US2338306A - Electron discharge device - Google Patents

Description

Jan. 4, 1944. Q SMYTH 2,338,306

ELECTRON DISCHARGE DEVICE Filed Sept. 11, 1941 I/VL ENTOR QRN Y Patented Jan. 4, 1944 UNITED STATES PATENT OFFICE ELECTRON DISCHARGE DEVICE Application September 11, 1941, Serial No. 410,351

In Great Britain August 23, 1940 5 Claims.

This invention relates to electron discharge apparatus incorporating high frequency resonators of the coaxial conductor type.

In a co-pending application of J. H. Fremlin, Ser. No. 367,401, filed November 27, 1940, various electron discharge devices are disclosed comprising lengths of coaxial conductor line constituting very high frequency resonators and means for passing electron beams through the fields of the resonators for the velocity modulation of the electrons.

In such arrangements, and generally where coaxial conductor type resonators are employed as frequency determining circuits in electron discharge apparatus, it is desirable to provide means for tuning the resonator. Where, however, the resonator is wholly enclosed within an evacuated envelope, obvious dimculties immediately arise.

It is an object of the invention to provide a simple means, requiring no movable parts inside the evacuated envelope, for effecting such tuning of the resonator.

According to the invention in an electron discharge device comprising -a resonator of the coaxial conductor type wholly enclosed within an evacuated envelope, adjustable tuning means is provided external to the envelope for varying a capacity applied across an end of the resonator.

According to a further feature of the invention an electron discharge device comprises a quarter-wave coaxial conductor type resonator wholly enclosed within an evacuated envelope, means for producing an electron beam traversing the field of the coaxial conductors for the velocity modulation of electrons and an adjustable tuning device external to the envelope adapted to apply a variable capacity across an open end of the resonator.

A preferred arrangement in accordance with the invention is illustrated in the accompanying drawing which is a sectional view of an electron discharge device utilising the principles of velocity modulation.

Referring to the drawing, a quarter-wave type coaxial resonator R closed at one end and consisting of a tubular outer conductor A and a central conductor B, is mounted inside an evacuated glass envelope E by means of mica positioning members M. The conductors A and B are provided with apertures in a common diameter and fins L bounding the apertures. A cathode C and focussing electrode K are provided to project an electron beam through the apertures to the anode P, for producing resonant oscillations in the resonator, in accordance with the principles of operation fully described in the copending application referred to above. A collecting rod or probe S is sealed into the envelope opposite the closed end of the resonator and projects into the interior thereof.

The outer conductor A is extended sufliciently far beyond the central conductor B at the open end to prevent radiation, and the closed envelope E is formed with a re-entrant end portion D which dips into the open end of the tubular conductor A nearly as far as the extremity of the central conductor B.

A small copper disc F is mounted on one end of a threaded rod G of insulating material which is threaded through a fixed support H and is provided at its other end with an adjusting knob T. The disc F can, by rotation of the knob T, be moved inside the extended portion of the tubular conductor A but still be outside the evacuated envelope and thus throw a variable capacity across the open end of the resonator R. It will be seen that the movement of disc F is in a direction parallel to the axis of the coaxial conductors.

It is appreciated that a quarter-wave oscillator of this type can only provide half the output of an oscillator employing a half-wave closed resonator, and that moreover some small loss may be introduced by the presence of the dielectric constituted by the glass wall of the envelope. It is thought, however, that for receiving purposes the reduction in oscillator output will not be serious and that the dielectric loss can be very small if a suitable glass is used and only sufficient capacity is added externally to give a frequency variation of the order of Modifications within the scope of the appended claims will occur to those versed in the art. For example, the tuning device inserted into the extended end of the resonator may be a dielectric rod having low loss properties instead of the metal disc described above. Moreover, the external tuning device may be ganged with the means for adjusting the voltage supplies to the tube in order to maintain synchronism between the oscillations of the electrons and the natural frequency of the resonator.

What is claimed is:

1. An electron discharge device including an evacuated envelope, an open ended resonator having coaxial conductors, said resonator being wholly within said envelope, oscillation generating means combined with the resonator and adjustable tuning means including a capacity element coaxial with and positioned at the open end movably mounted within said reentrant portion of said envelope.

3. An electron discharge device according to claim 1 in which the outer one of said coaxial conductors has an open end and said envelope has a reentrant portion extending into said open end, said external capacity element consisting of a disc located Within said reentrant portion of said envelope, and which includes adjusting means to move said disc in a direction parallel to the axis of said conductors,

4. An electron discharge device according to claim 1 in which the outer one of said coaxial conductors has an open end and said envelope has a reentrant portion extending into said open end, said external capacity element consisting of a disc located within said reentrant portion of said envelope, and a rod of insulating material supporting said disc, said rod being threaded whereby rotation of the rod produces movement thereof parallel to the axis of said coaxial conductors.

5. An electron discharge device according to claim 1 in which said coaxial conductors constitute a resonator of the quarter wave length type, said conductors having apertures therein along a common diameter, and which includes electrode means for projecting an electron beam through said apertures for the velocity modulation of electrons to produce resonant oscillations in said resonator.

CHARLES NORMAN SMYTH.

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