JPH0498788A - Microwave application device - Google Patents

Abstract

PURPOSE:To prevent the leakage of moding frequency, and to reduce cost by fixing a filter to an H-surface which is parallel to a magnetic field of a wave guide, and by providing a slit which is at least of the length of 1/4 wavelength of a moding frequency of a magnetron, and which is parallel or perpendicular to the H-surface, on the front end. CONSTITUTION:A microwave generated by a magnetron 8, is irradiated from an antenna 8a into a wave guide 9, is guided by the wave guide 9, and is stirred by a stirrer 5, so as to heat a food stored in a heating chamber 2. In the wave guide 9, a stub 10 as well as a filter 11 for auxiliary use, are arranged. The filter 11 is molded out of metal plate by stamping and folding process, and is formed out of a mounting part 11b to be fixed to an H-surface 9a or 9b which is parallel to the magnetic field of the wave guide 9 by welding and the like, a raised part 11b which is raised vertically from the mounting part 11a, and of a slit part lid which runs parallel to the H-surfaces 9a, 9b from the raised part 11b, and on which a slit part 11c is provided. The length (h) of the slit 11c is determined as 1/4 wavelength of a moding frequency.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to microwave application equipment, and particularly relates to a filter structure for suppressing leakage of specific strong noise radio waves such as moding frequencies or harmonics generated from a magnetron. .

[Conventional technology]

Conventionally, in a microwave oven, in order to prevent harmonics generated from a magnetron from leaking and causing reception interference to a TV receiver, for example, Japanese Patent Laid-Open No. 63-248088 (hereinafter referred to as Publication Example 1) and Kaisho 63-2480
As shown in Japanese Patent No. 89 (hereinafter referred to as known example 2), a filter is proposed in which a filter is provided in a waveguide that guides microwaves generated from a magnetron to a heating chamber.

In known example 1, in order to suppress (attenuate) the fifth harmonic,
A filter is attached to the E-plane (the plane perpendicular to the magnetic field) of the waveguide so as to divide the inside of the waveguide into upper and lower halves, and the filter is also provided with irregularities arranged periodically in parallel and perpendicular directions to the tube axis. are integrally formed.

In order to suppress the second harmonic or higher, in the known example 2, in the structure of the known example 1, the depth and interval of the unevenness arranged in the direction parallel to the tube axis are sequentially changed.

By the way, the standards under the Radio Law are for measurements after the operation has stabilized, so radio wave leakage during transient phenomena is outside the regulations of the leakage power density and the regulations under the Radio Law. For this reason,
In the above-mentioned conventional technology, no measures are taken against radio wave leakage during transient conditions.

[Problem to be solved by the invention]

The above-mentioned conventional technology is not designed to suppress radio waves during transient phenomena, and there is a risk of interference with other communications. This will be explained in detail below.

In the case of a microwave oven, the magnetron's filament voltage and anode voltage are usually applied at the same time. In this case, normal oscillation (r mode oscillation) occurs after modeding for 0.1 to 0.5 seconds after 1 to 2 seconds.

In a commercial microwave oven or an industrial magnetron application device, the anode voltage is applied after the magnetron filament voltage is preheated. In this case, if the filament emits enough emissions, no moding will occur. However, if the magnetron is used for a long time and the amount of electrons emitted under preheating conditions is insufficient, moding will occur. When operating in moding or normal mode, the cathode is reverse heated and its temperature rises, so unless enough electrons are emitted, it will operate in normal mode after a single time of moding. .

In this way, there is always a moding period as a transient phenomenon. This moding power can be large as a peak value, and in extreme cases it can be
Exceeds 1ruW/a/l=2 at I#.

As for moding, the 7r-1 mode usually has the largest energy. The frequency of this 'E-1 mode is 3.6 to 4
．． The frequency is 8 GHz, and the oscillation frequency changes depending on the anode structure of the magnetron itself and the load impedance of the magnetron.

Even if such a transient phenomenon passes the standard, if the moding frequency is within the satellite broadcasting band, for example, it may cause interference to the satellite broadcasting receiving system. For example, 3.8~4.2GH2 is the satellite broadcasting frequency band,
Depending on the magnetron, the moding frequency is in the above satellite broadcasting frequency band, so there is a possibility of interference.

The above-mentioned conventional technology has problems in that it does not take into consideration the moding frequency as described above, and the filter structure is complicated and costs are high.

An object of the present invention is to provide an entire microwave application device equipped with a filter that can suppress leakage of moding frequency and can be manufactured at low cost.

[Means to solve the problem]

In order to achieve the above objective, the filter is fixed on the H-plane parallel to the magnetic field of the waveguide, and a slit parallel or perpendicular to the H-plane with a length of at least /4 wavelength of the moding frequency of the magnetron is inserted at the tip. It is set up in the department.

[Effect]

The slit is formed to a length of 4 wavelengths at the moding frequency and is fixed to the H-plane of the waveguide, so the slit resonates at the moding frequency, but not so much at the fundamental wave. , it becomes a large impedance with respect to the moding frequency. Therefore, the moding frequency cannot be transmitted, and its propagation is suppressed.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 3. As shown in FIG. 1, a door 3 is provided in front of a heating chamber 2 in which a tray 1 for placing food is provided. Further, a starter 5 made of metal blades rotated by a motor 4 is arranged above the heating chamber 2, and a starter cover 6 usually made of an insulating material is provided between the starter 5 and the heating chamber 2. ing. A magnetron 8 driven by a magnetron drive power source 7 consisting of a transformer, a diode, a capacitor, etc. is provided outside the heating chamber 2. An antenna 8a of the magnetron 8 transmits microwaves generated by the magnetron 8 to the heating chamber. It is provided in a waveguide 9 that leads to the waveguide 2.

Therefore, the microwaves generated by the magnetron 8 are radiated from the antenna 8a into the waveguide 9, guided by the waveguide 9, and stirred by the gas starter 5 to destroy the food stored in the heating chamber 2. Heat.

Inside the waveguide 9, an auxiliary stub 10 and a filter 11 are arranged. The filter 11 is formed by punching and bending a metal plate as shown in FIG. , a rising portion 11b rising vertically from this mounting portion 11a, and this rising portion 11
The slit portion lid is parallel to the H planes 9a and 9b from b and is provided with a slit (slin) llc. Here, the length h of Surin) is set to the wavelength of the moding frequency. The height j of the rising portion 11b and the mounting position of the mounting portion 11a to the waveguide 9 are determined by the magnetron 8.
The impedance when looking at the load from the center of the antenna 8a is
The operating point is selected to be optimal for the fundamental wave of the magnetron 8.

In this way, the length h of one slit llc is set to /4 wavelength of the moding frequency, so the slit portion llc is set to /4 wavelength of the moding frequency.
id resonates with the moding frequency, resulting in infinite impedance. This resonant radio wave is filtered by filter 1
1, the transmitted power is greatly reduced, and leakage from the door 3 portion beyond the waveguide 9 is greatly reduced.

Further, as shown in FIG. 3, if the lateral dimension of the waveguide 9 is A1 and the height dimension is B, the C dimension, which is the height dimension B minus the height dimension jt of the rising portion 11b, is at least attempted to be suppressed. It is necessary to set a value such that radio waves propagate only in TEmo mode. That is, the Kj dimension is selected so that C≦I. Here, is the wavelength of the radio waves you want to suppress. Generally, the waveguide 9 of a microwave oven has A=80 Tsuru and B=about 40111. Now, assuming that the moding frequency is 41 GHz, in this case, if j≧3.4 WIC is set,
The only propagation mode propagating through the filter 11 of the waveguide 9 is the T E m o mode, and the propagating electric field is only in the direction perpendicular to the tube axis 9 of the waveguide 9 (perpendicular to the 8th plane). Become.

In the case of such a propagation mode, it is affected by the slit portion lid of the filter 11, and only the frequency at which the slit portion lid resonates is reflected from the filter 1, and the amount that passes through the filter 1 is attenuated.

On the other hand, Surin)llc is the mounting part 11a1 rising part 11
It has impedance even if the fundamental wave pressure is higher than bK. This impedance is 5K, which is in the stable region at or near the matching of the magnetron 8.

The attachment of the filter 1 can be selected depending on the position and the height dimension j of the rising portion 11b. This has both a moding frequency suppression effect and an impedance matching effect.

In addition, the width dimension I of the sulin) 11c and the slit portion 11d
The width dimensions may be the same or different;
No matter how many pieces of 11c there are, they work the same way. The one with more is T
This is preferable because it can handle even if there are many E mo mode electric currents.

Also, as a way to use only TEmo mode, filter 1
The method of changing the height j of the waveguide 9 so that it becomes 'ft(', ;-) has been described above. SaB'f
r, 4th round) A similar deterrent effect can be obtained by making the filter 11 part higher as shown in K, or lowering the filter 11 part as shown in FIG. 4 (bl).

Although the above description has been made regarding the moding frequency, the slit section lid has a similar effect on harmonics as well. For example, for the second harmonic, A=80111. B
=40111, j=9.4tm, h:l 5.3
101. J=14fi1. ? By setting =1410, two slits 11 cf can be provided. Similarly, by setting 1=sta and y=s Yukitomi, four slits 11c't can be provided. With this configuration, h is the second harmonic (4.9GHz)
Therefore, it has the same suppressing effect on the first and second harmonics as it does on the moding frequency.

Note that the stub 10 is used to modify and optimize the impedance when the impedance of the fundamental wave does not reach the best operating point of the magnetron 8 with the filter 11 alone. Therefore, if the impedance of the fundamental wave can be optimized depending on the height j of the rising portion 11b of the filter 11 and the mounting position of the filter 11, the stub 10 may be omitted.

5 to 7 show other embodiments of the invention.

In the above embodiment, Surin)llc is H of the waveguide 9.
The case where they are provided parallel to the surfaces 9a and 9bK has been described. In this embodiment, the slit 12b? H side 9a,
It is provided perpendicularly to 9bK. In short, stub) 12.
b may be a resonance condition for the frequency to be suppressed. That is, the filter 12 is formed into a serrated shape by bending a metal plate, and includes a mounting portion 12a that is fixed to the waveguide 9 by welding or the like, and slits perpendicular to the H surfaces 9a and 9bK of the waveguide 9. a slit portion 12c in which 12b is formed;
It consists of a mounting part 12a of the slit part 12c and a connecting part 12d that connects the part between the mounting parts 12a at the opposite end.

Therefore, in order to avoid setting the size of the slit portion 12c to a quarter wavelength of the desired wavelength, as in the above embodiment,
Since the slit section 12c resonates at the wavelength to be suppressed and its impedance increases, the amount of transmission of radio waves of that frequency becomes extremely small, and leakage beyond the waveguide 9, that is, from the door section 3, is greatly reduced. Therefore, if the moting frequency is 4.1 GHz, the wavelength will be 73.2 GHz, so if A=8011L B=4 On, h=
When set to 18.3118, it has a moding frequency filter effect.

The length k of the connecting portion 12d has a relatively wide margin, but the best dimension is preferably one that matches the wavelength to be suppressed. However, they do not necessarily have to match.

Also, the width y of the stub 12b and the width of the connecting portion 12d need only be less than h of the wavelength to be suppressed, and the same function can be achieved no matter how many slits 12b there are, but it is better to have more slits 12b. preferable. Also, depending on the setting of the h dimension of the stub section 12c, similar to the above embodiment, for a specific frequency such as the second harmonic, by adjusting the wavelength to '7'4, the moding frequency can be adjusted. At the same time, it has a similar suppressing effect on second harmonics and the like.

〔Effect of the invention〕

According to the present invention, since a specific wavelength is equal to the resonant frequency of the slit provided at the tip of the filter, the impedance becomes large and the amount of transmission of the specific wavelength can be suppressed. In addition, since the filter can select the impedance of the fundamental wave so that the magnetron operates optimally, it is possible to suppress specific noise radio waves with a stable and long-life device. Furthermore, since the filter can be manufactured very easily by punching and bending a metal plate, manufacturing costs can be reduced.

[Brief explanation of drawings]

1 to 3 show one embodiment of the present invention, FIG. 1 is a schematic sectional view of the whole, FIG. 2 is a perspective view of the filter, and FIG. 3 is a waveguide portion. is a plan view, (b) is a sectional view, FIGS. 4(a) and 4(b) are sectional views showing other embodiments of the waveguide portion, and FIGS. 5 to 7 are other embodiments of the present invention. An example is shown, FIG. 5 is a schematic sectional view of the whole, FIG. 6 is a perspective view of the filter, and FIG. 7 is a waveguide portion, where (a) is a plan view and (bl is a sectional view). ...Heating chamber, 8...Magnetron, 9...
・Waveguide, 9a, 9b...H plane, 11.12・
...filter, llc, 12c...slit. 2: Power 0 bleeding ￥ 9a, 9b: 1-1 side: Filling C: Three, G Fig. 4 (b) Fig. 2 2 Calo fever 1 de 90.9b: H side 2 : Filter 12C: Pickpocket, Noto

Claims (1)

[Claims] 1. In a microwave application device in which a filter is provided in a waveguide that guides microwaves generated by a magnetron to a heating chamber, the filter is fixed to an H plane parallel to the magnetic field of the waveguide, and the filter is fixed to an H plane parallel to the magnetic field of the waveguide, and the filter is fixed at least at the modeding frequency of the magnetron. A microwave application device characterized in that the tip has a slit having a length of 1/4 wavelength and parallel or perpendicular to the H plane.