GB759937A - Improvements in or relating to travelling wave tubes - Google Patents

Abstract

759,937. Waveguides. WESTERN ELECTRIC CO., Inc. Dec. 29, 1953 [Dec. 30, 1952], No. 36054/53. Class 40 (8). [Also in Group XL (a)] A travelling-wave tube has a delay line comprising a rectangular sectioned waveguide having secured to one internal face thereof a hollow ridge formed with an array of slot resonators extending along the direction of wave propagation, the individual resonators being transverse to this direction and the beam is projected along the guide parallel with the wave. In one embodiment, Fig. 1, a rectangular waveguide 11 has a hollow ridge 12 brazed or soldered to the bottom wall thereof, and the ridge has #/4 slot resonators 14. Slit 15 provides a path for the beam, or alternatively there may be no slit. The envelope is completed by windows (not shown) in guide ends 20, 21 which are curved so that the ridge ends decrease in height for impedance matching. The lower wall of the guide has openings for the insertion of ridge 12 during assembly. The guide parts are of copper, or of silver-plated molybdenum. A magnetic focusing field is provided by polepieces integral with and at either end of the envelope, Fig. 3 (not shown). The mode used is a conventional mode, or preferably a spatial harmonic, of positive or negative phase velocity and the device may be an amplifier or oscillator. In another embodiment, Fig. 2 (not shown), wire of cylindrical or ribbon section is wrapped helically around a U-shaped channel; the wire lengths across the open end of the U are #/2. This structure forms a ridge fastened to the bottom wall of the guide, and the beam passes on both sides of the wires. Alternatively, lengths of wire can be laid across the open side of the U and secured thereto by a frame. The circuit may be used in a backward wave oscillator, Fig. 3 (not shown), when its end adjacent the collector is terminated by wedges of loss material on either side of ridge 32, and its end adjacent the gun is bent through 90 degrees and continued outside the envelope. Frequency modulation is effected by suitable modulation of the beam velocity. The waveguides need not be of rectangular cross-section. The devices may work at millimetre wavelengths. The design is discussed mathematically, and a numerical example is given.