Measurements of Non-linearities in a Travelling-wave Tube†

Abstract

ABSTRACT Measurements of the non-linear amplitude distortion and phase shift in a travelling-wave tube (TWT) are reported. The test object is a commercial 2 w, S-band, O-type TWT with a helical slow-wave structure. An extensive set of output amplitude and phase data was recorded for a wide range of input powers and helix voltages. The results are in good qualitative agreement with a recent non-linear field theory developed by Nilsson. The best helix voltage settings, in order to obtain minimum distortion in amplitude and phase respectively, are located on opposite sides of the voltage that gives maximum small-signal gain. This fact, which is theoretically well founded, is a complication in such applications where demanding specifications concerning amplitude and phase linearity must be met simultaneously. The measured non-linearities are about three or four times larger than theoretical predictions. This discrepancy deserves a thorough investigation since it indicates that there is a margin for improving ...