JPH0675431B2 - microwave - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure for guiding a microwave generated by a magnetron to a heating chamber in a microwave oven, and a means for removing unnecessary radiation components other than the fundamental wave component generated by the magnetron. It is about.

PRIOR ART Magnetron used in microwave oven is the fundamental wave
It has an unnecessary radiation component over a wide frequency band other than 2450MHz, and it is necessary to prevent it from leaking outside through the heating chamber.

Generally, a waveguide used in a microwave oven has a cross-sectional shape as shown in FIG. 5, and the long side a and the short side b are each a> for the free space wavelength λ of the microwave 2450 MHz used.
It is set so that λ / 2, b <λ / 2, and only the fundamental mode of TE ₁₀ propagates.

Problems to be Solved by the Invention However, as described above, the magnetron has a noise component in a wide frequency range, and is 2200MHz lower than 2450MHz.
There is often a high noise component near 2300MHz, and for the waveguides that are currently generally used, the value with the long side a of around 90mm is often used due to the wavelength inside the pipe and the transmission loss. The components are also transmitted to the heating chamber, and finally leak to the outside through a gap that cannot be avoided, such as a gap with the door.

The aim is to reduce the emission of noise components around 2200 to 2300MHz, which is close to the fundamental frequency of 2450MHz, to the outside of the microwave oven.

As a means for solving the above problems, as a means for solving the above problems, the microwave oven of the present invention has a rectangular waveguide for transmitting microwaves generated by a magnetron, which is substantially parallel to the wall surface forming the short side. , A metal wall reaching both wall surfaces forming the long side is provided in a part of the entire length in the waveguide propagation direction, and the distance between the metal wall and one of the wall surfaces forming the short side is used as a fundamental wave. 1/2 of wavelength λ
By setting the wavelength to ½ or less of the wavelength λ of the unwanted radiation to be blocked, it is possible to prevent the unwanted radiation having a frequency equal to or lower than the fundamental wave from propagating into the heating chamber.

The distance between the working metal wall and the short side wall surface is the wavelength λ of the fundamental wave 2450 MHz.
There is a noise component in more than 1/2 of the wavelength λ of 2300MHz
If set to 1/2 or less, the fundamental wave propagates, but noise components below 2300MHz are blocked, and noise leakage can be prevented.

On the other hand, since the metal wall is only part of the entire length of the waveguide, if the long side a of the waveguide is set sufficiently larger than 1/2 of the fundamental wave λ, for example, around 90 mm, The guide wavelength is almost not longer than the free space wavelength, so that impedance adjustment such as phase is easy and the transmission loss is small.

Embodiments Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a sectional view of a main part of a microwave oven according to the present invention, FIG.
FIG. 3 is a sectional perspective view of the waveguide portion, and FIG. 3 is a sectional view of the waveguide portion. 1, 2, and 3, 1 is a magnetron, 4 is a heating chamber, 2 is a rectangular waveguide connecting the magnetron 1 and the heating chamber 4, and 3 is provided in the rectangular waveguide 2. This is a metal wall, and this metal wall 3 is a wall surface that constitutes the short side of the waveguide.
The two walls 2a, 2a ', which are substantially parallel to 2b, 2b' and which form long sides, reach the wall surfaces 2a, 2a ', and have a length 1 which is a part of the entire length in the waveguide propagation direction. Assuming that the length of the long side of the waveguide 2 is a ₁ and the distance between the short side 2b of the waveguide 2 and the metal wall 3 is a ₂ , for example, a ₁ = 90 mm, a ₂ = 64 mm, l
= 108mm is set.

In the above configuration, the microwave radiated from the antenna 5 of the magnetron 1 into the waveguide 2 is guided into the heating chamber 4 through the waveguide opening 6, and the relationship between the frequency and the transmission characteristic at this time will be described. FIG. 4 is used to do this. FIG. 4 shows the frequency and the guide wavelength λg in the rectangular waveguide.
Of the cutoff frequency c and the free space wavelength λ, respectively. FIG. 4 shows that when the frequency approaches the cutoff frequency c, the guide wavelength λg rapidly increases, and when it coincides with c, λg becomes infinity and radio waves above that frequency no longer propagate.

Now, in the above configuration, the waveguide 2 in the section where the metal wall 3 is present
The cutoff frequency is determined by the distance a ₂ between the metal wall 3 and the short side 2b of the waveguide. If a ₂ = 64 mm, then c≈2350 MHz is the cutoff frequency for this portion. Therefore, the noise component of ≈2350 MHz or less attenuates exponentially in the propagation direction of the waveguide and does not propagate to the waveguide opening 6 side. On the other hand, the fundamental wave of 2450 MHz used for heating propagates above the cutoff frequency without being attenuated.
What is important here is that the tube wavelength λg of the fundamental wave of 2450 MHz in a certain section of the metal wall 3 is c / = 2350/2450 = 0.96.
Therefore, from Fig. 4, it is about 3.5 times the free space wavelength λ, that is, a large value of λg ≈ 430 mm, but in other parts, the cutoff frequency c is determined by a ₁ = 90 mm c ≈
Since it is 1670MHz, c / = 1670/2450 ≒ 0.7, which is about 1.5 times the free space wavelength λ, that is, λg
It is as short as ≈180 mm. That is, according to the configuration of the present invention, the fundamental wave = 2450 is obtained by using the cutoff characteristic of the rectangular waveguide.
While removing noise components at frequencies very close to MHz, a sufficiently wide waveguide width is maintained in the vicinity of the coupling portion with the magnetron 1 and the heating chamber opening 6, and the phase begins by increasing the guide wavelength λg. This makes it possible to prevent the impedance adjustment from becoming difficult and to minimize the decrease in efficiency due to the increase in transmission loss near the cutoff frequency. Further, the length l of the metal wall 3 is the guide wavelength for the fundamental wave in this section (the guide wavelength λg≈430 mm in the above embodiment).
It is set to about 1/4 of that to suppress the occurrence of reflection.

Effects of the Invention As described above, according to the microwave oven of the present invention, the following effects are obtained.

(1) The metal wall provided inside the waveguide can increase the cutoff frequency of the waveguide to the very vicinity of the fundamental frequency, thus preventing leakage of noise components around 2200MHz to 2300MHz, which was difficult to remove in the past. Made possible.

(2) Further, regardless of the above effect, since the metal wall is provided in a limited part of the entire length of the waveguide, the cutoff frequency is low in the part without the metal wall, so the waveguide wavelength is compared to the free space wavelength. Since it can be set so that it does not become so large, it is easy to adjust the impedance such as the phase adjustment from the magnetron to the waveguide aperture, and the increase in transmission loss that generally occurs when approaching the cutoff frequency can be minimized. it can.

[Brief description of drawings]

FIG. 1 is a sectional view of a main part of a microwave oven according to the present invention, FIG. 2 is a partially cutaway perspective view of the waveguide, FIG. 3 is a sectional view of the waveguide, and FIG. 4 is a rectangular waveguide. Frequency and wave number in pipe λ
FIG. 5 is a characteristic diagram showing the relationship with g, and FIG. 5 is a waveguide sectional view of a conventional microwave oven. 1 ... Magnetron, 2 ... Waveguide, 3 ... Metal wall, 4
…… Heating chamber, 6 …… Waveguide opening.

Claims (1)

[Claims] 1. A heating chamber, a high-frequency oscillator, and a rectangular waveguide for transmitting microwaves generated by the high-frequency oscillator to the heating chamber. The waveguide has therein a short side of a rectangular cross section. A metal wall that is approximately parallel to the wall surface that reaches both wall surfaces that form the long side, is provided in a part of the entire length in the waveguide propagation direction,
The distance between the metal wall and one of the wall surfaces forming the short side is set to be ½ or more of the wavelength λ of the microwave used and ½ or less of the wavelength λ of unnecessary radiation to be blocked. microwave.