Patent GB-814120-A (GB)
Title: Improvements in or relating to delay lines for use in travelling wave-tubes
IPC: H01J23/24
Filed: 1957-05-28
Abstract: 814,120. Travelling wave tubes. COMPAGNIE GENERALE DE TELEGRAPHIE SANS FIL. May 28, 1957 [May 31, 1956], No. 16872/57. Class 39(1). The delay line of a travelling wave tube amplifier or oscillator comprises a plate or crossed wire structure having a series of identical apertures so distributed as to give the structure a geometrically periodical construction in two perpendicular directions each aperture having a centre of symmetry and different dimensions in two mutually perpendicular directions passing through the centre, the largest dimension of the aperture is X Free space/2 measured at the centre of the design band. The apertures are arranged in a checkerwise manner. The electron beam passes along and parallel to the delay line or two beams from guns 21, 22, Fig. 6, travelling in different directions may travel on either side of the plate delay line. The apertures may be diamond shaped, rhombic, rectangular with square or rounded corners. The plate may be flat or, in Fig. 5, is rolled up into a cylinder. The larger diagonal or major axis of each aperture has a length of #Fsp/2 and the smaller diagonal or minor axis a length of #Fsp/2 v/c at the centre of the design band. The electron beam travels parallel to the short diagonal of diamond or rhombic apertures, Figs. 1, 2 (not shown), or if there are two beams, as in Fig. 6, each beam goes perpendicular to a corresponding pair of opposite sides of the apertures 24. The apertures can be cut or punched in the sheet. The cathode can be a rectangular metal block, Figs 1, 2 (not shown) coated with emissive material which emits a ribbon beam and is focused by an electrode to enter a region of crossed electric and magnetic fields, the sole plate and cathode being at the same D.C. potential. The magnetic field is generated by an electromagnet or permanent magnet and an intermediate portion of the delay line is coated with loss material e.g. Kanthal (Registered Trade Mark). The input and output feeders are connected to the points of the delay line arrowhead ends, and the design is such as to give in phase propagation over any transverse plane. The operating mode is a forwardfundamentalwave component and spurious backward spatial harmonic waves are suppressed; alternatively the device may function as a backward wave oscillator. The forward wave amplifier on Fig. 5, has an annular cathode 40 and collector 110 for passing a tubular beam around the cylndrical delay line 100. The input and output feeders 181, 191 are connected to the delay line ends by radial spokes 182 which give in phase connections to all parts of the delay line. The delay line has a lossy coating 150 over an intermediate region thereof. In a backward wave oscillator, Fig. 6, the two guns 21, 22 emitting the crossed beams and corresponding collector surfaces 26 are parallel to the arrowhead end surfaces of the delay line plate. Operation is as disclosed in Specification 797,772. The collector end has a lossy coating 25 and the output is at the gun end. Alternatively the delay lines of Figs. 3 or 4 can be used in the backward wave oscillator of Fig. 6 or in the amplifier of Fig. 5.