Third-order intermodulation reduction by harmonic injection in a TWT amplifier

A method for reducing the two-tone third-order intermodulation products arising from two carrier frequencies at 1.95 and 2.00 GHz is demonstrated in a traveling wave tube-distributed amplifier. The optimum amplitude and phase of an injected second harmonic and the resulting intermodulation suppression of up to 24.2 dB are examined for fundamental drive levels approaching saturation.