GB603715A - Improvements in or relating to circuit arrangements embodying velocity modulation electron discharge devices - Google Patents

Abstract

603,715. Velocity-modulated tubes. BARFORD, N. C. March 22, 1945, No. 7317. [Class 39 (i)] An electron discharge device of the velocity modulation type comprises a coiled length of waveguide with apertures through which is projected an unmodulated beam of electrons. In Fig. 3, the waveguide is coiled in a helical manner, and the electron beam is projected through apertures 2 in adjacent walls arranged in a line parallel with the axis of the helic. The whole coil may be enclosed in an evacuated envelope, or the apertures and electrodes may be enclosed, the remainder of the waveguide being external to the envelope. Alternatively, the first aperture, the cathode and focusing electrode are enclosed in one envelope and the last aperture and anode in another, the guide being evacuated and the ends sealed. More than one series of apertures 2 may be provided, and their shape may be circular, arcuate or even annular. In Fig. 4, the electron beam passes down the axis of the coiled waveguide, a helical slot 6 in the wall yielding a continuous interchange of energy between wave and electron beam. The wall mav however be omitted entirely. The pitch of the coils may be constant or variable, preferably the latter to compensate for the slowing down of the electron beam. The helix may be square and the cross-section of the wave guide may vary from circular to square. The devices can be employed as amplifiers, as mixers of high frequency waves to give an intermediate frequency, as detectors for modulated waves and as generators of self-maintained oscillations ; in the latter case, a coupling is provided between the ends of the coil such as a cavity resonator chosen to give fine, coarse or wide band tuning or one end of the guide is closed so as to set up a system of standing waves.