JPH0155745B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a magnetron, and particularly to a magnetron that suppresses emission of unnecessary noise components to the cathode input terminal side.

[Background technology and its problems]

Consideration of the causes of unnecessary noise components in continuous wave magnetrons for microwave ovens, and as a countermeasure, it is effective to provide a third electrode near the cathode and apply a negative potential to it to collect positive ions. This has already been proposed in Japanese Patent Laid-Open Nos. 57-57452 and 176645-1980.

Although the techniques disclosed in these documents are extremely effective in reducing noise, they have disadvantages in that the structure of the cathode electrode is complicated and an extra power source is required.

[Purpose of the invention]

The present invention provides a magnetron that has a simple structure, does not require an extra power source, and can reduce emission of unnecessary noise components to the cathode input side.

[Summary of the invention]

The present invention has a structure in which a thermionic emitting part made of a spiral filament and a conductive part that does not emit thermionic electrons are continuously provided along the axial direction of the cathode electrode, and the conductive part is arranged opposite to the anode vane. However, the thermionic emission portion is located axially away from the majority of the anode vane portion. Thermionic electrons contributing to the oscillation operation of the magnetron are generated from a thermionic emission section located apart from the anode vane portion, and introduced into the electron action space. The thermionic emission part and the conductive part are at the same potential, so there is no need for an extra power source, and the positive ions generated in the working space are always collected in the conductive part, so there is almost no oscillating current to the cathode, that is, noise. .

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings. Note that the same parts are represented by the same symbols.

In the embodiment shown in FIG. 1, a cathode electrode 11 and a plurality of anode vanes 12, 12 constituting a part of a cavity resonator are coaxial, and the anode vane 12 has a pair of strap rings 13. It will be done. The anode electrode 11 is supported by a support rod 14 and a support sleeve 15. Support rod 14
A cup-shaped end hat 16 is fixed to the tip of the cap, and a cylindrical metal 17 is fixed to the inside of the end hat 16, the outer peripheral surface of which constitutes a conductive part 18. The cylindrical metal 17 is made of a high melting point metal such as molybdenum (Mo), has a surface that does not emit thermoelectrons, and faces the majority of the axial region of the inner end surface 12a of the anode vane 12. It is located.
A support disk 19 is fixed to the support rod 14 at the end of the cylindrical metal 17, and one end of a helical filament 20 is fixed to this support disk 19. The other end of the filament 20 is fixed to the bottom of another cylindrical end hat 21 with a bottom. The end hat 21 is supported by the support sleeve 15 and surrounds the filament 20 at a distance. Also, the tip opening 21 of this end hat 21
a is extended to the vicinity of the anode vane 12, and a space P is left so that the thermoelectrons generated from the filament 20 are introduced into the working space S. The support sleeve 15 and the support rod 14 are electrically separated by a ceramic spacer 22 and mechanically held coaxially. The diameter of the outer peripheral surface of the cylindrical metal 17 and the diameter of the outer peripheral surface of the filament 20 are formed to have the same dimensions, and are integrally constructed so that they have the same potential as shown in the figure.
The filament 20 is made of a thorium-tungsten wire with a carbonized surface layer, and the surface portion constitutes a thermionic emission section 23.

In the magnetron of the present invention having the above configuration, heating power is applied to the filament, that is, the thermionic emission part, and the generated thermionic electrons are introduced into the electron action space S to perform an oscillating operation. That is, the thermoelectrons are guided into the working space by the repulsive force between electrons and the positive potential entering from the anode vein. In the working space, positive ions formed by electrons colliding with gas molecules always immediately collide with the nearest conductive part 18 and are neutralized, without staying in a certain area or flowing toward the filament. For this reason, the anode,
An unstable current between the cathodes does not occur, and unnecessary noise is hardly generated. In experiments conducted by the present inventors, the value of noise components below 100 MHz was approximately 10 dB lower in the present invention than in general magnetrons. Moreover, as a matter of course, no extra power source is required and the structure of the cathode electrode is relatively simple, which is advantageous for mass production.

In the embodiment shown in FIG. 1, a cylindrical metal is used as the member constituting the conductive part 18, but the present invention is not limited to this, and a cylindrical metal or a thin cylindrical metal may be used. . The material is a high-melting point metal that can sufficiently withstand temperatures caused by electron back impact during operation and heat from the filament, and is made of a material that does not easily generate thermal electrons (primary electrons) from its surface.

In the embodiment shown in FIG. 2, the electron emitting part 23 and the conductive part 18 are constructed of a single spiral made of thorium tungsten as the cathode electrode 11 . The conductive part 18 is short-circuited and supported by the support rod 14 by a pair of support disks 19 and 24, and its surface is not carbonized, so that almost no thermoelectron emission (primary electrons) is generated.

The magnetron of this embodiment is easier to manufacture, especially since the electron emitting part and the conductive part are constructed of a single spiral.

In the above description of the embodiment, it is assumed that the conductive part does not generate thermal electrons, but this is a range in which electrons do not accumulate in the close vicinity of the conductive part and a region where the space potential becomes negative does not occur. Therefore, there is no problem even if some primary or secondary electrons are generated. For example, in a magnetron with a relatively large output power, it is effective to configure the magnetron so that secondary electrons are easily generated from the conductive part and maintain the stability of oscillation. Suitable materials for this purpose include Mo containing lanthanum (La) or W containing thorium (Th). Furthermore, in order to suppress the emission of secondary electrons in a relatively low-power magnetron, it may be coated with carbon or the like as a material.

〔Effect of the invention〕

In the present invention, the thermionic emission section is located away from the electron action space in the axial direction, and positive ions generated in the action space are prevented from flowing into the electron action space, thereby suppressing the generation of undesired current oscillations, that is, noise. Ru. Moreover, it requires a relatively simple cathode electrode structure and does not require an extra power source, making it highly practical.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view of a main part showing one embodiment of the present invention, and FIG. 2 is a longitudinal sectional view of a main part showing another embodiment of the invention. 11 ... Cathode electrode, 12... Anode vane, S... Electron action space, 14... Support rod, 1
6, 21... End hat, 18... Conductive part, 1
7... Cylindrical metal, 20... Spiral filament,
23...Thermionic emission part.

Claims (1)

[Claims] 1. An anode vane having a built-in cathode electrode and a cavity resonator arranged coaxially with each other,
In a magnetron in which a magnetic field parallel to the cathode axis is applied to the electron action space between the cathode electrode and the anode vane, the cathode electrode has a conductive portion in which most of the portion facing the anode vane does not emit thermoelectrons. A thermionic emission part made of a spiral filament is arranged at a position axially away from the conductive part, and a cylindrical end hat is arranged around the thermionic emission part. A magnetron featuring 2. The magnetron according to claim 1, wherein the conductive part comprises a cylindrical body or columnar body made of a high melting point metal supported by a support rod that supports a cathode electrode. 3. The magnetron according to claim 1, wherein the conductive part is made of a helical body of a high melting point metal. 4. The conductive part and the thermionic emission part are made of a single helical body, and the conductive part is made of a material whose surface is not carbonized, and the heating current does not flow therethrough. magnetron.