Patent GB-852012-A (GB)
Title: Improvements relating to high frequency electronic oscillators
IPC: H01J25/52
Filed: 1958-02-27
Abstract: 852,012. Magnetron oscillators ; travelling wave tubes. COMPAGNIE FRANCAISE THOMSON-HOUSTON. Feb. 27, 1958 [Feb. 27, 1957], No. 6420/58. Class 39(1). An electron oscillator of the magnetron type has an anode of electrically resistant material to serve as an impedance wall so that the rotating electrons induce electric charge waves therein which rotate in synchronism therewith so as to cause bunching of the electrons and build up of the amplitude of the charge waves, and output coupling means for the charge waves. There may be 1, 2, 3 or 4 complete charge waves. Electronic tuning by varying the anode voltage is achieved since the structure is dispersive and is especially useful in frequency modulation systems. The resistance of the anode is greater than 1000 ohms/cm. In one form, Fig. 2, 2 series of 4 metal bars, preferably of Mo, extend axially through the material of the cylindrical resistive anode in which they are embedded. They are connected alternately to ring straps 13, the spacing between adjacent bars being half an induced charge wavelength and the total cylinder circumference four such wavelengths. The output is taken off from rings 13, 13<SP>1</SP> by a lecher line system 14 coupled by loops 18, 20 to load 19. The directly heated cathode 8 may be of pure tungsten and the heating current and therefore the emission may be varied by variable resistor 17. If the full cathode (temperature limited) emission is used the electronic tuning range is further increased. Electron confining discs 15, 151 are connected to the cathode supports and leads 9, 10 so as to heat cathode potential. The axial magnetic field is produced by a permanent magnet NS. The resistance cylinder-anode 11 may be of or having an internal conductive layer of high resistivity or small thickness or ceramic containing graphite or containing metal. Heat dessipation therefrom is improved by a radial disc at one end of the discharge space which absorbs a proportion of electrons which would otherwise strike the resistance anode, the proportion being adjusted by varying the position of taps connected to disc and assistance anode on a potentiometer. Fig. 5 (not shown). The resistance cylinder-anode may have an axial nonemissive conductor enclosed thereon, the cathode being outside the cylinder and around part of the axial conductor. and surrounded by an auxiliary not so positive anode, this system forming an auxiliary magnetron diode for injecting the electrons into the resistance cylinder. The relative potentials of the 2 anodes are adjusted by taps on a potentiometer, Fig. 4 (not shown). Figs. 4 and 5 can be combined in a single embodiment, Fig. 6, 26 being the auxiliary anode, 36 the auxiliary collector, 24 the axial conductor, 23 the resistance cylinder, and 37, 38 the potentiometer. The bars 12 can rest on the inner or outer surface or be embedded by the resistance cylinder, Figs. 8, 9 (not shown). The bars 12 can be equally spaced circumferentially, Fig. 7, where two groups of two conductors 40, 41 are connected by straps 43, the output lecher line 44 being connected to the straps. Conductors 40 are spaced apart by one induced charge wavelength while conductors 41 are similarly spaced, the unequal circumferential spacings below the sets 40, 41 being each an odd multiple of half this wavelength. The output may alternatively be two plates partially embedded in or attached to the sides of a slot in the resistance cylinder ; in the latter case the line and slot impedance must be matched. The velocity modulation of the beam may be sinusoidal in which case the induced charge wave is also sinusoidal.