Patent GB-665341-A (GB)
Title: Improvements in or relating to electronic discharge devices
IPC: H01J25/00
Filed: 1944-04-19
Abstract: 665,341. Electron transit time apparatus. PHILIPS LAMPS, Ltd. April 19, 1944, [Feb. 3, 1943], No. 7264/44. Class 39 (i). [Also in Group XL (c)] Electron discharge apparatus for producing a retardation of an input signal which retardation is proportional to the amplitude variations of a separate time-varying control field applied thereto, comprises means for generating a beam and intensity modulating it with the signal, means to generate an electric and/or magnetic director field extending over most of the distance between the beam producing means and the collector so as to impress a curvilinear path of a plurality of complete turns on the electron beam, the control field serving to vary the direction of entry of the beam into the director field or fields so as to vary the curvilinear path length and so produce variations in the electron transit time which are proportional to the amplitude variations of the control field. The control field may be magnetic or electrostatic. In one form, Figs. 3, 4, the intensity of the magnetic director field decreases radially outwardly inversely with the radial distance from the axis and the beam is projected into the magnetic field in a direction inclined at a small angle to the tangential so that a two-dimensional spiral path results. The desired magnetic field distribution is obtained by a winding 38<SP>1</SP>, preferably with the help of two pancake coils 42. To maintain a stable central axis for the spiral a certain mathematical relation must hold between the beam velocity, angle of injection, radius at which injection takes place, and magnetic field. The width of the final collector must not be greater than the separation between the last and last but one convolutions of the spiral path. In practice, the magnetic field variation at this point may be increased in order to increase the pitch of the spiral in the last few convolutions. In another form, Fig. 5 (not shown), the magnetic director field is replaced by a radial electric field between two concentric cylinders. The form of path and stability conditions are similar to those obtaining in the form of Figs. 3 and 4. In another form, Fig. 8 (not shown), the beam moves in a helix about a two dimensional spiral path by means of a radial electric field and a circumferential magnetic field. In another form, Figs. 6, 7 (not shown), a magnetic director field is used and the beam is given a small longitudinal velocity component so that a helical path results. The velocity and direction of injection may be modulated together; it is not necessary in this case to maintain a stable central axis for the electron orbits. The last few convolutions of the helix may be spread out by means of a weak additional electric field parallel to the magnetic director field. Fig. 9 shows the preparation chamber enclosing cathode 30a, control grid rods 32a, 64, and focusing electrode 62. The chamber has sheet metal walls, preferably of non- magnetic material so that the main magnetic field of the device is also in the chamber. This magnetic field together with an electric field between plates 60 or an auxiliary magnetic field from pancake coils at the top and bottom of the chamber, bends the beam so that it passes out of slot 36a. Alternatively the chamber walls may be constructed of high permeability material so as to form a magnetic shield, the beam being curved in the chamber by an elaborate electrical field or a separate magnetic field. The magnetic director field is corrected to compensate for the magnetic shield. The control field is applied to either or both pairs of plates 56, 58. Grid 32a suppresses the electrons in directions away from slit 68; it is used to signal-modulate the beam. On emerging from slot 36a the beam may proceed on a two dimensional spiral path or alternatively plates 70, Fig. 10, may be used to give the beam a preliminary helical path after which it follows the two dimensional spiral path; or it may continue in the helical path. Instead of being symmetrically inside the retardation chamber, the preparation chamber may be disposed eccentrically so that curvature of the beam therein may be unnecessary. In this case chamber wall 66 may be omitted. Alternatively the preparation chamber may be disposed outside the retardation chamber, Fig. 11 (not shown). The final collector may be disposed outside the retardation chamber, Fig. 12 (not shown), rather than within it, the chamber being shielded from the collector by suitable construction and spacing of the overlapping sheet metal edges of the chamber. In a modification, Fig. 13 (not shown), a secondary emission electrode is interposed between the chamber and the collector. More than one stage of secondary emission may be used in cascade. The statistical fluctuations in omission velocity of the electrons may be reduced by velocity filters adjacent to the cathode. The devices may be used for frequency or phase modulation by using the integrated intelligence for the control signal, and constant frequency oscillations for intensity modulating the beam. Specification 541,301 is referred to. The Specification as open to inspection under Sect. 91 refers generally to delaying signals with. or without the use of additional control fields. In one form, Fig. 3 (Cancelled), the beam generated by cathode 30 and signal modulated by grid 32 is accelerated by slotted plate 34, and projected tangentially into a retarding chamber III<SP>1</SP> in which a magnetic director field is maintained by winding 38. The beam describes a path of about ¥ of a circle and is collected at 40. Alternatively the beam may be initially directed towards the centre of chamber III<SP>1</SP> in which case apparently an electric director field is used in addition to the magnetic director field. The ensuing beam path is circular or cycloidal depending on the relative values of the electric and magnetic director fields. The beam velocity and magnetic director field may be modulated simultaneously or only the magnetic director field may be modulated. In the former case the beam trajectory remains fixed provided that du/u = 2dH/H, where u is the accelerating voltage and H the magnetic field, and in the latter case different trajectories result which must all be the same fraction of a revolution if the retardation is to be proportional to the magnetic director field modulation. In the form of Figs. 3, 4 (as accepted), the velocity of the electrons and/or the magnetic director field may be modulated instead of the direction of entry. If only the velocity or the magnetic director field is modulated, the trajectory is a more general form of spiral, so that a larger collector is necessary. In this case the variations in the positions of the ends of the trajectories must be less than the separation between the last two convolutions of the beam path but here again , the magnetic director field variation may be increased at this point to spread out the last few convolutions. If both the velocity and magnetic field are modulated the two dimensional spiral path may be maintained provided a certain relation exists between these quantities. In the form of Fig. 5 (as accepted) (not shown), the velocity and/or electric director field may be modulated instead of the direction of entry. In the form of Figs. 6, 7 (as accepted) (not shown), the velocity alone may be varied without varying the direction of entry. It is stated that a helical trajectory may also be obtained by providing an electric director field parallel to the magnetic director field and injecting the electrons perpendicularly to the magnetic field. The electric director field may be modulated in this case. The cathode in all forms may be a star-type source producing a. plurality of beams of equal velocity the device being a multiply slotted wall enclosing a single cathode. If parallel beams of unequal velocity are required, a plurality of cathodes may be used or a single cathode with a surrounding member having radially stepped slots. The devices have an amplification factor of about 30 in addition to serving as signal-retarding devices; retardations of 1-10 milliseconds are obtainable within the 15-50 cm. range. Fig. 16 (Cancelled) (not shown), shows a circuit for measuring retardations, in which a signal from the output of the device, of known retardation, is balanced against a signal, the retardation of which is to be measured. The balancing may be made automatic. Such an arrangement may be used as a distance measuring device in a system for detecting obstacles. Alternatively the device may be used to measure phase displacements. In Fig. 17 (Cancelled) (not shown), the output of the device containing the delayed signal of 35 Mcs. is mixed with 28 Mc. oscillations and the output from the mixer is 7 Mcs. but with all the phase displacement originally impressed on the 35 Mcs, signal. The 7 Mcs. output is then passed into a multiplier to convert it into 42 Mcs. In Fig. 18 (Cancelled), the intelligence is applied to terminals 98, 100, integrated and applied to plates 56d, and the local oscillations to terminals 102, 104 and thence to control electrode 32d. Magnetic coil 38d is provided and the collecting system of the device has one stage of secondary emission. The output is taken from terminals 106, 108. Specification 656,871 also is referred to. This subject-matter does not appear in the accepted Specification.