US2576702A - Velocity modulation electron discharge device - Google Patents

Description

Patented Nov. 27, 1951 VELOCITY MODULATION ELECTRON DISCHARGE DEVICE William J. Scott, Rugby, England, assignor to General Electric Company, a corporation of New York Application December 27, 1946, Serial No. 718,797

In Great Britain December 22, 1941 Section 1, Public Law 690, August 8, 1946 Patent expires December 22, 1961 5 Claims.

My invention relates to electron discharge devices of the velocity modulation type employing one or more cavity resonators, and is particularly concerned with such devices in which at least one of the walls of the resonator is flexible and adjustable relative to an opposed Wall to vary the resonant frequency of the cavity.

Hitherto the dimensions of the resonating chamber have usually been such that the diameter of the glass portions of the envelope necessary to support and seal the electron gun and electron collecting or reflecting electrode to the cavity resonator is less than that of the resonator. The glass, portions have thus been ring sealed to opposite faces of the resonator which forms a part of the evacuated envelope of the device. With an increase in the operating frequency at which the device operates, however, the size of the resonator becomes such that it may readily be included Within the envelope. My invention relates to an improved structure for velocity modulation devices and particularly to such devices for higher operating frequencies which may be more readily manufactured with the required accuracy.

It is the object of my invention to provide a sim lified construction for devices of the above type which facilitates their manufacture and assembly.

It is another object of my invention to provide an improved tunable resonator for velocity modulation devices.

According to one illustrated embodiment of my invention, one wall of the resonating chamber is made rigid and is rigidly mounted with relation to a stem which also supports the electron gun or cathode structure while the other wall of the chamber is made resilient and is connected with a resilient wall portion of the envelope so that the dimensions of the chamber may be varied. The reflecting electrode is also supported by a lead sealed through the stem to provide a singleended construction of the device and to render the position of the reflecting electrode independent of the flexible wall.

My invention will be better understood by reference to the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims. In the drawing, Fig. 1 is an elevational view in section of an electric discharge device embodying my invention and Fig. 2 is an elevational view in section of a modification.

Referring now to Fig. 1 of the drawing, the member I forming a rigid wall of a resonating chamber 2 is located wholly within the envelope of the device. The envelope includes a stem 3 attached to a glass wall portion 4 to which is sealed a metal wall portion 5 terminating at its end remote from the stem 3 in a resilient wall portion 6. These three parts are sealed together so as to form a vacuum-tight envelope, the glass portion 4 and the metal portion 5 being of such compositions that their thermal expansion characteristics are matched to insure a substantially strain-free seal between them.

The member 1 consists of a relatively heavy disc of metal, such as copper, which is recessed to provide part of the resonating chamber 2. The resonating chamber 2 is completed by a resilient wall portion 8 secured to the open face of the member I. The resonator is supported from the stem 3 by means of rigid leads I, which are joined to the member I and are sealed to the stem 3. A cathode or electron gun 9 is also supported on the stem 3 and positioned to direct an electron beam through aligned apertures formed in the walls of the resonating chamber 2. As illustrated, the rigid member I is provided with an inwardly directed conical flange I which terminates just short of the apertured resilient wall to define a gap 2 across which the beam of electron passes. A reflector electrode l0 positioned beyond the wall 8 is supported from the stem 3 upon a relatively rigid member II which is offset to accommodate the resonator. The resonator may be slotted as illustrated at I! to receive the member ll.

Preferably the rigid part I of the resonator fitsclosely into the metal portion 5 of the envelope and its thermal contact with the envelope may be improved by the known method of melting pure tin during the exhaust into the minute space so formed.

Secured to the resilient wall portion 6 of the envelope is a member 13 having a threaded shank l4 extending through the resilient wall of the envelope in a vacuum-tight manner. The member 13 is secured at its lower end l5 to the resilient wall portion 8 of the resonating chamber and owing to the ability of the resilient Wall portion 6 of the envelope to deflect, it is possible by deflecting the resilient wall 8 to alter the width of the gap 2' across which the electron beam is projected and consequently to alter the resonant frequency of the cavity. This deflection may be effected with considerable accuracy in accordance with the invention by means of a differential screw supported in a fixed ,part' external to the envelope and mechanically connected with the screw-threaded shank [4 of the member l3.

3 As illustrated in the drawing, a rigid transverse member IB is provided with an opening for the reception of the envelope 5 and its suitably bonded thereto as by welding; A. similar rigid member H is secured to the flexible wall 6 and through the member 13 is directly connected with the flexible wall 8 of the resonator. Member 16 carries a pair of vertical rigid arms |8which are interconnected at their upper ends by a rigid transverse member l9. In a similar way the member I! carries a pair of vertically extending arms 20 which are interconnected at their upper ends by a transverse member 2|. Transverse members I9 and 2| are interconnected by a differential screw mechanism including a thumb screw 22 having an external thread received in a threaded opening in the transverse member i9 and having an internal thread for receiving a threaded stud 23 which is rigidly secured to the transverse member 2|. The external and internal threads of the screw 22are of the same hand but of different pitch so that rotation of the screw 22 effectsrelative movement of the members l9 and 2| in accordance with the difference inpitch of the two threads. In order to minimize the effect of backlash in the threads, 21. compression spring 24 is interposed between the members l9 and 2|. It is well understood that resonators of the type provided by the rigid member and flexible. wall 8 tend to change dimensions with changes in operating temperature.. In order to compensate for terminal changes and: maintain the operating frequency substantially constant, the rigid portions l8 and 20 may be formed respectively of materials having different temperature coefficients of. expansion. By a proper selection of the materials and the dimensions of the parts employed, it will be apparent that automatic compensation for temperature changes are effected. Iron and brass may be employed as suitable materials for the parts i8 and 20. High-frequency energy maybe extracted from the resonator by means of a section of concentric transmission line including an inner conductor 25-andanouter conductor 26. The inner conductor is coupled to the interior of the resonator by meansof a suitable coupling loop 21 and the end of the transmission line section is closed by abody of glass 28-sealed to the outer conductor and enclosing the end of the. inner conductor.

It will also be appreciated that suitable leadin conductors connected with the various electrodes may be sealed'in the stem 3 and connected with thecontact prongsof a conventional tube base (not shown).

The discharge device described above is a reflexed type velocity modulation oscillator, and-its operation is believed to be well understood. Electronsv emitted by the cathode structure 8 pass. throughthe aligned aperture in. the resonatorz'. As itis assumed that a high frequency voltage appears across the gap 2, the beam is velocity modulated. The electrons of the seal are then re'sealed by the reflex electrode 0 which is operated at a suitable positive potential, and returned through the resonator in proper phase returns to reinforce the high frequency oscillation which produced the. modulation of the beam. In this way substantially high frequency voltages are built up across the gap and high frequency energy may be extracted from the cavity by means of the transmission line including 'conductors: 25,-.and26'.

In Fig. 2 I have shown a modification of my invention which is in general similar to that shown in Fig. 1 and corresponding parts have been designated by the same reference: numerals. In Fig. 2 the rigid body I forming part of the resonator is of larger diameter than the body of the envelope and extends beyond the envelope wallas illustrated.

The body is received between the opposed flanges 29 of envelope sections 30 and 3| which correspond to the rigid envelope member 5 of Fig. 1. In the'modification shown in Fig. 2, the outer conductor of the transmission is provided by-the. defining wall of a cylindrical recess provided in the resonator body The inner conductor of the transmission line is sealed through the glass body 28 so that the output may be conductively connected with a further. section of concentric transmission line.

It will be apparent from the foregoing description thatv myinvention provides a tube structure which is particularly, well adapted for the manufactureof very high frequency devices and which provides for the ready adjustment of the operating frequency.- The construction also provides a single-ended discharge device in which the refleeting electrode is supported independently of the movable wall of the resonator.

While I have described and illustrated a particular embodiment of my invention, it will be obvious to those skilledi'n the art that changes and modifications may be madewithout departing from my invention in its broader aspects and I therefore aim in the appended claims to cover all such changes and modifications. as an. within the true spirit and scope of my invention.

What I claim as new andv desire to secure by Letters Patent of'the United States is:

1. An electric discharge device of the velocity modulation type including an envelope, a cavity resonator including a rigid wall part supported in fixed relation to saidenvelope and. a flexible wallsecured to said rigidwall and cooperating therewith to define the resonator, a cathode supportedon the side of said resonator opposite said flexible. wall, areflector electrode on the opposite side of said resonator and supported in fixed relation to said envelope, said envelope including a flexible wall, and-mechanical means connecting said flexible wall of said resonator with said flexible wall of said envelope for producing movement of said flexible wall with respect to said rigid wall.

2. Anelectric discharge device of the velocity modulation type including an envelope, a cavity resonator including a rigid wall part supported in fixed relation Within said envelope and a flexible wallsecured to said rigid wall and cooperating therewith to define the resonator, a oath ode supported on one side of said resonator from one end of said envelope, a reflector electrode on the'opposite side of said resonator and supported in fixed relation to said envelope, and mechanical means connecting said flexible wall with a flexible wall portion provided in the-opposite end of said envelope for producing movement of said-flexible wallof'said resonator with respect to said rigid wall thereof.

3. An electric discharge device of the velocity modulation type including an'envelope, a cavity resonator supported within the envelope and including opposedwalls having aligned entrance and exit openings respectively, the wall in which saidexit'opening is provided being'fi'exible, a oathodesupported. in fixed relation with respect to awavoe said envelope on the side of said resonator nearer the entrance opening for providing a stream of electrons which pass through the entrance and exit openings of said resonator, a reflecting electrode supported in fixed relation with respect to said envelope on the side of said resonator nearer said exit opening and in alignment with said entrance and exit openings, means joined to the flexible wall of said resonator adjacent said exit opening and means interconnecting said last-mentioned means and a rigid portion of said envelope for producing movement of the flexible wall of said resonator with respect to the opposite wall thereof.

4. An electric discharge device of the velocity modulation type including an envelope, a cavity resonator supported wholly within the envelope and including aligned entrance and exit openings formed in the walls thereof, the wall around said exit opening being flexible, a cathode supported in fixed relation with respect to said envelope on the side of said resonator nearer the entrance opening for providing a stream of electrons which pass through the entrance and exit openings of said resonator, a reflecting electrode supported in fixed relation with respect to said envelope on the side of said resonator 1 nearer said exit opening and in alignment with said entrance and exit openings, a tubular member joined to the flexible wall of said resonator adjacent said exit opening and recessed to receive said reflecting electrode and means interconnecting said last-mentioned means and a rigid portion of said envelope for producing movement of the flexible wall of said resonator with respect to the opposite wall thereof.

5. An electric discharge device of the velocity modulation type including an envelope, a cavity resonator supported within the envelope and including aligned entrance and exit openings formed in the walls thereof, the wall around said exit opening being flexible, a cathode supported in fixed relation with respect to said envelope on the side of said resonator nearer the entrance opening for providing a stream of electrons which pass through the entrance and exit openings of said resonator, a reflecting electrode supported in fixed relation with respect to said envelope on the side of said resonator nearer said exit opening and in alignment with said entrance and exit openings by means including a conductor extending around said resonator, means joined to the wall of said resonator adjacent said exit opening and means interconnecting said last-mentioned means and a rigid portion of said envelope for producing movement of the flexible wall of said resonator with respect to the opposite wall thereof.

WILLIAM J. SCOTT.

REFERENCES CITED The following references are of record in the ,file of this patent: v

UNITED STATES PATENTS Number Name Date 2,167,201 Dallenbach July 25, 1939 2,259,690 Hansen et a1 Oct. 21, 1941 2,406,850 Pierce Sept. 3, 1946 2,439,387 Hansen et al. Apr. 13, 1948

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