US2975316A

US2975316A - Beam deflection type electron discharge device

Info

Publication number: US2975316A
Application number: US709565A
Authority: US
Inventors: Mark B Knight
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1958-01-17
Filing date: 1958-01-17
Publication date: 1961-03-14
Anticipated expiration: 1978-03-14
Also published as: GB904222A; FR1214035A; DE1095406B

Description

March 14, 1961 M. B. KNIGHT ,9 5,3

BEAM DEFLECTION TYPE ELECTRON DISCHARGE DEVICE Filed Jan. 17. 1958 INVENTOR. MARK B. KNIGHT United States Pateti't G BEAM DEFLECTION TYPE ELECTRO DISCHARGE DEVICE Mark B. Knight, West Caldwell, N.J., assignor to Radio I Corporation of America, a corporation of Delaware 7 Filed Jan. 17, 1958, Ser. No. 709,565 14 Claims. (cl. 313-82) This invention relates to beam deflection type electron tubes and particularly to those in which the electron beam is deflected to selectively divide beam impingement viding'a sheet electron beam; one or two conventional grid electrodes adjacent the cathode and disposed transversely of thebeam path; a pair of imperforate beam de-.

flection plates, one extending along. the sheet beam on either side thereof; and a pair of anode plates disposed substantially transversely of the sheet beam at the end i of the. deflection plates remotefrom the cathode. While providing the general advantages inherent-to beam deflection type electron tubes as mentioned above, such prior art tubes have lacked reasonably good sensitivity and have been subject to electron impingement on the deflection plates. As is well known, the latter is undesirable in that output current is undesirably decreased or otherwise adversely affected due to many of the electrons failing to reach the anode. Also, harmful loading of the signal input circuit results giving an attendant loss of A.C. power and a lower Q in those cases where selective circuits are connected to the deflection plates.

In order to achieve some reasonable measure of sensitivity, priorart tubes have, by necessity, relied upon selectively dividing a sharply focused beam between closely abutting or overlapped anode plates disposed in the central beam path at the focus point of the beam. Thus, a given deflection of the sharply focused beam produces a maximum change of output signal for the given prior an electrode structure. However, even with skilled design of electrodes for sharp beam focus, sensitivity of prior art tubes having beam currents as high as a few milliamperes is low.

Basic electrostatics theory would suggest that sensitivity could otherwise be improved in such prior art tubes focus for obtaining sensitivity, the loss of such focus tends to cancel the advantage of reduced electron beam velocity. It the beam deflection plates are lengthened or are placed closer together in an attempt to achieve greater sensitivity, electron impingement upon: these plates is increased giving the attendant harmful efiects thereof.

Providing a sufliciently negative bias voltage on the deflection plates in order to prevent electron impingement during peak excursions of the signal voltage is impractical because such a measure makes it diflicult, if not impossible, to obtain electron beam flow past the deflection plates to the anodes.

It is therefore an object of my invention to provide an improved beam deflection type of electron tube having high sensitivity and being generally devoid of the undesirable characteristics enumerated above.

Briefly, according to my invention, a beam deflection type electron tube includes means for providing a sheet electron beam, e.g., an elongated cathode and electron beam accelerating grid. A pair of anode plates are disposed one on either side of the beam and extend generally therealoug. One of a pair of foraminous beam deflection grid electrodes is disposed substantially coextensive with each anode plate intermediate that anode plate and the electron beam. In operation, the electron beam is deflected by the foraminous deflection electrodes away from a central path through one or the other of said foraminous deflection electrodes and onto an adjacent anode plate.

In the drawings:

Fig. 1 is a schematic plan view in section of the electrode cage portion of an electron tube illustrating the basic concepts according to my invention;

Fig 2 is an elevation view partly in section of the device of Fig. 1 taken along line 2-2 of Fig. 1; I

Fig. 3 is a schematic transverse sectional view of the electrode cage portion of an electron tube according to modification of my invention;

Fig. 4 is a cut-away perspective view of a preferred embodiment of my invention;

Fig. 5 is a view in cross-section of the device of Fig. 4 taken along line 5-5 of Fig. 4; and

Fig. 6 is a fragmentary sectional view illustrating a modification of the device of Figs. 4 and 5.

Referring to Figs. 1 and 2, an electron tube 10 is shown illustrating the basic concept of my invention. The tube 10 comprises an envelope 12 enclosing an electrode cage including an elongated cathode 14 having an electron emissive coated surface 16. An electron accelerator grid 15 is disposed adjacent the cathode 14 coextensive with the emissive surface thereof. The cathode-accelerator grid arrangement 14-15 is adapted to provide a sheet beam of electrons directed in a path away from and generally perpendicular to the emissive surface 16. A pair of sheet metal anode plates 18 are disposed one on either side of the beam path and extend therealong. A pair of foraminous electron beam deflection grid electrodes 20 are disposed between the anode plates 18 with each grid substantially coextensive with an adjacent one of said anode plates and disposed intermediate that anode plate and the beam path. The foraminous deflection electrodes 20, as illustrated, comprise planar parallel-wire structures. These electrodes may, however, comprise any suitable perforate grid structure known to the art, e.g., wire mesh. Also, as suggested in the preceding brief description of my invention, some conventional means other than the cathode and accelerator grid arrangement 14-15 may be used to provide the desired electron beam. Moreover, this beam need not be of sheet form, but is made so only as an expedient of available power.

With such an electrode disposition, electrons emitted from the cathode 14 pass through the accelerator grid 15 and centrally along and between the two foraminous deflection electrodes 20 when these two electrodes are operated at the same electrical potential. When a potential diiference is applied to the foraminous deflection -electrodes 20, the electron beam is deliberately deflected from the straight central path between these electrodes and caused to pass through one or the other of them and to impinge on the anode plate 18 adjacent thereto.

Analyzing the theoretical operation of the device 10, it will be apparent to one skilled in the art that many of the disadvantages inherent with prior art beam deflection tubes is avoided. For example, according to my' in vention, as schematically illustrated in Fig. 1, it is possible to operate the tube It with a negative bias on the deflection electrodes 20. This is'generally not practical in tubes of prior art design since there a negative bias on the deflecting electrodes prevents passage of the electron beam past the deflection plates and onto the anodes. In the tube according to my invention such is not the case since the potential on the anode plates 18 provides a positive field whose influence is felt in the space between the foraminous deflection electrodes 20 notwithstanding the negative 'bias thereon. This, of course, is possible due to the foraminous nature of the deflection electrodes according to my invention; Furthermore, even though the beam is deliberately deflected into the foraminous deflection electrodes 20, and even though these electrodes may have an instantaneous positive potential on them, electron impingement is at a minimum.

As will be readily appreciated, beam focus per se is not a fundamental requirement for beam deflection type tubes. Rather, this measure was used by the prior art only to obtain some degree of sensitivity. Since, according to my invention, sensitivity is not directly dependent uponbeam focus as it is in prior art tubes, limitations present in prior artdesigns are nonexistent or less severe in my invention. This means that according to my in vention sensitivity maybe improved by the measures-hereinbefore mentioned which could not be applied to the prior art designs. For example: beam velocity may be decreased; the deflection electrodes may be lengthened; or the deflection electrodes may be pcsitioned closer together.

Fig. 3 illustrates an electron tube 30*, according to a modification of my invention. The tube 30 comprisesan envelope 32 enclosing an electrode cage including a cathode 34 having an electron emissive coated surface 36, a control grid 38 adjacent the cathode 34, and an accelerator grid 40 adjacent the control grid 38. Both the control grid 38 and the accelerator grid 40 are disposed substantially coextensive with the cathode emissive surface 36. A pair of anode plates 42 anda pair of foraminous beam deflection grid electrodes 44 (e.-g., parallel cereals wire structures) are provided similar to the anode plates and foram-inous. deflection electrodes 18 and 20- respectively of tube 10, except that they are spaced closer together at their ends remote from the cathode than they are at their ends adjacent the cathode. Theelectrodes of the tube 30 are elongated in a direction as illustrated into and out of the paper similar to the electrodes of tube. 10 in order to utilize the advantages of'a sheet electron beam.

The V-like arrangement of the anode plates and

foraminous deflection electrodes

42 and 44, respectively, serves to provide an even more sensitive deflection control. In this arrangement, as in the tube 10, a given deflection signal will produce a given amount of beam deflection, but the amount of beam deflection necessary to cause the beam to pass through one of the foraminous deflection electrodes 44 and onto its adjacent anode 42 is less than would be necessary in a'parallel arrangement such as illustrated in. Fig. 1. In addition any adverse effects of the undeflected beam completely passing the anode plates and foraminous'deflection electrodes is reduced.

Figs. 4 and 5 illustrate an electron tube 60 according to a preferred embodiment of my invention. The tube 60 comprises an envelope 62 enclosing an electrode cage structure. An elongated cathode 64 is provided with an electron emissive coating 66 on one surface thereof, Conventional wire-wound half grids 68 and 17.0 are. disposed adjacent to and substantially coextensive with. the

emissive surface 66 of the cathode 64. The

half grids

68 and 70 serve respectively as a control grid and an accelerator grid. Such a cathode and grid arrangement is adapted to provide a sheet beam ofelectrons along a path generally perpendicular .to and away from the coated surface 66 of the cathode 64.

A V-like disposition of'anode plates 72 and foraminous deflection grid electrodes 73 opening toward the cathode 64 is provided somewhat similar to the arrangement of the anode plates 42 and foraminous deflection electrodes 44 of tube 3%, excepting that a foraminous deflection electrode 73 does not lie parallel to its adjacent anode plate 72. Rather, eachyforaminous deflection electrode 73 and its adjacent anode plate 72 are disposed closer together at their ends remote from thecathode 64 than at their ends adjacent the cathode 64. Stated otherwise the V angle formed by the anode plates 72 is greater than the V angle formed by the deflection grid electrodes 73. A plurality: of lead-ins 74 are provided through one end of the envelope 62 to permit application of suitable electrical potentials to the electrodes therein.

In the tube 60 the use of conventional wire-wound half grids for the foraminous deflection electrodes 73 permits the relatively heavy side rods 75 at the end remote from the cathodeto be disposed out and away from the central, no-deflection-signal beam path. With the forarninous deflection electrode side rods 75 soshielded the anode plates 72, electron reception therebyis practically eliminated.

The'tube 60. also includes a sheet metal tubular shield 76 snrrounding t he tube electrodes. The shield 76 serves to reduce certain interelectrode capacitances, to shield the tube electrodes from external magnetic fields, and to prevent any of theelectron beam from passing completely past the anode plates '72 via a central beam path. Merely operatingthe. shield, 76 at; cathode potential provides a substantially complete. reflector to" electrons tending to follow a central beam path through the. opening between the anode plates 72 at the end remote from the cathode. Howevena more effective reflection of the beam can be achieved according to the structure illustrated in Fig. 6.

Big. 6 shows a modification of the shield 76 of Figs. 4 and 5 which can be incorporated in place of the shield 76 thereof. According to Fig. 6 a shield 80 is provided which includes a re-entrant portion 82 at the end thereof remote, from the cathode. The re-entrant, portion 82 is contoured, along the, ends of the foraminous deflection electrodes '73 such. that it extends] closely adjacent he 'e ds' f he anode'pl tes 72. Sucha ge me ric disposition; or; the end or the shield 80 provides a more effective, reflection of electrons by returning the electrons which pass the anode plates 72 back-toward these plates in trajectories which are less likely to encounter the dcfiection electrode side rods 75;

According, to a preferred: practice of my invention, the, various'electrodes' are so dimensioned and disposed as to provide for the formation of a properly directed sheet electron beam which tends toconverge at the far endsof the anode plates.. Accordingly, one experimental tube2 design constructed according to Figs. 4 and 5 had the following dimensions and relative disposition.

(a) A control grid 68 of 2 mil wire, 'turns per inch,

and mil distance between side rods.

(12) An accelerator grid 70 of- 2.5 'mil wire, 72 turns per I inch, and 220 mildistancebetween side rods.

(e);;Fe1-aminous deflection electrodes74 of 2 mil wire, 'Zflturnsper'inch, and 400 mil distance between side rods.

(it) Length; of anode plate; 72 asviewed in Fig. 5, 340

mils.

(2}) Width of, cathode 64; (extentalong control grid 68 asyiewedin Fig- 5). 8 .111ils. Y

(f), Spacing between, cathode 64, and. control, grid 68', 6

76 j mils. Y

(g) Spacing between control grid 68 and

accelerator grid

70, 16 mils.

(h) The V angle disposition of anode plates 72, 10.2. (i) The .V angle disposition of foraminous deflection electrodes 74, 85. (j) Spacing between the two anode plates 72 at the ends adjacent cathode 64, 150 mils.

(k) Spacing between the two foraminous deflection electrodes 74 at the ends of the planar portion thereof adjacent cathode 64, 120 mils.

(l) Spacing between the two anode plates 72 at the ends remote from cathode 64, 36 mils.

(m) Spacing between the two foraminous deflection electrodes 74 at the ends of the planar portion thereof remote from cathode 64, mils.

(n) Spacing between cathode 64 and anode plates 72,

1 55 mils.

(0) Spacing between cathode 64 and foraminous deflection electrodes 74, 125 mils.

(p) Spacing between a foraminous deflection electrode 74 and its adjacent anode plate 72 at the end adjacent cathode 64, mils.

(q) Spacing between a foraminous deflection electrode 74 and its adjacent anode plate 72 at the end remote from cathode 64, 10 mils.

It will be appreciated that various. modifications can be made according to my invention. For example, conventional screen and suppressor grids can be added between each of the foraminous deflection electrodes 74 and its adjacent anode plate 72. This and other modifications will be readily suggested to one skilled in the art.

Y What is claimed is: i

1. An electron tube of the beam deflection type comprising means for providing a single beam of electrons generally along a predetermined path; a pair of anode plates disposed in substantially mutual facing relationship on opposite sides of said predetermined path; and a pair of separate foraminous electron beam deflection grid electrodes disposed substantially coextensive with said anode plates and adapted to have an electric signal applied between them, each of said foraminous deflection electrodes being intermediate a different one of said anode plates and said predetermined path.

2. A beam deflection type electron tube comprising a pair of anode plates in substantially facing relation to each other; a pair of separate foraminous electron beam deflection grid electrodes intermediate said anode plates and substantially coextensive therewith and adapted to have an electric signal applied between them; a cathode disposed adjacent one end of said anode plates and having an emitting surface facing along a predetermined path intermediate said foraminous deflection electrodes; and an electrode adjacent said emitting surface and adapted to accelerate electrons emitted by said emitted surface along said predetermined path.

3. A beam deflection type electron tube comprising a cathode having an emitting surface for generating electrons adapted to be beamed generally along a single predetermined path; a pair of anode plates disposed one on either side of said predetermined path and extending generally therealong in facing relation to each other; a pair of separate foraminous electron beam deflection grid electrodes adapted to have an electric signal applied between them, each disposed adjacent to and substantially coextensive with a different one of said anode plates and intermediate said adjacent anode plate and said predetermined path.

4. An electron tube of the beam deflection type comprising a cathode having an emitting surface facing generally along a predetermined path; a pair of anode plates, one disposed on either side of said predetermined path and extending therealong facing said predetermined path, said cathode being disposed adjacent one end of said pair of anode plates, said anode plates being spaced further apart at said one end than at the end remote from said one end; and a pair of separate foraminousfelectron beam deflection grid; electrodes disposed between said anode plates substantially coextensive therewith and adapted to have an electric signal applied between them, one on either side of said predetermined path.

5. An electron tube of the beam deflection type comprising a cathode having an emitting surface facing generally along a predetermined path; a pair of anode plates, one disposed on either side of said given path and extending therealong facing said predetermined path, said cathode being disposed adjacent one end of said pair of anode plates, said anode plates being spaced further apart at said one end than at the end remote from said one end; and a pair of separate foraminous electron beam deflection grid electrodes disposed between said anode plates substantially coextensive therewith one on either side of said predetermined path, each of said foraminous deflection electrodes being spaced further from its adjacent anode plate at said one end thereof than at said end remote from said one end, said cathode, anode plates, and deflection grid electrodes forming a structure symmetrical about said path.

6. A beam deflection type electron tube comprising: a cathode having an emitting surface facing generally along a predetermined path; a pair of anode plates spaced from each other in a V-like arrangement, each of said anode plates being disposed on opposite sides of and along said predetermined path away from said cathode with the V thereof opening toward said cathode; and a pair of separate foraminous electron beam deflection grid electrodes spaced fro-m each other in a V-like arrangement, said pair of foraminous deflection electrodes being disposed substantially between said anode'plates on opposite sides of said predetermined path with the V thereof opening toward said cathode, each of said foraminous deflection electrodes being substantially coextensive with .its adjacent anode plate, the V of said foraminous deflection electrodes being more acute than the V of said anode plates.

7. An electron tube of the beam deflection type comprising a cathode having an emitting surface facing generally along a predetermined path; at least one grid electrode disposed adjacent said cathode transversely of said predetermined path; a pair of anode plates disposed on the opposite side of said at least one grid electrode from said cathode in substantially mutual facing relationship on opposite sides of said predetermined path; and a pair of separate foraminous electron beam deflection grid electrodes disposed substantially coextensive with said anode plates, each of said foraminous deflection electrodes being intermediate a different one of said anode plates and said predetermined path.

8. An electron tube of the beam deflection type comprising an electrode cage including a cathode having an emitting surface facing generally along a predetermined path; a pair of anode plates, one disposed on either side of said given path and extending therealong facing said predetermined path, said cathode being disposed adjacent one end of said pair of anode plates, said anode plates being spaced further apart at said one end than at the end remote from said one end; at least one grid electrode disposed intermediate said cathode and said pair of anode plates transversely of said predetermined path; and a pair of separate foraminous electron deflection grid electrodes disposed between said anode plates substantially coextensive therewith, one oneither side of said predetermined path.

9. An electron tube of the beam deflection type comprising a cathode having an emitting surface facing generally along a predetermined path; a pair of anode plates, one disposed on either side of said predetermined path and extending therealong facing said predetermined path, said cathode being disposed adjacent one end of said pair of anode plates, said anode plates being spaced further apart at said one end than at the end remote from said one end; an electron control grid disposed intermediate said cathode and said pair of anode plates transversely of said predetermined path; an electron accelerator grid disposed intermediate said electron control grid and said pair of anode plates transversely of said predetermined path; and a pair of separate foraminous electron beam deflection grid electrodes disposed between said anode plates substantially coextensive therewith, one on either side of said predetermined path.

10. An electron tube of the beam deflection type comprising an electrode cage including a cathode having an emitting surface facing generally along a predetermined path; a pair of anode plates, one disposed on either side of said given path and extending therealong facing said predetermined path, said cathode being disposed adjacent one end of said pair of anode plates, said anode plates being spaced further apart at said one end than at the end remote from said one end; at least one grid electrode disposed intermediate said cathode and said pair of anode plates transversely of said predetermined path; and a pair of separate foraminous electron deflection grid electrodes disposed between said anode plates substantially coextensive therewith one on either side of said predetermined path, each of said foraminous deflection electrodes being spaced further from its adjacent anode plate at said one end thereof than at said end remote from said one end.

ll. A beam deflection type electron tube comprising: an electrode cage including a cathode having an emitting surface facing generally along a predetermined path; a pair of anode plates spaced from each other in a V-like arrangement, each of said anode plates being disposed on opposite sides of and along said predetermined path away from said cathode with the V thereof opening toward said cathode; an electron control grid disposed intermediate said cathode and said pair of anode plates transversely of said predetermined path; an electron aceelerator grid disposed intermediate said electron control grid and said pair of anode plates transversely of said predetermined path; and a pair of separate foraminous electron beam deflection gridelectrodesspaced from each other in a V-like arrangement, said pair of foraminous deflectionelectrodesfbeing disposed substantially between said anode plates on opposite sides of said predetermined path with the. V thereof openingtoward said cathode, each of said foraminous deflection electrodes being substantially coextensive with its adjacent anode plates, the V of said forarninous deflection electrodes being more acute than the V of said anode plates, said electrode cage being symmetrical about said path.,

12. An electron tube according to claim 8 and including a tubular metallic shield member surrounding said electrode cage.

13. An electron tube according to claim 10 and including a tubular metallicfshield member surrounding said electrode cage. 7

14.. An electron tube according to claim 11 and including a tubular metallic. shield member surrounding said electrode cage, said shield member having a reentrant'portion disposed adjacent the ends of said foraminous deflection electrodes. and said anode plates remote from said cathode.

References Cited in the file of this patent UNITED STATES PATENTS 1,630,753 Massolle May" 31, 1927 2,075,379 V-arian Mar. 30, 1937 2,143,378 Kallmann Ian. 10, 1939 2,190,069 Hollmann Feb 13, 1940 2,193,959 Bull" Mar. 19, 1940 2,256,335, Aldous, Sept. 16 1941 2,273,546, Van Weel Feb. 17, 1942 2362.916 Van Overbeek Sept 11, 1956.