GB1196285A - Improvements in Electron Discharge Devices - Google Patents

Abstract

1,196,285. Transit-time tubes. GENERAL ELECTRIC CO. 16 June, 1967 [29 Sept., 1966], No. 27880/67. Heading H1D. A broad-band power amplifier discharge tube includes a periodic interaction structure, a portion of which exhibits a log-periodic variation of resonance frequency along its length, an electron beam which is tapered at least over substantially that portion of the path corresponding to the log-periodic portion of the structure, whereby the input signal interacts with the beam at regions of the structure which are dependent upon the frequency of the input signal, to provide an amplified output signal from the structure. In the klystron structure of Fig. 1, a tapered electron beam produced by a gun 85 and focused by a tapered solenoid 104 is directed through the sequence of coaxial cavities 11 to 18, the diameter and axial length of which, together with the length of the interaction gaps 49 or 56, exhibit a geometrical progression along the sequence. The input signal is applied to the conductive rod 107 which passes through, but is insulated from, the sequence of cavities, the signal interacting with the beam at that region of the structure at which the resonance frequency approximates the frequency of the signal, to provide an amplified output signal at 108<SP>1</SP>. The effective input and output regions of the periodic interaction structure may immediately follow one another, or may be spaced apart by sections of negligible response, to provide an output which is an harmonic of the input frequency. In modified arrangements, the radially outer walls of the cavities 11 to 18 may be cylindrical, providing a stepped outer surface approximating the taper of Fig. 1 ; different progression ratios may apply along different sections of the sequence; and a permanent magnet focusing arrangement may replace the solenoid 104. To avoid the use of inconveniently small cavities at the output end, the final portion 28 of the structure is uniform, and preferably extends to the apex of the cone defined by the produced walls of the tapered section; over a range of frequencies the output and input are located in regions of only weak interaction between the beam and the structure, whereby end effects are rendered unimportant. In a modified arrangement (Fig. 2, not shown), the conductive rod 107 is coupled only to alternate cavities or groups of cavities, and different progression ratios may apply to the two sets. In a further device (Fig. 4, not shown), the periodic interaction structure is a travelling wave tube helix, the diameter and pitch of which vary along its length, or an interdigitated structure. In a device employing backward wave interaction, the input and output are at the collector and the gun end of the tube respectively, and the sense of the geometrical progression is reversed, such that the interaction structure is smallest at the gun end. Values for the progression ratio of from 0À9 to unity are referred to.