JP3261726B2 - Magnetron - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an unnecessary harmonic, especially a fifth harmonic.
The present invention relates to a magnetron suitable for use in a microwave oven in which a choke effective for reducing harmonics is inserted into a microwave output unit.

[0002]

2. Description of the Related Art In a magnetron, not only a fundamental wave of a so-called π mode but also a group of cavity resonators formed on an inner periphery of an anode are provided.
Harmonics such as the second, third, fourth, fifth, sixth, and seventh harmonics are also generated at the same time. When these harmonics are radiated to the outside together with the fundamental wave, other than the fundamental wave are so-called unnecessary waves, which cause communication failure as noise radio waves. Magnetrons are designed to minimize the emission of the unwanted harmonics as much as possible.In order to suppress the emission of such unwanted harmonics, the propagation of specific unwanted harmonics to the output of the coaxial structure has been conventionally required. Chokes to control

FIG. 2 is a sectional view taken along a plane including a tube axis of an example of a conventional magnetron. In the figure, 1 is a cathode, 2 is an anode cylinder, 3 is a vane projecting radially from the inner wall of the anode cylinder, 4
Are magnetic poles for forming a static magnetic field in the tube axis direction in a cylindrical working space sandwiched between the cathode 1 and the tip of the vane 3, and 5 is an annular permanent magnet serving as a magnetomotive force source for forming the magnetic field. ,
Reference numeral 6 denotes a yoke that is divided into upper and lower parts for convenience of assembly to form an extra-tube magnetic circuit, 7 denotes an output unit, and 8 denotes an alumina ceramic that insulates the output unit from an anode at a ground potential or a yoke at the same potential. An output-side insulator 9 consisting of a cylinder, an output having one end connected to the upper end surface of one vane of a group of cavity resonators formed on the inner periphery of the anode by the anode cylinder and the vane, and the other end connected to the output section One end of the conductor 10 is an anode cylinder 2
A metal piece which is fixed to the upper end portion and has the other end fixed to the output side insulator 8;
Is an end of a metal exhaust pipe cut off and sealed together with an output conductor 9 passing through the inside, and 14 is a cup around an inner hole is fixed to the outer surface of the end 13 of the exhaust pipe to form a harmonic choke. Metal pieces (the output section 7 is formed by covering a metal cover over the end 13 and the metal piece 14 of the metal exhaust pipe), 15, 1
Numeral 6 is a harmonic choke formed by the sealing metal body 10 and the metal pieces 11 and 12 (each of the portions surrounded by these members has a quarter wavelength with respect to the specific harmonic (here, the fifth harmonic). , 17 is a gasket formed by braiding a metal wire and press-molding, 18 is a metal cylinder fixed to the sealing metal body 10 and having an upper end in electrical contact with the gasket 17, 19 Is a cooling fin in which a short cylindrical portion around the center hole is fitted and fixed to the outside of the anode cylinder and the yoke side end is also bent short to provide a contact surface. The output conductor 9 of the output portion and the sealing metal body 10 form a so-called coaxial structure. The sealing metal body 10 functions as an outer conductor having a coaxial structure, and the output conductor 9 functions as an inner conductor. The gasket 17 is in close contact and electrically connected to the outside of the metal cylinder 18 fixed to the sealing metal body 10 to prevent the electric wave from leaking from the output unit. The annular bottom surfaces of the metal pieces 11 and 12 forming the harmonic choke are conventionally formed so as to be orthogonal to the axial direction of the coaxial structure.

A portion forming the outer surface of the magnetron, such as the anode cylinder 2, is grounded for safety, whereas a large negative voltage is applied to the cathode. The electrons emitted from the cathode and accelerated toward the anode orbit around the working space in an electron cloud due to the static magnetic field in the axial direction of the tube in the working space and the Lorentz force orthogonal to the direction of movement, and the anode cylinder and the vane With this, a high-frequency vibration is formed in the cavity resonator group formed on the inner periphery of the anode cylinder. In the steady state, the vibration in the adjacent cavity resonators is overwhelmingly strong with the π-mode vibration having just the opposite phase as the fundamental wave, but the second, third, fourth, fifth, sixth, and
Harmonics such as the seventh harmonic are also generated at the same time. When these so-called unnecessary harmonics are radiated to the outside, they become noise radio waves for communication devices using the same frequency band.
It is also regulated by law. Therefore, conventionally, as described above, in the middle of the output conductor that guides microwave power from the cavity resonator to the output unit, a specific harmonic cavity resonator that surrounds the output conductor is provided, and the output conductor passes therethrough. As a choke or trap that generates a resonant vibration tuned to the harmonics, that part of the output conductor presents a high impedance to the unnecessary harmonics and weakens the radio wave intensity of the unnecessary harmonics radiated from the output unit to the outside It works.

[0005] The structure similar to the above-mentioned chalk is
For example, it is described in JP-A-63-131438.

[0006]

In recent years, satellite broadcasting of television has started, and its broadcasting frequency band of 12 GHz is a 2450 MHz magnetron used for microwave ovens widely used in ordinary households. Corresponds to the 5th harmonic and the 5th harmonic
Harmonic suppression measures have been strongly required. Therefore, a magnetron having a cavity resonator as shown in FIG. 2 has already been produced, and the effect of suppressing the emission of the fifth harmonic in the 12 GHz band from the output unit has been obtained. Since the five-harmonic choke needs to be manufactured with small dimensions and high accuracy, and the frequency band to be suppressed is substantially as wide as 11.75 to 12.75 GHz, FIG.
In the conventional structure as shown in FIG.
It is divided into 5 and 16, and it is trying to correspond to a wide frequency band by shifting each resonance frequency.

Since the depth of the cross section (from the lowest part of the annular bottom surface to the upper end of the inner cylindrical surface) greatly affects the resonance frequency of the chokes 15 and 16 and the like, when the dimensions are specifically set, Several types of metal pieces are prepared for the estimated target value, and prototypes are made and tested. At that time, in the choke 15 of FIG. 2, if it is desired to adjust the resonance frequency to be lower, the other component of the choke may be used even if the resonance frequency is lowered by increasing the height of the inner cylindrical portion of the metal piece 11. The height of the outer cylindrical portion of the sealing metal body 10 is fixed, and the resonance frequency cannot be lowered only by increasing the height of the inner cylindrical portion (the choke is formed between the outer cylindrical surface and the annular bottom surface. It is formed of a cylindrical surface, but the part where the inner cylindrical surface and the outer cylindrical surface do not face each other does not work effectively, and even if the inner cylindrical surface is extended, the part facing the output side insulator is useful. Absent).

It is possible to increase the height of the outer cylindrical portion of the sealing metal body 10, but this would change the total length of the output portion of the magnetron, changing the phase of the microwave output and the degree of coupling with the load. As a result, there arises a problem that compatibility with a magnetron having the same sealing metal body 10 in operating characteristics is lost.

An object of the present invention is to provide a magnetron which solves the above-mentioned conventional problems and facilitates adjustment of the choke resonance frequency.

[0010]

In order to solve the above-mentioned problems, according to the present invention, in order to extract microwave power generated in a group of cavity resonators, an inner conductor connected to a vane of the cavity resonator and an anode cylindrical end are provided. In the output portion of the coaxial structure formed of an outer conductor that is an extension of the metal vacuum envelope that covers the portion and the magnetic pole, the periphery is coaxial with the inner conductor from the annular bottom portion and the inner circumference thereof that are in close contact with the outer conductor. In a magnetron having a plurality of chokes each including a cylindrical portion extending and forming a cavity resonator for a specific harmonic of the fundamental wave of the microwave power to prevent propagation of the harmonic, the ring of the choke is provided. The bottom portion is formed in a conical shape by inclining with respect to the axial direction of the coaxial structure output portion.

[0011]

If the choke arranged around the inner conductor, that is, the output conductor is arranged in the middle of the coaxial structure output part of the magnetron as described above, for example, the height of the inner cylinder of the metal piece forming the choke is increased, At the same time, if the annular bottom surface is inclined with respect to the axial direction and formed into a conical shape, the choke size is substantially increased (L is increased), so that the resonance frequency is reduced and a choke is formed. By inclining the annular bottom surface of the metal piece in the opposite direction (raising the position from the bottom surface to the inner cylindrical surface without changing the position of the sealing metal body side), the upper end of the inner cylinder of the metal piece of the chalk is sealed. The portion of the inner cylinder of the metal piece facing the output side insulator becomes longer, but this portion affects the resonance frequency as described above. Without substantially reducing the height of the inner cylinder L is the resonance frequency increases smaller supposed to have.

[0012]

FIG. 1 is an enlarged sectional view showing the vicinity of a place where a harmonic choke is installed in an output section according to an embodiment of the present invention. In the output section 7, the inner conductor, that is, the output conductor 9, is disposed on the tube axis of the magnetron, passes through the metal exhaust pipe 13, and the inside of the pipe is evacuated to vacuum.
A cup-shaped metal piece 14 is sealed around the hole on the top surface of the exhaust pipe 13, and the lower end of the metal piece 14 is sealed to the upper end of a cylindrical output-side insulator 8 made of alumina ceramics or the like. The exhaust pipe 1 is located outside these as shown in the figure.
The metal cover for protecting the pressed-off end of No. 3 is press-fitted. A sealing metal body 10 serving as a vacuum envelope is coaxially joined to the lower end of the output side insulator 8. This output side insulator 8
The lower outside of the gasket (not shown in FIG. 2).
7), a metal cylinder 18 fitted to the sealing metal body 10 at the lower side to prevent radio wave leakage and to surround the metal cylinder 18 is surrounded. The outer peripheral portions of the metal pieces 11 and 12 constituting the chokes 15 and 16 for preventing the fifth harmonic leakage are joined to the inner peripheral surface of the upper part of the sealing metal body 10. Here, the flat plate portion 11a of the metal piece 11 forming the bottom surface of the choke 15 is formed in a conical shape by being inclined with respect to the tube axis.
The effective height of the choke 1b is increased, and the resonance frequency of the choke 15 is lower than that of the related art (the flat portion 11a is orthogonal to the tube axis). In this embodiment, the chalk 1
Although the resonance frequency is adjusted only for No. 5, it is apparent that the resonance frequency can be similarly adjusted for the choke 16.

[0013]

As described above, according to the present invention, the resonance frequencies of a plurality of chokes provided in the output portion of the coaxial structure for preventing unnecessary harmonics from being radiated are set within the unnecessary harmonic band. In this case, the magnetron can be easily adjusted, so that a magnetron having good low noise performance can be obtained.

[Brief description of the drawings]

FIG. 1 is an enlarged sectional view showing a main part of an embodiment of the present invention, that is, a vicinity of a place where a harmonic choke is installed in an output part.

FIG. 2 is a sectional view of a plane including a tube axis of an example of a conventional magnetron.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Cathode, 2 ... Anode cylinder, 3 ... Vane, 4 ... Magnetic pole, 5 ... Permanent magnet, 6 ... Yoke, 7 ... Output part, 8
... output side insulator, 9 ... output conductor, 10 ... sealing metal body, 11, 12 ... metal piece, 13 ... end of exhaust pipe, 1
4: cup-shaped metal piece, 15, 16: chalk, 1
7 gasket, 18 metal cylinder, 19 cooling fin.

Claims (1)

(57) [Claims] A cathode concentric with a tube axis and an even number of cavity resonances composed of an anode cylinder and an even number of vanes radially protruding from an inner wall of the anode cylinder across a working space in which a static magnetic field is formed in the tube axis direction. The inner conductor is concentrically surrounded by the inner conductor connected to the cavities of the cavity to extract the microwave power generated in the cavity, and the outer conductor is an extension of the metal vacuum envelope that covers the anode cylindrical end and the magnetic pole. The output portion having a coaxial structure formed by the above, further comprising, in the output portion, an annular bottom surface portion whose peripheral edge is in close contact with the outer conductor, and a cylindrical portion extending coaxially from the inner circumference to the inner conductor. In a magnetron in which a plurality of chokes for forming a cavity for a specific harmonic of a fundamental wave of wave power and preventing the propagation of the harmonic are arranged, an annular bottom portion of the choke is used as an output of the coaxial structure output portion. Inclined with respect to the axial direction Magnetron, characterized in that formed in the conical shape Te.