic output while suppressing original carrier and other harmonics. They include amplification to increase the output level and an internal band-pass filter may be integrated for further suppression of the output frequency.

RF multipliers will be specified for their phase noise characteristics and suppression of spurious output energy caused by non-ideal transfer characteristics of the non-linear device. They will also be specified for original RF carrier suppression. They are invariably followed by further band-pass filtering. High power systems may also require subsequent amplification stages.