GB774240A - Improvements in or relating to travelling-wave tubes - Google Patents

Abstract

774,240. Travelling wave tubes. COMPAGNIE GENERALE DE TELEGRAPHIE SANS FIL. April 12, 1955 [April 8, 1954; June 28, 1954], No. 10567/55. Class 39(1). [Also in Groups XL(b) and XL(c)] A travelling wave amplifier or oscillator using forward or backward waves has an annular beam passing along and within a cylindrical delay line, Fig. 1 and a high frequency coaxial feeder line 7, 8 extending axially within the annular beam and out through the tube envelope in the same axial direction the inner conductor of the feeder line being connected to the gun end of the delay line by a rod extending perpendicular to the axes and passing through a slot in the outer conductor. The feeder line 7, 8 which as shown is the coaxial output line of a backward wave oscillator may be taken out through the collector 3 as shown, or through the gun, Fig. 3 (not shown). The delay line is of interdigital form comprising a bar 1 carrying incomplete rings 2 attached alternately to opposite face thereof. The bar 1 is secured at one end to collector 3 and carries at the other end support 6 to which are secured rods 17 carrying mica members 18 supporting the gun electrodes. The inner conductor 8 of the output line is connected to the last finger of the dalay line by rod 11 and is spaced from outer conductor 7 by mica spacers 9. The gun comprises annular indirectly heated cathode 14, Webnelt electrodes 15, 19 with separate leads and gun anode 6, 13. Magnetic focusing means comprising an annular body made up of juxtaposed permanent magnets 22 with pole pieces 20, 21 act on the whole length of the beam ; the permanent magnet 22 may alternatively be an assembly of parallel bars disposed edge to edge in which case the pole pieces are circular or polygonol e.g. square or hexagonal. In a modification, Fig. 3 (not shown) the Webnelt disc 15 is replaced by a cylinder and a steatite spacer is interposed between the outer Webnelt annular electrode and the gun anode. Since the output power increases with the frequency, for constant output power means must be provided for increasing output power for low frequencies and decreasing it for high frequencies. The input D.C. power and consequently the h/f. output power can be reduced by making the outer Webnelt electrode and if desired also the inner Webnelt electrode more negative to reduce the beam current to increase the output power for low frequencies the inner Webnelt electrode is made more negative to force the electrons nearer to the delay line and so to increase the interaction between beam and wave. If the attenuator 29 is dispensed with and replaced by a second output line 23, the tube may function as a for wardwave amplifier or as a forward wave oscillator (with an external feedback channel).