US2877380A - Magnetrons - Google Patents

Description

March 1959 M. ESTERSON ETAL MAGNETRONS Filed March 14, 1958" F/GJ u INVENTQRJ 77 MW g- 4%7m @zmw 36% W ATTORNEYS United States Patent MAGNETRONS Maurice Esterson and Alec Peter Orme 'Collis, Essex, England, assignors to English Electric Valve Company Linuted, London, England, a company of Great Britain Application March 14, 1958, Serial No. 721,374 Claims priority, application Great Britain April 26, 1957 2 Claims. (Cl. SIS-39.61)

This invention relates to magnetrons and more specifically to multiple resonant cavity tunable magnetrons of the kind in which tuning is accomplished by means of conductive pins carried upon an adjustable conductive carrier member and which project into the resonant cavities to an extent which can be altered by altering the position of the carrier member carrying the pins.

The invention is illustrated in and explained in connection with the accompanying drawings in which Figure 1 is a highly simplified diagrammatic representation of a known magnetron of the kind to which the invention relates and Figures 2 and 3 are mutually perpendicular views of a tuning assembly comprising a set of tuning pins with their carrier member as used in one embodiment of this invention.

Referring to Figure 1 this represents a multiple cavity magnetron of generally known form with a cylindrical cathode structure 1 coaxially within the usual anode system which is provided with resonant cavities 2 in a ring round the cathode.

The anode block is drilled parallel to the axis to take tuner pins 3 one of which extends into each resonant cavity (except the cavity provided with an energy takeoif loop in magnetrons in which there is such a cavity) to an extent which can be adjustable for purposes of tuning variation. The magnetron represented in Figure 1 is of the strapped typed, straps being indicated at 4. The tuner pins are carried on a carrier disc 5 which can be adjusted in the axial direction by means of a lead screw member or nut 6. The screw is external to the evacuated space of the magnetron, vacuum being preserved by means of a flexible diaphragm 7 which completes the evacuated space and permits the required axial movement for tuning.

This known magnetron is reasonably satisfactory but it has the defect that spurious resonances are apt to occur at different frequencies in the tuning range. These spurious resonances reduce the output power and increase the liability to internal flashing at tuning positions in which the spurious resonance tuning curves cross the curve of anode tuning.

Although most spurious resonances can be kept out side the working frequency range by suitable choice of end space and other dimensions, it has been found by experiment that most persistant resonances are associated with the tuner pins themselves and are critically dependent upon the clearances between the pins and the resonant cavity walls through which those pins pass. It is extremely difiicult in practical manufacture to keep these clearances at the same required values from magnetron to magnetron with the required precision. Because of this it is in practice common for diiferent magnetrons of the same design and which should give the same performance in fact to give considerably different performances. This is a serious defect which it is the object of the present invention to eliminate or reduce.

Experiment has shown that objectionable spurious resonances occur due to voltages which are induced in the tuner pins causing currents to flow axially along the pins and around the carrier disc by which they are supported. These resonances are very dependent on small displacements of the entire pin and carrier assembly, for example on small rotations about the axis.

According to this invention the tuning pin carrier member of a multiple resonant cavity tunable magnetron of the kind referred to is slotted between successive pairs of tuning pins (counting round the carrier) so that successive pairs of pins are divided off from one another by a slot.

Preferably the carrier is a disc with radial slots therein.

Figures 2 and 3 show one form of construction of tuner assembly for use in a magnetron in accordance with this invention.

Referring to these figures the tuning assembly therein shown comprises a ring of metal tuner pins 3 mounted on and at right angles to a metal carrier disc 5 provided with a lead screw member or nut 6. The assembly as so far described is as well known and is mounted in the magnetron in the manner shown in Figure 1 or in some similar known manner so that each pin projects into one of the cavities of the anode system to an extent which can be adjusted by adjusting the whole assembly axially of the magnetron.

In accordance with this invention slots 7, 7a extending radially of the carrier member 5 are provided with each slot being between successive pairs of tuning pins counting round the carrier, so that each pair of pins is between two slots. In the particular construction shown in Figures 2 and 3 one of the radial slots-that designated 7a and shown at three oclock in Figure 3-is made much wider than the others, 7, and is also tapered. This is for a reason which has nothing to do with the present invention as such but is merely because, in the particular magnetron for which the tuning assembly of Figures 2 and 3 is designed, the wide slot 7a is necessary in order to clear a part of the magnetron structure used for supporting the cathode. The widening of this particular slot 7a is thus, as it were, fortuitous, and if it were not necessary to provide a clearance this particular slot would be like the others. Also in the construction shown in Figures 2 and 3 the pins do not occur at regular intervals all round the carrier member 5, there being a considerably larger space between the two pins shown at the top of Figure 3 than between any other two pins. As will be seen this considerably larger space corresponds to the omission of a pin which, if the required spacing was equal throughout, would be provided at 12 oclock in Figure 3. This omission has again nothing to do with this invention as such, but is due to the fact that, in the particular magnetron for which the tuning assembly of Figures 2 and 3 is designed, one of the resonant cavities (that corresponding in position to the omitted pin) contains an energy take-oil loop and, of course, no tuning pin is provided to enter that cavity. The pins 3 shown in Figures 2 and 3 are hollow but, of course, they could be solid.

We claim:

1. A multiple resonant cavity tunable magnetron having a tuning pin carrier disc and a plurality of tuning pins carried thereon, said disc having a plurality of radial slots respectively extending between and dividing successive pairs of tuning pins from one another.

2. A multiple cavity magnetron comprising a cathode and an anode system co-axial with said cathode and having a plurality of resonant cavities in a ring round the axis, each cavity extending parallel to said axis and opening into an interaction space co-axially within the anode system, said anode system including a conductive disc carrier member at right angles to said axis, a plurality of parallel conductive tuner pins carried by said carrier member and extending parallel to said axis and entered respectively into said cavities, said carrier member having a plurality of slots lying along radii of said carrier member and between successive pairs of said tuning pins, and means for adjusting said carrier member longitudinally of said axis to adjust the positions of said tuning pins longitudinally of said cavities.

References Cited in the file of this patent UNITED STATES PATENTS

Images