JPS61292888A - Waveguide filter for electronic oven range - 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] Industrial Field of 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 microwave oven.

The frequency (fundamental wave) assigned to conventional technology microwave ovens is 2.
．． The frequency is 45GHz±50MHz. This magnet) a generates frequencies (noise) other than the fundamental wave, albeit at a relatively low level. If noise leaks to the outside of the microwave oven, it may have a serious effect on other electronic devices, so various countermeasures are taken at the design stage of the microwave oven. Therefore.

Conventional microwave ovens include 2, for example, Japanese Patent Publication No. 59-16713.

As described in Japanese Patent No. 59-16714, a filter is provided in a waveguide that guides microwaves from a magnetron to a heating chamber to remove noise. In this case, although it is effective against noise at a frequency relatively close to the fundamental wave, removal of harmonics was not considered.

Problems to be Solved by the Invention In recent years, broadcasting satellites have been launched, and television signals have come to be transmitted directly from the satellites to homes. The assigned frequency of this broadcasting satellite is 11.7 to 12.7 GHz.

On the other hand, the fifth harmonic of a microwave oven is 12fl~12
．． 5 GHz and completely redundant. If the fifth harmonic from the microwave oven leaks, it may have an adverse effect on the satellite television receiver. In order to remove such harmonics, a wideband filter as described in Japanese Patent Publication No. 52-17891 has been proposed. However, this technology has the problems of not considering higher-order modes and being relatively expensive.

Means for Solving the Problems The present invention has been made to eliminate the above-mentioned drawbacks, and can effectively eliminate the fifth harmonic despite the occurrence of a large number of higher-order modes.

At the same time, it is an object of the present invention to provide a waveguide filter for a microwave oven that is low in manufacturing cost.

It is a well-known fact that a large number of modes can be transmitted when the fifth harmonic is transmitted in the k-th waveguide, which currently transmits the entire fundamental wave. For example, the fundamental wave (2,45GHz±50MH
2) The cross-sectional dimensions of the standard waveguide WRJ-2 (EI standard wR-430) for transmitting are 109.22 x 54.6.
1-, so the fifth harmonic (12.0 to 12.50H
1) can be transmitted in several dozen higher-order modes. Since it is difficult to block microwaves transmitted in a large number of higher-order modes, we use a plurality of uneven parts formed on a plurality of metal plates fixed in the waveguide to block the transmission of the TEmo mode and to Ternws, TMIII! by nine spacers welded between metal plates. It is designed to block 1 mode transmission.

By doing this, -fi is introduced into the waveguide.
:, the fifth harmonic TEmo mode, TERnfi mode, and FMmn mode are completely removed.

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 crystal main wave generated by this magnetron is radiated from an antenna 2 and guided by a waveguide 6 to a heating chamber 4.
heats the food stored inside. 5 is the door, heating chamber 4
Used to take food in and out. 6 is a waveguide filter (hereinafter referred to as a filter) that blocks the fifth harmonic generated by the magnetron 1 and radiated into the waveguide 6 by the antenna 2, so that it is not radiated into the heating chamber 4. It is.

FIG. 2 shows a perspective view of the filter 6. 7 is an elongated metal plate with both ends pointed, and a plurality of spacers 8, 8
．． Two ... are welded to one side, and eight similar sets are lined up in parallel. However, only the leftmost metal plate 7 in FIG. 5 has spacers a8 housed on both sides. The eight metal plates 7 are connected by a metal shaft 9 passing through a hole formed approximately in the center of each spacer 8, and are kept parallel to each other. As shown in the figure, both ends of the metal plate 7 are pointed like an arrow, and the upper and lower edges are uneven. Reed.

The spacer 8 is a metal plate formed in the shape of a rectangular gutter with a U-shaped cross section. The shaft 9 is a metal rod threaded at both ends.

FIG. 6 shows a cross-sectional view of the main part of the filter 6 housed within the waveguide 3. A shaft 9 passes through approximately the center of the side wall of the waveguide B, and a nut 10. It is fixed by a screw on the shaft 9. In order to locate the filter 6 almost at the center of the waveguide 3, a gap g1 is provided between the upper and lower wall surfaces of the waveguide 3 and the long side of the metal plate 7, and a gap g1 is provided between the upper and lower walls of the waveguide 3 and the long side of the metal plate 7. Gatte g2 is provided in between.

Next, the operation of this embodiment will be explained.

In the filter 6 having such a structure, (1) the fundamental wave is transmitted almost without loss; t2+% Transmission of the 5th harmonic is almost completely blocked. Among (2), modes other than TEmo mode (TEn+n, TMmn) f are almost completely blocked for the following reasons.

That is, since modes other than the TEmo mode always have electric field components parallel to the upper and lower wall surfaces of the waveguide 3, they cannot pass through the filter 6. Passage is possible only when the gap g2 in the figure is large. g2
It is well known that if λ0 is less than one of the spatial wavelength λ0 of the fifth harmonic, there is a cutoff and the $5 harmonic of the mode having one electric field cannot pass through. In other words, by appropriately selecting the height of the spacer 8, TEm
Prevents transmission of modes other than o mode.

In particular, in this embodiment, since the spacer 8 has a U-shape as shown in FIG. 2, it has a four-stage blocking structure in the tube axis direction, thereby achieving high performance.

The reason why the fundamental wave can be transmitted with almost no loss and the reason why the TEmo mode of the fifth harmonic can be almost completely blocked will be described below.

First, we will discuss transmission of the fundamental wave, but to make the explanation easier, we will discuss a structure that does not have any spacer 8 and has no unevenness on both long side edges of metal plate 7. Describe the case where there is.

FIG. 4 shows a sectional view seen from the side showing how the fundamental wave is transmitted. The fundamental wave travels from left to right in the diagram. As is well known, the fundamental wave is TEIo mode, so
The electric field is 12. The magnetic field has a shape as shown at 16. When the electromagnetic field reaches the metal plate 11, since the tip of the metal plate 11 is sharp, the electromagnetic field is quickly divided into upper and lower parts. As mentioned in Figure 3.

Since the gap gr is almost equal, the upper and lower parts are equally divided. Figure 5 shows the state of the electromagnetic field after division.
A sectional view seen from the cron side is shown. The electric field is as shown in 14.
Further, the magnetic field is divided into upper and lower parts as shown in 15. The reason why there is no electromagnetic field between the metal plates 11 and 11 is because
This is because the interval G is sufficiently narrower than the cutoff dimension of the fundamental wave. However, an electromagnetic field cannot help but enter between the side walls at both ends and the metal plate 11 as shown in the figure. The electric field in that part becomes 0 on the center line 16 because the upwardly divided component and the downwardly divided component are equal in magnitude and opposite in direction. Further, the magnetic field in that part has a shape perpendicular to the plane of the paper, as shown by symbols 17 and 18. 19 in the figure conceptually shows the electric field strength ETH near the upper wall surface of the waveguide 6, and 21 conceptually shows the electric field strength E TE k near the right side wall surface of the waveguide 6. E
TH is large near the metal plate 11 and becomes small between the metal plates 11 and fluctuates.

The envelope 20 retains remnants of the original TEIo mode. The ETE is maximum near the long side edges of the metal plate 11 and becomes 0 on the center line 16. However, the center line 16
Even if it is partitioned vertically with metal along the paper surface, it will not affect the transmission in any way. Since the electromagnetic field is concentrated on the outside of the eight metal plates 11, this transmission line is equivalent to two waveguides with a U-shaped cross section facing each other vertically, separated by the center line 16. It is. This will become clearer from the following explanation of surface current.

FIG. 6 shows the current flowing through the metal plate 11.

A cross-sectional view of the waveguide O seen from the top is shown. The lower half with the tube axis 23 as a boundary is shown. The dotted arrow indicates the current flowing on the surface of the metal plate 11, and the solid arrow indicates the magnetic field. As a matter of course, the two must be perpendicular to each other, so the current 22 flowing at the edge of the metal plate 11 flows only in a direction parallel to the tube axis 23, and the direction of flow is reversed every half wavelength.

FIG. 7 shows the surface current flowing to the outside of the end metal plate 11 among the eight metal plates 11, and the dotted line arrow represents the surface current, and the solid line arrow represents the magnetic field. As can be seen from the surface currents in Figures 6 and 7, the normal waveguide mode T
This is equivalent to an EIO with two U-shaped waveguides facing each other vertically. Therefore, this transmission line transmits the fundamental wave with almost no loss.

Here, the effects of the above-mentioned spacer 8 and the uneven portions of the metal plate 7 on the fundamental wave will be described. As can be seen by comparing FIG. 3 and FIG. 5, only the spacer 8 at the end affects the transmission of the fundamental wave. Since the degree of this only affects the ETE that has entered both sides of FIG. 5, it is insignificant compared to the overall energy, and only causes a slight discontinuity. Discontinuities of this degree can be sufficiently matched, but by appropriately selecting the spacing of the subbeams f8 in FIG. 2, the reflections can be canceled each other and matching can be achieved automatically.

Furthermore, as will be described later, since the uneven portions are provided for the purpose of removing the fifth harmonic, their depth and spacing are extremely small relative to the fundamental wave.

can be largely ignored. However, since the wavelength is somewhat shortened, care must be taken when matching the load impedance.

The reason why the fundamental wave is transmitted with almost no loss has been explained above, and next, the reason why the transmission of the fifth harmonic in TEmo mode can be prevented will be described.

As in the case of the fundamental wave, in order to simplify the explanation, we will describe the structure in which there is no spacer 8 in FIG. Let's talk about.

First, the TBlo mode of the fifth harmonic will be described.

Even though it is the fifth harmonic, the TEL mode has the same shape as the fundamental wave. The only difference is the shorter wavelength, so it is essentially the same as the electromagnetic field in Figure 4.

Assuming that the wavelength is short, FIG. 4 directly shows the state of the fifth harmonic TE and o mode. Similarly, FIG.

6 and 7 can also be considered in this way.

However, in FIG. 5, the interval G between the metal plates 11 is set to be less than one of the spatial wavelength λo5 of the fifth harmonic. If this is not the case, an electric field component parallel to the metal plates 11 will enter between all the metal plates 11, resulting in no effect.

As shown in Figure 5, when the TElo mode of the fifth harmonic is transmitted, it is equivalent to two waveguides with a U-shaped cross section facing each other at the boundary of the center line 16, and there is almost no loss. As stated earlier. Therefore, if the TE2o mode advances from the left side in FIG. 4, the electromagnetic field divided by the metal plate 11 should become as shown in FIG. 8. That is, the electric field in the left half is divided into 24.24,
The magnetic field is divided into 26.26. Similarly, the electric field in the right half is 25.25, and the magnetic fields are 27, 27, and their respective directions are the directions of the arrows. An electromagnetic field also enters between the metal plates 11 in the center.

Therefore, in this case, it is equivalent to two waveguides each having a U-shaped cross section facing each other with the center line 16 as a boundary, and transmission is possible with virtually no loss.

Similarly, in the case of TE8o, Figure 9 shows that the electromagnetic field penetrates between all the metal plates 11, so it is equivalent to a total of 16 waveguides, 8 each facing each other with the center line 16 as the boundary. It is. Although not shown in the diagram.

Other TE10, TE40 + TE50, TE6
0 and TE70 have similar results. however,
TE3 (1, TE10. The three odd modes of TE7o are slightly different from those shown in the figure because the number of metal plates 11 is eight, an even number, but there is essentially no difference.

What is important here is that the surface current flowing through the upper and lower edges of the metal plate 11 is determined in which mode (TEmo) as shown in FIG.
) is also parallel to the tube axis 23.

What is even more important is that the tube wavelengths are almost the same in all modes of the fifth harmonic.

It will be explained with reference to FIG. 10 that the wavelengths in the tube are almost equal.

In the figure, in a normal waveguide without any metal plates 7, the cutoff wavelength λcm of the TEmo mode is expressed by the following equation.

lm=-・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・il+However,
A is the lateral dimension of the waveguide.

On the other hand, since the cutoff wavelength of the TElo mode described in FIG. 5 is a waveguide with a U-shaped cross section, it is equal to the waveguide whose lateral dimensions are points 3Q, 31, 32, and 63 in FIG. . Therefore, TE, the o-mode cutoff wavelength λel
is λc+=2('+a+")-2(a+b) +++
+++ t21. However, a, bilj, the first
These are the dimensions shown in Figure 0. Similarly, the cutoff wavelength λc2 of the TE2o mode is 2 points 301 points 3 from Figures 8 and 10.
The cutoff wavelength of the waveguide whose horizontal dimension is 11 points 34 1 points 35 1 points 34 1 points 32 1 points 6 ro. That is, = a + 2b ・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・(3) Therefore, the cutoff wavelength λ of the Terno mode
cIT+ is λ・m = ” +2b・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・ +4
It is represented by 1.

Although it is a rough approximation in order to compare equations (1) and (4).

a Mai A, b″:B=-・・・・・・・・・・・・
If we set ・・・・・・+51, equation (4) becomes λ・・萄ZA+A ・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・ (6) becomes, which shows that the di-cutoff wavelength becomes longer by A for any mode according to equation (1). There is.

First, in the standard waveguide WRJ-2/EIA standard WR-430 for the fundamental wave, the fifth harmonic TElo, TE, , o
In-tube wavelength λglo at 12.25 GHz of mode
and λggo are respectively λglo = 24.65 mm and λgso = 50.38 mm as described above. On the other hand, according to equation (6).

λg + o = 24.56 fins, o = 24.89 fins, so there is almost no difference between λglo and λggo. That is, #TEIO to TE8. This means that the eight modes have approximately the same wavelength within the tube. This is extremely important. This is because the structure for blocking the transmission of the fifth harmonic (described later) only needs to have one size.

Next, the effects of the spacer 8 and the uneven portion will be described.

First, when spacer 8 in Figure 2 is used, it is somewhat effective as it blocks the electromagnetic field that enters between the metal plates 7, as is clear when compared with Figure 9, but this alone is not enough. Out. In particular, as described with reference to FIG. 5 regarding transmission of the fundamental wave, the spacer 8 can hardly be expected to have any blocking effect on the 'rgio mode of the fifth harmonic. Therefore, the main blocking effect on the TEmo mode of the fifth harmonic is due to the uneven portion described below.

(1) in FIG. 11 is an example of an uneven portion provided on the metal plate 7. As shown in FIG. In a part of the tube wavelength λg, recesses each having a relatively narrow width W and a depth are regularly arranged.

Since a surface current 40 flows in this portion as shown in FIG. 6, a surface current 41 in the opposite direction flows in the upper and lower wall surfaces of the waveguide 5 corresponding thereto. Therefore, this part can be represented by an equivalent circuit using parallel lines shown in FIG. 2(2). In the recessed portion, a tank circuit resonating at a frequency corresponding to λg is connected in series with parallel lines. As for the insertion loss of this equivalent circuit, if λg is made to match 5ro (fifth harmonic) as shown in FIG. 3(3), a very large blocking effect can be expected. As mentioned above, λg is approximately constant regardless of the mode in the TEmo mode, so the same effect can be obtained in any mode.

FIG. 12(1) is an example of another uneven portion. Recess dimension λ
g thx , the dimension of the convex portion is h2, and the width thereof is respectively i. The equivalent circuit in this case is expressed as shown in FIG. 2 (2). The characteristic impedance Z, and the line length of 22 is λ
g = 7 are connected to each other.

The insertion loss of this equivalent circuit is as shown in (3) in the same figure, and the blocking effect at one frequency 5to is not as great as in the case of FIG. 11, but it has the characteristic that a wide band characteristic can be obtained.

Since the characteristic impedance is considered to be proportional to the distance from the upper and lower wall surfaces of the waveguide 3, this relationship is established. Therefore, the larger the ratio between hl and h2, the greater the blocking effect will be.As explained in detail, according to the present invention, the fifth harmonic can be effectively removed despite the generation of many higher-order modes. At the same time, it is possible to provide a waveguide filter for a microwave oven that has a simple structure using only a metal plate and a spacer and is inexpensive to manufacture.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a main part of a waveguide filter for a microwave oven showing one embodiment of the present invention, FIG. 2 is a perspective view of the filter, and FIG.
The figure is a partial cross-sectional view of the filter housed in the waveguide.
Figures 4, 5, and 6. Figures 7, 8, and 9 are explanatory diagrams showing the electromagnetic field and surface current, Figure 10 is a conceptual diagram for determining the cutoff wavelength, and Figure 11 is a diagram showing the shape and performance of the uneven part. It is a figure explaining the relationship, (1) shows the shape of the uneven part, (
2) shows its equivalent circuit, and (3) shows its characteristics. FIG. 12 shows another example of the uneven portion, and similarly to FIG. 11, (1) shows the shape of the uneven portion, (2) shows its equivalent circuit, and (3) shows its characteristics. 6... Waveguide, 7... Metal plate. 8...Sweet! ), 9...shaft. g2...gap.

Claims (1)

[Claims] In a filter made by arranging multiple metal plates parallel to the side wall surface inside a waveguide, the multiple metal plates (
7, 7, ...) with multiple metal spacers (8, 8,
) are arranged parallel to each other at intervals, and gaps (g_1) are formed between these metal plates (7, 7, ...) and the upper and lower inner wall surfaces of the waveguide (3). At the same time, metal plates (7, 7,...) facing the upper and lower inner wall surfaces of the waveguide
The metal plates (7, 7,...), the spacers (7, 7,...), and the locks are connected to the metal spacers (8, 8,). A waveguide filter for a microwave oven, characterized in that it is attached between both side walls of a waveguide via.