Dual beam dual mode TWT

Design principles for a high pulse-up dual mode TWT employing dual electron beams are discussed. The tube employs a large hollow beam for CW mode operation and a reduced diameter, dense solid beam for the pulse mode. This scheme affords greater CW mode efficiency, reduced gain change between modes, and higher stability against backward wave oscillation than other, more conventional, pulse-up techniques. A dual-cathode electron gun incorporating an annular hollow beam cathode, concentric and co-planer with a solid beam cathode, has been designed and evaluated. By allowing a tailored magnetic field to penetrate the cathode region, both beams have been focused in a solenoid with excellent transmission to the collector. An S-band unifilar helix TWT operated with these electron beams has exhibited a minimum of 7 dB power pulse-up over an octave frequency band. The tube also demonstrated low gain change between modes and unconditional stability to backward wave oscillation.