JPH09293458A - Magnetron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetron which can suppress the radiation of a spurions electromagnetic wave (noise) by a simple structure, relating to even a higher harmonic of grade higher than the conventionally considered higher harmonic, over only the specific higher harmonic but also the whole wide frequency band. SOLUTION: This magnetron has an anode part, cathode part 5 provided in the center of this anode part, output antenna lead 17 drawing out a microwave oscillated in the anode part and an output side metal cylinder 13 provided in the periphery of partly this output antenna lead 17 to be electrically connected to the anode part. Inside this output side metal cylinder 13, a metal plate (doughnut-shaped disk 21, 22), forming a capacitor component between itself and the output antenna lead 17, is connected, by this capacitor component and an inductance component of the output antenna lead 17, a low/pass filter is formed.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a magnetron used for microwave heating equipment such as a microwave oven. More specifically, the present invention relates to a magnetron that suppresses unnecessary electromagnetic waves such as higher harmonics generated during operation of the magnetron from being radiated from the output side to achieve low noise.

[0002]

2. Description of the Related Art Microwave ovens have become widespread as one of microwave devices and are widely used in the world. However, when unnecessary electromagnetic waves are radiated from the microwave oven, noise enters radios, televisions, communication devices, etc. Normal operation is disturbed. Therefore, it is necessary to prevent noise from the microwave oven, but the noise from the microwave oven is mainly generated from the magnetron used as the microwave oscillation source. The main noise generated from the magnetron is a harmonic wave which is an electromagnetic wave having an integral multiple frequency of the fundamental wave (a microwave having an original oscillation frequency of the magnetron, for example, an electromagnetic wave of 2450 MHz), and the frequency thereof is several tens. It has a wide band up to GHz.

In a magnetron used in a microwave oven or the like, as a conventional means for suppressing the radiation of higher harmonic waves from the output side, for example, as shown in FIG. 6, a sectional explanatory view of the output part of the magnetron is used. Means have been proposed for forming a choke structure near the antenna lead.

In FIG. 6, reference numeral 17 denotes an output antenna lead, one end of which is connected to a vane of an anode portion (not shown) and the other end of which is fixed by a sealing portion of an exhaust pipe 16 which constitutes a part of a vacuum wall. The microwave power generated in the part is conducted and is radiated from the tip which is the other end. The output antenna lead 17 is covered with an insulating cylinder 15 forming a part of the vacuum wall and an output side metal cylinder 13 electrically connected to the anode part. Inside the output-side metal cylinder 13, choke metal cylinders 14a and 14b are provided, and the length thereof is set to about 1/4 of the wavelength λ of the electromagnetic wave whose radiation is suppressed. The impedance becomes infinite, and the structure is a choke that blocks electromagnetic waves of that wavelength. That is, in the example shown in FIG. 6, the length of the cylinder of the metal cylinder 14a is adjusted to about 1/4 of the wavelength of the fifth harmonic, and the length of the cylinder of the metal cylinder 14b is adjusted to the third harmonic. By adjusting the length to about 1/4 of the wavelength of, the radiation of the third and fifth harmonics is suppressed.

As another method for suppressing the radiation of higher harmonic waves from the output antenna lead side, for example, Japanese Patent Laid-Open No. 1-276.
As described in Japanese Laid-Open Patent Publication No. 540, a metal plate having a slot having an electric length corresponding to about a quarter wavelength of the nth harmonic (n is an integer of 2 or more) component is provided on the output side metal cylinder,
As disclosed in Japanese Utility Model Application Laid-Open No. 59-130360, by providing a choke structure directly on the output antenna lead or providing a folded portion having a length of about ¼ of the wavelength of a specific harmonic on the output antenna lead, Similarly, a method of suppressing electromagnetic wave radiation of each harmonic is also used.

[0006]

The suppression of unnecessary electromagnetic wave radiation (noise) of the conventional magnetron is achieved by the fifth harmonic (1) which overlaps with the satellite broadcasting band (11.7 to 12.7 GHz).
The main focus is to suppress the radiation of 2.25 GHz), and as described above, the method of suppressing the harmonic of a specific frequency by the choke structure is adopted. However, due to the recent development of communication technology, the frequency band used for communication is widened, and it is now necessary to suppress noise in a wide band up to 18 GHz. In this band, the 7th harmonic of the magnetron with an oscillation frequency of 2.45 GHz (17.
Noise up to 15 GHz) will be included,
It is necessary to suppress all the noises in this range except the 7th harmonic and the higher harmonic.

In order to cope with such suppression of wideband noise by a conventional choke structure, it is necessary to form a choke structure corresponding to each harmonic frequency. However, if many choke structures are formed in multiple stages in a limited space, the structure becomes complicated and the damping characteristics of the individual chokes are restricted, so that a sufficient suppression effect cannot be obtained. Further, due to the interference between the chokes, the attenuation frequency characteristic is likely to deviate from the designed value.

Further, in the choke structure, as shown in the attenuation characteristics with respect to frequency in FIG. 7, a large amount of attenuation is obtained at the set frequency (usually the frequency of the harmonic of the magnetron), but at other frequencies. The amount of attenuation is small, and no effect can be obtained with respect to radiation of unnecessary electromagnetic waves having a frequency in the middle of the set frequency. FIG. 7 shows the second
It is a figure which shows the attenuation characteristic with respect to the frequency of the magnetron provided with the 4 choke structure for 5 harmonics, the 2nd harmonic (4.9 GHz), the 3rd harmonic (7.35 GHz), and 4th.
Harmonics (9.8 GHz), and 5th harmonics (12.25)
Although a large amount of attenuation occurs at each frequency of (GHz), the amount of attenuation is small at the intermediate frequency.

The present invention has been made in order to solve such a problem, and can suppress higher harmonics higher than those considered in the past and only suppress specific harmonics. Another object of the present invention is to provide a magnetron capable of suppressing unnecessary electromagnetic wave radiation (noise) with a simple structure over a wide range of frequencies.

Still another object of the present invention is to provide means for increasing the inductor component and the capacitor component of the low-pass filter for suppressing the radiation of the aforementioned unwanted electromagnetic waves,
It is to optimize each component of the low-pass filter to improve the filter characteristics and to improve the degree of freedom in designing the magnetron having the low-pass filter.

[0011]

In the magnetron according to the present invention, a metal plate is provided inside an output side metal cylinder which covers the output antenna lead, and a capacitor component formed between the metal plate and the output antenna lead. A low pass filter is formed by the inductor component of the output antenna lead. As a result, it is possible to attenuate harmonics and suppress unnecessary electromagnetic radiation without attenuating the fundamental wave by the low-pass filter.

If there are a plurality of metal plates, especially two metal plates, a π-type low-pass filter is formed. That is, the metal plate is electrically connected to the output side metal cylinder connected to the anode part, and no capacitor component is formed between the adjacent metal plates. Therefore, the π-type low-pass filter is formed by the inductor component of the output antenna lead and the capacitor component formed in the gap between the tip of the adjacent metal plate on both sides of the output antenna lead and the output antenna lead. As a result, a ripple of an attenuation characteristic at a low frequency, which is a pass band, which occurs in an elliptic function type filter does not appear, and a low-pass filter having a high characteristic is obtained.

Since the output antenna lead is provided with the antenna lead narrowing portion whose cross-sectional area is partially reduced, the inductance can be increased without affecting other electrical characteristics. Therefore, the inductance can be adjusted to obtain desired filter characteristics without lengthening the output antenna lead.

The metal plate is provided by adjusting the inductance of the output antenna lead and the capacitance formed by the metal plate so that the filter resonates with respect to the frequency of the fundamental wave of the magnetron (for example, 2.45 GHz). As a result, the attenuation of the fundamental wave is almost zero.
This is preferable because the amount of attenuation with respect to unnecessary electromagnetic waves of the second and higher harmonics higher than that becomes large.

Here, the fundamental wave means a microwave having an original oscillation frequency of the magnetron.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Next, the magnetron of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional explanatory view of the main body of the magnetron of the present invention. In FIG. 1, reference numeral 1 denotes an anode cylinder made of oxygen-free copper or the like, which is a part of a vacuum wall (wall surface of a vacuum container, the same applies hereinafter), and a plurality of vanes 2 are radially provided on the inner circumference of each of the vanes 2. Are alternately connected by strap rings 3 and 4 having a large diameter and a small diameter to stabilize the π-mode oscillation. At both ends of the anode cylinder 1 there are vanes 2
Pole piece 1 for concentrating the magnetic field in the working space between the tip of the cathode and the cathode 5 provided at the center of the anode cylinder 1.
0 and 11 are provided, respectively, and the anode portion is formed by these.

The cathode 5 is made of a filament in which, for example, thorium tungsten wire is wound in a coil shape, and is provided in the center of the anode cylinder 1 in the space surrounded by the tips of the vanes 2. End hats 6 and 7 are fixed to both ends thereof, and the end hats 6 and 7 are connected to cathode leads 8 and 9, respectively. The cathode leads 8 and 9 are connected to an external lead 20 via a cathode stem 19 made of an insulating material such as ceramics, and these form a cathode portion. The cathode stem 19 is fixed to the anode cylinder 1 via the input side metal cylinder 12. The input side metal cylinder 1
2 and the cathode stem 19 form the vacuum wall on the input side.

One of the vanes 2 has an output antenna lead 1
One end of 7 is electrically connected, and the other end thereof penetrates the through hole 18 of the pole piece 11, the output side metal cylinder 13 and the center of the insulating cylinder 15 composed of a ceramic cylinder and the like, and is a sealing portion of the exhaust pipe 16. It is fixed. A cap (not shown) is placed over the sealing portion. The output side metal cylinder 13 is directly electrically connected to the anode cylinder 1, and the microwave power oscillated in the anode portion travels through the output antenna lead 17 extending on the central axis of the output side metal cylinder 13 as a coaxial line. Emitted from the tip. This output side metal cylinder 13, insulating cylinder 1
5 and the exhaust pipe 16 form a vacuum wall on the output side. Reference numeral 17a denotes an antenna lead narrowing portion in which the output antenna lead 17 is formed thinner than the other portions and the cross-sectional area thereof is reduced. Reference numerals 21 and 22 denote metal plates electrically connected to the inside of the output-side metal cylinder 13 by brazing or the like, which are donut-shaped disks made of oxygen-free copper, for example.

The doughnut-shaped disks 21 and 22 face each other so that their inner peripheral ends have a constant gap with the output antenna lead 17, and the capacitor component formed in the gap and the inductor component of the output antenna lead 17 cause a gap. A low pass filter is formed. The present invention is characterized in that the low-pass filter suppresses the radiation of unnecessary electromagnetic waves of high frequency equal to or higher than the second harmonic. Further, in the present invention, donut-shaped disks 21 and 22 for forming a capacitor component forming the low-pass filter are connected inside the output side metal cylinder 13. Therefore, it can be manufactured by a manufacturing process similar to the conventional choke structure attachment, and can be easily manufactured. Further, since the output side metal cylinder 13 is electrically connected to the anode part, No capacitor component is generated between the donut-shaped disks 21 and 22. As a result, a π-type low-pass filter can be formed as described below.

The low-pass filter in the magnetron of the present invention has a structure of a part of the output side metal cylinder 13 and the output antenna lead 17 in FIG. (Inductance of the output antenna lead 17 between the two donut-shaped discs 21 and 22) L ₁ and the gap between the inner peripheral end of the donut-shaped discs 21 and 22 and the output antenna lead 17, respectively. The capacitance C ₁ is mainly formed. Therefore, in order to obtain the inductance L ₁ and the capacitance C ₁ that resonate at the oscillation frequency of the fundamental wave of the magnetron,
By setting the thickness of the antenna lead narrowing portion 17a and the intervals and diameters of the donut-shaped disks 21 and 22, the fundamental wave is not attenuated and the fourth harmonic of 4.
It functions as a π-type low-pass filter that can obtain a large attenuation characteristic for high frequencies of 9 GHz or higher.

It is known that the output antenna lead 17 has an inductor component for microwaves, and the inductance increases as the cross-sectional area of the output antenna lead 17 decreases. Therefore, as shown in FIGS.
A large inductance can be obtained by providing the antenna lead narrowing portion 17a, and two donut-shaped discs 2 can be provided.
The same characteristics can be obtained even if the distance between 1 and 22 is narrowed. The cross section of the output antenna lead 17 may be circular or rectangular. This output antenna lead 17
The cross-sectional area of is restricted when it is matched with the output impedance, but the influence is small when it is partially thinned. Therefore, the antenna lead narrowing portion 17a can be thinned within a range where the mechanical strength can be endured, and the desired impedance can be set. Due to the mechanical strength, when the cross section of the antenna lead narrowing portion 17a is circular,
The diameter is preferably 1 mm or more. In this case, the inductance L ₁ can be increased by increasing the length of the portion having a small cross-sectional area.

In order to reduce the cross-sectional area of the output antenna lead 17 in order to obtain a desired inductance,
Unless the other electrical characteristics of the magnetron are affected, the output antenna lead 17 can be made thin as a whole or the two discs 2
It is also possible to make the output antenna lead 17 thin, not only between 1 and 22, but only in a portion between them. In these cases, the inductance L ₁ constituting the π-type low-pass filter includes an inductor component of the output antenna lead 17 between the two donut-shaped disk 21 acts as an inductance L _1.

The capacitance C ₁ between the doughnut-shaped disks 21 and 22 and the output antenna lead 17 becomes larger as the distance between them becomes narrower. However, if they are too close to each other, electric discharge occurs between them, which is not preferable in terms of electrical characteristics. Therefore, the distance between them is preferably 1 mm or more, and the donut-shaped disc 2 is provided so that the inductance L ₁ and the capacitance C _{1 of} the antenna lead narrowing portion 17a resonating with the fundamental wave can be obtained within that range.
The inner diameters of 1 and 22 and the distance between the two disks 21 and 22 are set.

On the other hand, as shown in FIG. 3, the capacitance C ₁ between the donut-shaped disks 21 and 22 and the output antenna lead 17 is equal to the inner peripheral edge of the donut-shaped disks 21 and 22 and the output antenna lead 17. It is increased by interposing a dielectric material such as the ceramic sleeve 25 in the gap between and. For example, the relative permittivity of ceramics is about 10
By inserting the ceramic sleeve 25, the capacitance is about 1 at the same interval as in the case of vacuum.
It becomes 0 times. Moreover, the ceramic sleeve 25 is interposed between the two.
By interposing such a dielectric material, electric discharge between them is suppressed, electric discharge does not occur even in a narrow interval, and electric characteristics are not deteriorated. But the ceramic sleeve 2
From the viewpoint of strength of No. 5, the thickness is preferably about 1 mm or more.

As described above, by interposing the dielectric material in the gap between the inner peripheral ends of the donut-shaped disks 21 and 22 and the output antenna lead 17, the capacitance C ₁ is increased and the same resonance frequency is obtained. The inductance can be reduced. Therefore, the length of the output antenna lead 17 can be shortened, and the antenna lead narrowing portion 17a can be thickened. As a result, by shortening the output antenna lead 17, the magnetron can be downsized and the cost can be reduced. Further, by thickening the output antenna lead 17, the assembling work can be simplified, the cost can be reduced, and the mechanical strength can be sufficiently maintained and the reliability can be improved.

As a method of attaching the ceramic sleeve 25 described above, for example, the shape of the ceramic sleeve 25 is formed so as to match the shape of the output antenna lead 17, and is inserted into the output antenna lead 17, and the output antenna lead 17 is crimped or brazed. It is carried out by fixing with adhesion such as. Further, the dielectric material may be attached to the outer peripheral surface of the corresponding portion of the output antenna lead 17 by coating or deposition. The ceramic sleeve 25 is shown in FIG.
As shown in FIG. 3, since the dielectric material need not be in the integral shape as long as it is in the gap between the inner peripheral ends of the donut-shaped disks 21 and 22 and the output antenna lead 17, the disk 21 and the disk are not in contact with each other. It is also possible to interpose different ceramic parts in the portion of 22 and to attach the dielectric material only to that portion.

Next, FIG. 4 shows the results of simulation by concrete numerical values in the magnetron which constitutes a π-type low-pass filter composed of two donut-shaped disks 21 and 22 having the structure shown in FIG. For example, a magnetron with an oscillation frequency of 2.45 GHz and an output of 800 W,
The thickness of the disks 21, 22 is 1 mm, the inner diameter is 7 mm (the inner diameter of the output side metal cylinder 13 is 16 mm), and the two disks 21, 2 are
The interval between the two is 9 mm, and the diameter of the antenna lead narrowing portion 17a is 1.4 mm (the diameter of the other output antenna lead 17 is 4 mm). When the magnetron having the structure of this output section was analyzed by an electromagnetic field simulator, the attenuation characteristics shown in FIG. 4 were obtained.

As can be seen from FIG. 4, by adopting this structure, the fundamental wave of the magnetron (2.45 GHz)
There is no ripple in the attenuation characteristic for frequencies near z), and there is almost no attenuation for frequencies near the fundamental wave. On the other hand, the attenuation amount gradually increases with respect to the high frequency of the second harmonic (4.9 GHz) or more, and the required attenuation amount of 10 dB or more is obtained in the high frequency band. As a result, 4.5-18GH including the 7th harmonic
Radiation of unnecessary electromagnetic waves can be suppressed over a wide range of frequencies up to z. Moreover, it is possible to suppress not only noise of a specific frequency such as a harmonic, but also noise of the entire frequency including frequencies between the harmonics.

FIG. 5 is a diagram showing an equivalent circuit diagram of a filter portion of another embodiment of the magnetron of the present invention in the same manner as FIG. 2 in relation to parts. In the example shown in FIG. 1, the capacitor forming the low-pass filter is formed by two metal plates (donut-shaped discs) to form the π-type low-pass filter, but in the example shown in FIG. 5, one donut is formed. The circular disk 21 constitutes the simplest low-pass filter of the LC circuit. That is, the inductance L ₁ of the antenna lead narrowing portion 17a of the output antenna lead 17 shown in FIG. 5 and the capacitance C formed between the inner peripheral end of the donut-shaped disc 21 and the output antenna lead 17 are shown.
_If the thickness of the antenna lead constriction 17a and the inner diameter of the donut-shaped disk 21 are set so that 1 and 1 satisfy the relationship of the following formula (1) with respect to the oscillation frequency f of the fundamental wave of the magnetron, the fundamental wave becomes A low-pass filter that resonates with respect to the resonance frequency and increases in attenuation at higher frequencies is formed.

F = 1 / {2π (L ₁ C ₁ ) ^1/2 } (1) In this structure, the change of the attenuation characteristic with respect to the frequency higher than the resonance frequency is gentle and is inferior to that of the π-type low-pass filter. However, a sufficient amount of attenuation can be obtained for high-order harmonics, etc., and unnecessary radiation at high frequencies can be reliably suppressed with a simple structure. Note that, as shown in FIG. 3, if a dielectric material is interposed in the gap between the inner peripheral end of the donut-shaped disc 21 and the output antenna lead 17, the capacitance C ₁ therebetween increases, as described above. Is. Further, the low-pass filter can be configured by a plurality of metal plates (donut-shaped disks) of three or more.

[0032]

According to the magnetron of the present invention, since the output antenna lead and the low-pass filter are provided in the vicinity thereof, it is possible to stably suppress the emission of unnecessary electromagnetic waves having a frequency higher than the fundamental wave of the magnetron. You can do it. Further, the resonance can be resonated with the oscillation frequency of the fundamental wave of the magnetron, so that the attenuation of the fundamental wave can be almost zero. Further, since there is no frequency that causes attenuation even in the vicinity of the frequency of the fundamental wave (ripple in the attenuation characteristic), stable attenuation characteristics can be obtained even with variations in the manufacturing stage. Moreover, according to the present invention, since the radiation of the electromagnetic wave at a specific frequency is not suppressed, it is possible to reliably suppress the radiation (noise) of the unnecessary electromagnetic wave in the entire wide frequency band.

Furthermore, according to the present invention, it is not necessary to provide a multi-stage structure for suppressing each specific frequency, and the variation of the frequency characteristic due to the dimensional tolerance of the parts unlike the choke structure is small. Further, as in the case of the conventional choke structure, it is only necessary to attach a donut-shaped metal plate to the inner circumference of the output side metal cylinder, and therefore it is possible to manufacture in the same manner as the conventional manufacturing process. Therefore, it is possible to obtain an inexpensive magnetron which is easy to manufacture.

As a result, it is possible to reduce the cost of the microwave heating equipment such as the magnetron and the microwave oven, and even if the microwave heating equipment such as the microwave oven is used at home, satellite television and communication equipment. It does not interfere with the communication system due to the noise entering. Further, it is possible to reliably suppress the generation of noise even at high frequencies such as the seventh harmonic (17.15 GHz) of the magnetron for microwave heating, and the high frequency due to the recent development of communication systems Even for a new communication device, the interference can be effectively eliminated.

[Brief description of drawings]

FIG. 1 is a cross-sectional explanatory view of a main body of an embodiment of a magnetron of the present invention.

FIG. 2 is an equivalent circuit diagram of a filter unit of the magnetron shown in FIG.

FIG. 3 is a cross-sectional explanatory view of an output antenna section of another embodiment of the magnetron of the present invention.

FIG. 4 is a diagram showing the attenuation characteristic of the output of the magnetron of FIG. 1 with respect to frequency.

FIG. 5 is an equivalent circuit diagram of a filter unit of another embodiment of the magnetron of the present invention.

FIG. 6 is a cross-sectional explanatory view of a main body of a conventional magnetron.

FIG. 7 is a diagram showing attenuation characteristics with respect to frequency of a magnetron provided with a conventional multi-stage choke structure.

[Explanation of symbols]

 1 Anode Cylinder 2 Bain 5 Cathode 13 Output Side Metal Cylinder 17 Output Antenna Lead 17a Antenna Lead Constriction Part 21, 22 Donut Disk 25 Ceramic Sleeve

Claims (5)

[Claims] 1. An anode part, a cathode part provided at the center of the anode part, an output antenna lead for leading out a microwave oscillated in the anode part, and a part provided around the output antenna lead. An output side metal cylinder electrically connected to the anode part, and a metal plate forming a capacitor component between the output side metal cylinder and the output antenna lead is connected to the inside of the output side metal cylinder. A magnetron in which a low-pass filter is formed by the inductor component of the output antenna lead. 2. The magnetron according to claim 1, wherein a plurality of the metal plates are provided and a π-type low pass filter is formed. 3. The magnetron according to claim 2, wherein the two metal plates are provided. 4. The magnetron according to claim 1, wherein the output antenna lead near the metal plate is provided with an antenna lead narrowing portion having a reduced cross-sectional area of the output antenna lead. 5. The thickness of the output antenna lead is set so that the low-pass filter formed of the inductor component and the capacitor component formed of the output antenna lead and the metal plate resonates at the frequency of the fundamental wave oscillated in the anode part. The magnetron according to claim 1, 2, 3 or 4, which is set and provided with the metal plate.