GB680796A - Improvements in or relating to electron discharge apparatus - Google Patents

Abstract

680,796. Travelling wave tubes. STANDARD TELEPHONES CABLES, Ltd. Jan. 21, 1949 [Jan. 27, 1948], No. 2436/48. Class 39(i) [Also in Group XL(b)] A travelling wave amplifier tube of the helix type is coupled to an input waveguide by a doorknob probe; the output coupling may be similar. In one form, Fig. 1, the input and preferably also the output ends of the helix 3 are coupled to a waveguide 6 or waveguides without distortion of the end turns of the helix 3 by means of a tubular probe 5 connected to the helix by a straight rod or wire 4 and co-operating with a tapered " doorknob probe 7 secured to a wall of the guide 6. Probe 7 and flange member 8, together with probe 5 forms a "quarter wave sleeve," i.e. of an odd number (including unity) of quarter wavelengths long at the mean frequency to be amplified. The input and output couplings may both be as shown; in some forms, the inner probe at the output end may be a solid block formed with a cup-shaped depression and serving as the final collector. The electron gun 10 is designed for magnetic focusing produced by a coil wound around glass bulb 2 and an auxiliary coil wound around brass cylinder 9. The helix 3 may be supported on internal projections of the glass envelope 1. In a modification, Figs. 2, 3 (not shown), a single probe member only is used instead of the two members 5, 7, and at the input end of the device is formed with feathered flanges for sealing to glass envelope portions on either side; at the output end it has only one feathered flange for sealing to a single glass envelope portion and has a cup-shaped depression and serves as the final collector. In a further modification using only a single probe member, Fig. 4, the probe 20 is of sheet metal and glass envelope portions 21, 22 are sealed thereto on either side. The electron gun is brought up inside probe 20 which may also form the final gun anode so that electrostatic focusing at the beam entry to the helix 3 may be had. In a further modification, Fig. 5, also using a single probe, the latter comprises a metal disc 23 and resilient tapered metal part 26 sprung over the disc. The disc 23 may serve as the final gun anode. In all forms the probe projects approximately halfway across the waveguide and the helix 3 projects slightly into the waveguide at the opposite wall thereof. The characteristic impedance of the probe is made to match the waveguide impedance as nearly as possible at the centre of the band to be amplified. A prior art travelling wave amplifier is referred to in which the end turns of the helix are opened out and connected to a straight conductor formed as a hollow stub which co-operates with a flange on the waveguide wall to form a quarter wave sleeve.