JPH08167383A - Magnetron for microwave oven - Google Patents

Abstract

PURPOSE: To improve the oscillation spectrum of the fundamental wave by making the diameter of a through-hole to be formed in the center of a pole piece of a magnetron larger than the prescribed percentage of the diameter of an envelope circle to be formed by connecting each tip of an anode vane. CONSTITUTION: Pole pieces 15a, 15b are provided on an opening part at upper and lower end of an anode 11. Annular permanent magnets 16a, 16b are respectively provided on the upper side of the pole piece 15a or on the lower side of the pole piece 15b. Cathode supporting bodies 17, 18 are extended in the shaft axis direction, and extended to the outside of recessed parts of the pole pieces 15a, 15b. A through hole of the prescribed inner diameter is formed in the recessed parts of the center of the pole pieces 15a, 15b so that the cathode supporting bodies 17, 18 may pass through. The inner diameter Dpi of the center through hole of the pole pieces 15a, 15b is e.g. >=110% of the diameter Da of the assumed envelope circle to be formed by connecting each tip of a vane 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetron for a microwave oven having an improved fundamental wave oscillation spectrum.

[0002]

2. Description of the Related Art A conventional magnetron for a microwave oven will be described with reference to FIG. Reference numeral 61 is a cylindrical anode, and the cathode 62 is located at the center of the anode 61. The space between the anode 61 and the cathode 62 is divided by a plurality of anode vanes 63 provided radially. Further, pole pieces 64a and 64b are provided at the upper and lower ends of the anode 61, respectively. The pole pieces 64a and 64b have a shape in which the center is recessed inward. Then, annular permanent magnets 65a and 65b are arranged above and below the pole pieces 64a and 64b, respectively.

End shields 66a and 66b are provided at the upper and lower ends of the cathode 62. Cathode 6
2 surrounds the cathode support 67 in a spiral shape, the upper end of which is connected to the cathode support 67, and the lower end thereof is connected to another cathode support 68. The cathode supports 67 and 68 extend in the axial direction of the anode 61 and extend to the outside through the recessed portions of the upper and lower pole pieces 64a and 64b. The pole pieces 64a, 6
A through hole having a predetermined inner diameter is formed in the center of 4b so that the cathode supports 67 and 68 can pass therethrough.

By the way, the permanent magnets 65a and 65b are small in size so as to be inexpensive. Therefore, the permanent magnet 65 is attached to the pole pieces 64a and 64b.
It is desired to have a shape in which the magnetomotive forces of a and 65b are small. Therefore, the inner diameter Dpi of the through hole formed in the center of the pole pieces 64a, 64b is the diameter Da of the virtual envelope circle formed by connecting the inner end surfaces of the vanes, that is, the tip portions.
Is selected to be equal to or slightly larger than.

Further, the end shields 66a and 66b located at both ends of the cathode 62 confine the electrons emitted from the cathode 62 in the working space S, and a current that does not contribute to oscillation does not flow due to the electrons flowing out in the axial direction. I am trying. However, if the end shields 66a and 66b are provided, the electromagnetic field distribution in the vicinity Se of both ends of the cathode 62 is distorted, and the range in which the lines of magnetic force and the equipotential lines are parallel becomes narrow near the vane 63 in the axial direction of the action space. As a result, the frequency of the high frequency electric field induced in the resonance cavity by the electron cloud is different between the central portion Sc of the cathode 62 and the vicinity Se of both ends. Therefore, when the microwave electric field is strong, the oscillation frequency spectrum becomes steep, and when the microwave electric field is weak, the oscillation frequency spectrum becomes broad.

In the case of a microwave oven, a half-wave voltage doubler power source is usually used. Therefore, the anode current changes instantaneously and constantly, and the oscillation frequency spectrum takes a form in which steep and broad spectrums are combined.

[0007]

As the oscillation frequency of the magnetron for microwave ovens, the ISM band of 2400 to 2500 MHz, which is the frequency band for microwave devices, is used. The existence of radio waves that deviate from this band and leak to adjacent frequency bands is strictly limited by the Radio Law. By the way, in order to prevent the oscillation frequency of the magnetron for a microwave oven from leaking to other bands, it is important to improve the oscillation spectrum of the fundamental wave of the magnetron. Here, an example of the oscillation spectrum of the fundamental wave of the conventional magnetron for a microwave oven is shown in FIG. In FIG. 7, the vertical axis represents the generation level (dBm) and the horizontal axis represents the frequency (MHz). As can be seen from the figure, 2380 to 2400 MH out of the ISM band
Unnecessary radio waves are generated in z. Magnetrons for microwave ovens are often used in microwave ovens for cooking and heating.
In this case, in order to prevent unnecessary radio waves from leaking from the microwave oven, it is effective to prevent the magnetron from emitting unnecessary radio waves.

The present invention solves the above-mentioned drawbacks, and an object of the present invention is to provide a magnetron for a microwave oven in which the oscillation spectrum of the fundamental wave is improved.

[0009]

The present invention provides a cylindrical anode, a cathode located at the center of the anode, a pole piece provided at the end of the anode, and a space between the anode and the cathode. In a magnetron for a microwave oven having a plurality of anode vanes radially arranged, a diameter of a through hole formed in the center of the pole piece is set to a diameter of an envelope circle formed by connecting each tip of the anode vane. 110% or more.

[0010]

First, let us consider a virtual envelope circle formed by connecting the inner end faces of a plurality of vanes, that is, the tip portions located on the cathode side, and the inner diameter of the through hole at the center of the pole piece is approximately the diameter of the envelope circle. A plurality of samples varying from 103% to 136% were prepared. Then, the characteristics of each sample were measured.

FIG. 2 is a sectional view of the main part of the sample.
Oscillation frequency is 2450MHz band, and output is 800W
It belongs to the class. Outer diameter Dk of the spiral cathode 21
Is 3.9 mm, the diameter Da of a virtual envelope circle formed by connecting the inner end surfaces of the plurality of vanes 22, that is, the tip portions is 9.08 mm, the height Ha of the vanes 22 is 9.5 mm, and the upper end shield is The outer diameter De 1 of 23a is 7.2 mm,
The outer diameter De 2 of the lower end shield 23b is 8.15 m.
m, the distance Le between the upper and lower end shields 23a and 23b is 10.5 mm, the facing distance Lp in the flat portion of both pole pieces 24a and 24b is 12.7 mm, and the pole piece 2
The outer diameter Dp of 4a and 24b is 37.5 mm, and its height Hp
Is 7.0 mm and the plate thickness Tp is 1.6 mm.

The inner diameter Dpi of the through hole at the center of the pole pieces 24a, 24b and the outer diameter Dpo of the flat portion are as shown in the table below.
The inner diameter Dpi of the through hole at the center of the pole pieces 24a, 24b is
It is selected in the range of approximately 103% to 136% of the diameter Da of the envelope circle.

Sample (Dpi / Da) × 100 (%) Dpi (mm) Dpo (mm) A (conventional example) 103.5 9.4 12.0 B (conventional example) 103.5 9.4 18.0 C 114.5 10.4 18.0 D 125.6 11.4 18.0 E 136.6 12.4 18.0 Samples A and B are the inner diameter Dpi of the central through hole of the pole piece (Dpi = Dpi = 9.4 mm) is a conventional example in which the diameter Da of the envelope circle of the vane is set to be slightly larger than Da (Da = 9.08 mm).

The oscillation spectra of the fundamental wave of each of the samples A to E are shown in FIG.
Shown in D and E. In FIG. 3, the vertical axis represents the generation level (dBm) and the horizontal axis represents the frequency (MHz). Also, 2350 to 255
FIG. 4 shows the width f of the frequency at which the generation level in the 0 MHz band exceeds -50 dB. The vertical axis of FIG. 4 indicates the frequency width f (MH
z), the horizontal axis shows the ratio of the inner diameter Dpi of the central through hole of the pole piece to the diameter Da of the envelope circle of the vane in%. In addition,
In FIG. 4, the white spots are for sample A.

2350-240 outside the ISM band
Peak value P of generation level in 0 MHz band, and 235
The frequency width f in which the generation level exceeds -50 dB in the 0 to 2550 MHz band is as shown in the table below.

Sample P (dBm) f (MHz) A (conventional example) -20.0 135.4 B (conventional example) -20.1 110.3 C-55.0 68.6 D-55.4 47 .4 E-52.5 41.4 The peak value P of the generation level in the 2350 to 2400 MHz band, which is out of the ISM band, is (Dpi / Da) × 100 of 1
10% or more (Samples C, D and E) are 30 dBm higher than 103.5% of the conventional example (Samples A and B).
It has been improved over. Further, it can be seen that when (Dpi / Da) × 100 is large, the frequency width f in which the generation level exceeds −50 dB becomes narrow in the 2350 to 2550 MHz band, and the oscillation spectrum of the fundamental wave becomes clean.

In the conventional example, the flat portion of the pole piece has an outer diameter Dpo of 18.0 mm (Sample B).
And the 12.0 mm sample (Sample A) are compared, the frequency width f in which the generation level exceeds −50 dB in the 2350 to 2550 MHz band is 2 in Sample B.
It is 5MHz narrower. Therefore, the larger the outer diameter of the flat portion of the pole piece, the better the oscillation spectrum of the fundamental wave.

The reason why the oscillation spectrum of the fundamental wave is improved is the ratio (Dpi / Da) of the inner diameter Dpi of the through hole at the center of the pole piece and the diameter Da of the envelope circle formed by the inner end surface of the vane.
It is considered that the increase in × 100 improves the electromagnetic field distribution near both ends of the cathode and widens the range in which the magnetic lines of force and the equipotential lines are parallel in the axial direction of the working space. If the range in which the lines of magnetic force and equipotential lines are parallel spreads,
It is considered that the frequency of the high frequency electric field induced in the resonant cavity by the electron cloud is almost equalized in the axial region near the vane, and the oscillation spectrum of the fundamental wave is improved.

The mode boundary decreases as (Dpi / Da) × 100 increases, as shown in FIG. The vertical axis in FIG. 5 represents the current (A), and the horizontal axis represents the ratio of the inner diameter Dpi of the central through hole of the pole piece to the diameter Da of the envelope circle of the vane in%. Also, the white spots are in the case of sample A.

In a microwave oven, a half-wave voltage doubler circuit is generally used as a driving power source for a magnetron. At this time, if the mode boundary is 1.0 to 1.2 A or more, it is considered that there is no problem of load stability. Therefore, when the inner diameter of the through hole at the center of the pole piece is 140% or less of the diameter of the envelope circle formed by the inner end surface of the vane, no practical problem occurs.

The above-mentioned operation is explained by an example in which the inner diameter of the through hole at the center of the two pole pieces provided at the upper and lower ends of the anode is 110% or more of the diameter of the envelope circle formed by the inner end surface of the vane. . However, even when the relationship between the inner diameter of the through hole of either of the two pole pieces and the diameter of the envelope circle formed by the inner end surface of the vane is similar, the same effect as above is obtained, and the oscillation spectrum of the fundamental wave is Improved compared to technology.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG.

Reference numeral 11 is a cylindrical anode, and the cathode 12 is located at the center thereof. End shields 13 a and 13 b are provided on the upper and lower ends of the cathode 12.
Further, the space between the anode 11 and the cathode 12 is partitioned by a plurality of vanes 14 provided radially. Further, pole pieces 15a and 15b are provided at the upper and lower openings of the anode 11, respectively. Further, annular permanent magnets 16a and 16b are provided on the upper side of the pole piece 15a or the lower side of the pole piece 15b, respectively.

The cathode 12 is the cathode support 1
The outside of 7 is spirally surrounded, and the upper end is connected to the cathode support 17. The lower end is connected to the cathode support 18. The cathode supports 17 and 18 respectively extend in the tube axis direction and extend to the outside of the recessed portions of the pole pieces 15a and 15b. Therefore, a through hole having a predetermined inner diameter is formed in the recessed portion at the center of the pole pieces 15a and 15b so that the cathode supports 17 and 18 can pass therethrough.

In the above structure, the pole piece 15
The inner diameter Dpi of the central through holes of a and 15b is 110% or more of the diameter Da of the virtual envelope circle formed when the tips of the vanes 14 are connected.

In the above embodiment, the anode 11
The inner diameter Dpi of the central through hole of each of the pole pieces 15a and 15b located at the upper and lower ends is 110% or more of the diameter Da of the virtual envelope circle formed when the tips of the vanes 14 are connected. However, the two pole pieces 15a, 1
For either one of 5b, the inner diameter Dpi of the central through hole is
A configuration may be made in which the diameter Da of the virtual envelope circle formed when the tips of the vanes 14 are connected to each other is 110% or more, and in this case also, the oscillation spectrum of the fundamental wave is improved as compared with the conventional configuration.

[0027]

According to the present invention, it is possible to realize a magnetron for microwave oven in which the oscillation spectrum of the fundamental wave is improved.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating the present invention.

FIG. 3 is a characteristic diagram illustrating the present invention.

FIG. 4 is a characteristic diagram illustrating the present invention.

FIG. 5 is a characteristic diagram illustrating the present invention.

FIG. 6 is a sectional view showing a conventional example.

FIG. 7 is a characteristic diagram illustrating a conventional example.

[Explanation of symbols]

 11 ... Anode 12 ... Cathode 13a, 13b ... End shield 14 ... Vane 15a, 15b ... Pole piece 16a, 16b ... Permanent magnet 17, 18 ... Support

Claims (1)

[Claims] 1. A cylindrical anode, a cathode located at the center of the anode, a pole piece provided at an end of the anode, and a plurality of anodes radially arranged in a space between the anode and the cathode. In a magnetron for a microwave oven including a vane, the diameter of a through hole formed in the center of the pole piece is 110 times the diameter of an envelope circle formed by connecting the tips of the anode vanes.
% Or more, a magnetron for a microwave oven.