GB687149A - Microwave amplifiers - Google Patents

Abstract

687,149. Magnetron amplifiers. STANDARD TELEPHONES & CABLES, Ltd. Jan. 10, 1950 [June 25, 1949], No. 593/50. Class 39(i) A magnetron of the multi-cavity type is modified by making a helical cut 6, Fig. 1, in the anode structure so as to divide it into a plurality of cavity resonators arranged in a helix about the elongated cathode 1, end plates 10, 11 are provided between which a DC field is set up to give the electrons a helical path, and input and output coaxial lines 18, 19 are coupled to the end resonators by loops 16, 17 so that the device functions as an amplifier. The device operates on travelling wave principles, the helically moving electrons travelling at the same velocity as the helically travelling wave and the DC potential between plates 10, 11 being adjusted so that the pitch of the electron paths equals the pitch of the resonator slots. To prevent field interactions between adjacent ends of end-to-end resonators, an edge wound metal strip 7 is threaded into the helical cut, and a second strip 14 may be moved longitudinally by dielectric rod 15 passing through bellows to the exterior for tuning. The cathode 1 is indirectly heated and has a helical emissive coating as shown to confine emission to the spaces opposite the resonator slots; it is supported at either end by leads 8, 9. Local feedback between resonators may be reduced by roughening the resonator surfaces to introduce resistive losses or by choosing anode material of low specific conductance. To increase the gain, positive regeneration may be employed e.g. by feedback through transmission lines which are adjustable for regulating the amplitude and phase of the feedback energy.