Reduction of intermodulation distortion with harmonic injection for wideband traveling-wave tubes

Large signal studies on octave bandwidth traveling-wave tubes show that significant improvements in tube linearity can be achieved with harmonic injection, in addition to efficiency enhancements and suppression of parasitic harmonic signals. In multisignal operation considerable reduction of the intermodulation distortion can be expected with this scheme. This requires that the injected harmonic signals be optimized in amplitude and phase with respect to the fundamental signals. In practice the harmonic signals can be generated with an octave bandwidth driver tube, and a harmonic conditioner can be designed to optimize the injection conditions. With two and four simultaneous signals improvements in intermodulation distortion by about 6 dB have been demonstrated at saturation with intermodulation levels of approximately 18 dB below the signals.