Patent GB-797772-A (GB)
Title: High frequency discharge tubes employing delay lines
IPC: H01J25/36
Filed: 1956-01-12
Abstract: 797,772. Travelling-wave tubes. COMPAGNIE GENERAL DE TELEGRAPHIE SANS FIL. Jan. 12, 1956 [Jan. 13, 1955], No. 1130/56. Class 39(1). A travelling-wave tube has a delay line formed as a geometrically periodical delay structure in two intersecting preferably perpendicular directions two electron beams perpendicular to one another being directed parallel to the structure in the said perpendicular directions respectively. In one form, Fig. 2, the input wave can travel in the direction of electron beam 3 or 6 (as shown in the direction of beam 6) and output is taken by tapered horn 8 to waveguide 11 the tapered wall 9 also serving as a collecting electrode. There may be a plurality of electron beams 3. The device can be an amplifier or oscillator using forward or backward waves or an amplifier the beam velocities are equal and the same as the phase velocity of the wave of the frequency to be amplified. In another embodiment, Fig. 3, the structure is cylindrical and has standing waves circumferentially and travelling waves axially. The device resembles a vane type magnetron with axial cathode 5 and axial magnetic field produced by coil 24, but the vanes are subdivided in the axial direction. The frequency is uniquely determined when the velocities of the rotating electron cloud and of the 3 axial beams from arms 2<SP>1</SP>, 2<SP>11</SP> are suitably selected since the structure is highly dispersive. A few of the intermediate vanes 27 are 'coated with lossy material (cross hatched in drawing) and the vanes are strapped together to favour spatial harmonic operation and the straps connected to bifilar feeders 28, 31. The emissive part of the cathode extends only along the non-lossy vanes on the output side of the lossy vanes. In another form, Figs. 5, 6, 7 (Fig. 6 only shown) oscillators are described which may have travelling or standing waves in two perpendicular directions or travelling waves in one direction and standing waves in the other direction. A short section of output guide can be sealed to the tube envelope and terminates in a window, Fig. 5 (not shown). In Fig. 6 a plurality of electron beams 3 from gun 2 are projected between the rows of fingers 13 and a beam 6 is projected at right angles to the other beams (i.e., perpendicular to the plane of the paper), a magnetic field being provided by polepieces 18, 19 and an electric field being provided between 12, 14, the latter electrode being at cathode potential. Beams 3 are therefore in a longitudinal magnetic field and transverse electric field, while beam 6 is in crossed electric and magnetic fields. A lossy coating can be provided on the inner face of collector block 4 or on horn 7 for backward wave oscillator operation; the device may however be a forward wave oscillator or an amplifier. For standing wave operation reflectors R, R<SP>1</SP> or Ra. R<SP>1</SP>a are provided at the edges of the delay structure. R<SP>1</SP>a can be dispensed with if the output is mismatched. Another form, Fig. 7 (not shown) is similar in construction to Fig. 2, each collector having a loss coating for backward wave oscillator operation. In a backward wave oscillator, Figs. 8, 9 (not shown) the construction is similar to Fig. 3, but the emissive part of the axial cathode extends along all the delay line except the collector end which is coated with lossy material the strapping arrangement being as in Fig. 10, and having a bifilar output line adjacent three guns arranged as in Fig. 3. The strapping favours a spatial harmonic mode. The potentials of the electrodes can be modulated. Specification 699,893 is referred to.