JPS60243941A - Filter circuit element for noize elimination of magnetron - Google Patents

Abstract

PURPOSE:To make fundamental frequency and its higher harmonic to be efficiently attenuated and eliminated by providing a choke construction inside a through-type capacitor. CONSTITUTION:Inside the first case 6a constituting a through-type capacitor 6', a cup-shaped choke 6i having an open end at the opening end of an annular ceramic capacitor element 6e and the depth (l) is coaxially formed and arranged between the opening end of the annular ceramic capacitor element 6e and the central conductor 6c. In said constitution, the depth (l) of the choke 6i is so set up as to be lambda/4 of electric wave length of the specific higher harmonic desired to be attenuated and eliminated, whereby the impedance at the open end of said choke 6i gets to be the maximum, while the microwave voltage at this part reaches a maximum so as to be able to attenuate and eliminate the correscponding higher harmonic.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a filter circuit element for eliminating noise in a magnetron used in microwave application equipment such as a microwave oven, and particularly relates to a filter circuit element for eliminating noise in a magnetron used in microwave application equipment such as a microwave oven. This invention relates to the structure of a feedthrough ceramic capacitor that suppresses strong leakage radio waves.

[Background of the invention]

Equipment that uses high frequencies, such as microwave ovens, is required to keep the noise level below the specified level in order to eliminate interference with wireless communications. However, with recent advances in communication technology, it has become possible to communicate with less power, and there has been a movement to further tighten regulations on noise levels.

On the other hand, when the magnetron oscillates, harmonics including the magnetron's oscillation fundamental wave, as well as VHF and UHF band waves, are radiated to the outside through its input and output sections. For this reason, the magnetron is made to attenuate and eliminate the noise radio waves from this input section or output section.
A noise-cancelling filter (hereinafter referred to as a filter) is installed to eliminate the influence on radio, wireless communications, etc. In recent years, many countries are considering making the regulation values for radio wave noise more stringent, and countermeasures against radio wave leakage have become an inevitable issue even for magnetrons alone.

This filter generally has a filter structure in which a choke coil and a feedthrough capacitor are combined and connected to a cathode terminal on the input side of a magnetron. 51-6
7353) and a filter structure in which multiple chokes are attached to the antenna on the output side of the magnetron (Japanese Patent Publication No. 5
6-21215) is known.

However, the fundamental frequency of the magnetron is 2450MH
When oscillating and outputting z, its harmonics are also output at the same time, and the frequency and level of the harmonics change non-uniformly with respect to the fundamental wave. Furthermore, up to the seventh harmonic has been confirmed, and it has recently become possible to measure the fifth and subsequent harmonics.

For this reason, with conventional filter configurations in which the band and amount of attenuation to be attenuated are set for VHF and UHF TV broadcast bands and harmonics below the fourth harmonic, a sufficiently large amount of attenuation can be achieved over a wide range. The problem was that I couldn't get it.

FIG. 1 is a partially cutaway side view showing an example of a conventional magnetron. In the figure, a magnetron main body 1 which has a known internal structure and outputs high-frequency energy has a pair of annular magnetic shunt plates and permanent magnets (not shown) on the microwave output section 2 and cathode input section 3 sides, respectively. It is clamped by a yoke 4 which is arranged and forms a magnetic circuit.

In addition, a choke coil 5 is provided at the cathode input section 3 of the magnetron main body 1 to attenuate and eliminate noise radio waves leaking to the outside.
A filter case 8 housing a filter γ consisting of a feedthrough capacitor 6 and a feedthrough capacitor 6 is fixedly attached. In this filter 7, the choke coil 5 is connected to the cathode input section 3.
The feedthrough capacitor 6 is connected to the cathode terminal 10 provided at the tip of the insulating nut 9, and the feedthrough capacitor 6 is connected to the filter case 8.
It is held through and the other end side protrudes to the outside,
An input terminal 11 connected to an external AC power source is integrally provided.

FIG. 2 is an enlarged sectional view of a main part of the through-hole conduit 6 shown in FIG. 1, and the same parts as in FIG. 1 are given the same reference numerals. In the same figure, 6a is an insulating first case that covers the outer side of the filter case 8 of the feedthrough capacitor 6, and 6b is an insulating second case that covers the inner side of the filter case 8. These cases 6a+6b A center conductor 6c that conducts the AC power supply is disposed through the center of the center conductor 6c, and the center conductor 6c on the first case 6a side serves as the input terminal 11 shown in FIG. 1, and the second case 6b The side thereof is electrically connected to the choke coil 5 described above. 6d is an insulated pipe covered with the center conductor 6c, 68 is an annular ceramic capacitor element fixedly arranged at the opening end of the filter case 8, and 6f is the other end of the ceramic capacitor element 6e and the center conductor 6c.
The electrode 6g is fixedly arranged between the first case 6a and
A molding material is enclosed in the second case 6b to hold and fix the above-mentioned components, and 6h is an opening into which the molding material 6g flows.

In the magnetron configured as described above, microwaves are oscillated in the magnetron main body 1, and the microwaves are emitted from the output section 2 and are converted into energy to heat an object such as food in the case of a microwave oven. . on the other hand,
The microwave and its harmonics propagate through the cathode lead, pass through the cathode terminal 10, and propagate to the choke coil 5.
It leaks to the outside from the filter case 8 via the feedthrough capacitor 6 and becomes a noise radio wave.

However, in the magnetron configured in this manner, the filter 7 consisting of the choke coil 5 and the feedthrough capacitor 6 has only the shielding effect of the feedthrough capacitor 6 for the low-pass filter and the upper frequency band.

Therefore, a sufficient shielding effect cannot be obtained against noise radio waves in the microwave band such as harmonics of the magnetron's fundamental wave of 2450 MHz, and noise radio waves caused by particularly high-level harmonics are radiated to the outside of the filter case 8. It had been.

[Purpose of the invention]

Therefore, the invention was made in view of the above-mentioned problems, and its purpose is to provide a noise canceling filter circuit element that can efficiently attenuate and cancel the fundamental frequency and its harmonics. be.

[Summary of the invention]

In order to achieve such an object, the present invention provides a choke structure within a feedthrough capacitor.

[Embodiments of the invention]

Next, embodiments of the present invention will be described in detail using the drawings.

FIG. 3 is a cross-sectional view of a main part of a feedthrough capacitor for explaining one embodiment of a noise canceling filter circuit element according to the present invention, and the same parts as in the previous figures are given the same reference numerals. In the figure, a first case 6IL constituting the feedthrough capacitor 6
Inside, a cup-shaped choke 61 having an open end at the open end of the ceramic capacitor element 6° and having a depth t is coaxially disposed between the open end of the annular ceramic capacitor element 6e and the center conductor 6c. Formation is arranged.

In such a configuration, by setting the depth t of the choke 61 to be λ/4 of the electrical length of the specific harmonic to be erased and attenuated, the impedance at the open end of the choke 61 becomes extremely thick, and this The microwave voltage at that part becomes maximum and the corresponding harmonics can be eliminated and attenuated.

FIG. 4 is a cross-sectional view of a main part of a feedthrough capacitor for explaining another embodiment of the noise canceling filter circuit element according to the present invention, and the same parts as in the previous figures are given the same reference numerals. In the figure, a second case 6b constituting the feedthrough capacitor 6
Inside, a cup-shaped choke 6j having an open end toward the outside of the filter case 8 and having a depth Lxk is formed and arranged coaxially with the center conductor 6c.

Even in such a configuration, exactly the same effect as in the case of FIG. 3 can be obtained.

FIG. 5, FIG. 6, and FIG. 7 are sectional views of main parts of a feedthrough capacitor for explaining still other embodiments of the present invention, and the same parts as in the previous figures are given the same reference numerals. In these figures, the feedthrough capacitor 6 shown in FIG. 5 has a plurality of openings provided in the ceramic capacitor element 6e, and a central conductor 6 that is passed through the insulating vibro d through these openings.
The structure is the same as that shown in FIG. 4 except for the ce arrangement, and the same effects can be obtained.

The feedthrough capacitor 6 shown in FIG. 6 is the same as that shown in FIG. It is constructed in the same way as the original, and provides the same effects. In addition, the feedthrough capacitor 6 shown in FIG.
connects multiple chokes of depth t1+tz to the center conductor 6c.
The configuration is the same as in Figure 4, except for the configuration arranged in Figure 4.
For multiple specific radio waves corresponding to zt l z2,
Similar effects can be obtained.

〔Effect of the invention〕

As explained above, according to the present invention, by providing a choke structure in the feedthrough capacitor, harmonics leaking to the outside can be efficiently attenuated and canceled, thereby providing a noise cancellation filter with high quality and reliability. The extremely excellent effect of providing a circuit can be obtained.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway side view showing an example of a conventional magnetron, FIG. 2 is an enlarged cross-sectional view of a main part showing a feedthrough capacitor, and FIG. 3 is a diagram showing a noise canceling filter circuit element for a magnetron according to the present invention. A cross-sectional view of a feedthrough capacitor for explaining one embodiment, and FIGS. 4 to 7 are cross-sectional views of feedthrough capacitors for explaining other embodiments of the present invention. 1... Magnetron main body, 2... Microwave output section, 3... Cathode input section, 4... Own yoke, 5...
・Salary・Choke coil, 6.6, 6゜6. 6. 6
...Feedthrough capacitor, 6a...first case,
6bφ・φ・Second case, 6c@...Center conductor, 6
d... Insulation pipe, 6el... Ceramic capacitor element, 6f... Reference Φ electrode, 6, ---- Mold material, 6h... Opening, 61°J, 6...・Choke, 7 skewers, filter, 8...◆ken filter case, 9--@-insulation stem, 10...ψ/cathode terminal, 11
...Input terminal. 7 ・) 1 figure, ゛・31 s i) 6″ - Absolute 5 figure 6″′ Flood 6 figure dan”″ 郎7 figure 6 LJr′L

Claims (1)

[Claims] A noise canceling filter circuit element for a magnetron comprising a coil connected to a cathode terminal of a cathode input section of a magnetron main body and a feedthrough capacitor, characterized in that a choke structure is provided in the feedthrough capacitor. .