Nonlinear Multi-Signal Traveling Wave Tube Theory.
CHALMERS UNIV OF TECHNOLOGY GOETEBORG (SWEDEN) RESEARCH LAB OF ELECTRONICS
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The report gives an analysis of the nonlinearities arising in a TWT with N input signals. The signal frequencies are assumed to be confined within a narrow frequency band. The sum of the input signals is then equivalent to a single signal with a slow modulation of the amplitude and the phase and the multi-signal nonlinearities can be predicted from the single-signal nonlinearities. These have been theoretically calculated in an earlier paper. Fifth order power series expansions of the single-signal nonlinearities are used. Minimum amplitude nonlinearities are obtained for a beam voltage higher than that giving maximum small signal gain and minimum phase shift nonlinearities are obtained for a beam voltage lower than that. The power of the third and fifth order modulation products is minimum for a beam voltage between that for maximum small signal gain and that for minimum amplitude nonlinearities. The self-distortion, i.e. the compression and the AM-to-PM conversion of one of the signals, is strongly influenced by the total power carried by the other signals. The cross-distortion quantities are generally about twice as large as the self-distortion quantities. Author
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