US3849737A

US3849737A - Magnetron with choke structure for reducing harmonics in output

Info

Publication number: US3849737A
Application number: US00426705A
Authority: US
Inventors: T Oguro
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1972-12-18
Filing date: 1973-12-13
Publication date: 1974-11-19
Anticipated expiration: 1991-11-19
Also published as: DE2362734A1; GB1452307A; DE2362734C2

Abstract

A magnetron greatly reducing the radiation of at least one of unnecessary harmonics contained in the microwave output of the magnetron by providing a simple choke structure within the output portion of the magnetron.

Description

United States Patent [1 1 Oguro [451 Nov. 19, 1974 MAGNETRON WITH CI-IOKE STRUCTURE FOR REDUCING HARMONICS IN OUTPUT [75] Inventor:

[73] Assignee: Hitachi, Ltd., Tokyo, Japan [22] Filed: Dec. 13, 1973 [21] Appl. No.: 426,705

Tomokatsu Oguro, Mobara, Japan [30] Foreign Application Priority Data Dec. 18, 1972 Japan 47-144213 Jan. 16, 1973 Japan 48-7073 Jan. 8, 1973 Japan 48-5363 [52] US. Cl 331/86, 313/158, 315/3953,

[51] Int. Cl H0lj 23/32, H03b 9/10 [58] Field of Search 331/86-91;

[56] References Cited UNITED STATES PATENTS 2,680,827 6/1954 Randall et a1 331/86 3,315,121 4/1967 Staats 315/3953 X Primary Examiner-John Kominski Assistant ExaminerSiegfried H. Grimm Attorney, Agent, or Firm-Craig & Antonelli [5 7] ABSTRACT A magnetron greatly reducing the radiation of at least one of unnecessary harmonics contained in the microwave output of the magnetron by providing a simple choke structure within the output portion of the magnetron.

18 Claims, 9 Drawing Figures PAIENTEL NOV 1 91914 SHEET 2 OF 4 FIG.5

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lllll'll MAGNETRON WITH CHOKE STRUCTURE FOR REDUCING HARMONICS IN OUTPUT The present invention relates to a magnetron, and more particularly to the structure of the output portion of a magnetron.

Generally, microwaves produced by a magnetron contain many necessary harmonics. Conventional magnetrons'are of such a structure that microwaves produced are radiated outside as they are. As a result, when such a magnetron is used in a microwave cooking oven, for example, there is the danger that harmonics leak outside through the gap between the cooking chamber and the door and through the observation window to disturb communications. In order to prevent these dangers various countermeasures have been taken, some of which are the employment of electromagnetic wave absorbers as the sealing material for the door and reduction of the size of the observation window at thecost of the observability. However, such expedients give rise to such inconveniences as complicate the structure and impair the function of the cooking oven.

As a prior art of the magnetron provided with a choke for higher harmonics at the output portion of the magnetron there is known one disclosed in US. Pat. No. 3,559,094. In this patent, however, since the choke is provided outside the body of the magnetron, the voltage-withstanding property thereof deteriorates due to' its exposure to the ambient temperature. In order to prevent this inconvenience it employs an insulating majunction with the accompanying drawings, in which:

terial, which, however, gives rise to another inconvenience that the structure of the magnetron becomes complicated. In addition, the magnetron of the above US. patent has the further disadvantage that a number of unnecessary harmonics cannot be choked.

Therefore, an object of the present invention is to provide a magnetron of a simple structure without necessity of increasing its component parts for preventing the harmonics of the microwave produced by the magnetron from radiating outside by choking them in the magnetron.

Another object of the present invention is to provide a magnetron of a simple structure capable of preventing a number of unnecessary harmonics of the microwave produced by the magnetron from radiating outside the magnetron.

According to the present invention there is provided a magnetron comprising a cylindrical anode, a cathode disposed coaxially with the cyindrical anode, a plurality of vanes protruding from the inner face of the anode towards the cathode for forming cavity resonators, a cathode stem provided gas-tightly at one opening end of the cylindrical anode for supporting the cathode and insulating the cathode from the anode, a hollow insulating body having at least one opening provided on the side of the other opening end of the cylindrical anode in a gas-tight relation with the cylindrical anode, an output conductor one end of which is connected to one ofthe vanes and the other end of which extends in the hollow of the hollow insulating body, an output portion composed of at least the hollow insulating body and the output conductor, and a choke structure provided inside the output portion for blocking at least one of the harmonics contained in the microwave output of the magnetron.

FIG. 1 is a partly cutaway elevational view of an embodiment of the magnetron according to the present invention;

FIG. 2 is an elevational cross-sectional view of an important part of a modification of the embodiment of FIG. 1;

FIG. 3 is a partly cutaway elevational view of another embodiment of the present invention;

FIGS. 4 and 5 are elevational cross-sectional views of important parts of modifications of the embodiment of FIG. 3;

FIG. 6 is a partly cutaway elevational view of a further embodiment of the magnetron according to the present invention;

FIG. 7 is an elevational cross-sectional view of an important part of a modification of the embodiment of FIG. 6;

FIG. 8 is a partly cutaway elevational view of a still further embodiment of the magnetron according to the present invention; and

FIG. 9 is an elevational cross-sectional view of an important part of a modification of the embodiment of FIG. 8.

Referring now to FIG. 1 a magnetron 10 includes a hollow cylindrical anode 11 and a cathode 12 disposed inside and coaxially with the anode 11. The cathode I2 is provided at its both ends with circular disks l3 and 13a for preventing electrons from diverging in the axial direction. A plurality of vanes 14 protrude from the inner face of the anode 11. The vanes 14 are arranged around the cathode l2 and form cavity resonators with themselves. To the upper and lower opening parts of the anode 11 are connected substantially conical iron

magnetic pole pieces

15 and 16 gas-tightly. Circular openings 15a and provided at the centers of the

magnetic pole pieces

15 and 16 are arranged near the circular disks l3 and l3a.To the upper face of the magnetic pole piece 15 is adhered the larger opening part of a stepped substantially funnel'shaped metal tube 17. To the smaller opening part of the metal tube 17 is connected gas-tightly a-cylindrical insulating body 18 of, for example, ceramic to the upper end of which is adhered the opening part of a metal evacuating tube 19 of a cup shape formed by tipping off in evacuation process of the magnetron. The evacuating tube 19 has an effective depth l (=k/4n) of one-fourth of the wavelength )t/n of the nth higher harmonic (n 2, 3, of the microwave (the fundamental wavelength A) radiated by the magnetron 10. The upper part of the evacuating tube 19 is capped with a metal protecting cover 20 which also serves as an output antenna. The tip 19a of the evacuating tube 19 is, after evacuating the magnetron therethrough, sealed gas-tightly by being compressed against one end 21a of an output conductor 21 made of, for example, oxygen-free copper by hydraulic rollers, for example. The other end 21b of the output conductor 21 is connected to one of the vanes 14 by, for example, soldering through a circular through-hole 15b formed at a part of the magnetic pole piece 15. To the magnetic pole piece l6 a cathode stem 31 having a pair of leads 32 for flowing a heat cur rent is fixed for supporting the cathode l2 and insulating the same from the anode 11.

As is apparent from the structure of the above embodiment, the microwave produced in the cavity resonator reaches the evacuating tube 19 through the output conductor 21. Since the evacuating tube 19 has only a relatively low series reactance for fundamental microwaves, the fundamental microwaves are radiated outside without any interruption. However, the evacuating tube 19 presents a very high series reactance for a particular harmonic, so that the harmonic component is very little radiated outside being choked by the series reactance of the evacuating tube 19.

For example, if the depth 1 of the evacuating tube 19 is taken to be about M8, the evacuating tube 19 presents a very high series reactance for the most intense second harmonic, so that the radiation of the second harmonic component is greatly reduced. The most intense second harmonic is reduced by more than db compared with the conventional magnetrons one. It is evident that by varying the effective depth 1 of the evacuating tube 19 any desired harmonic can be prevented from radiating outside. When a metal film 22 is provided on the inner face of the insulating body 18 such that it connects with the evacuating tube 19 as shown in FIG. 2, the effective depth 1 is measured from the lower end 22a of the metal film 22.

In the above embodiments the output portion is provided in the axial direction of the anode 11. However, it may be that the output portion is provided laterally to and outside of the anode 11 and the output conductor 21 is connected to the vane 14 through a throughhole formed in the wall of the anode 11.

In the embodiment of FIG. 3, in addition to the feature that the effective depth 1 of the evacuating tube 19 is one-fourth of the wavelength Mn of the nth harmonic, a metal cup 23 is held by the output conductor 21 on its way in such a manner that the center of the bottom of the cup is penetrated by the conductor for preventing the radiation of the n'th harmonic component (n' 9* n) outside. The metal cup 23 has the effective depth 1 equal to one-fourth of the wavelength k/n' (=)\/4n') and the mouth of the cup 23 is in a direction towards the vanes 14.

Since the metal evacuating tube 19 and the metal cup 23 present only very low series reactances for the fundamental wave, the microwave produced in the cavity resonator and reaching the metal evacuating tube 19 through the metal cup 23 on the output conductor 21 is radiated outside without interruption. However, the nth harmonic is choked by the very high series reactance of the metal evacuating tube 19, and likewise the n'th harmonic is choked by the very high series reactance of the metal cup 23. Consequently, by selecting the effective depths l and 1 of the metal evacuating tube 19 and the metal cup 23 to be about )t/S and 7t/ 1 2, respectively, the most intense second harmonic and the third harmonic are markedly reduced in their radiation.

It is evident that similarly a number of harmonics can be choked by providing a number of metal cups at the effective depths of one fourth of desired individual harmonics. Also, the output portion may be provided laterally to the anode as described above. Still also, the inner face of the insulating body 18 may be covered with a metal film 22 as shown in FIG. 4 similarly to the embodiment of FIG. 2.

In the embodiment of FIG. 5 the metal cup 23 is formed of a metallized cylindrical dielectric body 24 made of, for example, an alumina ceramic having a central through-hole through which the output conductor 21 passes. According to the embodiment of FIG. 5 the positioning of the metal cup 23 is accurate and never tilts due to the passing of the output conductor 21 through the central hole of the dielectric body 24. In order to ensure the fixing of the metal cup 23 formed of a metal film prepared by metallization to the output conductor 21, the fixing is made ofsoldering through a washer 25. However, when the hole of the dielectric body 24 and the output conductor 21 fit closely to each other, it is possible to solder them without the washer 25. In such a case that the dielectric body 24 exists in the metal cup 23 as shown in FIG. 5, the effective depth 1 for choking the nth harmonic may be taken to be about lt/4n \/'e where e is the dielectric constant of the dielectric body 24.

In the embodiments of FIGS. 3 to 5 the mouth of the metal cup 23 may be directed towards the metal evacuating tube 19. If it is desired to better ensure the block ing of only one harmonics, it is sufficient to place the metal cup 23 at the length to choke the same harmonic that the metal evacuating tube 19 chokes. Though in the above embodiments the metal evacuating tubc I9 is made of a single body. It may be composed of a plurality of components.

In the embodiment of FIG. 6, in addition to the feature that the effective depth 1 of the metal evacuating tube 19 is a quarter of the wavelength km of the nth harmonic contained in the microwave output of the magnetron 10, a hollow metallic cylinder 26 is inserted in and fixed to the smaller opening part of the stepped funnel shaped metal tube 17. The metal cylinder 26 fomis an annular space or groove 27 between it and the metal tube 17. The depth 1 of the annular groove 27 is selected to be a quarter of the wavelength A/n' of the n'th harmonic (n a n). i.e. I A/4n'. On the upper end of the metal cylinder 26 is mounted in registered relationship and gas-tightly the insulating body 18.

According to the embodiment of FIG. 6 the nth and n'th harmonics are choked by the metal evacuating tube 19 and the annular groove 27, respectively, on account of their very high series resistances. Consequently, by selecting the effective depths I and I of the metal evacuating tube 19 and the annular groove 27 to be about M8 and A/l2, for example, respectively, the radiation of the second and third harmonic components can be reduced markedly. Similarly to the embodiments of FIGS. 2 and 4 a metal film 22 may be laid on the inner face of the insulating body 18 as shown in FIG. 7, in which case the effective depth I l of the metal evacuating tube 19 is likewise measured from the lower end 22a of the metal film 22.

In the embodiment of FIG. 8 a long dome shaped insulating body 28 is coupled to the upper end of the metal cylinder 26 in registered relationship and gastightly in place of the insulating body 18 in FIG. 6 and covering a metal cup 29. The metal cover 20 in FIG. 6 is eliminated. The metal cup 29 is supported by the output conductor 21 at its center of the bottom from inside. The effective depth l of the metal cup 29 is a quarter of the wavelength of the nth harmonic.

In the embodiment of FIG. 8 the nth and n'th harmonies are choked by the metal cup 29 and the annular groove 27, respectively, due to their very high series resistances therefor. Consequently, by appropriately selecting the values of the effective lengths I and 1 the radiation of the unnecessary harmonics can be reduced markedly.

In the embodiment of FIG. 9 a flanged sleeve 30 is utilized to form the annular groove 27 in place of the metal cylinder 26 in FIG. 8. The mouth of the long dome shaped insulating body 28 is coupled to the smaller opening part of the stepped funnel shaped metal tube 17 gas-tightly, and the flange of the flanged sleeve 30 is fixed to the inner face of the shoulder of the stepped metal tube 17. In the embodiments of FIGS. 6 to 9 the metal tube 17 and the metal cylinder 26 or the flanged sleeve 30 fonning the annular groove 27 may be made into a single integral unit.

In the embodiments of FIGS. 6 to 9 the output portion is provided in the axial direction of the anode. However, the output portion may be provided laterally to the anode as described above. In the embodiments of FIGS. 8 and 9 the metal cup having no sealing member is fixed to the output conductor. However, the metal cup may be eliminated with the advantage of preventing the deformation of the output conductor due to the provision of the metal cup when the prevention of the radiation of only the most intense second harmonic is intended because the most intense second harmonic can be choked by the annular groove by making the effective depth of the annular groove one eighth of the fundamental wavelength. Further, in the embodiments of FIGS. 6 to 9, if it is desired to better ensure the blocking of only one harmonic, the lengths l, and 1 may be determined to choke the same harmonic, i-.e., to be equal with each other, as described with respect to the embodiments of FIGS. 3 to 5. Furthermore, the mouth of the annular groove is not necessarily directed towards the vanes.

What is claimed is: a

l. A magnetron comprising a cylindrical anode, a cathode disposed coaxially with the cylindrical anode, a plurality of vanes protruding from the inner face of the anode towards the cathode for forming cavity resonators, a cathode stem provided gas-tightly at one opening end of the cylindrical anode for supporting the cathode and insulating the cathode from the anode, a hollow insulating body having at least one opening provided on the side of the other opening end of the cylindrical anode in a gas-tight relation with the cylindrical anode, an output conductor one end of which is con-. nected to one of the vanes and the other end of which extends in the hollow of the hollow insulating body, an output portion composed of at least the hollow insulating body and the output conductor, and a choke structure provided inside the output portion for blocking at least one of the harmonics contained in the microwave output of the magnetron.

2. A magnetron according to claim l, in which the magnetron further comprises a hollow metal member having openings one of which is connected gas-tightly to said other opening end of the cylindrical anode and a cup shaped metal member having an opening to the bottom of which said output conductor is connected, said hollow insulating body is an insulating cylinder having two openings, one of the openings being coupled gas tightly to the other opening of the hollow metal member, the other of the openings being coupled gas-tightly to the opening of the cup shaped metal member, thereby forming said output portion, and the cup shaped metal member hasan effective depth of a quarter of the wavelength of a particular harmonic of the microwave output and forms a choke structure member for the particular harmonic.

3. A magnetron according to claim 2, in which a cylindrical metal film is overlaid on at least a part of the inner face of the cylindrical insulating body in such a manner that one end of the cylindrical metal film is electroconductively connected to the cup shaped metal member and the effective depth of the cup shaped metal member is measured from the bottom thereof to the other end of the cylindrical metal film.

4. A magnetron according to claim 2, further comprising at least one metal cup held by the output conductor in such a manner that it is penetrated by the output conductor at the center of its bottom, the metal cup having an effective depth of a quarter of the wavelength of one of the harmonics including the particular harmonic and forming another choke structure member for said one of the harmonics.

5. A magnetron according to claim 4, in which a cylindrical metal film is overlaid on at least a part of the inner face of the cylindrical insulating body in such a manner that one end of the cylindrical metal film is electroconductively connected to the cup shaped metal member and the effective depthof the cup shaped metal member is measured from the bottom thereof to the other end of the cylindrical metal film.

6. A magnetron according to claim 2, in which at least one dielectric cylinder having a central throughhole through which the output conductor passes and metallized at its side and upper faces is held by the output conductor, the dielectric cylinder having a height of A V? times the wavelength of one of the harmonics including the particular harmonic and forming another choke structure member for said one of harmonics, where e is the dielectric constant of the dielectric cylinder.

7. A magnetron according to claim 6, in which a cylindrical metal film is overlaid on atleast a part of the inner face of the cylindrical insulating body in such a manner that one end of the cylindrical metal film is electroconductively connected to the cup shaped metal member and the effective depth of the cup shaped metal member is measured from the bottom thereof to the other end of the cylindrical metal film.

8. A magnetron according to claim I, further comprising a first metal member connecting gas-tightly the hollow insulating body to the anode and having a through-hole through which the output conductor passes, the inner face of the first metal member being provided with an annular groove encircling the output conductor, the annular groove having an effective depth of a quarter of the wavelength of a particular harmonic of the microwave output and forming a choke structure member for the particular harmonic.

the harmonics including the particular harmonic and forms another choke structure member for said one of the harmonics.

10. A magnetron according to claim 9, in which a cylindrical metal film is overlaid on at least a part of the inner face of the cylindrical insulating body in such a manner that one end of the cylindrical metal film is electroconductively connected to the cup shaped metal member and the effective depth of the cup shaped metal member is measured from the bottom thereof to the other end of the cylindrical metal film.

11. A magnetron according to claim 8, in which the hollow insulating body is formed into a long dome shape.

12. A magnetron according to claim 11, further comprising a metal cup fixedly supported by the other end of the output conductor at the center of its bottom and having an effective depth of a quarter of the wavelength of one of the harmonics including the particular harmonic to form another choke structure member for said one of the harmonics.

13. A magnetron according to claim 8, in which said first metal member consists of a stepped funnel shaped metal tube with the opening of the larger diameter part being connected to the anode and a hollow metal cylinder having a diameter substantially equal to that of the opening of the hollow insulating body and connected thereto gas-tightly and inserted in and fixed to the smaller diameter part of the stepped funnel shaped metal tube so that the hollow metal cylinder extends to within the larger diameter part of the stepped funnel shaped metal tube, thereby forming said annular groove between the hollow metal cylinder and the larger diameter part of the stepped funnel shaped metal tube.

14. A magnetron according to claim 13, in which the hollow insulating body is formed into a long dome shape.

15. A magnetron according to claim 14, further comprising a metal cup fixedly supported at the center of its bottom by said other end of the output conductor. the metal cup having an effective depth of a quarter of the wavelength of one of the harmonics including the particular harmonic of the microwave output and forming another choke structure member for said one of harmonics.

16. A magnetron according to claim 8, in which said first metal member consists of a stepped funnel shaped metal tube with the opening of the larger diameter part being connected to the anode and a flanged sleeve through which the output conductor passes having a flange portion fixed to the inner face of the shoulder of the stepped funnel shaped metal tube, thereby forming said annular groove between the sleeve portion of the flanged sleeve and the larger diameter part of the stepped funnel shaped metal tube.

17. A magnetron according to claim 16, in which the hollow insulating body is formed into a long dome shape.

18. A magnetron according to claim 17, further comprising a metal cup fixedly supported at the center of its bottom by said other end of the output conductor, the metal cup having an effective depth of a quarter of the wavelength of one of the harmonics including the particular harmonic of the microwave output and forming another choke structure member for said one of harmonics.

Claims

1. A magnetron comprising a cylindrical anode, a cathode disposed coaxially with the cylindrical anode, a plurality of vanes protruding from the inner face of the anode towards the cathode for forming cavity resonators, a cathode stem provided gas-tightly at one opening end of the cylindrical anode for supporting the cathode and insulating the cathode from the anode, a hollow insulating body having at least one opening provided on the side of the other opening end of the cylindrical anode in a gas-tight relation with the cylindrical anode, an output conductor one end of which is connected to one of the vanes and the other end of which extends in the hollow of the hollow insulating body, an output portion composed of at least the hollow insulating body and the output conductor, and a choke structure provided inside the output portion for blocking at least one of the harmonics contained in the microwave output of the magnetron.

2. A magnetron according to claim 1, in which the magnetron further comprises a hollow metal member having openings one of which is connected gas-tightly to said other opening end of the cylindrical anode and a cup shaped metal member having an opening to the bottom of which said output conductor is connected, said hollow insulating body is an insulating cylinder having two openings, one of the openings being coupled gas tightly to the other opening of the hollow metal member, the other of the openings being coupled gas-tightly to the opening of the cup shaped metal member, thereby forming said output portion, and the cup shaped metal member has an effective depth of a quarter of the wavelength of a particular harmonic of the microwave output and forms a choke structure member for the particular harmonic.

5. A magnetron according to claim 4, in which a cylindrical metal film is overlaid on at least a part of the inner face of the cylindrical insulating body in such a manner that one end of the cylindrical metal film is electroconductively connected to the cup shaped metal member and the effective depth of the cup shaped metal member is measured from the bottom thereof to the other end of the cylindrical metal film.

6. A magnetron according to claim 2, in which at least one dielectric cylinder having a central through-hole through which the output conductor passes and metallized at its side and upper faces is held by the output conductor, the dielectric cylinder having a height of 1/4 Square Root epsilon times the wavelength of one of the harmonics including the particular harmonic and forming another choke structure member for said oNe of harmonics, where epsilon is the dielectric constant of the dielectric cylinder.

7. A magnetron according to claim 6, in which a cylindrical metal film is overlaid on at least a part of the inner face of the cylindrical insulating body in such a manner that one end of the cylindrical metal film is electroconductively connected to the cup shaped metal member and the effective depth of the cup shaped metal member is measured from the bottom thereof to the other end of the cylindrical metal film.

8. A magnetron according to claim 1, further comprising a first metal member connecting gas-tightly the hollow insulating body to the anode and having a through-hole through which the output conductor passes, the inner face of the first metal member being provided with an annular groove encircling the output conductor, the annular groove having an effective depth of a quarter of the wavelength of a particular harmonic of the microwave output and forming a choke structure member for the particular harmonic.

9. A magnetron according to claim 8, in which the magnetron further comprises a cup shaped second metal member having an opening to the bottom of which said output conductor is connected, said hollow insulating body is an insulating cylinder having two openings, one of the openings being coupled gas-tightly to the first metal member, the other of the openings being coupled gas-tightly to the opening of the cup shaped metal member, thereby forming said output portion, and the cup shaped metal member has an effective depth of a quarter of the wavelength of one of the harmonics including the particular harmonic and forms another choke structure member for said one of the harmonics.

15. A magnetron according to claim 14, further comprising a metal cup fixedly supported at the center of its bottom by said other end of the output conductor, the metal cup having an effective depth of a quarter of the wavelength of one of the harmonics including the particular harmonic of the microwave output and forming another choke structure member for said one of harmonics.