JPS62241290A - Waveguide filter for microwave oven - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a microwave oven that heats food stored in a heating chamber by irradiating it with microwaves. This invention relates to a waveguide filter for microwave ovens that blocks radiation to the outside.

Conventional technology Frequencies assigned to microwave ovens (hereinafter referred to as fundamental waves)
is 2.45GHz±50MHf. However, the magnetron also generates frequencies other than the fundamental wave (hereinafter referred to as noise), albeit at extremely low levels. If noise leaks outside the microwave, it may seriously affect other electronic devices.

Broadcasting satellites have been launched in recent years, and TV signals are now being transmitted directly from the satellites to homes. The frequency assigned to this broadcasting satellite varies depending on each region of the world, but it ranges from 11°7 to 12°.
It is 7GHz. On the other hand, the fifth harmonic of a microwave oven is 12.0 to 12.5 GHz, which completely overlaps.

If the fifth harmonic leaks from the microwave oven, there is a risk that reception interference will occur in the satellite TV receiving device.

In general, the door used to take food in and out of a microwave oven has a sufficient effect of preventing leakage of fundamental waves to the outside.
This effect cannot be expected for harmonic noise. Therefore, the harmonics generated by the magnetron must be stopped before being radiated into the heating chamber.

Problems to be solved by the invention In order to prevent the radiation of such harmonics into the heating chamber,
Conventionally, a waveguide filter as described in Japanese Patent Publication No. 52-17891 has been proposed.

However, the above-mentioned conventional technology does not take into account the higher-order modes of harmonics, particularly the modes where n≠0 among the TEmn and TMmn modes, resulting in a problem in which the blocking effect deteriorates.

Measures to solve the problem The waveguides currently used in microwave ovens are intended to transmit the fundamental wave, so they are oversized for the fifth harmonic. It is a well-known fact that many higher-order modes occur.

The present invention has been made to solve the above problems, and effectively blocks transmission of the n#O mode to reduce the level of fifth harmonic noise radiated from the magnetron into the heating chamber. Another object of the present invention is to provide a waveguide filter for a microwave oven that eliminates reception interference with a satellite TV receiver.

To this end, multiple partition plates are provided that divide the inside of the waveguide parallel to the ceiling surface of the heating chamber at arbitrary intervals, and the space in the axial direction of the waveguide is divided discontinuously into these partition plates. It has a slit formed therein.

By doing this, the distance between the partition plates becomes very narrow, and the n≠0 mode among the TEmn and TMmn modes is completely eliminated. Also 1, n=0 for TM mode
Since this mode does not exist, the length of the remaining TEmO mode in the tube axis direction of the non-slit portion with low impedance (area Q1 to be described later) and the slit portion with high impedance (area Q2 to be described later) is set to 1 of the tube wavelength of the harmonic. /4 to stop it. Furthermore, since the wavelength of the fundamental wave is much longer than that of the fifth harmonic, it is hardly affected and is quickly transmitted with some matching.

Example An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a sectional view of essential parts of the present invention. In the figure, 1 is a magnetron, and the fundamental wave generated by this magnetron 1 is radiated from an antenna 2, guided by a waveguide 3, and placed in a heating chamber 4.
heats the food stored inside. A door 5 is used to take food into and out of the heating chamber 4. 6 is a waveguide filter (hereinafter referred to as a filter) provided inside the waveguide 3;
It has almost no effect on the fundamental wave, and also blocks the fifth harmonic generated by the magnetron 1 and radiated into the waveguide 3 by the antenna 2, so that it is not radiated into the heating chamber 4. It is something.

FIG. 2 shows a sectional view taken along line a-b in FIG.

A plurality of partition plates 8.8" each having a square gutter-like cross section;
Both ends of the waveguide 3 are welded to the side walls of the waveguide 3 so as to be parallel to the heating chamber ceiling surface 7, and the space constituted by the waveguide 3 and the heating chamber ceiling surface 7 is divided into partition plates 8. 8′, 8″′...
are divided at equal intervals. Furthermore, partition plate 8.8',
8#... is a rectangular sulin 1 at equal intervals as shown in Figure 3.
-9.9', 9'', 9' are opened in multiple places, so the tube axis direction near the filter 6 shown in FIG.
A cross section along the c-d direction in the figure has a structure as shown in FIG.

Next, the operation of this embodiment will be explained.

As shown in FIG. 4, in the filter 6, the fifth harmonic is transmitted from left to right in the figure. The electric field of the fifth harmonic at that time always has one or both of the vertical component shown by 10 and the horizontal component shown by 11, which differs depending on the mode. 'r'Emo mode (m=1.2.3,...) has only the vertical component, TE
It is well known that the on mode (n=1.2.3, . . . ) has only a horizontal component, and the TEmn and TMmn modes have both components.

In Figure 4, the fifth harmonic transmitted from the left is the partition plate 8.8.
', 8'''... and when trying to proceed further to the right, the distance g between the partition plates 8.8', 8'... is selected to be less than half the spatial wavelength of the 5th harmonic. Therefore, the mode that is cut off and has the horizontal electric field component 11 cannot proceed.Therefore, the only mode that can proceed is the TE:mo mode that has only the vertical electric field component 10.

The other modes that cannot be progressed are either reflected and returned in the opposite direction, or the mode is converted to the TEmo mode, which allows progress, and the vehicle moves to the right.

The reasons why modes other than the TEmo mode are blocked have been described above, but the TEmo mode can also be blocked for the reasons described below.

The vertical electric field component 10 in Fig. 4 is the partition plate 8.8', 8''...
When it reaches ・, it enters between each of the partition plates 8.8', 8"... and moves to the right through area Q in a shape represented by arrows 12.12'-12". In region Q2, the vertical electric field component 13 becomes similar to 10 again. therefore,
The characteristic impedance of the region Q□ is smaller than that of the region Q2. This is because the characteristic impedance of the waveguide 3 for the TEmo mode is proportional to the height of the waveguide 3. The height of the area Q1 is lower than the height H of the area Q2 by the number of thicknesses tl of the partition plates 8.8', 8'', . . . In FIG. Since six 8#... are shown, the height of area Q1 is isometrically 6t higher than H.
only becomes lower. Since the regions Q□ and Q2 exist alternately along the tube axis direction, this waveguide 3 is, after all, similar to the waveguide 14 whose height changes alternately as shown in FIG.

FIG. 5 is a sectional view of a waveguide in which the height of the region Q□ is h and the height of the region Q2 is H, viewed from the side. By selecting the lengths of regions Q1 and Q2 in the tube axis direction to 174, which is the tube wavelength of the fifth harmonic, the center frequency f is set as shown in FIG. A large amount of attenuation can be obtained over a wide band centered on the fifth harmonic (in this case, the fifth harmonic).

If the waveguide 14 is configured from the beginning as shown in FIG.
Since modes other than mo mode can also be transmitted, the blocking effect is inferior, but in the configuration of the present invention, for the reasons stated above, TE
Since modes other than the MO mode cannot be transmitted, a large blocking effect can be obtained.

FIG. 7 shows another embodiment of the invention.

In Figures 3 and 4, partition plates 8.8', 8#...
・The larger the number, the smaller the interval g becomes, isometrically the fifth
As the height h in the figure becomes smaller, the effect of blocking the fifth harmonic increases. However, since the number of parts increases, the number of parts can be reduced by using thicker partition blocks as shown in FIGS. 7 and 8. In this case, the partition block 15.15'
, 15' is connected to the waveguide 3 by the screw hole 17 and set screw 16.
The structure is fixed to the side wall of the

Furthermore, FIGS. 9 and 10 show another embodiment of the present invention. In this case, partition block 181. L8'
, 18"... are divided perpendicularly to the tube axis, so the distance G between the partition blocks 18, 18', 18#... can be freely adjusted, making it possible to perform delicate frequency adjustments and other harmonic adjustments. Application to waves is easily possible.

As described in detail, according to the present invention, it is possible to effectively block the transmission of modes in which n≠0 among many higher-order modes, so that the fifth harmonic noise radiated from the magnetron into the heating chamber is suppressed. It is possible to provide a waveguide filter for a microwave oven that reduces the level and eliminates reception interference to a satellite TV receiver.・

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of essential parts of a waveguide filter for a microwave oven showing an embodiment of the present invention, FIG. 2 is a cross-sectional view taken along line a-b of FIG. 1, and FIG. Figure 4 shows c-d in Figure 2.
5 is a sectional view of an equal groove wave tube, FIG. 6 is a conceptual diagram showing the frequency characteristics of a filter according to the present invention, and FIGS. 7 and 8 are sectional views showing other embodiments of the present invention. and a perspective view. FIGS. 9 and 10 are sectional views and perspective views showing other embodiments of the present invention. 3... Waveguide, 7... Heating chamber ceiling surface, 8
．． 8', 8"...partition plate, 9.9', 9"'...slit.

Claims (1)

[Claims] Inside the waveguide (3), there are a plurality of partition plates (
8, 8', 8''...) and a waveguide (3
) to discontinuously divide the space in the tube axis direction (9,
9', 9''...) to the partition plate (8, 8', 8''...)
・) A waveguide filter for a microwave oven, characterized in that it is formed in a.