Patent GB-868853-A (GB)
Title: Travelling wave tubes
IPC: H01J25/36
Filed: 1957-07-02
Abstract: 868,853. Travelling-wave tubes. RADIO CORPORATION OF AMERICA. July 2, 1957 [July 5, 1956; July 31, 1956], No. 20928/57. Class 39(1). A travelling-wave tube has a wave transmission structure providing distinct mutually intersecting paths for the propagation of the waves and means for directing electrons along the structure at an acute angle to these parts to interact with a space harmonic of the waves along the entire length of the structure. The wave transmission structure may be periodic in two directions. In Fig. 3 electrons from an annular cathode 54 are given a spiral motion by a radial electric field between electrodes 61 and 64 and an axial magnetic field produced by a coil 60, and are injected into a transmission line composed of an annulararray of conductors 12, 14 disposed about a central conductor 16. Alternate conductors 12 are connected together at their ends by rings 66, 68; the other conductors 14 are connected together by rings 70, 72. Ring 66 is also the electron collector. The central conductor 16 is supported from the collector ring 66 by a ceramic ring 74 which is slidable to take up thermal expansions and contractions. The spiralling electron beam may be produced by an array of inclined guns 80, Fig. 5. The tube may operate with a forward or backward wave in the axial direction. Wave delay may be introduced in the axial direction by strapping alternate conductors 12, 14 of the transmission line together by a series of rings 82, 84, Fig. 7. The transmission line structure may be inverted with the transmission line conductors within the electron beam and the beam surrounded by a cylindrical conductor. In another embodiment, Fig. 8, with a flat transmission line 112 and a sheet of electrons 122 projected at an angle to the line condunctors 124 in the space between the line and a flat conductor 114, the line is periodic in both the directions Z and Y. The periodicity is such that a change in the phase-velocity versus frequency characteristic in one direction is compensated by an opposite change in that characteristic in the other direction to give wide bandwidth operation. A magnetic field in the direction H is at right angles to the direction A of electron flow and a transverse electric field is set up between the line and the electrode 114. The electrons are projected from a cathode 118 and accelerating electrode 120 to a collector 123. The line conductors 124 have interdigitating fingers 125. The magnetic field and the transverse electric field may however be omitted and a magnetic field parallel to the electron flow provided, only for focussing purposes. The wave is introduced at 128 and taken off at 129. Standing waves are set up in the Y direction A forward wave component is propagated in one direction and a backward wave-component in another direction. The system of Fig. 8 may be adapted to the circular structure of Fig. 3 with the line conductors extending either in the transverse or axial directions and with the electron beam either inside or outside the transmission line structure. The line conductors are supported from the envelope, by stubs which together with the intervening portions of the envelope constitute the inductive coupling between the conductors. The stubs of adjacent conductors may be displaced to favour backward wave operation in the axial direction. The sizes and spacings of the interdigitating fingers are so chosen that most electric energy is stored in the circumferential direction. Suitable dimensions are given The tubes may be used as amplifiers or oscillators. Reference has been directed by the Comptroller to Specification. 814,120.