Electronic Tuning of Magnetrons

This paper describes an experimental investigation of a simple method of achieving a limited degree of electronic tuning in medium power magnetrons, originally proposed by Willshaw(l). By the insertion of an extra cathode in one (or more) of the block resonators, ancillary crossed-field diodes are formed which can be used to modulate the magnetron frequency by pulsing the current taken by the diodes. Initial experiments with a 100kW X-band magnetron showed small frequency shifts of a few MHz per tuning cathode. Experiments still in progress with a moveable cathode in a passive, driven, resonator, suggest that 10MHz tuning in an S-band magnetron should be feasible corresponding to 30MHz at X-band.