Nonlinear Distortion and Suppression in Traveling Wave Tubes: Insights and Methods

Traveling Wave Tubes (TWTs) are microwave and millimeter wave amplifiers used in radar, satellite communications, and electronic countermeasure applications. On a satellite, the TWT provides the final communications signal boost before transmitting the signal back to earth. In electronic countermeasures, TWTs boost signals that are sent out to deny detection by an enemy radar. The TWT, as with any amplifier, has a less than ideal behavior due to the amplifier nonlinearities. The non-idealities typically result in decreased amplifier efficiencies or reduced bandwidth. Such compromising behavior can be extremely expensive where a 1% increase in efficiency of a TWT could save $100, 000, 000 over the operating lifetime of a communications satellite. In this dissertation new advances in nonlinear modeling of TWTs are presented. These advances include new techniques for calculating properties of nonlinear behavior, and new insights into the physical processes responsible for the nonlinear distortions. In particular, the physics of intermodulation distortion, phase distortion, and harmonic injection are studied in detail. The new ideas on intermodulation distortion and phase distortion presented in the thesis revise long-standing assumptions about TWT nonlinearity, and should ultimately play a role in improving TWT designs through improved understanding. The new ideas and explanations of harmonic and signal injection may enable new technologies that would increase efficiency, bandwidth, and linearity, and provide increased functionality and higher data rates with large cost savings for electronic countermeasure and satellite communications markets.