JPS61121285A - Waveguide tube filter for high frequency heater - 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 the Invention The present invention relates to a waveguide filter device used in a high frequency heater such as a microwave oven.

Conventional technology The high frequency oscillation @ (magnetron) used in microwave ovens etc. is basically tLf o (915MHz or 2450MHz
), harmonic nfo (n: integer) radio waves are generated.

These harmonics adversely affect communications and the like, so a means to suppress them is required.

Providing frequency i and selectivity to the waveguide is effective as a solution, and a configuration in which a "resonance window" is provided as a passband filter (Japanese Patent Application Laid-Open No. 52-56425) (Oguchi "Microwave and Millimeter Wave Circuits") P171 Maruzen 1964) has been proposed.

Problems to be Solved by the Invention However, when applying the facts known in the literature to microwave ovens, etc., the length of the waveguide is shorter than that for communication, as the internal wavelength is about the same wavelength. It is necessary to use the radio waves emitted from the magnetron when they are not completely aligned, and because the radio waves emitted from the magnetron must be used in an inconsistent state due to food loads.
, some ingenuity is required.

In other words, unless you devise a method for installing a "resonant window," installing a window can create conditions where harmonics from the magnetron are more likely to come out, or where it is effective against some harmonics but increases other harmonics. In particular, in the waveguide filter of the present invention, the installation of a flat plate with a rectangular window of a'Xb' on the waveguide (width a, height b) is difficult to achieve due to the electric field strength of the constant pressure wave due to positional mismatch. We are trying to decide based on the relationship.

Function The dimensions width a, height b, width a', and height b' essentially have the following relationship.

λ: Wavelength for the fundamental wave fo The filter of the present invention was created by actually measuring the distortion of standing waves that occur as a result of short waveguides and mismatching, and by providing windows to avoid areas where the electric field strength is weak. Embodiment The waveguide filter according to an embodiment of the present invention will be explained with reference to the drawings. do. As shown in Figure 1, the microwave oven has a bottom plate 1
, a body cover 2, a heating chamber 3, a waveguide 4, a window plate 5, and a magnetron 6, and power is supplied to the magnetron 6 from a power source 7. A saucer 8 and a rotary wheel 9 are disposed inside the heating chamber, and the saucer 10 is rotatably provided so as to be rotated by a drive shaft 10. The bottom plate 1 is provided with legs 11.

FIG. 2 shows how the window plate 5 having the window 11 is installed on the waveguide wall 12 and the heating chamber wall 13 (as viewed along the line A--A in FIG. 1). The window plate 5 is fixed to the heating chamber wall surface with screws 15. The window plate 5 is provided at a position where the electric field is strong. FIG. 3 shows the electric field distribution inside the waveguide when viewed from the top of the waveguide when there is no window plate. You can see how the equipotential lines spread around the magnetron antenna installed at point B. The position where the electric field is 96 degrees away from the magnetron (marked with an x) is the position where the electric field is weak, and the position where the electric field is strong (marked with △) is the intermediate position. The load is water 11. A probe with a length of 4 fi was inserted into the upper wall of the waveguide to form a large number of punched holes in the measurement beams 1 and 4 at the vertices of an equilateral triangle with 2 sides on each side. An SG was used for the signal wave, and a probe for operating point measurement was used as the magnetron antenna.

Although this relationship varies from vehicle to vehicle depending on the type of load, ordinary microwave ovens are designed so that it does not change to the extent that it is reversed. In FIG. 4, an example of the electric field strength at the time of water load 11 is shown in the fb1 diagram as a relative value in relation to the front cross-sectional fat diagram (the window plate 5 is omitted).

Figure 5 shows a microwave oven set with a fundamental wave of 2450 MHz (Matsushita Electric NE-651) with window size a = 63.6 mm.
It is a graph showing the results of measuring harmonic leakage by changing the location of the window plate 5 provided with the windows 14 of L, b'=81all, in comparison with the case where the windows 14 are not provided. The waveguide 4 is a=
92ffl+11. b=32fifi.

When the window plate 5 is installed in a place where the electric field is weak (data marked with an x), the radiated power increases compared to when there is no window plate 5, and by providing the window plate 5 in a place where the electric field is strong, the radiated power increases from 2 to 6 of the fundamental wave fO. It can be seen that the harmonics are reduced by about 4 to 11 dB. The same set has a window shape (a'=65.2M, b'=
10.5M) (a'=70.2°b'=16
) shows a similar tendency. Also, a = 73
Even if the prototype set with the waveguide 4 with ttun and b = 31 am has the following window size combination of 11, a large filter effect can be obtained when it is installed in a position where the electric field is strong.

It could be confirmed.

In Fig. 6 of the field, the operating points when the water load 21 is placed in the heating chamber are shown without the window plate 5 (), with the window plate 5 in a weak electric field (×),
The cases where the electric field is placed in a strong electric field (◯) and in an intermediate position (△) are shown. If the waveguide length is long and the load is matched, window 1
By designing the dimensions (a', b') of 4 using the relational expression shown earlier, the 14 windows will act as a "resonant window" with parallel resonance, and the mounting of the window plate 5 should not change depending on the position. , is actually changing. This result shows that by setting the window size to the size shown by the previous relational expression and placing a window metal film in a place where the electric field is strong, it can act as a filter without necessarily causing "resonance".

Although the embodiment shows a rectangular window 14, many variations of the window shape are possible.

Effects of the Invention As described above, the waveguide filter according to the present invention can be realized by providing a window plate in a short and mismatched waveguide of a microwave oven, avoiding areas where the electric field strength of standing waves is weak. ,
It is possible to produce a stable filter effect over a wide range of harmonics.

[Brief explanation of the drawing]

FIG. 1 is a front cross-sectional view of a microwave oven according to an embodiment of the present invention, FIG. 2 is a cross-sectional view taken along the line A-A in FIG. 1, FIG. 3 is an electric field distribution diagram, and FIG. Cross-sectional view of the tube, Figure 4 (b
) is a diagram showing the electric field strength at each part of the waveguide, Figure 5 is a diagram showing the measured value of the radiated power due to changes in the position of the window plate installation,
FIG. 6 is a diagram showing the change in the operating point due to the change in position when the window plate is attached, in comparison with the case without the window plate. 4...Waveguide, 5...Window plate, 14...Window, ×
Mark: A place where the electric field is weak. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 4
Figure 5 gd6rence ylane

Claims (3)

[Claims] (1) A window plate with a window smaller than the cross-sectional shape of the waveguide,
A waveguide filter device for high-frequency heating equipment that is installed at right angles to the waveguide wall, avoiding locations where the electric field strength of the fundamental wave is weak within the waveguide. (2) When the window is rectangular with dimensions a' in length and b' in width, and the width of the waveguide is a and height b, the relationship between these dimensions is essentially a'/b' = (a/ b)/{√[1-(λ/2a)^2
]/√[1-(λ/2a')^2]} The waveguide filter device for a high-frequency heating device according to claim 1, characterized in that: (3) A waveguide filter device for a high-frequency heating device according to claim 1, characterized in that a window plate is attached at a position next to the magnetron antenna where the electric field strength of the fundamental wave is strongest.