JP3015450B2 - Magnetron for microwave oven - Google Patents

Description

The present invention relates to a magnetron for a microwave oven, and more particularly to an improvement in a metal cylinder for a harmonic choke.

(Prior Art) The main part of a magnetron for a microwave oven is generally a fourth type.
The configuration is as shown in the figure. In the figure, reference numeral 11 denotes an oscillation part main body, 12 denotes an anode cylinder, 13 denotes a plurality of anode vanes constituting a part of a cavity resonator, 14 denotes a strap ring, 15 denotes a filament cathode, 16 denotes an end shield thereof, 17, 18
Is a pole piece fixed to the open end of the anode cylinder 12, 19
Is a cylindrical metal container, 20 is a high-frequency output section, 21 is an output section ceramic cylinder, 22 is an output end sealing ring, 23 is a metal exhaust pipe hermetically bonded thereto, 24 is an output section metal cap, and 25 is an output antenna One end 25 a is electrically connected to one of the vanes 13, passes through the through hole 17 a of the pole piece 17, penetrates the metal container 19, the ceramic cylinder 21, and has a metal end pipe 25 b. It is sandwiched between 23 and hermetically sealed.

Further, reference numeral 26 denotes a ring-shaped permanent magnet coaxially arranged on the outer periphery of the metal container 19, 27 denotes a yoke made of a ferromagnetic material, 28 denotes a ferromagnetic thin plate, and 29 denotes a reticulated conductive gasket. A small-diameter first harmonic choke metal cylinder 30 is hermetically soldered to the lower end of the ceramic cylinder 21, and a second harmonic choke metal cylinder 31 is positioned on the outer periphery thereof. Touched. The second harmonic choke metal cylinder 31 is hermetically soldered to the tip of the metal container 19, and the tip 31 a holds the inner periphery of the gasket 29.

With this structure, the quarter-wave choke groove C _{2 for the second} harmonic, the choke groove C ₄ for the fourth harmonic, and the metal container 19 and its inner space 2 are formed in the metal exhaust pipe 23.
5th harmonic choke groove C ₅ by three metal cylinders 30 and 31
Third harmonic choke groove C ₃ are formed.

In addition, the metal container 19 and the metal cylinders 30 and 31 for both chokes are formed of thin ferromagnetic cylinders made of iron or an iron alloy. The first harmonic choking metal cylinder 30, in order to obtain a necessary and sufficient choke action, the inner diameter D ₁ is smaller than the inner diameter D ₂ of the ceramic cylinder 21, and the fifth harmonic wave 1 / It is set to a dimension smaller than 2.

In such a magnetron, the output
While a fundamental wave from 20 to 2450 MHz, for example, is efficiently radiated, external radiation of each harmonic component is suppressed by the choke effect of the choke groove.

(Problems to be Solved by the Invention) As described above, in order to obtain a reliable choke effect on a higher harmonic component such as the fifth harmonic, the inner diameter of the first harmonic choke metal cylinder 30 is increased. Needs to be reduced to some extent. With such a small diameter, the distance S between the first harmonic choke metal cylinder 30 and the antenna lead 25 passing through the inside thereof naturally becomes short.
A high high-frequency voltage is applied between them, and high-frequency discharge may occur due to the relationship with a reflected wave from a high-frequency load such as a microwave oven.

Assuming an extreme case, during use of the microwave oven, if the rotation of the stirrer fan stops for any reason and there is little or no heated object that is a high-frequency load,
High frequency reflections into the magnetron can have a standing wave ratio (VSWR) of 30 or more. In such a case, a discharge occurs between the antenna lead 25 and the metal cylinder 30 for harmonic choke, and in an extreme case, a part of the antenna lead 25 or the metal cylinder 30 for harmonic choke generates heat due to high-frequency discharge and melts. It is also possible to do. If any part is melted, a gas discharge is locally caused by the generated gas, and furthermore, the high frequency electric field is disturbed or reflected by them, and a chain discharge or a fatal part of each part occurs in the output part region. Melting and breakage may occur.

Such high-frequency discharge can be presumed to be a multipactor discharge phenomenon in many cases. That is, the antenna lead 25
The leaked DC magnetic flux from the permanent magnet 26 extends substantially in parallel with the tube axis in the space between the permanent magnet 26 and the metal cylinder 30 for harmonic choke. The magnetic flux in this space has a substantially axially symmetric distribution. Since these metal components usually have a secondary electron emission ratio of greater than 1, secondary electrons are generated when floating electrons or the like collide with the antenna lead 25 or the inner surface of the metal cylinder 30 for harmonic choke.

The electrons are accelerated or decelerated by a high-frequency electric field between the antenna lead 25 and the harmonic choke metal cylinder 30. If an electron emitted from one of the two conductors encounters a high-frequency accelerating electric field, it is accelerated and collides with the other conductor, emitting many secondary electrons. If this high-frequency electric field is reversed and becomes an electric field that accelerates these secondary electrons in the direction of the original conductor, these secondary electrons are also accelerated and collide with the original conductor, and emit many secondary electrons again. I do.

Thus, when the electrons and the high frequency electric field are synchronized in both directions, the secondary electrons will increase exponentially and increase in energy, so that both conductors will heat up and eventually cause melting. Such a phenomenon is a discharge called a double side multipactor.

On the other hand, the electrons make a swirling motion due to the DC magnetic field existing in this region. If the cycle of the high-frequency electric field and the cycle of the circling motion of the electrons are synchronized, it is estimated that secondary electrons are cumulatively generated, and the metal cylinder material rapidly generates heat due to its collision energy, and finally melts. Such a phenomenon is called one-sided multipactor discharge.

Incidentally, JP-A-61-281433 describes a `` magnetron output structure '' in which a metal cylinder for harmonic choke is provided so as to surround the antenna lead at a distance,
In this case, since the antenna lead and the metal cylinder for harmonic choke are parallel to each other, there is a disadvantage that a multipactor discharge occurs.

The present invention more reliably suppresses the occurrence of multipactor discharge in the high-frequency output section even when operated under the above-mentioned severe conditions, and prevents the metal cylinder for harmonic choke and the antenna lead from being blown. It is an object of the present invention to provide a magnetron for a microwave oven.

[Constitution of the Invention] (Means for Solving the Problems) According to the present invention, there is provided at least one inner side of a metal container so as to surround the antenna lead with a smaller diameter than the antenna lead.
This is a magnetron for a microwave oven in which a plurality of metal cylinders for harmonic choke are provided, and the innermost metal cylinder for harmonic choke is formed in a tapered or shrouded shape with respect to the tube axis.

(Function) According to the present invention, since the innermost metal cylinder for harmonic choke is formed in a tapered or wrapped shape with respect to the tube axis, multi-pactor discharge is suppressed, and the metal cylinder for harmonic choke is obviated. And antenna leads are prevented from melting.
Reliability can be improved.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

A magnetron for a microwave oven that generates a fundamental wave in the 2450 MHz band to which the present invention is applied is configured as shown in FIG. 1, and the same parts as those in the conventional example (FIG. 4) are denoted by the same reference numerals.

That is, a plurality of vanes 13 are radially arranged inside the anode cylinder 12 constituting the oscillating portion main body 11 to constitute a cavity resonator. Upper and lower ends of each vane 13 are connected to every other by a pair of large and small strap rings 14, respectively. In the electron working space surrounded by the free ends of the plurality of vanes 13, a helical filament cathode 15 is disposed along the axis of the anode cylinder 12, and both ends are fixed to end shields 16, 16, respectively. . Further, at both ends of the anode cylinder 12, substantially funnel-shaped pole pieces 17 and 18 are fixed, respectively. On one pole piece 17, a cylindrical metal container 19 is also fixed while being in contact with one end of the anode cylinder 12. I have. This metal container
A second harmonic choke metal cylinder 31 having a large-diameter portion and a small-diameter portion is hermetically bonded to the upper opening end of the 19. In this case, the step between the large-diameter portion and the small-diameter portion is air-tightly joined to the opening end of the metal container 19, the large-diameter portion has substantially the same diameter as the metal container 19, and the output portion ceramic cylinder 21 Around the lower end, the tip 31a is in contact with the gasket ring 29. or,
The small diameter portion is disposed coaxially inside the metal container 19 so as to extend in the vane direction. By the metal container 19 and the small diameter portion of the second harmonic choking metal cylinder 31, the third 1-wavelength choke C ₃ quarters for harmonic suppression is configured.

Inside this second harmonic choke metal cylinder 31,
The innermost small diameter metal cylinder 32 for the first harmonic choke 32
Is a second harmonic choke metal cylinder 31 and a metal container 19.
Are arranged coaxially. In this case, the first harmonic choke metal cylinder 32 is the second harmonic choke metal cylinder.
Spiral filament cathode, shorter in length than 31
It is formed in a tapered shape with respect to the tube axis so that the inner diameter becomes gradually smaller in the direction of 15, and an antenna lead 25 to be described later is formed.
And not parallel. And the flange part 32 at one end
a, the periphery of the flange portion 32a is hermetically joined to a step between the large-diameter portion and the small-diameter portion of the second harmonic choke metal cylinder 31, and the flange portion 32a The vicinity of the center is brazed to the lower end of the ceramic cylinder 21. Then, the second harmonic small diameter portion and the first harmonic choking metal cylinder 32 of choking metal cylinder 31, 1-wavelength choke groove C ₅ quarters for the fifth harmonic suppression is configured ing.

As described above, the lower end surface of the ceramic cylinder 21 constituting the output portion is air-tightly joined to the flange portion 32a of the first harmonic choke metal cylinder 32 by brazing. , A holding ring 22 is hermetically joined. An output portion metal cap 24 is fixed to a side surface of the holding ring 22, and a metal exhaust pipe 23 is hermetically joined and held at an inner bent portion of the holding ring 22. or,
One end 25a of an antenna lead 25 is electrically connected to one of the vanes 13, and this antenna lead 25 is
Extends through the output portion 20 along the tube axis through the through hole 17a,
The other end 25b is fixedly held by the exhaust pipe 23. The fourth 1-wavelength choke groove C ₄ quarters for harmonic suppression is formed by a retaining ring 22 and the exhaust pipe 23, 4 min for the second harmonic suppression by the exhaust pipe 23 and the antenna lead 25 Of 1
Wavelength-type choke groove C ₂ is formed.

Further, on the outer periphery of the metal container 19, a permanent magnet 26 whose inner surface is tapered on the lower side is provided. These permanent magnets
A frame yoke 27 is provided so as to surround the anode cylinder 12, the cooling fins (not shown) attached to the outer periphery of the anode cylinder 12, and the like. The center hole of the frame-shaped yoke 27
A gasket ring 29 is provided between the metal cylinder 31 for harmonic choke and the tip 31a. And permanent magnet 26
One surface is in contact with the frame-shaped yoke 27 and the gasket ring 29 via the magnetic conductive plate 28, and the other surface is in contact with the projection of the metal container 19.

In the present invention, since the first harmonic choke metal cylinder 32 is formed in a tapered shape with respect to the tube axis, the axial component is stably present in the microwave electric field. For this reason, the electrons move in the axial direction, but since the first harmonic choke metal cylinder 32 has a tapered shape and the inner diameter changes, the microwave electric field distribution also changes. Therefore, the oscillation of the electrons cannot be stably synchronized with the microwave frequency. As a result, generation and continuation of the multipactor discharge can be prevented.

(Modification) FIGS. 2 and 3 show modifications (two examples) of the present invention, and the same effects as in the above embodiment can be obtained. That is, the first harmonic choke metal cylinder 32 in the above embodiment has a tapered shape whose inner diameter gradually decreases in the direction of the helical filament cathode 15, but the first harmonic choke metal cylinder in FIG. 33 has a tapered shape in which the inner diameter gradually increases in the direction of the spiral filament cathode 15. Further, the first harmonic choke metal cylinder 34 in FIG. 3 is formed in the shape of a shroud whose inner diameter changes, as is apparent from the figure.

[Effects of the Invention] As described above, according to the present invention, since the innermost metal cylinder for harmonic choke is formed in a tapered shape or a wrapped shape with respect to the tube axis, multi-pactor discharge is suppressed, and beforehand In addition, the melting of the metal cylinder for harmonic choke and the antenna lead is prevented, and the reliability can be improved.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a magnetron for a microwave oven according to one embodiment of the present invention, FIGS. 2 and 3 are longitudinal sectional views showing a modification of the present invention, and FIG. It is a longitudinal section showing a magnetron. 12 ... Anode cylinder, 13 ... Vane, 17, 18 ... Pole piece, 19 ... Metal container, 21 ... Ceramic cylinder, 25 ... Antenna lead, 26 ... Permanent magnet, 32, 33, 34 ... Metal cylinder for harmonic choke.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-296642 (JP, A) JP-A-61-281433 (JP, A) JP-A-2-78133 (JP, A) 74748 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01J 23/00-25/78

Claims (1)

(57) [Claims] 1. A cavity resonator having a plurality of anode vanes fixed inside an anode cylinder. A pole piece is fixed to the open end of the anode cylinder, a cylindrical metal container is joined, an output ceramic cylinder is joined to the open end of the metal container, and one end is electrically connected to the cavity resonator. The connected antenna lead extends through the inside of the metal container and the ceramic cylinder, a ring-shaped permanent magnet is arranged on the outer periphery of the metal container, and the antenna lead having a smaller diameter than the antenna lead is provided inside the metal container. At least one metal cylinder for harmonic choke surrounding the antenna, and in the region of the innermost metal cylinder for harmonic choke, the antenna lead is extended in parallel with the tube axis. In the magnetron, the metal cylinder for the innermost harmonic choke is formed in a tapered shape or a wrapped shape with respect to a tube axis. Magnetron for Ji.