JPS61292889A - 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.
．． 45 GHz±50 MHz. However, the magnetron also generates frequencies (noise) other than the fundamental wave, albeit at extremely low levels. If noise leaks to the outside of the microwave oven, it may seriously affect other electronic devices, so various countermeasures are taken at the design stage of the microwave oven. Therefore, conventional microwave ovens remove noise by installing a filter in the waveguide that guides the microwave from the magnetron to the heating chamber, as described in, for example, Japanese Patent Publication Nos. 59-16713 and 59-16714. There is. in this case.

Although it is effective against noise with 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 12.0 to 12
．． At 5GHz, we are fully focused on it. 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, conventionally,
A wideband filter as described in Japanese Patent No. 17891 has been proposed. However, this technique has a problem in that it does not take into account higher-order modes.

Means for Solving the Problems The present invention has been made to eliminate the above-mentioned drawbacks, and effectively prevents the fifth harmonic from leaking into the heating chamber despite the occurrence of a large number of higher-order modes. An object of the present invention is to provide a waveguide filter for a microwave oven that can block the problem. the current,
It is a well-known fact that a large number of modes can be transmitted when the fifth harmonic is transmitted in a waveguide for transmitting the fundamental wave.

For example, the standard waveguide WRJ-2 (EZA standard wn-4) for transmitting the fundamental wave (2,45 GHz ± 50 MHz)
The cross-sectional dimensions of 30> are 109.22 x 54.61 m
Therefore, the fifth harmonic (12.0 to 12.5 GHz
) 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 in this way, the transmission of the TEmo mode is blocked by a plurality of concave and convex portions formed on a plurality of parallel metal plates placed inside the waveguide. TEn+n, TMmn by selecting the opposing gaps of the plane parts connected to the parallel plates.
It is designed to prevent mode transmission.

By doing this, the fifth wave introduced into the waveguide
Harmonic TEeno mode, TErnn mode.

TMmn mode is to be 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, reference numeral 1 denotes a magnetron, and a fundamental wave generated by the magnetron is radiated from an antenna 2 and guided through a waveguide 3 to heat food stored in a heating chamber 4. 6 is a waveguide filter (hereinafter referred to as filter).

generated by the magnetron 1 and transmitted to the waveguide 3 by the antenna 2.
This prevents the fifth harmonic from being radiated into the heating chamber 4 by blocking it. 5 is the door, heating chamber 4
It is used to take food in and out. 7 is the ceiling surface of the heating chamber 4, which also serves as the bottom surface of the waveguide O.

FIG. 2 shows a perspective view of the filter. A flat part 10.10 is formed at both ends of the upper surface of the upper surface of the metal trapezoidal member with a space therebetween, and tapered parts 9, 9 are formed between the flat part 10.10 and the lower surface, respectively, and parallel to both side surfaces of the space. A plurality of parallel plates 1 (in this example, 11 plates arranged at equal intervals) are arranged.
1, and a plurality of concave and convex portions are regularly formed on the edge of the parallel plate 11 such that the convex surface is flush with the flat portion 10.10, and a set screw 13.13 for mounting is formed. The filter 6 is attached to the ceiling and bottom surfaces of the waveguide 6 facing each other through the parallel plates 11, and arranged so that the parallel plates 11 are parallel to the tube axis.
It constitutes. 12 is a screw hole for mounting.

Next, the operation of this embodiment will be described.

With this structure, the microwaves generated by the magnetron 1 are transmitted from left to right in FIG. 6, but the fundamental wave can pass through the filter 6 with almost no loss, while the microwave The fifth harmonic is transmitted but reflected to the left. Therefore, among the fifth harmonics, modes other than TEmo mode (m=1.2.3...) (TEm
n, TMmn, n=1.2.3-...') is almost completely blocked for the following reason.

In other words, since modes other than the TEmo mode always have electric field components parallel to the upper and lower wall surfaces of the waveguide, the waveguide G formed between the flat parts 10 and 10 in Fig. 3 is shown as G. If the gap is narrow, the light cannot pass through this filter 6. The value of the gap G is 1 of the spatial wavelength λO of the fifth harmonic.
It is a well-known fact that if it is less than /2, there is a cutoff and the fifth harmonic of the mode having this electric field component cannot pass.

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

First, the transmission of the fundamental wave will be described, but in order to simplify the explanation, only the parallel plate 14 is present as shown in FIG. 5, and
The electromagnetic field when the parallel plate 14 has no uneven portion will be described, and later the case where the parallel plate 14 has an uneven portion will be described.

Since the fundamental wave is in the TElo mode, the electric field has the form shown by 15. The distance between the parallel plates 14 is sufficiently narrow that no electric field (parallel to the parallel plates 14) can exist therebetween. In other words, the surface current flows through the parallel plate 14 in a concentrated manner only at its tip, and its direction is only the component parallel to the tube axis. However, between the parallel plates at both ends of 7 and the side walls, 17.
An electric field like 17 must exist. therefore,
The magnetic field 16 is divided into two at both ends, and components such as 18 and 18 exist. This can be considered in place of the waveguides 19 and 19 having a U-shaped cross section as shown in FIG. 6, in which the fundamental wave is transmitted. In this case, the fundamental wave can be transmitted without loss, but the narrow part at both ends is the short part 2 in Figure 2.
Since there is a zero, a reflected wave is generated. However, since this is the end of the waveguide B, its energy component is very small, so it does not pose a problem. It is enough to be luxurious in parts of the pond other than the filter. In FIG. 6, the width of the waveguide 3 is increased by about 2 at each end. However, ■ is the height of the waveguide 6. In other words, the cutoff wavelength λCIO in the TE1o mode of the waveguide 19.19 with a U-shaped cross section is λC4o# 2(A+2') = '2(A+H), assuming that the width of the waveguide 3 is a person.
...------=-fl).

This does not have much effect on the fundamental wave.

This has an important meaning for the higher-order mode of the fifth harmonic, which will be described later.

As mentioned above, it has been shown in Fig. 5 that the fundamental wave can be transmitted without loss, but even if there are uneven parts on the parallel plate 11 as shown in Fig. If it is negligible relative to the wavelength, it is not a problem at all. As will be discussed later, the dimensions of the uneven portion are determined by the spatial wavelength λ0 of the fifth harmonic.
Since the distance is around 6 m for 4, the fundamental wave can be transmitted without any loss without any problem.

Next, the reason why transmission of the fifth harmonic in TEmo mode can be blocked will be explained.

First, it will be shown that the tube wavelength of the TEm6 mode is #1i' constant regardless of the mode order, and finally, the reason why the uneven portion of the parallel plate 11 can block the fifth harmonic will be explained.

As in the case of the fundamental wave, the electromagnetic field when only the parallel plate 14 exists and there are no uneven parts as shown in FIG. 5 will be described.

Even though it is the fifth harmonic, the TE and o modes have the same shape as the fundamental wave. The only difference is that the wavelength is shorter.
It is essentially the same as the electromagnetic field in Figure 5.

Assuming that the wavelength is short, FIG. 5 shows the state of the fifth harmonic TE and o mode. Similarly, FIG. 6 can be considered in the same way. However, the interval between adjacent parallel plates 140 is set to 1/ or less of the spatial wavelength λ· of the fifth harmonic. The cutoff wavelength λCIO in this case is expressed by equation (1). FIG. 7 shows the state of the electromagnetic field in the TE2o mode, where the tube wavelength λgio is well known. TE2 at the top of the figure
As shown conceptually, the magnitude of the o-mode electric field is 0 at the center of the tube and the phase is reversed on the left and right sides, so the electric field inside the tube has a shape of 20.22 and the magnetic field has a shape of 21°23. becomes. therefore.

As shown in FIG. 8 as well as FIG. 6, it can be equivalently represented by four waveguides 24, 25, 26, and 27 each having a U-shaped cross section. Therefore, the cutoff wavelength λC2Q in this case is expressed as λC2Q.

Similarly, FIG. 9 shows the state of the electromagnetic field for the TE8o mode drawn based on the same concept as FIGS. 7 and 8. Although only two waveguides 28 and 29 having a U-shaped cross section at the lower left are shown, 16 similar waveguides can be shown, 8 at the top and 8 at the bottom. Therefore, the cutoff wavelength λcoo is as follows.

From the above results, the cutoff wavelength λ of TERno mode is
cITIo is expressed by the following formula.

2(A+mH) λCmo哄□ ・・・・・・・・・・・・・・・・・・
(5) Generally, the cutoff wavelength of a waveguide with width A is two people.
・・・・・・・・・・・・ Since (6), equation (5) is larger than equation (6) by 2H.

Previously, the standard waveguide WRJ-2 for the fundamental wave has a TE of 10.5 at the fifth harmonic at 12.25 GHz. It has already been mentioned that the tube wavelength λff1 (1+λgso of the TE80 mode is λIso = 24.65 1 m λrtBo = 50.38 wm, respectively.On the other hand, according to equations (5) and (2), λtB6 # 24 .56 m λg8# 24.89 Therefore, there is almost no difference between λ11o and λff80.In other words, the eight mode wavelengths of +TE+o -TEAo are almost equal, and therefore the structure that blocks transmission of the fifth harmonic is Only one size is required.

Finally, the reason why the fifth harmonic can be blocked by the unevenness of the parallel plate 11 will be described.

(1) in FIG. 10 is an example of a parallel plate 11 and an uneven portion provided on the parallel plate 11 facing thereto. In-tube wavelength λσ1
Recesses each having a depth of 4 and a relatively narrow width ω are regularly arranged every / of λg. Since the surface currents shown by 30.31 flow in opposite directions in this part, it can be represented by an equivalent circuit with two parallel lines shown in (2) of the same figure, and the recess is λg
A tank circuit that resonates at a frequency corresponding to is connected in series to two parallel wires. As for the loss of this equivalent circuit, if λg is made to match the fifth harmonic (5fo) as shown in FIG. 3(3), an extremely large blocking effect can be obtained. As mentioned above, λg is approximately constant regardless of the mode in the TEma mode, so the same effect can be obtained in any mode.

(1) in FIG. 11 is an example of another uneven portion. Recess size λ
The method is hl, the dimension of the convex portion is h2, and the width is /4. The equivalent circuit in this case is expressed as shown in FIG. 2 (2). The characteristic impedance zl and 22 lines are connected alternately at each peak. The loss of this equivalent circuit is shown in the figure (3)
Although the blocking effect at 9 frequencies 5f is not as great as in the case of FIG. 10, a broadband characteristic can be obtained. The relationship holds true because the characteristic impedance Zl+z2 is proportional to h1h2. Therefore, the greater the ratio between hI and h2, the greater the blocking effect.

Note that the present invention is not limited only to the removal of the fifth harmonic, but can also be applied to the removal of other frequency bands by appropriately determining the dimensions of the uneven portions and the number of parallel plates.

As described in detail, the present invention provides a waveguide filter for a microwave oven that can effectively prevent the fifth harmonic from leaking into the heating chamber (2) despite the occurrence of a large number of higher-order modes. can be provided.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a main part of a waveguide filter for a microwave oven showing an embodiment of the present invention, FIG. 2 is a perspective view of the main part, and FIGS. 6 and 4 are main parts of FIG. 1. Cross-sectional view. Figures 5, 6, 7, 8, and 9 are sectional views of important parts for explanation showing the state of the electromagnetic field in each mode, and Figure 10 is the shape and performance of the uneven part. FIG. 3 is a diagram illustrating the relationship between the two, in which (1) shows the shape of the uneven portion, (2) shows its equivalent circuit, and (3) shows its characteristic diagram. FIG. 11 shows another example of the uneven portion, in which (1) shows the shape of the uneven portion, (2) shows an equivalent circuit, and (3) shows its characteristics. 3... Waveguide, 10... Planar part. 11...Parallel plate, G...Gap.

Claims (1)

[Claims] A plurality of metals arranged on the ceiling and bottom surfaces of the waveguide (3) so as to be parallel to the tube axis of the waveguide (3), and having a plurality of periodic irregularities formed on mutually opposing edges. Parallel plate (11
), and plane parts (10), (10) are provided at both ends of the parallel plate (11), respectively, and are connected to each other, and the parallel plate (
11) Mutual spacing and the opposing plane parts (10), (
10) A waveguide filter for a microwave oven, characterized in that the gap (G) between them is 1/2 or less of the spatial wavelength of the noise frequency to be blocked.