JP2001023531A - Magnetron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent product defect or characteristic degradation, to maintain a long life, and to increase reliability by securing temporary welding of a bottom end seal and a negative electrode lead. SOLUTION: The negative electrode structure 70 has a filament 7 provided between a top end seal 17a and a bottom end seal 17b, and negative electrode leads 12a, 12b feeding electricity to the filament 7. A thin part 16 is provided at a welded part between the negative electrode lead 12b and the bottom end seal 17b structuring a negative electrode structure 70.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetron, and more particularly to a magnetron which can accurately and easily fix an end shield and a cathode lead constituting a cathode assembly, and improve reliability.

[0002]

2. Description of the Related Art Magnetrons are widely used in the fields of high-frequency cookers such as radar devices, medical equipment, microwave ovens, and other microwave application equipment because they efficiently generate high-frequency output, that is, microwave output.

In this magnetron, a cathode structure is usually disposed in the center of a vacuum vessel, and a cathode (hereinafter, also referred to as a filament) constituting the cathode structure is separated by a working space in which a tube axial magnetic field is formed. A group of cavity resonators is arranged around the periphery.

[0004] The cavity resonator comprises a filament disposed at the center along the tube axis, an anode cylinder surrounding the filament and disposed coaxially with the working space, and an anode cylinder disposed at a position close to the filament. The oscillating phases of a plurality of plate-like bodies or anode vanes (hereinafter, also simply referred to as vanes) arranged radially in the direction and a plurality of cavity resonators formed in a space formed by the vanes and the anode cylinder are matched. In order to electrically connect every other vane to the same potential, a pair of upper and lower straps or a pair of upper and lower strap rings are arranged.

[0005] The microwave generated in the group of cavity resonators passes through an antenna lead which is connected to the cavity resonator at one end and arranged at the other end in a dome-shaped antenna ceramic (antenna dome) constituting a main force portion. To radiate.
The anode cylinder, the vane, and the strap ring are generally made of copper, and brazing using silver brazing or the like is employed for joining and fixing them.

[0006] The vanes and antenna leads are also connected by similar brazing. Needless to say, in the magnetron in which the anode cylinder and the vane are integrated, it is not necessary to consider the brazing of the anode cylinder and the vane.

One of the factors that hinder the reliability of such a magnetron is the assembly accuracy of the structure around the filament (hereinafter, also referred to as a cathode assembly). In particular, an end shield (upper end shield and lower end shield) for holding a filament constituting the cathode assembly along the center of the tube axis, a cathode lead fixed to the upper end shield and the lower end shield to supply heating power, Is required to be accurately performed at a predetermined position.

[0008] In the magnetron assembling process, the cathode assembly is assembled with another structure while the end shield and the cathode lead are temporarily fixed, and brazed when the assembly is finally completed. Is common.

[0009] Magnetrons of this type are required to have a large size (large output) due to the expansion of their applications. Therefore, the size of the filament must be increased, and accordingly, the end shield needs to be increased.

The above-mentioned temporary fixing is performed by laser welding or plasma welding. In particular, in the temporary fixing of the lower end shield and the cathode lead, the thickness of the lower end shield increases due to the enlargement of the lower end shield. In some cases, the temporary fixing performed by the melting of the resin is not sufficiently performed. For this reason, the final positions of the two cannot be accurately fixed, which causes deterioration of characteristics and reliability.

FIGS. 13A and 13B are explanatory views of a cathode structure in a conventional magnetron. FIG. 13A is a longitudinal sectional view, and FIG. 13B is an enlarged partial view of a portion A in FIG. FIG. 14 is an exploded view of the filament and the end shield of the cathode assembly in FIG.

The cathode assembly passes through an upper end shield 17a and a lower end shield 17b for holding the filament 7 in the tube axis direction, two cathode leads 12a and 12b for supplying power to the filament 7, and a lower end shield 17b. In order to hold the cathode leads 12a and 12b insulated from each other, a ceramic spacer 18 is provided below the lower end shield 17b to penetrate the cathode leads.

In order to prevent the ceramic spacer 18 from moving in the tube axis direction, the ceramic spacer 18 is brought into contact with the lower end shield 17b side of the ceramic spacer 18 and the cathode lead 12
b, and a metal sleeve 19a which is in contact with the ceramic spacer 18 on the side opposite to the metal sleeve 19b side and is caulked and fixed to the cathode lead 12a.

The filament 7 and the upper end shield 17a
And the lower end shield 17b are finally brazed WD1
WD3. The upper part of the filament 7 is fixed to the upper end shield 17a, and the lower part is fixed to the lower end shield 17b. The cathode lead 12a extending to the upper end shield 17a penetrates the through hole 17b-1 formed in the lower end shield 17b, and the cathode lead 12b fixed to the lower end shield 17b penetrates the through hole 17b-2. I have. The cathode lead 1
2a is electrically insulated from the through hole 17b-1 of the lower end shield 17b.

[0015] Examples of this kind of prior art are disclosed in, for example, JP-A-5-198266 and JP-A-61-218045.

[0016]

In the above prior art, the lower end shield 17b is fixed to the cathode lead 12b by temporarily fixing the brazed WD3 portion by welding and passed to a subsequent assembly process. When the magnetron becomes large and the lower end shield 17b becomes large, the thickness of the member also increases. Therefore, even if the side surface of the lower end shield is irradiated with a laser beam for temporary welding or the like, the lower end shield has a large thickness. It cannot be sufficiently dissolved, and does not reach the cathode lead 12b inserted through the through hole 17b-2.

Therefore, the temporary fixing of the lower end shield 17b and the cathode lead 12b is performed as shown by WD '.
Temporary welding is performed on the bottom surface (lower surface) of the lower end shield 17b located on the side surface of the cathode lead 12b. However, since this portion is close to the seal 6 (lower seal), it is difficult to approach the welding head, and it is difficult to sufficiently irradiate the laser beam.

[0018] For this reason, the temporary welding of the relevant portion becomes insufficient, the welding is not performed at an accurate position, or the weld is removed in a subsequent step, and the final brazing cannot be performed accurately. There has been a problem that the magnetron may cause a product failure or characteristic deterioration, resulting in a shortened life and reduced reliability.

An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a magnetron with a long life and high reliability, which ensures temporary welding and does not cause a product failure or characteristic deterioration.

[0020]

In order to achieve the above object, the present invention provides a thin end portion for temporarily welding a cathode lead on the lower surface (seal side) of a lower end shield, so that a welding head is provided from the side. It is characterized by being easily accessible, facilitating melting of a thick portion with a small welding power, and performing reliable temporary welding.

A typical configuration of the present invention is described as follows. (1): a filament provided between the upper end shield and the lower end shield, a cathode assembly having two cathode leads for supplying power to the filament, an anode cylinder installed around the filament, and an anode cylinder A cavity resonator group formed of a plurality of anode vanes radially provided with the filament as a center, a microwave generated in the cavity resonator group, one end of which is connected to the cavity resonator; and A thin portion was provided at a cathode lead welded end of a lower end shield constituting the cathode assembly in a magnetron which radiates to the outside through an antenna lead disposed in an antenna dome having an end constituting a main force portion.

(2) The lower end shield in (1) has a through hole for inserting the two cathode leads on a surface opposite to a surface facing the filament, and the thin portion is formed in the lower end shield. It was provided in a region adjacent to one of the cathode leads and the through hole of the lower end shield.

(3): The thin portion provided in the lower end shield in (2) is formed by a step provided on a part or the entire periphery of the edge surrounding the through hole of the lower end shield.

(4): The thin portion provided in the lower end shield in (2) may be provided in the longitudinal direction of the cathode lead provided at a part or the entire periphery of the edge surrounding the through hole of the lower end shield. The protrusions were formed.

With the configuration of the present invention, the heat capacity of the thin portion of the lower end shield is reduced during the temporary welding, and the welded portion faces in a direction perpendicular to the side surface of the cathode lead. To provide a magnetron with uniform characteristics, long life and high reliability that can be easily welded without increasing the welding energy of lasers, etc. it can.

As a specific configuration of the thin portion,
By providing it in a region close to the through hole of the lower end shield as in (2), the thickness of the welded portion can be reduced.

Further, the thick portion is stepped as shown in (3),
Alternatively, it can be formed by a projection as in (4).

It is desirable that these shapes be formed at the same time when the lower end shield is formed. That is, since the end shield is manufactured by firing a high melting point metal powder such as molybdenum, the end shield can be easily formed by providing the above-mentioned thin portion in the mold. Further, a thin portion can be formed in the fired lower end shield by a cutting operation. The above-mentioned steps and projections can be selected for their ease of production.

It should be noted that the present invention is not limited to the above configuration and the configuration of the embodiment described later, and various modifications can be made without departing from the technical idea of the present invention.

[0030]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a sectional view of a cathode structure for explaining one embodiment of a magnetron according to the present invention. FIG. 2 is an exploded view of the filament and the end shield of the cathode assembly in FIG.

The cathode structure of the present embodiment is a cathode lead 12a.
Upper end shield 1 installed at predetermined intervals in the pipe axis direction
The filament 7 is provided between the lower cathode 7a and the lower end shield 17b, another cathode lead 12b is provided so as to terminate at the lower end shield 17b, and two cathode leads 12a and 12b are provided.
Power is supplied to the filament 7 at b.

Reference numeral 18 denotes two cathode leads 12a and 12
It is a ceramic spacer for holding at predetermined intervals so that b does not contact. Although this ceramic spacer 18 penetrates and holds two cathode leads, it does not have a function of fixing itself, so that one of the cathode leads 12
The metal sleeve 19b is inserted through the lower end shield 17b of the b, and is fixed by caulking with the lower end in contact with the ceramic spacer 18. Further, a metal sleeve 19a is provided on the side opposite to the lower end shield 17b of the cathode lead 12a.
Is fixed by caulking with the upper end in contact with the ceramic spacer 18.

The cathode leads 12a and 12b extending downward from the ceramic spacer 18 penetrate the seal 6 and the ceramic base 8 to reach a filter case described later with reference to FIG.

The filament 7 and the upper end shield 17a
And the lower end shield 17b are finally brazed WD1
WD3. As shown in FIG. 2, the filament 7 has an upper part fixed to the upper end shield 17a and a lower part fixed to the lower end shield 17b.
Then, the through hole 17 formed in the lower end shield 17b is formed.
A cathode lead 12a extending to the upper end shield 17a penetrates b-1 and a cathode lead 12b fixed to the lower end shield 17b penetrates a through hole 17b-2. The cathode lead 12a is electrically insulated from the through hole 17b-1 of the lower end shield 17b.

A thin portion 16 is formed below the lower end shield, that is, on the side opposite to the filament 7. The thin portion 16 is a through hole 1 through which the cathode lead 12b passes.
7b-2. By forming this portion as a temporary welded portion, the heat capacity is reduced, the material is easily melted, and the cathode lead 12b can be reliably temporarily fixed.

FIG. 3 is an explanatory view of the first embodiment of the thin portion formed on the lower end shield. In this example, a step 16a is formed at the lower end of the lower end shield 17b, that is, at the edge opposite to the filament over the entire periphery thereof, so that the gap between the lower end shield 17b and the through hole 17b-2 is made thin.

According to this structure, the cathode lead 12b which is made to penetrate the through hole 17b-2 by melting the thin portion 16a
Can be securely and accurately welded to an accurate position.

FIG. 4 is an explanatory view of a second embodiment of the thin portion formed on the lower end shield. In this example, the thin portion 16b is formed by providing a step near the lower end of the lower end shield 17b and the through hole 17b-2.

According to this configuration, the cathode lead 12b which is made to penetrate the through hole 17b-2 by melting the thin portion 16b
Can be securely and accurately welded to an accurate position.

FIG. 5 is an explanatory view of a thin portion formed on the lower end shield according to a third embodiment. In this example, a step (in this case, a notch shape) is provided only at the lower end of the lower end shield 17b and at a portion adjacent to the through hole 17b-2 to form the thin portion 16c.

According to this structure, the cathode lead 12b which is made to penetrate the through hole 17b-2 by melting the thin portion 16c
Can be securely and accurately welded to an accurate position.

FIG. 6 is an explanatory view of a thin portion formed on the lower end shield according to a fourth embodiment. In this example, a thin projection is provided at the lower end of the lower end shield 17b and at a portion adjacent to the through hole 17b-2 to form a thin portion 16d.

According to this configuration, the cathode lead 12b is made to penetrate the through hole 17b-2 by melting the thin portion 16d.
Can be securely and accurately welded to an accurate position.

FIG. 7 is an explanatory view of a fifth embodiment of the thin portion formed on the lower end shield. In this example, the projections forming the thin portion 16e formed on the lower end shield are formed linearly downward from the inner wall of the through hole 17b-2. The shape of this projection may be a straight wall or a curved wall. However, when a function as a guide for inserting the cathode lead 12b into the through hole 17b-2 is provided, at least the wall surface on the cathode lead 12b side has the shape of the cathode. It is preferable to use a curved wall that is concave toward the lead 12b.

As described above, according to the embodiments of the present invention, the thin end portion is formed near the through hole 17b-2 through which the cathode lead 12b of the lower end shield 17b is inserted, so that the magnetron can be assembled in the assembling step. Temporary welding of the lower end shield 17b and the cathode lead 12b can be performed accurately and reliably, without causing product defects and characteristic deterioration.
A magnetron with improved reliability can be provided.

Next, the overall configuration and specific application of the magnetron according to the present invention will be described.

FIG. 8 is a sectional view for explaining an example of the overall configuration of the magnetron according to the present invention. In the figure, 1 is an anode cylinder, 2 is an anode vane, 3 is an antenna lead, 4 is an antenna dome, 5a is an upper magnetic pole, 5b is a lower magnetic pole, 6a is an upper seal, and 6b is a lower seal (in the above embodiment, it is assumed as 6). The reference numeral 70 denotes a cathode structure, which is shown in detail in FIG.

8a is an upper magnet, 8b is a lower magnet, 9 is a metal gasket, 10 is a cooling fin,
11a denotes an upper yoke, 11b denotes a lower yoke, 13 denotes a choke coil, 14 denotes a feedthrough capacitor, 15 denotes a filter case, and 20 denotes an exhaust pipe.

A plurality of anode vanes 2 are electrically connected to each other by a pair of strap rings (not shown) to have the same potential. The anode vane 2 and the strap ring are firmly brazed to fix the anode vane so that a variation in characteristics does not occur. The configuration of the cathode assembly 70 is as described in FIG.

A cylindrical upper magnet 8a is provided at the upper part of the anode cylinder 1, and a cylindrical lower magnet 8 is provided at the lower part.
b, and the magnetic flux from the upper magnet 8a and the lower magnet 8b is supplied to the upper magnetic pole 5a and the lower magnetic pole 5b.
A required DC magnetic field is generated in the vertical direction (tube axis direction) with respect to the working space formed between the cathode filament 7 and the anode vane 2 through the cathode filament 7. The upper yoke 11a and the lower yoke 11b form a magnetic flux path from upper and lower magnets.

The filament 7 shown in FIG. 1 has a negative high potential. That is, the filament 7 is connected to the choke coil 13 via the two cathode leads 12a and 12b, and the other end of the choke coil 13 is connected to the feedthrough capacitor 14. The terminal of the feedthrough capacitor 14 has a negative high potential. Is connected to a filament transformer (described later).

The element of the feedthrough capacitor 14 is as follows.
A dielectric porcelain is used, a filter is formed together with the choke coil 13, and this filter is shielded by the filter case 15, so that the oscillated microwave does not affect external devices through the power supply line.

The antenna dome 4 has an upper seal 6
The antenna lead 3 is installed at a position separated from the upper yoke by the metal gasket 9 in the portion a.

FIG. 9 is a top view of the magnetron shown in FIG. 8, and the antenna dome 4 is installed at the center of the metal gasket 9 installed at the center of the upper yoke 11a.

In such a structure, the filament 7
The electrons emitted from the electrodes form a high-frequency potential in each anode vane 2 while circulating under the influence of the DC magnetic field, and oscillate a high frequency (microwave). The oscillated microwave is output from the antenna dome 4 to a waveguide (not shown) through the antenna lead 3.

In this configuration example, as the constituent material of the antenna dome 4, for example, a material containing 96% by weight or more of alumina and silicon oxide is used (for example, 92% by weight of alumina).
As described above, silicon oxide is 6 to 8% by weight, and its dielectric loss tangent is 6 or more.
Thus, when the microwave emitted from the antenna lead 3 passes through the antenna dome 4, the amount of absorption of the microwave by the antenna dome 4 becomes very small, and the temperature rise of the antenna dome is reduced.

FIG. 10 is a circuit diagram illustrating an example of a magnetron drive circuit. The reference numeral 231 indicates the magnetron according to the above-described embodiment.

This circuit example uses a switching power supply device for obtaining a required voltage by switching a commercial AC power supply at high speed as a magnetron power supply, that is, a so-called inverter power supply, and a DC power supply for supplying DC power to the switching power supply device 209. Reference numeral 201 denotes a commercial AC power supply 203 and a full-wave rectifier 205.

The DC output terminal of the full-wave rectifier 205 is connected to a filter 207 composed of a reactor and a capacitor. This filter 207 is not used for smoothing the rectified current, but for high-frequency noise included in the oscillation current. Is prevented from leaking through the AC power supply, thereby preventing the propagation of interfering waves.

The switching power supply 209 includes a transistor 211 and is turned on and off by a drive circuit 241 driven by an on signal of an on signal generation circuit 237 controlled by a synchronization pulse generated by a synchronization pulse generator 235. .

The switching power supply 209 includes a damper diode 21 connected in anti-parallel to the transistor 211.
5 and a resonance capacitor 213 connected in parallel.

This switching power supply device 209 comprises a primary winding 219 and secondary windings 221, 223 and 224, 225.
, The primary winding 219 is connected to the filter 207 via the switching power supply 209, and the capacitor 213 and the primary winding 219 form a series resonance circuit.

The secondary winding 221 is connected to a magnetron 231 through a voltage doubler rectifier including a capacitor 227 and a high voltage diode 229. The current detector 233 detects the load current flowing through the magnetron, and the averaging circuit 249 adds the difference from the set value of the output setting unit 251 to the synchronization pulse from the synchronization pulse generator 235 via the amplifier 257 as an average value. The ON signal generator 237 is provided as a control signal.

The secondary winding 225 is provided for heating the filament of the magnetron 231, and the other secondary winding 223 is for producing a voltage for output feedback. After the shaping, the signal is subjected to a predetermined time delay by the delay circuit 245, and is provided as a control signal of the ON signal generation circuit 237.

The secondary winding 224 is supplied to an auxiliary power supply 247, rectified and used as a power supply for a control circuit and the like.

Here, a high voltage of usually several KV is applied to the filament and the anode.

In the figure, reference numeral 232 denotes a waveguide, and 234 denotes a cooking chamber of a microwave oven. The microwave oscillated by the magnetron 231 is supplied to the cooking chamber 234 through the waveguide 232. .

FIG. 11 shows an example of a circuit using a general commercial power supply as it is as a magnetron power supply. Reference numeral 203 denotes a commercial AC power supply, 217 ′ denotes a high-voltage transformer, 219 ′ denotes a primary winding, 221 ′, 225 ′ denotes a secondary winding. Lines 227 'are capacitors, 229' are high voltage diodes, and 231 is a magnetron. The primary winding 219 'of the high voltage transformer 217' is connected to the commercial AC power supply 203, and the secondary winding 221 'is connected to a half-wave voltage rectifying circuit including a capacitor 227' and a high voltage diode 229 '.

The secondary winding 225 ′ is connected to the magnetron 2
The heater is heated by an electric current which flows by applying a required voltage to the heater connected to the heater terminal 31.

The capacitor 22 of the half-wave multiple voltage rectifier circuit
A connection point between 7 'and the high voltage diode 229' is connected to one of the heater terminals to apply a negative anode voltage. One of the secondary windings 225 'is connected to the anode of the magnetron 231 and the ground.

The magnetron power supply using the general commercial power supply as it is is not limited to the above half-wave voltage rectifier circuit.
A known full-wave rectifier circuit can also be used.

FIG. 12 is a conceptual diagram illustrating a specific example in which the magnetron according to the present invention is applied to a microwave oven.
Numeral 01 denotes a microwave oven, and the object to be heated 3
03 is set. 304 is a magnetron, 305 is an antenna, 306 is a magnetron power supply, 307 is a cooling fan, 308 is cooling air, 309 is a waveguide, and 310 is a stirrer.

The microwave generated by the magnetron 304 is supplied from the antenna 305 through the waveguide 309 to the cooking chamber 301 in which the object 303 to be heated is set. The stirrer 310 rotates in the cooking chamber 301 to rotate the object 30 to be heated.
3 is for diffusing the microwave so as to be uniformly heated.

The cooling fan 307 sends cooling air 308 to the magnetron 304 to cool the magnetron 231.

The circuits shown in FIGS. 10 to 12 are merely examples, and may have a separate configuration as a high-output magnetron power supply.

The present invention is particularly applicable to a microwave power of 2 kW.
As described above, the present invention is preferably applicable to a magnetron having an output of 10 kW or more. However, it is needless to say that the present invention can be applied to a magnetron having a low output less than this.

[0078]

As described above, according to the present invention,
The thin end for provisionally welding the cathode lead to the lower end shield allows the welding head to be easily accessible from the side, facilitates melting of the thick part with less welding power, and ensures accurate positioning. Temporary welding can be performed, and a magnetron having uniform characteristics, long life, and high reliability can be provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a cathode structure illustrating one embodiment of a magnetron according to the present invention.

FIG. 2 is an exploded view of a filament and an end shield of the cathode assembly in FIG.

FIG. 3 is an explanatory diagram of a first embodiment of a thin portion formed on a lower end shield.

FIG. 4 is an explanatory view of a thin portion formed in a lower end shield according to a second embodiment.

FIG. 5 is an explanatory view of a thin portion formed in a lower end shield according to a third embodiment.

FIG. 6 is an explanatory view of a thin portion formed in a lower end shield according to a fourth embodiment.

FIG. 7 is an explanatory view of a thin portion formed in a lower end shield according to a fifth embodiment.

FIG. 8 is a sectional view illustrating an example of the overall configuration of a magnetron according to the present invention.

FIG. 9 is a top view of the magnetron shown in FIG. 8;

FIG. 10 is a circuit diagram illustrating an example of a magnetron drive circuit.

FIG. 11 is a circuit example using a general commercial power supply as it is as a magnetron power supply.

FIG. 12 is a conceptual diagram illustrating a specific example in which a magnetron according to the present invention is applied to a microwave oven.

FIG. 13 is an explanatory diagram of a cathode structure in a conventional magnetron.

FIG. 14 is an exploded view of a filament and an end shield of the cathode assembly in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Anode cylinder 2 Anode vane 3 Antenna lead 4 Antenna dome 5a Upper magnetic pole 5b Lower magnetic pole 6a Upper seal 6b Lower seal 7 Filament 8a Upper magnet 8b Lower magnet 9 Metal gasket 10 Cooling fin 11a Upper yoke 11b Lower yokes 12a, 12b Cathode lead 13 Choke coil 14 Feed-through capacitor 15 Filter case 16 (16a to 16e) Thin portion 17a Upper end shield 17b Lower end shield 18 Ceramic spacer 19 Metal sleeve 20 Exhaust pipe.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shigekatsu Yamada 3350 Hayano, Mobara-shi, Chiba F-term (reference) 5C029 CC05 CC08 in Hitachi Electronics Devices, Ltd.

Claims (4)

[Claims] 1. A filament provided between an upper end shield and a lower end shield, a cathode assembly having two cathode leads for supplying power to the filament, an anode cylinder installed around the filament, and an inside of the anode cylinder. A cavity resonator group formed of a plurality of anode vanes radially provided around the filament, and a microwave generated in the cavity resonator group is connected at one end to the cavity resonator, and at the other end. Is a magnetron that radiates to the outside through an antenna lead arranged in an antenna dome constituting a main part, wherein a thin portion is provided at a cathode lead welding end of a lower end shield constituting the cathode assembly. Magnetron. 2. The lower end shield has a through hole through which the two cathode leads are inserted on a surface opposite to a surface facing the filament, and the thin portion is formed on one of the two cathode leads. 2. The magnetron according to claim 1, wherein the magnetron is provided in a region adjacent to the through hole of the lower end shield. 3. The thin portion provided on the lower end shield,
3. The magnetron according to claim 2, wherein the lower end shield is formed by a step provided on a part or an entire periphery of an edge surrounding the through hole. 4. 4. A thin portion provided on the lower end shield,
3. The magnetron according to claim 2, wherein the lower end shield is formed by a projection provided in a longitudinal direction of the cathode lead provided on a part or an entire periphery of an end edge surrounding the through hole. 4.