EFFICIENCY ENHANCEMENT OF COUPLED-CAVITY TWT's THROUGH CAVITY RESONANCE TAPERING.

An alternate approach to circuit-velocity reduction in coupled-cavity TWT's is suggested. This approach, referred to as cavity resonance tapering, allows the velocity reduction to continue beyond the limit of stable period tapering. Cavity resonance tapering is accomplished by a gradual reduction in the cavity resonant frequency with the period kept unchanged and the circuit bandwidth kept more or less unchanged. For any frequency that remains in the circuit passband, there is a gradual increase in phase shift per period and, hence, a gradual decrease in phase velocity. The advantages and disadvantages of cavity resonance tapering vis-a-vis period tapering are discussed. Cold test data and the results of large-signal computer calculations are presented for illustrative purposes. Results indicate that, when applicable, cavity resonance tapering can produce efficiencies as high as can period tapering without incurring the same risk of lower band-edge oscillations.