US3358180A

US3358180A - Electromagnetic wave confining structures having electrically conductive coated dielectric walls and electron tube incorporating them

Info

Publication number: US3358180A
Application number: US365257A
Authority: US
Inventors: James A Jolly
Original assignee: Varian Associates Inc
Current assignee: Varian Medical Systems Inc
Priority date: 1964-05-06
Filing date: 1964-05-06
Publication date: 1967-12-12
Anticipated expiration: 1984-12-12
Also published as: NL6505455A; GB1112026A; GB1112027A

Description

A. JOLLY ELECTROMAGNETIC WAVE GONFINING STRUCTURES HAVING ELECTRICALLY Dec. 12, 1967 J.

CONDUCTIVE COATED DIELECTRIC WALLS AND ELECTRON TUBE INGORPORATING THEM 2 Sheets-Sheet 1 Filed May a, 1964 CBYPASS gk INVENTOR.

JAMES A. JOLLY By H Wm ATTORNEYS 3,358, 1 80 ELECTROMAGNETIC WAVE CONFINING STRUCTURES HAVING ELECTRICALLY Dec. 12, 1967 J. A. JOLLY CONDUCTIVE COATED DIELECTRIC WALLS AND ELECTRON TUBE INCORPORATING THEM 2 Sheets-Sheet 2 Filed May 6, 1964 INVENTOR. JAMES A. JOLLY How WI MW ATTORNEYS United States Patent 3,358,180 ELECTROMAGNETIC WAVE CONFINING STRUC- TURES HAVING ELECTRICALLY CONDUCTIVE COATED DIELECTRIC WALLS AND ELECTRON TUBE INCORPORATING THEM James A. Jolly, San Carlos, Calif., assignor, by rnesne assignments, to Varian Associates, a corporation of California Filed May 6, 1964, Ser. No. 365,257 11 Claims. (Cl. 315-533) ABSTRACT OF THE DISCLOSURE A hollow dielectric body having an electrically conductive, plasma sprayed coating on the exterior surface thereof confining an electromagnetic wave. The interface of the conductive coating at the dielectric surface provides greatly reduced R.F. losses over that of metallized dielectric bodies.

This invention relates generally to electromagnetic Wave confining structures and more particularly relates to electromagnetic wave confining structures providing internal resonant cavities for an electron tube designed for operation in the high frequency ranges.

Electromagnetic wave confining structures have generally been made of an envelope of high electrically conductive material, such as copper. Typical examples of electromagnetic wave confining structures are waveguides and resonant cavities.

In some situations, it has been desirable to provide or insert portions of segments of dielectric materials within the metal envelope making up the electromagnetic wave confining structure so as to decrease the velocity of the electromagnetic energy located Within the electromagnetic wave confining structure. Dielectric materials which have been inserted in electromagnetic wave confining structures generally have a dielectric constant that is many times the dielectric constant that is provided by vacuum or air and hence, provide a velocity delay propagation factor that is much greater than the velocity delay propagation factor that is provided by vacuum or air. Consequently, dielectric materials have been used in the past as inserts Within electromagnetic wave confining structures to change the electrical characteristics therein.

The metal cavities of the prior art with or without dielectric inserts had the disadvantages of being fairly large, heavy, and lacked electrical stability due to distortion of the metal walls of the cavity because of the high thermal coeflicient of expansion characteristics of the metal. In addition, prior art resonant cavities were structurally restricted in size to a particular cavity configuration that would have a single resonant frequency for a particular mode of resonance.

Electron tubes designed for operation in the higher frequency ranges have been made with internal cavity resonator structures whereby R.F. energy can be coupled into an input cavity for interacting with the electrons in the tube and an output cavity was provided for extracting the amplified R.F. energy. In this type of electron tube, the envelop was generally made of an electrically conductive metal material that formed the cavity resonators for the electron tube. Consequently, the above enumerated disadvantages of metal cavities were present in prior art internal cavity types of electron tubes.

It is an object of this invention to provide an improved electromagnetic wave confining structure.

It is another object of this invention to provide an improved electromagnetic wave confining structure containing different dielectrics therein, each of which have different velocity delay propagation factors.

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It is a still further object of this invention to provide an improved resonant cavity.

It is another object of this invention to enable the construction of different sizes of cavity resonators which would have the same resonant frequency for a given mode of resonance.

It is a further object of this invention to enable the construction of a given size of cavity resonator which is designed in accordance with this invention to vary the resonant frequency for a given mode of resonance.

It is an object of this invention to provide an improved electron tube.

It is a further object of this invention to provide an improved internal cavity type of electron tube.

It is a still further object of this invention to provide an internal cavity type of electron tube whose cavities are light in weight, rugged, and formed from a material that has a relatively low thermal coefficient of expansion thereby increasing stability and preventing distortion by the cavity.

These and other objects of the invention will become more clearly apparent from the following description when taken in conjunction with the accompanying drawing.

Referring to the drawing:

FIGURE 1 is an elevational cross-sectional view of an electron tube;

FIGURE 2 is a perspective elevational view of a window for use in coupling R.F. energy into and out of the electron tube of FIGURE 1;

FIGURE 3 is a cross-sectional view of another embodiment of a capacitor which acts as a DC. block and R.F. by-pass for use in the electron tube of FIGURE 1;

FIGURE 4 is a schematic view of the electrical circuit provided by one of the two resonant cavities of the electron tube of FIGURE 1;

FIGURE 5 is a schematic view of an electrical circuit provided by the other of the two resonant cavities of the electron tube of FIGURE 1;

FIGURE 6 is a cross-sectional view of one cavity resonator embodiment made in accordance with this invention;

FIGURE 7 is a cross-sectional view of another cavity resonator embodiment made in accordance with this invention;

FIGURE 8 is a cross-sectional view of still another cavity resonator embodiment made in accordance with this invention; and

FIGURE 9 is a cross-sectional view of another cavity resonator embodiment made in accordance with this invention.

Briefly described, this invention relates to an electromagnetic wave confining structure which is formed by a hollow, evacuated dielectric body having an electrically conductive coating on the outer surface thereof. The electrically conductive coating that is on the dielectric body provides a very low R.F. loss interface. The electromagnetic wave energy permeates the dielectric body and is confined by the electrically conductive coating.

This invention also relates to an electron tube which has an envelope that encloses electrodes including a cathode. The envelope is a dielectric wall that has an electrically conductive coating that is on the dielectric body terior surface thereof. The electrically conductive coating on the dielectric wall defines at least one resonant cavity for interacting with the electrons in the electron tube.

Referring to FIGURE. 1, an electron tube 10 is shown having a first resonant cavity 12 and a second resonant cavity 14. The first resonant cavity 12 is provided by the combination of a substantially cup-shaped dielectric member 16, which is preferably ceramic, and an electrically conductive coating 18 provided on the exterior or outer surface of the dielectric member 16. The electrically conductive coating 18 is deposited onto the exterior surface of the dielectric member 16 by conventional coating techniques, flame spraying, etc., but the plasma spraying of a highly conductive metal material, such as copper, onto ceramic has been discovered to be the only way to form a permanent, substantially loss free, good electrical path for the conductive portion of a resonant cavity. By plasma spraying, copper is vaporized and caused to be densely deposited onto the ceramic due to the potential difference between the copper plasma and the ceramic that is created in the plasma spraying technique. The copper thickness that is plasma sprayed onto the ceramic is varied depending on the desired current carrying requirements that the copper coating must meet. In this manner, R.F. losses are avoided by eliminating the high R.F. interface loss caused by a metallized surface.

Similarly, the resonant cavity 14 is a substantially cupshaped dielectric member 20 which contains an electrically conductive coating 22 on the exterior surface thereof.

The dielectric cup-shaped member 16 supports a cylindrical cathode element 24 which contains an electron emitting surface 26. The electron emitting surface 26 of the cylindrical cathode element 24 is made from any conventional electron source material which is deposited on the flat end surface of the cylindrical cathode element 24. The cathode element 24 is preferably brazed to an annular metalized portion which is located on the outer surface of an inwardly protruding hollow, annular, dielectric portion, generally designated by numeral 28, which is formed in the dielectric cup-shaped portion 16. The electrically conductive coating 18 is deposited onto the lower portion of the cylindrical cathode element 24 so as to provide an electrical connection between the electrically conductive coating 18 and the metal cylindrical cathode element 24.

Supported between the cup-shaped

dielectric elements

16 and 26 is a metal disk 30 on which is mounted a control grid 32 which is preferably brazed thereto. The metal disk 30 is hermetically sealed to metallized portions formed on the contacting end surfaces of the cup-shaped

dielectric members

16 and 20 by being brazed thereto.

The substantially cup-shaped dielectric member 20 has an inwardly protruding, hollow, dielectric portion generally designated by the numeral 34. A cylindrical anode element 36 is preferably brazed to an annular metalized portion located on the outer surface of the inwardly protruding, hollow, dielectric portion 34. The anode element 36 has a flat electron receiving surface portion 38 positioned to receive electrons passing through the control grid 32 from the electron emitting portion 26 of the cylindrical cathode element 24. The electrically conductive coating 22 is deposited onto the lower portion of the cylindrical anode element 36 to form an electrical connection therewith.

The resonant cavity 12 is dimensioned so that the axial distance from the metal disk 30 to the electrically conductive coating 18 on the bottom exterior portion of the dielectric cup-shaped member 16 is preferably about 7t/4 electrical wavelengths long where is the resonant wavelength of the mode of resonance contained within the cavity 12. The resonant cavity 14 is dimensioned such that the axial distance from the metal disk 30 to the electrically conductive coating 22 on the top exterior portion of the dielectric cup-shaped member 20 is M2 electrical wavelengths long where A is the resonant wavelength of the mode of resonance in the cavity 14.

Along the surface of the dielectric cup-shaped member 16 which contacts the metal disk 30 is an annular dielectric flange portion 40 which functions as a combination D.C. block and by-pass capacitor for the RF. energy propagating along the electrically conductive coating 18 on the cup-shaped dielectric member 16. Similarly, the cup-shaped dielectric member 20 is provided with a D.C. block and by-pass capacitor formed by an annular dielectric flange portion 42 located adjacent the inwardly projecting dielectric portion 34. The by-pass capacitor formed by the dielectric flange portion 42 is adjustable by reducing or increasing the amount of surface on the dielectric flange portion 42 that the electrically conductive coating 22 covers in the region 43 of the by-pass capacitor. This adjustment of the by-pass capacitor 42 functions to tune the resonant cavity 14 to the desired resonant frequency for a particular mode of resonance propagating in the cavity. The resonant cavity 12 can be similarly tuned by varying the amount of surface on the dielectric flange portion 40 that the electrically conductive coating 18 covers in the region 45 of the by-pass capacitor.

It should be apparent to those skilled in the art that a heating element can be inserted into the annular hollow space formed by the inwardly protruding dielectric projection 28 to heat the electron emitting surface 26 of the cylindrical cathode element 24. Fluid cooling means can be inserted in the annular hollow space formed by the inwardly projecting dielectric portion 34 to cool the cylindrical anode element 36.

Referring to FIGURE 2, an R.F. coupling window 44 is shown which is located on the exterior surface of cupshaped

dielectric members

16 and 20. The R.F. coupling window 44 is preferably a substantially oval-shaped portion on the exterior surface of cup-shaped

dielectric members

16 and 20 that is not covered with the electrically

conductive coatings

18 and 22, respectively. The R.F. coupling window 44 can be adjusted to vary the amount of R.F. energy that is coupled through the dielectric member 16 of the window 44 by depositing or removing the electrically conductive coating 18 along the

end portions

46 and 43 of the window 44-.

FIGURE 3 illustrates another embodiment of a combination D.C. block and by-pass capacitor for the R.F. energy that is generally designated by the numeral 50. An annular dielectric member 52 substantially Z-shaped in cross-section is inserted along the wall of either dielectric cup-shaped

portions

16 or 20 and thus provides a by-pass capacitor for the RP. energy. The by-pass capacitor is formed between the electrically

conductive coatings

54 and 56. In this manner,

flange portions

40 and 42 can be eliminated and thus simplifying the fabrication of the cup-shaped

dielectric elements

16 and 20.

FIGURES 4 and 5 are schematic views of the electrical circuit that is provided by

resonant cavities

12 and 14, respectively. The resonant cavity 12 is depicted in FIG- URE 4 as having an inductance 58 and a pair of

capacitors

60 and 62. Capacitor 60 is the by-pass capacitor represented by the dielectric portion 40 of the cup-shaped dielectric member 16. Capacitor 62 is the capacitance formed between the grid 32 and the cathode 26. The capacitor 60, due to the dielectric flange portion 40, has a greater capacitance than the capacitance of the capacitor 62. Therefore, the cathode to grid capacitor 62 is not affected by the by-pass capacitor 60 in the circuit of FIG- URE 4 and consequently the resonance frequency of the resonant cavity 12 for a particular mode of resonance is not significantly influenced by the by-pass capacitor 60.

In FIGURE 5, the grid to anode capacitance is designated by the capacitor 64 and is symmetrically disposed with respect to the adjustable by-pass capacitor 66 which is provided by the dielectric portion 42 adjacent the inwardly protruding dielectric portion 34 of the dielectric cup-shaped member 20. The inductance of the resonant cavity 14 is designated by the numeral 68. The capacitance of the adjustable capacitance 66 should be substantially equal to the capacitance of the capacitor 68, and this can be done by varying the amount of surface on the dielectric flange 42 that the metallic coating 22 covers until a capacitance match is achieved.

FIGURES 6, 7, 8 and 9 depict various types of cavity resonators which can be used in accordance with the teachings of this invention. FIGURE 6 is a cross-sectional view of a rectangular type of cavity resonator. The cavity resonator of FIGURE 6 is formed by means of an electrically conductive coating 70 which is provided on the exterior surface of a hollow, rectangular, dielectric body 72. Similarly, in FIGURE 7 which is a cross-sectional view of a cylindrical type of cavity, the cavity resonator is formed by means of an electrically conductive coating 74 which is formed on the exterior surface of a hollow, cylindrical dielectric body 76. A pair of

metal end plates

78 and 80 are electrically joined to the electrically conductive coating 74 to form the resonator cavity.

FIGURE 8 is a cross-sectional view of a spherical cavity resonator formed by an electrically conductive coating 82 which is deposited on the exterior surface of a solid dielectric sphere 84.

In FIGURE 9, an electrically conductive coating 86 is formed on a hollow, cylindrical, dielectric body 8-8 and a pair of

metal plates

90 and 92 are electrically connected to the electrically conductive metal coating 86. The metal plate 90 is securely connected to a cylindrical metal rod 94 which forms the center conductor of the coaxial type of cavity resonator of this figure.

In FIGURES 6, 7, 8 and 9, RF. energy can be coupled into and out of the cavities by use of the RF. coupling window 44 of FIGURE 2.

Although the present invention has been shown with reference to specific embodiments, numerous modifications or alterations which are obvious to those skilled in the art may be made therein without departing from the spirit and scope of the invention as set forth in the appended claims.

I claim:

1. An electron tube having an envelope enclosing electrodes including a cathode, said envelope comprising a dielectric wall having an electrically conductive coating substantially covering the exterior surface thereof, said electric-ally conductive coating on said dielectric wall defining at least one resonant cavity for interacting with the electron beam in the electron tube, and by-pass capacitor means provided in said dielectric wall for permitting R.F. energy to be electromagnetically coupled across a portion of said dielectric wall.

2. An electron tube having an envelope enclosing electrodes including a cathode, said envelope comprising a dielectric wall having an electrically conductive coating substantially covering the exterior surface thereof, said electrically conductive coating on said dielectric wall defining at least one resonant cavity for interacting with the electron beam in the electron tube, and adjustable bypass capacitor means provided in said dielectric wall for permitting R.F. energy to be electromagnetically coupled across a portion of said dielectric wall and for tuning said resonant cavity to vary the frequency thereof.

3. An electron tube having an envelope enclosing electrodes including a cathode and anode, said envelope comprising a pair of substantially cup-shaped dielectric members each of which is provided with an electrically conductive coating substantially covering the exterior surface thereof, said electrically conductive coating on said cupshaped dielectric members defining a pair of resonant cavities for interacting with the electrons emitted from the cathode in the electron tube, said cathode being supported within one of said pair of cup-shaped dielectric members and electrically connected to said electrically conductive coating, said anode being supported within the other of said pair of cup-shaped dielectric members and electrically connected to said electrically conductive coating, and a control grid positioned between said anode and said cathode and supported on a metal disc which is hermetically sealed to each of said pair of substantially cup-shaped dielectric members.

4. An electron tube in accordance with claim 3, in which each of said pair of substantially cup-shaped dielectric members having an inwardly protruding portion on which said anode and said cathode are respectively mounted.

5. An electron tube in accordance with claim 4, in which by-pass capacitor means are provided in each of said pair of substantially cup-shaped dielectric members for permitting R.F. energy to be electromagnetically coupled across a portion of each of said dielectric members, and window means provided in both of said resonant cavities for inserting and extracting R.F. energy, respectively.

6. An electron tube having an envelope enclosing electrodes including a cathode, said envelope comprising a dielectric wall having an electrically conductive coating substantially covering the exterior surface thereof, said electrically conductive coating on said dielectric wall defining two resonant cavities for interacting with the electron beam in the electron tube, one of said two resonant cavities being an input cavity for inserting R.F. energy therein, the other of said two resonant cavities being an output cavity for extraction of amplified R.F. energy therefrom, said input resonant cavity being provided with a first by-pass capacitor means for electromagnetically coupling R.F. energy across a portion of said dielectric wall, and said output resonant cavity being provided with a second by-pass capacitor means for coupling RF. energy across a portion of said dielectric wall.

7. Claim 6 in which said second by-pass capacitor is adjustable for varying the frequency in said output cavity.

8. Claim 6 in which window means are provided for both said input and output cavities for inserting and extracting R.F. energy, respectively.

9. Claim 8 in which said window means is adjustable for varying the amount of RF. energy that is coupled into and out of the tube.

10. An electromagnetic wave confining structure comprising a hollow, evacuated, ceramic body having a plasma sprayed, highly conductive metallic coating on the exterior surface thereof, said highly conductive metallic coating providing a very low R.F. loss interface, the electromagnetic wave energy permeating said dielectric body and being confined by the highly conductive metallic coating.

11. Claim 10 wherein said plasma sprayed highly conductive metallic coating defines a resonant cavity.

References Cited UNITED STATES PATENTS 2,367,295 1/1945 Llewellyn 315-539 2,518,954 8/1950 Steele 3155.52 3,016,447 1/1962 Gage et al 117-105 3,066,268 11/1962 Karbowiak 333 OTHER REFERENCES Ceramic Elements for Vacuum Tubes, John T. Mark, RCA TN No. 144, 1958.

HERMAN KARL SAALBACH, Primary Examiner. ELI LIEBERMAN, Examiner.

P. L. GENSLER, Assistant Examiner.

Claims

1. AN ELECTRON TUBE HAVING AN ENVELOPE ENCLOSING ELECTRODES INCLUDING A CATHODE, SAID ENVELOPE COMPRISING A DIELECTRIC WALL HAVING AN ELECTRICALLY CONDUCTIVE COATING SUBSTANTIALLY COVERING THE EXTERIOR SURFACE THEREOF, SAID ELECTRICALLY CONDUCTIVE COATING ON SAID DIELECTRIC WALL DEFINING AT LEAST ONE RESONANT CAVITY FOR INTERACTING WITH THE ELECTRON BEAM IN THE ELECTRON TUBE, AND BY-PASS CAPACITOR MEANS PROVIDED IN SAID DIELECTRIC WALL FOR PERMITTING R.F. ENERGY TO BE ELECTROMAGNETICALLY COUPLED ACROSS A PORTION OF SAID DIELECTRIC WALL.