JPH0535531B2 - - Google Patents

Description

[Detailed description of the invention]

[Object of the Invention] (Industrial Application Field) The present invention relates to a magnetron for a microwave oven, and particularly to a combination structure of an anode vane, a strap ring, a pole piece, and an output antenna lead. (Prior Art) It is well known that in a magnetron, the magnetic field distribution in the interaction space has a strong influence on the oscillation operation. Ideally, the design should be such that the entire interaction space has a uniform magnetic flux density completely parallel to the tube axis direction. However, especially in magnetrons for microwave ovens, in order to position the cathode for electron emission on the tube axis, it is necessary to extend and install the cathode support along the tube axis. Holes must be formed. In addition, the permanent magnet must be as low-cost as possible, miniaturized, and installed outside the tube. Furthermore, at the end of the interaction space, in order to prevent electrons from jumping out towards the pole piece from between the end shield and the inner corner of the anode vane, it is better for the magnetic flux to be in an oblique direction in this area. It may be convenient. Due to these various constraints, it is not possible to achieve a uniform magnetic field distribution completely parallel to the tube axis in the entire interaction space. Conventionally, for example, as disclosed in Japanese Patent Application Laid-Open No. 53-38966, the safety of oscillation has been improved by configuring the magnetic field strength to be equal from the cathode surface of the working space to the inner end surface of the anode vane, or to be stronger on the anode vane side. It also suggests improvements. Furthermore, as disclosed in Japanese Patent Laid-Open Nos. 51-56172 and 51-58859, proposals have been made to improve the shape of the pole pieces so that the magnetic field distribution becomes more parallel in the working space. However, these are magnetrons with a base structure in which a permanent magnet is built into a tube, and a pole piece of the same diameter is joined to the magnet surface. Therefore, this cannot be directly applied to a base structure in which a ring-shaped ferrite permanent magnet is installed outside the tube and magnetic flux is guided into the working space via a funnel-shaped pole piece. Therefore, a general magnetron for a microwave oven generally has a configuration as shown in FIG. 16. In the same figure, reference numeral 21 indicates the oscillation unit main body, and 22
23 is a plurality of copper anode vanes, 24 is a strap ring, 25 is a coiled filament cathode, 26 and 27 are ring-shaped end shields provided at both ends of the anode cylinder, and 23 is a plurality of copper anode vanes.
28 is a cathode support, 29 and 30 are a pair of iron funnel pole pieces, 31 is an output antenna lead,
32 and 33 are thin-walled iron metal containers, 34 and 35 are a pair of ring-shaped strontium-based ferrite permanent magnets, 36 is a square-shaped iron yoke, 37 is an aluminum radiator, 38 is an output ceramic cylinder, and 39 is a gasket. The ring, S, represents the interaction space. When examining the magnetic flux distribution near the working space of such a conventional structure, it is roughly as shown in FIG. 17.
Near the approximate center in the axial direction of the working space S extending from the substantially cylindrical electron emitting surface K of the cathode to the vane inner end surface A, the magnetic flux B is approximately parallel to the tube axis Z.
In the opposing region Se between the end shields 26 and 27 and the inner end face of the vane, the direction of the magnetic flux B is an oblique direction toward the center. By the way, when examining the strength distribution of the magnetic field in the direction component along the tube axis of the magnetic field in the working space S, this conventional magnetron has a distribution as shown in FIG. In the figure, the average magnetic field strength from the cathode surface K to the anode inner end surface A at the center of the working space S (z = 0) is 100%.
As, each point in the tube axis direction (z = 0, z = ±1 mm,
z=±2mm, z=±3mm, z=±4mm, z=±5
The magnetic field strength in mm, ) is expressed as a relative value.
From the same figure, it can be seen that this magnetron has the most uniform axial magnetic field strength at the radially intermediate portion P of the working space, but there is large variation along the axial direction at the anode inner end surface A and its vicinity. ing.
Since the width of the anode vane, that is, the dimension La of the inner end surface along the axial direction, is 9.5 mm, the difference in axial magnetic field strength in that range is about 22%. And this magnetron line noise, i.e. detected on the input side through the cathode support.
The noise in the frequency components of 30 to 400 MHz was as shown in Fig. 19. The noise is particularly strong in the relatively low frequency components of 30 to 100 MHz, and if we focus on the 100 MHz band components (for convenience, this refers to the maximum noise level in the 80 to 120 MHz range), the level is approximately 42
(dbμV). Furthermore, taking a 2450MHz band, 600W output magnetron as an example, its load stability is approximately 1.55A at anode current (peak value). (Problems to be Solved by the Invention) Recently, there has been a strong demand for miniaturization of magnetrons, particularly reduction of the height in the axial direction, in order to miniaturize microwave ovens. If you try to use the magnet more effectively by simply shortening the pole piece spacing in order to shorten the height of the magnetron, the electromagnetic open coupling between the pole piece and the strap ring will increase, and as a result, the electron cathode will be reversed. The impact increases, causing a rise in the temperature of the cathode, and in extreme cases, there is a risk of thermal runaway. On the other hand, if the axial length of the anode vane is shortened in order to ensure a certain distance between the pole piece and the strap ring, the load stability will deteriorate. For example, it was confirmed that when the axial length of the vane was shortened by 8.0 mm from 9.5 mm, the load stability deteriorated to a peak value of 1.3 A. In addition, if you try to shorten the cathode introduction part, that is, the input stem part, for example, the stem length can be changed from 20.4 mm to 10 mm.
If it is set to mm, the reverse impact of electrons on the cathode will increase dramatically, the cathode temperature will rise, and in extreme cases, a part of the cathode may melt. This negative cathodic impact of electrons increases in proportion to the amount of stem shortening. This invention solves the above problems by focusing on the electromagnetic field distribution in the interaction space, especially near the inner end of the anode vane, and achieves high magnetic efficiency, suppresses unnecessary radiation such as line noise, and is compact. The purpose is to provide a highly reliable magnetron for microwave ovens. [Structure of the Invention] (Means for Solving the Problems) The present invention provides a cathode having a substantially cylindrical electron emitting surface and an electromagnetic field in an interaction space between a plurality of anode vanes surrounding the cathode. , the magnetic field is set so that the difference in axial strength at the position of the inner end face of the anode vane is within a range of 15% or less, and the electric field is set so that the strap ring is buried deeper inside the groove than the position of the side end face of the vane, so that the strap ring and the pole This is a magnetron for an electron lens configured to reduce electromagnetic coupling between the magnetron and the piece. (Function) According to this invention, the magnetic field in the working space is made uniform and the electromagnetic coupling between the pole piece and the strap is reduced, so even if the axial length of the vane is shortened,
There is almost no deterioration in load stability, and even if the length of the input stem is shortened, cathode reverse impact of electrons does not increase. In particular, the electrostatic and magnetic field distributions in the interaction space are improved, the generation of relatively low frequency noise components is suppressed, and a small, lightweight, and highly reliable magnetron for electron lenses can be obtained. (Example) An example will be described below with reference to the drawings. Note that the same parts are represented by the same symbols. The oscillation frequency shown in Figures 1 and 2 is 2450M
An example of a 10-vane magnetron with an output of 600W in the Hz band will be described. This magnetron includes a working space S of a pair of funnel-shaped pole pieces 29 and 30 and a side end surface 2 of an anode vane 23.
Flat portions 29a and 30a facing 3A have a relatively large diameter. The outer diameter dimension Dk of the substantially cylindrical electron emitting surface K of the coiled filament 25 is 3.9 mm, the envelope inner diameter dimension Da of the anode vane inner end surface A is 9.06 mm, the vane width La is 8.5 mm, and the end shield 26 The outer diameter De1 of the 27 is 7.2 mm, the outer diameter De2 of the 27 is 8.2 mm, and the distance between both end shields Le is 9.4
mm, the inner diameter Dpi of the central through holes 29b and 30b of the pole pieces is approximately 9.4 mm, the outer diameter Dpo of the flat parts 29a and 30a is 18 mm, and the distance between the flat parts of both pole pieces facing each other
Lp is approximately 11.7mm, outer diameter Dp of pole piece is approximately 37.5
mm, its height h is 7.0 mm, its wall thickness is 1.6 mm, the inner and outer diameters of the link-shaped ferrite permanent magnets 34 and 35 are respectively 20 mm and 54 mm, the thickness W1 of one magnet 34 is 12.6 mm, the other The thickness W2 of the magnet 35 is 9 mm.
It is. In addition, the thickness of the iron metal containers 32 and 33 is
0.5 mm, and are inserted into the inner surfaces of both magnets with a gap of about 0.5 mm or less. The iron yoke 36 has a thickness of 1.6 or 1.5 mm and is assembled in a square shape. Further, in each pair of strap rings 24 made of copper, the outer diameter of the larger diameter ring 24a is 17.8 mm, and the inner diameter of the smaller diameter ring is 12.9 mm. In this way, the diameter Dpi of the central through hole of each pole piece 29, 30 is set to be equal to or slightly larger (approximately 6.5% or less) than the inner diameter Da of the envelope formed by the inner end surfaces of the ten vanes. The outer diameter Dpo of the opposing flat portions 29a and 30a of the pole piece is approximately twice the inner diameter Da of the envelope of the inner end surface of the anode vane. Therefore, the outer diameter Dpo of the flat part of the pole piece is larger than that of the strap spring 2 with a larger diameter.
The dimensions are equal to or slightly larger than the outer diameter of 4a. In addition, the strap ring 24 is, for example, 0.3 to 0.7 mm (dimension h _s ) from the position of the side end surface 23a of the vane.
It is buried deep inside. The axial length Ls of the input side metal container is set to 11 mm. Table 1 shows a comparison of the dimensions of each part of the conventional structure and this embodiment.

[Table] Now, the magnetic field distribution near the interaction space S in a magnetron having such a configuration is as shown in FIG. That is, since the outer diameter of the opposing flat portion of the pole piece is large, the magnetic flux distribution is rather parallel to the tube axis in the vane region. The intensity distribution of the magnetic field component in the tube axis direction within the working space S became as shown in FIG. This axial magnetic field strength distribution was obtained by measuring the strength of the magnetic field component parallel to the tube axis direction at each point using a Gaussmeter using a Hall element as a detector. The results shown in the figure show that, due to the combination of pole pieces with wide flat parts, the point P that exhibits the most uniform strength throughout the axial direction of the working space is located near the inner end surface A of the anode vane. The magnetic field strength difference at the cathode surface K is larger than that of the conventional one (Fig. 16), but the strength difference at the vane inner end surface A is about 7%.
It has been reduced to Noise leakage to the input side of the magnetron in this embodiment was as shown in FIG. That is,
The noise level of the 100MHz band component is approximately 21 (dBμV)
This has been reduced by half compared to the conventional one (shown in Figure 17), and the entire noise component in the range of 30 to 150 MHz has been significantly reduced. This is because the axial magnetic field strength at or near the inner end surface of the anode vane is nearly uniform throughout the entire axial direction, so the rotational speed of the electron cloud is approximately uniform throughout the entire axial direction of the vane, causing the vane to It is considered that the frequency difference in the high-frequency electric field induced in the resonant cavity remains small and the force of the frequency difference component is at a small level. In this way, the nozzle level at the source itself is kept low. The magnetic field strength distribution shown in FIG. 6 is for the case where the outer diameter dimension Dpo of the opposing flat portions of the pair of pole pieces is 16 mm. In other words, the pole piece flat part outer diameter Dpo is approximately 177 times the vane inner end surface envelope diameter Da.
%. The dimensions and shapes of other parts are the same as those of the embodiment shown in FIGS. 1 and 2. According to this embodiment, the anode vane inner end surface A
The axial magnetic field strength difference at the position is about 11%. The noise level is as shown in Fig. 7, and the 100MHz band component is approximately 22 (dBμV). This also succeeded in sufficiently suppressing low frequency noise components. Similarly, the outer diameter Dpo of the opposing flat part of the pole piece
is approximately 155% of the vane inner end surface envelope diameter Da14
mm, the magnetic field strength distribution was as shown in FIG. 8, that is, the axial magnetic field strength difference at the vane inner end surface position was about 17%. The noise component is shown in Figure 9, and is 100MHz.
The band component was approximately 33 (dBμV). Similarly, the outer diameter Dpo of the opposing flat part of the pole piece
When set to 12 mm, which is approximately 132% of the vane inner end surface diameter Da, the difference in axial magnetic field strength at the vane inner end surface position was approximately 22%. In that case, the 100MHz band component noise level reached approximately 42 (dBμV). This is equivalent to the conventional product. The above results are summarized as shown in FIG. 10. In other words, the larger the difference in axial magnetic field strength (difference in relative ratio %) at the position of the inner end face of the vane, the more noise components of relatively low frequency, e.g.
The 100MHz band component has a large level. This confirms that a noise level of about 30 (dBμV) or less, which can be recognized as an improvement effect, can be obtained with a structure in which the difference in axial magnetic field strength at the inner end face of the vane is within a range of about 15% or less. FIG. 11 shows changes in load stability when the vane width La is 8.5 mm and 9.5 mm. Note that this is when the magnetic field strength difference is 20%, and the vane height La is 1 mm.
By shortening the load stability from 1.55A
Although it deteriorates to 1.32A, it is confirmed that if the magnetic field strength difference is 10%, that is, the outer diameter of the flat surface of the pole piece is 16mm, sufficient load stability can be obtained even with La = 8.5mm. Next, considering the influence of the length Ls of the input side metal container, as shown in Figure 12, in the conventional structure, when the length Ls of the metal container is shortened by 10 mm, the amount of negative cathode impact of electrons increases by 10%. As a result, the cathode temperature rises, resulting in an extreme deterioration of its life. On the other hand, if you put a trapping ring inside the vane, e.g.
It was found that when embedded by 0.5 mm, the amount of reverse impact did not increase as shown by the solid line curve. The embodiment shown in FIG.
4 is provided only on the extension side of the output antenna lead of the vane. In this way, the same effects as described above were obtained. Note that the strap ring may be provided only on the input stem side of the vane. In the embodiment shown in FIG.
A 1/4 wavelength type chiyoke cylinder 32a for suppressing unnecessary radiation is placed inside the radiator. The output antenna lead 31 is coupled to the vane to which the larger diameter strap ring 24a is fixed by soldering. It has been found that this structure improves the unnecessary radiation level of harmonic components such as the fifth harmonic by about 20 dB, as shown in FIG. With the above configuration, it is possible to shorten the pole piece spacing Lp by approximately 1 mm, and the magnetic efficiency is greatly improved, reducing the thickness W2 of the magnet on the input stem side.
It became possible to shorten the length from 13.5mm to 9mm.
It is also possible to shorten the length of the metal container on the input side, making it possible to shorten the axial length, or height, of the magnetron by approximately 15 mm compared to conventional tubes. [Effects of the Invention] As explained above, it is possible to effectively suppress unnecessary noise, ensure sufficient load stability, and significantly shorten the height of the magnetron.
This can greatly contribute to downsizing of microwave ovens.

[Brief explanation of the drawing]

Fig. 1 is a vertical cross-sectional view of the main part showing an embodiment of the present invention, Fig. 2 is an enlarged view of the main part, Fig. 3 is a characteristic diagram showing the magnetic flux distribution, and Fig. 4 is a diagram of the magnetic field strength distribution. , FIG. 5 is a noise characteristic diagram thereof, FIGS. 6 and 7 are magnetic field strength distribution diagrams and noise characteristic diagrams showing other embodiments of the present invention, and FIGS. 8 and 9 are magnetic field strength distribution diagrams of comparative examples. Figures and noise characteristics diagrams,
Figure 10 is a comparative characteristic diagram showing the relationship between magnetic field strength and noise level, Figure 11 is a characteristic diagram showing the relationship between magnetic field strength difference and load stability, and Figure 12 is the shortening amount of the metal container and the electron cathode reverse. Characteristic diagram showing the relationship between impact amount,
FIG. 13 is a vertical sectional view of a main part of another embodiment of the present invention, FIG. 14 is a longitudinal sectional view of a main part of still another embodiment, and FIG. 15 is a fifth harmonic characteristic diagram of the one shown in FIG. 14. , FIG. 16 is a longitudinal cross-sectional view of a main part showing a conventional structure, FIG. 17 is a magnetic field line distribution diagram, FIG. 18 is a magnetic field strength distribution diagram, and FIG. 19 is a noise characteristic diagram. 25...Cathode, K...Electron emission surface, 24...
...Strap ring, 24a...Large diameter ring, 2
6, 27... End shield, S... Interaction space, 23... Anode vane, 23a... Vane side end surface, A... Anode vane inner end surface, Da...
Vane end face envelope diameter, 29, 30...Pole piece, 29a, 30a...Pole piece flat part,
29b, 30b...Pole piece center through hole, 29
c, 30c...Protrusion part, Dpi...Inner diameter dimension of pole piece center hole, Dpo...Outer diameter dimension of pole piece flat part, Dp...Outer diameter dimension of pole piece,
Ls……Length dimension of metal container.

Claims (1)

[Scope of Claims] 1. A cathode having a substantially cylindrical electron emitting surface, an end shield connected to both ends of the cathode, and a plurality of end shields arranged radially around the cathode through an interaction space. an anode vane having a groove near the inner end thereof; at least a pair of large and small strap rings located in the groove of the vane and disposed horizontally in the radial direction of the vane and connecting every other anode vane; An output antenna lead electrically connected to the vane, a funnel-shaped pole piece with a through hole in the center provided on both sides with the interaction space and the anode vane in between, and a funnel-shaped pole piece provided on each of these pole pieces. a pair of ring-shaped permanent magnets having an inner diameter larger than the inner diameter of the central through-hole of the pole piece and an outer diameter larger than the outer diameter of the pole piece; and a yoke surrounding the permanent magnets and forming a magnetic path. In the magnetron for a microwave oven, the pole piece has an inner diameter of the central through hole equal to or slightly larger than the envelope diameter formed by the inner end surface of the vane, and an outer surface of the pole piece that is close to and opposite to the vane. A magnetron for an electronic lens, wherein the diameter is 160% or more of the vane envelope diameter, and a strap ring located in the groove of the vane is embedded deeper inside the vane than at a side end surface position. 2. The magnetron for a microwave oven according to claim 1, wherein the output antenna lead is drawn out from an anode vane to which a large diameter strap ring is connected.