JPWO2019203172A1 - Microwave heating device - Google Patents

Abstract

The microwave heating device (50) includes a heating chamber (2) for accommodating an object to be heated (1), a magnetron (3) for generating microwaves, and a waveguide (10) for transmitting microwaves to the heating chamber 2. ) And a directional coupler (6) including a reflected wave detection unit that detects a part of the reflected wave. The directional coupler (6) is located at the antinode (302) of the in-tube standing wave (301) generated in the waveguide (10). According to this configuration, the detection accuracy of the reflected wave can be improved, and the state of the object to be heated (1) can be detected more accurately.

Description

The present disclosure relates to a microwave heating device such as a microwave oven.

Conventionally, as this type of microwave heating device, for example, the device disclosed in Patent Document 1 is known. A conventional microwave heating device includes a heating chamber for accommodating an object to be heated, a microwave generating unit for generating microwaves, and a waveguide for propagating microwaves to the heating chamber. The waveguide is provided with a standing wave stabilizing portion for stabilizing the position of the standing wave in the tube generated in the waveguide. According to the conventional microwave heating device, the standing wave stabilizing portion suppresses the disturbance of the position of the standing wave in the pipe, so that the microwave having a desired phase can be continuously radiated into the heating chamber. As a result, the object to be heated in the heating chamber can be uniformly heated.

In Patent Documents 2 and 3, in order to prevent the microwave generating portion from being destroyed by the reflected wave returning from the heating chamber to the microwave generating portion, a directional coupler for detecting the reflected wave is provided in the waveguide. The microwave heating device is disclosed.

Japanese Patent No. 5816820 Japanese Patent No. 6176540 Japanese Patent No. 3331279

However, in the conventional microwave heating device, there is still room for improvement from the viewpoint of more accurately detecting the state of the object to be heated that changes as the heating progresses. In particular, there was no research example focusing on the relationship between the detection accuracy of reflected waves and the standing wave in the waveguide, and it was not clear where in the waveguide the directional coupler should be placed.

An object of the present disclosure is to provide a microwave heating device capable of improving the detection accuracy of reflected waves and more accurately detecting the state of an object to be heated.

The microwave heating device of one aspect of the present disclosure includes a heating chamber for accommodating an object to be heated, a microwave generating unit for generating microwaves, a waveguide, and a reflected wave detecting unit. The waveguide transmits the microwave generated by the microwave generator to the heating chamber. The reflected wave detection unit is arranged near the antinode of the standing wave in the tube generated in the waveguide, and detects a part of the reflected wave which is a microwave returning from the heating chamber to the microwave generation unit.

According to this aspect, the detection accuracy of the reflected wave can be improved, and the state of the object to be heated can be detected more accurately.

FIG. 1 is a schematic view of a microwave heating device according to an embodiment of the present disclosure. FIG. 2 is a schematic view showing a first modification of the microwave heating device according to the embodiment. FIG. 3 is a schematic view showing a second modification of the microwave heating device according to the embodiment. FIG. 4 is a schematic view showing a third modification of the microwave heating device according to the embodiment. FIG. 5 is a perspective view of the directional coupler according to the embodiment. FIG. 6 is a perspective view of the directional coupler according to the embodiment in a state where the printed circuit board is removed. FIG. 7 is a plan view of the waveguide according to the embodiment. FIG. 8 is a circuit configuration diagram of a printed circuit board provided in the directional coupler according to the embodiment. FIG. 9 is a diagram for explaining the principle of radiating circularly polarized microwaves from the cross aperture. FIG. 10 is a diagram for explaining the direction and amount of microwaves propagating through a microstrip line and changing over time. FIG. 11 is a diagram for explaining the direction and amount of microwaves propagating through a microstrip line and changing over time. FIG. 12 is a plan view showing a first modification of the microstrip line. FIG. 13 is a plan view showing a second modification of the microstrip line. FIG. 14 is a plan view showing a third modification of the microstrip line. FIG. 15 is a plan view showing a fourth modification of the microstrip line. FIG. 16 is a plan view showing a fifth modification of the microstrip line. FIG. 17 is a plan view showing a sixth modification of the microstrip line. FIG. 18 is a graph showing the relationship between the incident wave, the reflected wave, and the absorbed amount of the microwave of the heated object, which changes with the temperature rise of the heated object. FIG. 19 is a plan view showing an orthogonal waveguide for evaluating the detection accuracy of the reflected wave. FIG. 20 is a characteristic diagram in which the detection accuracy of the reflected wave is measured by the orthogonal waveguide for evaluation. FIG. 21 is a schematic view showing the positional relationship between the reflected wave detection unit and the standing wave in the waveguide in the waveguide.

(Knowledge on which this disclosure was based)
As a result of diligent studies to detect the state of the object to be heated more accurately, the present inventors have obtained the following findings.

The microwave generated by the microwave generator propagates as an incident wave to the heating chamber through the waveguide. A part of the microwave propagating in the heating chamber is absorbed by the object to be heated, while the other part returns from the heating chamber to the microwave generation part as a reflected wave through the waveguide.

Microwaves are not easily absorbed by ice, but are easily absorbed by water. Specifically, water absorbs about 8000 times more microwaves (based on the dielectric loss factor) than ice. Microwaves are less likely to be absorbed by water as the temperature of the water rises. Therefore, for example, when the object to be heated is a frozen food, the reflected wave and the amount of microwaves absorbed by the object to be heated have a relationship as shown in FIG.

FIG. 18 is a graph showing the relationship between the incident wave, the reflected wave, and the absorbed amount of the microwave of the heated object, which changes with the temperature rise of the heated object. In FIG. 18, the horizontal axis represents the temperature of the object to be heated, and the vertical axis represents the signal strength of the incident wave and the reflected wave. The graphs shown by the dotted line, solid line, and alternate long and short dash line show the amount of microwaves absorbed by the incident wave, reflected wave, and object to be heated, respectively. The amount of microwaves absorbed by the object to be heated is the difference between the incident wave and the reflected wave.

As shown in FIG. 18, in the initial stage of heating, the amount of microwaves absorbed by the object to be heated is small and the amount of reflected waves is large. As the heating progresses and the ice melts, the amount of microwaves absorbed by the object to be heated increases sharply, and the reflected waves sharply decrease. When the ice is completely melted, the amount of microwaves absorbed by the object to be heated is maximized and the reflected waves are minimized.

After that, as the temperature of water rises, the amount of microwaves absorbed by the object to be heated gradually decreases, and the reflected waves gradually increase. Therefore, for example, by detecting the state where the reflected wave is minimized, the end of thawing of the frozen food can be detected.

The present inventors have found that the above relationship holds regardless of the weight, shape, etc. of the object to be heated, and more accurately detect the state of the object to be heated based on the change in the amount of reflected waves during heating. I found out what I could do.

The microwave heating device of the first aspect of the present disclosure includes a heating chamber for accommodating an object to be heated, a microwave generating unit for generating microwaves, a waveguide, and a reflected wave detecting unit. The waveguide transmits the microwave generated by the microwave generator to the heating chamber. The reflected wave detection unit is arranged near the antinode of the standing wave in the tube generated in the waveguide, and detects a part of the reflected wave which is a microwave returning from the heating chamber to the microwave generation unit.

In the microwave heating device of the second aspect of the present disclosure, in addition to the first aspect, the reflected wave detection unit is arranged between the two nodes of the standing wave in the tube to obtain the standing wave in the tube. Placed near the belly.

In the microwave heating device of the third aspect of the present disclosure, in addition to the second aspect, the reflected wave detection unit is arranged so as not to overlap the two nodes of the standing wave in the tube, so that the standing wave in the tube is stationary. Placed near the antinode of the wave.

In the microwave heating device of the fourth aspect of the present disclosure, in addition to the third aspect, the reflected wave detection unit performs the in-tube wavelength of the in-tube standing wave back and forth from the central position of the two nodes of the in-tube standing wave. By arranging them at a distance of 1/8 or less of the above, they are arranged near the antinode of the standing wave in the tube.

In the microwave heating device of the fifth aspect of the present disclosure, in addition to the first aspect, the reflected wave detection unit is a distance of an odd multiple of 1/4 of the in-tube wavelength of the in-tube standing wave from the end of the waveguide. By being placed only apart, it is placed near the antinode of the standing wave in the tube.

In addition to the first aspect, the microwave heating device of the sixth aspect of the present disclosure further includes a standing wave stabilizing portion that stabilizes the position of the standing wave in the tube generated in the waveguide. The reflected wave detection unit is arranged near the antinode of the standing wave in the tube by being arranged at a distance of an odd multiple of 1/4 of the wavelength of the standing wave in the tube from the standing wave stabilizing unit.

In the microwave heating device of the seventh aspect of the present disclosure, in addition to the sixth aspect, the standing wave stabilizing portion is composed of a protrusion protruding into the waveguide.

In the microwave heating device of the eighth aspect of the present disclosure, in addition to the sixth aspect, the waveguide has an L-shaped bent bent portion, and the standing wave stabilizing portion is composed of the bent portion. Will be done.

In the microwave heating device of the ninth aspect of the present disclosure, in addition to the first aspect, the reflected wave detection unit has a wavelength of 1 of the tube wavelength of the standing wave in the tube from the coupling position between the microwave generation unit and the waveguide. By arranging them at a distance of an integral multiple of / 2, they are arranged near the antinode of the standing wave in the pipe.

In addition to the first aspect, the microwave heating device according to the tenth aspect of the present disclosure further includes a microwave emitting unit that radiates microwaves transmitted by a waveguide into a heating chamber. The reflected wave detection unit is located at a distance of an integral multiple of 1/2 the wavelength of the standing wave in the tube from the coupling position between the microwave emitting part and the waveguide, so that the antinode of the standing wave in the tube is located. Placed in the vicinity.

In the microwave heating device of the eleventh aspect of the present disclosure, in addition to the first aspect, the reflected wave detection unit has an opening provided in the waveguide and a coupling line facing the opening. The opening is placed near the antinode of the standing wave in the tube.

In the microwave heating device of the twelfth aspect of the present disclosure, in addition to the eleventh aspect, the openings include a first elongated hole and a second elongated hole that intersect with each other, and the tube of the waveguide is a tube in a plan view. The opening intersection, which is provided at a position not intersecting the axis and where the first elongated hole and the second elongated hole intersect, is arranged near the antinode of the standing wave in the pipe.

Hereinafter, the microwave heating device according to the embodiment of the present disclosure will be described with reference to the drawings.

(Embodiment)
FIG. 1 is a schematic view of a microwave heating device 50 according to an embodiment of the present disclosure. As shown in FIG. 1, the microwave heating device 50 includes a heating chamber 2 for accommodating an object to be heated 1, a magnetron 3, and a waveguide 10. The magnetron 3 is an example of a microwave generating unit that generates microwaves. The waveguide 10 transmits the microwave generated by the magnetron 3 to the heating chamber 2.

The object to be heated 1 is, for example, a frozen food. The heating chamber 2 is composed of, for example, a rectangular parallelepiped housing. The heating chamber 2 is provided with a mounting table 2a on which the object to be heated 1 is placed. The mounting table 2a is made of a material such as glass or ceramic that easily transmits microwaves.

The waveguide 10 is a rectangular waveguide having a rectangular cross section. The antenna 4 is arranged below the mounting table 2a. The microwave propagating in the waveguide 10 is radiated into the heating chamber 2 by the antenna 4, which is an example of the microwave radiation unit.

Due to this microwave, a standing wave in the tube of the microwave is generated in the waveguide 10 in the transmission direction of the microwave from the magnetron 3 to the antenna 4. FIG. 1 schematically illustrates an in-tube standing wave generated inside the waveguide 10. The in-tube wavelength λg of the waveguide 10 is determined by the oscillation frequency of the magnetron 3 and the shape of the waveguide 10.

The in-tube standing wave has antinodes and nodes that repeat every half the length of the in-tube wavelength λg in the longitudinal direction of the waveguide 10. A node is always generated at the end of the waveguide 10 in the microwave transmission direction. A belly is always generated in the portion where the magnetron 3 emits microwaves.

The waveguide 10 is provided with a standing wave stabilizing portion 5 for stabilizing the position of the standing wave in the tube generated in the waveguide 10. In the present embodiment, the standing wave stabilizing portion 5 is a protruding portion configured to locally narrow the waveguide 10 by projecting into the waveguide 10.

The standing wave stabilizing unit 5 matches the impedance in the vicinity of the magnetron 3 and the impedance in the vicinity of the heating chamber 2 in the waveguide 10. The standing wave stabilizing unit 5 is arranged at a distance of an integral multiple of 1/2 of the in-tube wavelength λg from the end of the waveguide 10 in the microwave transmission direction. As a result, the standing wave stabilizing unit 5 fixes the node of the standing wave in the pipe in the vicinity of the standing wave stabilizing unit 5.

On the wall surface (wide plane) of the waveguide 10, a directional coupler 6 having both functions of an incident wave detection unit and a reflected wave detection unit is provided. The incident wave detection unit detects a part of the incident wave, which is a microwave propagating from the magnetron 3 to the heating chamber 2. The reflected wave detection unit detects a part of the reflected wave which is a microwave returning from the heating chamber 2 to the magnetron 3.

The directional coupler 6 is arranged closer to the heating chamber 2 than the standing wave stabilizing portion 5. Specifically, the directional coupler 6 and the standing wave stabilizer 5 are microwaves by a distance of an odd multiple (1 times in this embodiment) of 1/4 of the in-tube wavelength λg of the in-tube standing wave. They are arranged apart from each other in the transmission direction (the left-right direction in FIG. 1). The directional coupler 6 is arranged between the standing wave stabilizer 5 and the antenna 4.

The directional coupler 6 detects the detection signal 6a and the detection signal 6b according to the incident wave and the reflected wave, respectively, and transmits the detection signal 6a and the detection signal 6b to the control unit 7. The specific configuration of the directional coupler 6 will be described in detail later.

The control unit 7 receives the signal 7a in addition to the detection signals 6a and 6b. The signal 7a includes the heating conditions set by the input unit (not shown) of the microwave heating device 50, the weight of the object to be heated 1 detected by the sensor (not shown), and the amount of steam.

The control unit 7 controls the drive power supply 8 and the motor 9 based on the detection signals 6a and 6b and the signal 7a. The drive power source 8 supplies electric power for generating microwaves to the magnetron 3. The motor 9 rotates the antenna 4. In this way, the microwave heating device 50 heats the object to be heated 1 housed in the heating chamber 2 by the microwave supplied to the heating chamber 2.

In the present embodiment, the directional coupler 6 is arranged closer to the heating chamber 2 than the standing wave stabilizing portion 5. According to this configuration, the influence of the directional coupler 6 on the standing wave stabilizing unit 5 can be reduced. Thereby, the state of the object to be heated 1 can be detected more accurately. As a result, for example, it is possible to accurately grasp the thawing status of frozen foods. By controlling the heating amount accordingly, it is possible to shorten the thawing time.

In the present embodiment, the directional coupler 6 and the standing wave stabilizing unit 5 are arranged apart from each other in the microwave transmission direction by an odd multiple of 1/4 of the in-tube wavelength λg of the in-tube standing wave. .. According to this configuration, the directional coupler 6 can be arranged in the vicinity of the antinode of the standing wave in the tube. Therefore, the amount of the reflected wave received by the directional coupler 6 can be increased to improve the detection accuracy of the reflected wave. As a result, the state of the object to be heated 1 can be detected more accurately.

The positions of the directional coupler 6 and the standing wave stabilizing portion 5 in the width direction (depth direction in FIG. 1) of the waveguide 10 are not particularly limited. The directional coupler 6 and the standing wave stabilizing portion 5 may be arranged at a distance of approximately 1/4 of the in-tube wavelength λg by an odd number of times.

If the temperature of the object to be heated 1 is high at the start of heating, or if the object to be heated 1 is heavy, the amount of reflected waves does not change much. Therefore, it may be difficult to determine the state in which the reflected wave is minimized.

In the present embodiment, the directional coupler 6 has the functions of both an incident wave detection unit and a reflected wave detection unit. According to this configuration, the amount of microwaves absorbed by the object to be heated 1 can be estimated more accurately based on the incident wave and the reflected wave detected by the directional coupler 6. For example, by detecting a change in reflectance obtained by dividing the amount of reflected waves by the amount of incident waves, it becomes easy to determine the state in which the reflected waves are minimized. As a result, the state of the object to be heated 1 can be detected more accurately.

In the present embodiment, the directional coupler 6 has the functions of both an incident wave detection unit and a reflected wave detection unit. However, this disclosure is not limited to this. The incident wave detection unit and the reflected wave detection unit may be provided separately. The incident wave detection unit may be arranged closer to the magnetron 3 than the standing wave stabilization unit 5.

In the present embodiment, one directional coupler 6 is provided closer to the heating chamber 2 than the standing wave stabilizing portion 5. However, this disclosure is not limited to this. FIG. 2 is a schematic view showing a first modification of the microwave heating device 50. Similar to FIG. 1, FIG. 2 schematically illustrates an in-tube standing wave generated inside the waveguide 10.

As shown in FIG. 2, the microwave heating device 50 according to the first modification further includes a directional coupler 60 having the same configuration as the directional coupler 6 in addition to the directional coupler 6. That is, the directional coupler 60 includes a second reflected wave detection unit having the same configuration as the reflected wave detection unit provided in the directional coupler 6. The directional coupler 60 is arranged closer to the magnetron 3 than the standing wave stabilizing portion 5.

According to this configuration, the second reflected wave detecting unit can also detect a part of the reflected wave that passes through the standing wave stabilizing unit 5 and returns to the magnetron 3. Thereby, for example, when the amount of reflected waves is very large, the magnetron 3 can be stopped to prevent the magnetron 3 from failing.

In the present embodiment, the standing wave stabilizing portion 5 is composed of a protruding portion protruding into the waveguide 10. However, the standing wave stabilizing unit 5 is not limited to the present embodiment as long as it stabilizes the position of the standing wave in the tube by locally narrowing the waveguide 10 and disturbing the propagation of microwaves.

FIG. 3 is a schematic view showing a second modification of the microwave heating device 50. Similar to FIGS. 1 and 2, FIG. 3 schematically illustrates an in-tube standing wave generated inside the waveguide 10. As shown in FIG. 3, the waveguide 10 has a bent portion 10b bent in an L shape.

In this case, the cross-sectional area of the bent portion 10b shown by the dotted line in FIG. 3 is larger than the cross-sectional area of the other portion of the waveguide 10. Therefore, the node of the standing wave in the pipe is easily fixed at the center of the bent portion 10b (the center of the dotted line in FIG. 3). In the second modification, the bent portion 10b constitutes the standing wave stabilizing portion 5.

The waveguide 10 shown in FIG. 1 is a rectangular waveguide having a uniform cross-sectional area except for a portion where the standing wave stabilizing portion 5 is arranged. However, this disclosure is not limited to this. FIG. 4 is a schematic view showing a third modification of the microwave heating device 50. Similar to FIGS. 1 to 3, FIG. 4 schematically illustrates an in-tube standing wave generated inside the waveguide 10.

As shown in FIG. 4, in the third modification, the waveguide 10 is a square waveguide whose cross-sectional area gradually decreases from the magnetron 3 toward the heating chamber 2. The waveguide 10 of the third modification has no locally narrowed portion other than the standing wave stabilizing portion 5. Therefore, the waveguide 10 of the third modification can obtain the same effect as the waveguide 10 shown in FIG.

The standing wave stabilizing unit 5 shown in FIG. 1 is composed of one element. However, the standing wave stabilizing unit 5 may be composed of a plurality of elements. In this case, the directional coupler 6 may be arranged closer to the heating chamber 2 than the components of the standing wave stabilizing portion 5 arranged closest to the heating chamber 2.

In this embodiment, the motor 9 rotates the antenna 4. However, this disclosure is not limited to this. For example, the antenna 4 may be an opening formed so as to radiate the microwave propagating in the waveguide 10 into the heating chamber 2 as a circularly polarized microwave.

Next, the configuration of the directional coupler 6 will be described. FIG. 5 is a perspective view of the directional coupler 6. FIG. 6 is a perspective view of the directional coupler 6 with the printed circuit board 12 removed. FIG. 7 is a plan view of the waveguide 10. FIG. 8 is a circuit configuration diagram of the printed circuit board 12 provided on the directional coupler 6.

1 to 4 show the directional coupler 6 provided on the bottom wall of the waveguide 10. However, FIGS. 5 and 6 show the directional coupler 6 provided on the upper wall of the waveguide 10 for ease of understanding. In the present embodiment, the cross section of the waveguide 10 orthogonal to the tube axis L1 has a rectangular shape. The tube axis L1 is the central axis in the width direction of the waveguide 10.

The directional coupler 6 includes a cross opening 11, a printed circuit board 12, and a support portion 14. The cross opening 11 is an X-shaped opening arranged on the wide surface 10a of the waveguide 10. The printed circuit board 12 is arranged outside the waveguide 10 so as to face the cross opening 11. The support portion 14 supports the printed circuit board 12 on the outer surface of the waveguide 10.

As shown in FIG. 7, the cross opening 11 is arranged at a position that does not intersect the tube axis L1 of the waveguide 10 in a plan view. The opening central portion 11c of the cross opening 11 is arranged apart from the tube axis L1 of the waveguide 10 by the dimension D1 in a plan view. The dimension D1 is, for example, 1/4 of the width of the waveguide 10. The cross opening 11 radiates the microwave propagating in the waveguide 10 toward the printed circuit board 12 as a circularly polarized microwave.

The opening shape of the cross opening 11 includes the width and height of the waveguide 10, the power level and frequency band of the microwave propagating in the waveguide 10, the power level of the circularly polarized microwave radiated from the cross opening 11, and the like. It is decided according to the conditions of.

For example, the width of the waveguide 10 is 100 mm, the height is 30 mm, the wall surface thickness of the waveguide 10 is 0.6 mm, the maximum power level of the microwave propagating in the waveguide 10 is 1000 W, and the frequency band is 2450 MHz. When the maximum power level of the circularly polarized microwave radiated from the cross opening 11 is about 10 mW, the length 11w and the width 11d of the cross opening 11 are determined to be 20 mm and 2 mm, respectively.

As shown in FIG. 8, the cross opening 11 includes a first elongated hole 11e and a second elongated hole 11f that intersect each other. The opening central portion 11c of the cross opening 11 coincides with the opening intersection where the first elongated hole 11e and the second elongated hole 11f intersect. The cross opening 11 is formed line-symmetrically with respect to the perpendicular line L2. The perpendicular line L2 is orthogonal to the pipe axis L1 and passes through the central portion 11c of the opening.

In the present embodiment, the first elongated hole 11e and the second elongated hole 11f intersect at an angle of 90 degrees. However, the present disclosure is not limited to this. The first elongated hole 11e and the second elongated hole 11f may intersect at an angle of 60 degrees or 120 degrees.

When the opening central portion 11c of the cross opening 11 is arranged at a position overlapping the tube axis L1 in a plan view, the electric field reciprocates along the microwave transmission direction without rotating. In this case, the cross aperture 11 emits linearly polarized microwaves.

If the central portion 11c of the opening deviates from the tube axis L1 even a little, the electric field rotates. However, when the opening central portion 11c is closer to the tube shaft L1 (the closer the dimension D1 is to 0 mm), a distorted rotating electric field is generated. In this case, the cross aperture 11 emits elliptically polarized microwaves.

In this embodiment, the dimension D1 is set to about 1/4 of the width of the waveguide 10. In this case, an electric field of rotation that is almost perfectly circular is generated. The cross opening 11 radiates microwaves having a substantially circularly polarized wave. Therefore, the rotation direction of the circularly polarized microwave becomes clearer. As a result, the incident wave and the reflected wave can be accurately separated and detected.

The printed circuit board 12 has a substrate back surface 12b facing the cross opening 11 and a substrate surface 12a on the side opposite to the substrate back surface 12b. The substrate surface 12a has a copper foil (not shown) formed so as to cover the entire substrate surface 12a as an example of the microwave reflecting member. This copper foil prevents the circularly polarized microwaves radiated from the cross opening 11 from passing through the printed circuit board 12.

As shown in FIG. 8, a microstrip line 13 which is an example of a coupling line is arranged on the back surface 12b of the substrate. The microstrip line 13 is composed of, for example, a transmission line having a characteristic impedance of approximately 50Ω. The microstrip line 13 is arranged so as to surround the opening central portion 11c of the cross opening 11.

Hereinafter, the effective length λ _re of the microstrip line 13 will be described. Assuming that the width of the microstrip line 13 is w, the thickness of the printed circuit board 12 is h, the speed of light is c, the frequency of electromagnetic waves is f, and the relative permittivity of the printed circuit board is ε _r , the effective length of the microstrip line 13 is λ. _re is expressed by the following equation. The effective length λ _re is the wavelength of the electromagnetic wave propagating in the microstrip line 13.

Specifically, the microstrip line 13 includes a first transmission line 13a and a second transmission line 13b. The first transmission line 13a has a first straight line portion 13aa which is an example of the first crossing line portion. The first straight line portion 13aa intersects the first elongated hole 11e at a position farther from the pipe axis L1 than the opening central portion 11c in a plan view. The first straight line portion 13aa extends away from the pipe axis L1 as it approaches the perpendicular line L2.

The second transmission line 13b has a second straight line portion 13ba, which is an example of the second crossing line portion. The second straight line portion 13ba intersects the second elongated hole 11f at a position farther from the pipe axis L1 than the opening central portion 11c in a plan view. The second straight line portion 13ba extends away from the pipe axis L1 as it approaches the perpendicular line L2. The first straight line portion 13aa and the second straight line portion 13ba are arranged line-symmetrically with respect to the perpendicular line L2.

The first transmission line 13a and the second transmission line 13b are connected to each other in a plan view outside the rectangular region E1 and at a position farther from the pipe axis L1 than the rectangular region E1. The first straight line portion 13aa intersects the first elongated hole 11e at a position closer to the opening tip portion 11ea than the opening central portion 11c in a plan view.

The first straight line portion 13aa is orthogonal to the first elongated hole 11e in a plan view. The second straight line portion 13ba intersects the second elongated hole 11f at a position closer to the opening tip portion 11fa than the opening central portion 11c in a plan view. The second straight line portion 13ba is orthogonal to the second elongated hole 11f in a plan view.

One end of the first transmission line 13a and one end of the second transmission line 13b are connected to each other outside the region overlapping the cross opening 11 in a plan view. One end of the first straight line portion 13aa is connected to one end of the second straight line portion 13ba outside the rectangular region E1 circumscribing the cross opening 11.

The first coupling point P1 is a point where the first straight line portion 13aa and the first elongated hole 11e intersect each other in a plan view. The second coupling point P2 is a point where the second straight line portion 13ba and the second elongated hole 11f intersect each other in a plan view. The straight line connecting the first coupling point P1 and the second coupling point P2 is defined as a virtual straight line L3. In the present embodiment, the total distance between the first transmission line 13a and the second transmission line 13b, which are farther from the tube axis L1 than the virtual straight line L3, is set to 1/4 of the _{effective length λ re.}

In a plan view, a line that passes through the central portion 11c of the opening and is parallel to the tube axis L1 is defined as a parallel line L4. In the present embodiment, the total distance between the first transmission line 13a and the second transmission line 13b, which are farther from the pipe axis L1 than the parallel line L4, is set to 1/2 of the _{effective length λ re.}

The first transmission line 13a includes a third straight line portion 13ab that connects the other end of the first straight line portion 13aa and the first output section 131. The first straight line portion 13aa and the third straight line portion 13ab are connected so as to form an obtuse angle (for example, 135 degrees).

The second transmission line 13b includes a fourth straight line portion 13bb that connects the other end of the second straight line portion 13ba and the second output section 132. The second straight line portion 13ba and the fourth straight line portion 13bb are connected so as to form an obtuse angle (for example, 135 degrees). The third straight line portion 13ab and the fourth straight line portion 13bb are arranged in parallel with the perpendicular line L2.

The first output unit 131 and the second output unit 132 are arranged outside the support unit 14 (see FIGS. 5 and 6) in a plan view. The first detection circuit 15 is connected to the first output unit 131. The first detection circuit 15 detects the level of the microwave signal and outputs the detected microwave signal level as a control signal. A second detection circuit 16 is connected to the second output unit 132. The second detection circuit 16 detects the level of the microwave signal and outputs the detected microwave signal level as a control signal.

In the present embodiment, the first detection circuit 15 and the second detection circuit 16 both include a smoothing circuit (not shown) composed of a chip resistor and a Schottky diode. The first detection circuit 15 rectifies the microwave signal from the first output unit 131 and converts the rectified microwave signal into a DC voltage. The converted DC voltage is output to the first detection output unit 18. The first detection output unit 18 transmits the detection signal 6a corresponding to the incident wave to the control unit 7 (see FIG. 1).

Similarly, the second detection circuit 16 rectifies the microwave signal from the second output unit 132 and converts the rectified microwave signal into a DC voltage. The converted DC voltage is output to the second detection output unit 19. The second detection output unit 19 transmits the detection signal 6b corresponding to the reflected wave to the control unit 7 (see FIG. 1).

The printed circuit board 12 has four holes (holes 20a, 20b, 20c, 20d) for attaching the printed circuit board 12 to the waveguide 10. A copper foil serving as a ground is formed around the holes 20a, 20b, 20c, and 20d on the back surface 12b of the substrate. The portion where the copper foil is formed has the same potential as the substrate surface 12a.

The printed circuit board 12 is fixed to the waveguide 10 by screwing it through the holes 20a, 20b, 20c, 20d to the support portion 14 with screws 201a, 201b, 201c, 201d (see FIG. 5).

As shown in FIG. 6, the support portion 14 has screw portions 202a, 202b, 202c, 202d for screwing the screws 201a, 201b, 201c, and 201d, respectively. The screw portions 202a, 202b, 202c, and 202d are formed on the flange portion provided on the support portion 14.

The support portion 14 has conductivity and is arranged so as to surround the cross opening 11 in a plan view. The support portion 14 functions as a shield that prevents the circularly polarized microwaves radiated from the cross opening 11 from leaking to the outside of the support portion 14.

The support portion 14 has a groove 141 and a groove 142 through which the third straight line portion 13ab and the fourth straight line portion 13bb of the microstrip line 13 pass. With this configuration, the first output section 131 and the second output section 132 of the microstrip line 13 can be arranged outside the support section 14. The grooves 141 and 142 function as an extraction unit for taking out the microwave signal propagating in the microstrip line 13 to the outside of the support unit 14. The grooves 141 and 142 can be formed by denting the flange portion of the support portion 14 so as to be separated from the printed circuit board 12.

5 and 6 show the connector 18a and the connector 19a connected to the first detection output unit 18 and the second detection output unit 19 shown in FIG. 8, respectively.

In the present embodiment, the directional coupler 6 has both functions of an incident wave detection unit and a reflected wave detection unit. However, this disclosure is not limited to this. The directional coupler 6 may be configured to have only one of the functions of the incident wave detection unit and the reflected wave detection unit. In this case, the directional coupler 6 is configured by replacing one of the first detection circuit 15 and the second detection circuit 16 shown in FIG. 8 with a terminating circuit (for example, a chip resistor of 50Ω).

Next, the operation and operation of the directional coupler 6 will be described.

First, with reference to FIG. 9, the principle of radiating circularly polarized microwaves from the cross aperture 11 will be described. In FIG. 9, the magnetic field distribution 10d generated in the waveguide 10 is shown by a dotted concentric ellipse. The direction of the magnetic field of the magnetic field distribution 10d is indicated by an arrow. The magnetic field distribution 10d moves in the waveguide 10 in the microwave transmission direction A1 with the passage of time.

At time t = t0 shown in FIG. 9A, the magnetic field distribution 10d is formed. At this time, the magnetic field indicated by the broken line arrow B1 excites the first elongated hole 11e of the cross opening 11. At the time t = t0 + t1 shown in FIG. 9B, the magnetic field indicated by the broken line arrow B2 excites the second elongated hole 11f of the cross opening 11.

At the time t = t0 + T / 2 (T is the period of the in-tube wavelength λg of the microwave) shown in FIG. 9C, the magnetic field indicated by the broken line arrow B3 excites the first elongated hole 11e of the cross opening 11. At the time t = t0 + T / 2 + t1 shown in FIG. 9D, the magnetic field indicated by the broken line arrow B4 excites the second elongated hole 11f of the cross opening 11. At time t = t0 + T, similarly to time t = t0, the magnetic field indicated by the broken line arrow B1 excites the first elongated hole 11e of the cross opening 11.

By sequentially repeating these states, a circularly polarized microwave rotating counterclockwise (microwave rotation direction 32) is radiated from the cross opening 11 to the outside of the waveguide 10.

Here, assuming that the microwave propagating along the arrow 30 shown in FIG. 7 is an incident wave and the microwave propagating along the arrow 31 is a reflected wave, the incident wave is in the same direction as the transmission direction A1 shown in FIG. Propagate. Therefore, as described above, the circularly polarized microwaves rotating counterclockwise are radiated from the cross opening 11 to the outside of the waveguide 10. On the other hand, the reflected wave propagates in the direction opposite to the transmission direction A1 shown in FIG. Therefore, a circularly polarized microwave rotating clockwise is radiated from the cross opening 11 to the outside of the waveguide 10.

Circularly polarized microwaves radiated out of the waveguide 10 couple to the microstrip line 13 facing the cross aperture 11. The microstrip line 13 outputs most of the microwaves radiated from the cross opening 11 by the incident waves propagating along the arrow 30 to the first output unit 131.

On the other hand, the microstrip line 13 outputs most of the microwaves radiated from the cross opening 11 by the reflected waves propagating along the arrow 31 to the second output unit 132. As a result, the incident wave and the reflected wave can be separated and detected with higher accuracy. This will be described in more detail with reference to FIG.

FIG. 10 is a diagram for explaining the direction and amount of microwaves propagating through the microstrip line 13 and changing with the passage of time. There is a gap between the microstrip line 13 and the cross opening 11. Originally, the time required for the microwave to reach the microstrip line 13 is delayed by the time for the microwave to propagate through this gap. However, for convenience, it is assumed that there is no time delay here.

Here, the region where the cross opening 11 and the microstrip line 13 intersect in a plan view is referred to as a coupling region. The first coupling point P1 is substantially the center of the coupling region where the first elongated hole 11e and the microstrip line 13 intersect. The second coupling point P2 is approximately the center of the coupling region where the second elongated hole 11f and the microstrip line 13 intersect.

In FIG. 10, the amount of microwaves propagating through the microstrip line 13 (current flowing due to the interlinking of magnetic fields) is represented by the thickness of the solid arrow line. That is, when the amount of microwaves propagating in the microstrip line 13 is large, the line is thick, and when the amount of microwaves propagating in the microstrip line 13 is small, the line is thin.

At time t = t0 shown in FIG. 10A, the magnetic field indicated by the broken line arrow B1 excites the first elongated hole 11e of the cross opening 11, and the microwave indicated by the thick solid arrow M1 is present at the first coupling point P1. Occurs. This microwave propagates on the microstrip line 13 toward the second coupling point P2.

At the time t = t0 + t1 shown in FIG. 10B, the magnetic field indicated by the broken line arrow B2 excites the second elongated hole 11f of the cross opening 11, and the microwave indicated by the thick solid arrow M2 is present at the second coupling point P2. Occurs.

When the effective propagation time of the microwave by the microstrip line 13 between the first coupling point P1 and the second coupling point P2 is designed to be time t1, it occurs at the first coupling point P1 at the time shown in FIG. 10 (a). The microwave propagates to the second coupling point P2 at the time shown in FIG. 10 (b). That is, at the time shown in FIG. 10B, the microwave indicated by the solid arrow M1 and the microwave indicated by the solid arrow M2 are generated at the second coupling point P2.

Therefore, the two microwaves are added and propagated along the microstrip line 13 toward the second output unit 132, and are output to the second output unit 132 after a predetermined time has elapsed. In the present embodiment, since the effective propagation time is set to the time t1, the total distance between the first transmission line 13a and the second transmission line 13b, which are farther from the tube axis L1 than the virtual straight line L3, is the effective length λ _re. It is set to 1/4 of. With this configuration, the design of the microstrip line 13 can be easily performed.

At the time t = t0 + T / 2 shown in FIG. 10 (c), the magnetic field indicated by the broken line arrow B3 excites the first elongated hole 11e of the cross opening 11, and the first coupling point P1 is the micro indicated by the thin solid arrow M3. Waves occur. This microwave propagates through the microstrip line 13 toward the first output unit 131, and is output to the first output unit 131 after a lapse of a predetermined time.

The reason why the thickness of the solid arrow M3 is made thinner than the thickness of the solid arrow M1 is as follows. Circularly polarized microwaves rotating counterclockwise (microwave rotation direction 32) are radiated from the cross opening 11 as described above.

At the time shown in FIG. 10A, the microwave indicated by the solid arrow M1 generated at the first coupling point P1 propagates in substantially the same direction as the rotation direction of the microwave radiated from the cross opening 11. Therefore, the energy of the microwave indicated by the solid arrow M1 is not reduced.

On the other hand, at the time shown in FIG. 10 (c), the microwave indicated by the solid arrow M3 generated at the first coupling point P1 propagates in a direction substantially opposite to the rotation direction of the microwave radiated from the cross opening 11. Therefore, the energy of the combined microwave is reduced. Therefore, the amount of microwaves indicated by the solid arrow M3 is smaller than the amount of microwaves indicated by the solid arrow M1.

At the time t = t0 + T / 2 + t1 shown in FIG. 10 (d), the magnetic field indicated by the broken line arrow B4 excites the second elongated hole 11f of the cross opening 11, and the second coupling point P2 is the micro indicated by the thin solid arrow M4. Waves occur. This microwave propagates toward the first coupling point P1. The reason for reducing the thickness of the solid line arrow M4 is the same as the reason for reducing the thickness of the solid line arrow M3 described above.

At time t = t0 + T, the magnetic field indicated by the broken line arrow B1 excites the first elongated hole 11e of the cross opening 11, similarly to the time t = t0 shown in FIG. 10 (a). In this case, the microwave indicated by the thin solid arrow M4, which was not described in the case of the time shown in FIG. 10A, exists on the microstrip line 13.

The microwave indicated by the thin solid arrow M4 propagates to the first coupling point P1 at time t = t0 + T (that is, t = t0). The microwave indicated by the thin solid arrow M4 propagates in the opposite direction to the microwave indicated by the thick solid arrow M1. Therefore, the microwave indicated by the solid arrow M4 is canceled and disappears, and is not output to the first output unit 131.

Strictly speaking, the amount of microwaves propagating from the first coupling point P1 at time t = t0 is the amount obtained by subtracting the amount of microwaves indicated by the thick solid arrow M1 from the amount of microwaves indicated by the thin solid arrow M4 (M1). -M4). Therefore, the amount of microwaves output to the second output unit 132 is the amount (M1 + M2-M4) obtained by adding the amount of microwaves indicated by the thick solid arrow M2 to the amount of microwaves propagating from the second coupling point P2. Become.

Even in consideration of this, the amount of microwaves (M1 + M2-M4) output to the second output unit 132 is much larger than the amount of microwaves (M3) output to the first output unit 131. Therefore, the microstrip line 13 outputs most of the microwaves radiated counterclockwise from the cross opening 11 to the second output unit 132 by the reflected waves propagating along the arrow 31. On the other hand, the microstrip line 13 outputs most of the microwaves radiated clockwise from the cross opening 11 by the incident wave propagating along the arrow 30 to the first output unit 131.

The amount of microwaves radiated from the cross opening 11 relative to the amount of microwaves propagating through the waveguide 10 is determined by the shape and dimensions of the waveguide 10 and the cross opening 11. For example, when set to the above shape and dimensions, the amount of microwaves radiated from the cross aperture 11 relative to the amount of microwaves propagating through the waveguide 10 is about 1/10000 (about −50 dB).

Next, in the present embodiment, the reason why the total distance between the first transmission line 13a and the second transmission line 13b, which are farther from the pipe axis L1 than the parallel line L4, is set to 1/2 of the _{effective length λ re.} explain.

FIG. 11 is a diagram for explaining the direction and amount of microwaves propagating through the microstrip line 13 and changing with the passage of time. 11 (a) to 11 (d) are diagrams showing a state in which t1 / 2 has elapsed from (a) to (d) of FIG.

Although the description is omitted above, the magnetic field distribution 10d moves in the waveguide 10 in the microwave transmission direction A1 with the passage of time. Therefore, as shown in FIGS. 11A to 11D, the magnetic fields indicated by the broken line arrows B12, B23, B34, and B41 excite the first elongated hole 11e and the second elongated hole 11f. As a result, the circularly polarized microwaves radiated outside the waveguide 10 are coupled to the microstrip line 13.

Here, the region where the perpendicular line L2 and the parallel line L4 intersect with the microstrip line 13 in a plan view is referred to as a coupling region. The third coupling point P3 is approximately the center of the coupling region where the perpendicular line L2 and the microstrip line 13 intersect. The fourth coupling point P4 is substantially the center of the coupling region where the parallel line L4 and the first transmission line 13a intersect. The fifth coupling point P5 is substantially the center of the coupling region where the parallel line L4 and the second transmission line 13b intersect.

At the time t = t0 + t1 / 2 shown in FIG. 11A, the magnetic field indicated by the broken line arrow B12 excites the cross opening 11, and the microwave indicated by the thick solid line arrow M11 is generated at the third coupling point P3. This microwave propagates on the microstrip line 13 toward the fifth coupling point P5.

At the time t = t0 + t1 + t1 / 2 shown in FIG. 11B, the magnetic field indicated by the broken line arrow B23 excites the cross opening 11. At the fifth coupling point P5, the microwave indicated by the thick solid arrow M12a is generated, and at the fourth coupling point P4, the microwave indicated by the thin solid arrow M12b is generated. The reason for reducing the thickness of the solid arrow M12b is the same as the reason for reducing the thickness of the solid arrow M3 described above.

When the effective propagation time of the microwave by the microstrip line 13 between the third coupling point P3 and the fifth coupling point P5 is designed to be time t1, it occurs at the third coupling point P3 at the time shown in FIG. 11 (a). The microwave propagates to the fifth coupling point P5 at the time shown in FIG. 11 (b). That is, at the time shown in FIG. 11B, the microwave indicated by the thick solid arrow M11 and the microwave indicated by the thick solid arrow M12a are generated at the fifth coupling point P5.

Therefore, the two microwaves are added and propagated along the microstrip line 13 toward the second output unit 132, and are output to the second output unit 132 after a lapse of a predetermined time. In order to set the effective propagation time to the time t1, in the present embodiment, the distance of the first transmission line 13a farther from the pipe axis L1 than the parallel line L4 is set to 1/4 of the _{effective length λ re.} .. The microwave indicated by the thin solid arrow M12b generated at the fourth coupling point P4 propagates through the microstrip line 13 toward the first output unit 131, and is output to the first output unit 131 after a lapse of a predetermined time.

At the time t = t0 + T / 2 + t1 / 2 shown in FIG. 11 (c), the magnetic field indicated by the broken line arrow B34 excites the cross opening 11, and the microwave indicated by the thin solid line arrow M13b is generated at the third coupling point P3. This microwave propagates along the microstrip line 13 toward the first output unit 131. The reason for reducing the thickness of the solid line arrow M13b is the same as the reason for reducing the thickness of the solid line arrow M3 described above.

At the time t = t0 + T / 2 + t1 + t1 / 2 shown in FIG. 11D, the magnetic field indicated by the broken line arrow B41 excites the cross opening 11. At the fifth coupling point P5, the microwave indicated by the thin solid arrow M14b is generated, and at the fourth coupling point P4, the microwave indicated by the thick solid arrow M14a is generated. The microwave indicated by the thin solid arrow M14b propagates through the microstrip line 13 toward the third coupling point P3. The reason for reducing the thickness of the solid line arrow M14b is the same as the reason for reducing the thickness of the solid line arrow M3 described above.

The microwave indicated by the thick solid arrow M14a propagates through the microstrip line 13 toward the third coupling point P3. When the effective propagation time of the microwave by the microstrip line 13 between the third coupling point P3 and the fourth coupling point P4 is designed to be time t1, it occurs at the third coupling point P3 at the time shown in FIG. 11 (c). The microwave propagates to the fourth coupling point P4 at the time shown in FIG. 11D.

That is, at the time shown in FIG. 11D, the microwave indicated by the thin solid arrow M13b and the microwave indicated by the thick solid arrow M14a are generated at the fourth coupling point P4. In order to set the effective propagation time to the time t1, in the present embodiment, the distance of the second transmission line 13b farther from the pipe axis L1 than the parallel line L4 is set to 1/4 of the _{effective length λ re.} ..

That is, the total distance between the first transmission line 13a and the second transmission line 13b, which are farther from the pipe axis L1 than the parallel line L4, is set to 1/2 of the _{effective length λ re.} The microwave indicated by the thin solid arrow M13b propagates in the opposite direction to the microwave indicated by the thick solid arrow M14a. Therefore, the microwave indicated by the thin solid line arrow M13b is canceled and disappears, and is not output to the first output unit 131.

At time t = t0 + T + t1 / 2, the magnetic field indicated by the broken line arrow B12 excites the cross opening 11 as at time t = t0 + t1 / 2 shown in FIG. 11 (a). In this case, the microwave indicated by the thin solid arrow M14b, which was not described in the case of the time shown in FIG. 11A, exists on the microstrip line 13.

The microwave indicated by the thin solid arrow M14b propagates to the third coupling point P3 at time t = t0 + T + t1 / 2. The microwave indicated by the thin solid arrow M14b propagates in the opposite direction to the microwave indicated by the thick solid arrow M11 and the thick solid arrow M14a. Therefore, the microwave indicated by the thin solid line arrow M14b is canceled and disappears, and is not output to the first output unit 131.

Strictly speaking, the amount of microwaves propagating from the third coupling point P3 at time t = t0 + t1 / 2 is the difference between the amount of microwaves indicated by the thick solid arrows M11 and M14a and the amount of microwaves indicated by the thin solid arrow M14b. (M11 + M14a-M14b). Therefore, the amount of microwaves output to the second output unit 132 is the amount obtained by adding the amount of microwaves indicated by the thick solid arrow M12a to the amount of microwaves propagating from the third coupling point P3 (M11 + M12a + M14a-M14b). Become.

Even in consideration of this, the amount of microwaves (M11 + M12a + M14a-M14b) output to the second output unit 132 is much larger than the amount of microwaves (M12b) output to the first output unit 131. Therefore, the microstrip line 13 outputs most of the microwaves radiated counterclockwise from the cross opening 11 by the reflected waves propagating in the direction of the arrow 31 to the second output unit 132. On the other hand, the microstrip line 13 outputs most of the microwaves radiated clockwise from the cross opening 11 by the incident wave propagating in the direction of the arrow 30 to the first output unit 131.

In the present embodiment, the incident wave detection unit and the reflected wave detection unit share a microstrip line 13 facing the cross opening 11 arranged on the wall surface of the waveguide 10. The incident wave detection unit extracts the incident wave from one end of the microstrip line 13. The reflected wave detection unit extracts the reflected wave from the other end of the microstrip line 13. With this configuration, the incident wave detection unit and the reflected wave detection unit can be miniaturized.

In the present embodiment, the directional coupler 6 has a cross opening 11 that emits circularly polarized microwaves and is arranged at a position that does not intersect the tube axis L1 of the waveguide 10 in a plan view. With this configuration, the rotation directions of the circularly polarized microwaves radiated from the cross opening 11 are opposite to each other for the incident wave and the reflected wave. By utilizing the difference in the rotation direction of the circularly polarized microwaves, the incident wave and the reflected wave can be detected separately.

In the directional coupler 6 according to the present embodiment, the first transmission line 13a includes a first straight line portion 13aa, and the second transmission line 13b includes a second straight line portion 13ba. With this configuration, the number of places where the microstrip line 13 bends can be reduced as compared with the conventional case. The need to bend the microstrip line 13 at a right angle can be eliminated. The bent portion of the microstrip line 13 can be separated from the vertical region of the cross opening 11. As a result, the incident wave and the reflected wave can be separated and detected with higher accuracy.

In the directional coupler 6 according to the present embodiment, the first transmission line 13a and the second transmission line 13b are connected to each other outside the rectangular region E1 in a plan view and at a position away from the pipe axis L1. Rectangle. With this configuration, the bent portion of the microstrip line 13 can be further separated from the vertical region of the cross opening 11. The first straight line portion 13aa and the second straight line portion 13ba can be made longer, and the flow of the current flowing through the microstrip line 13 can be suppressed from being obstructed. As a result, the incident wave and the reflected wave can be separated and detected with higher accuracy.

In the directional coupler 6 according to the present embodiment, the first straight line portion 13aa intersects the first elongated hole 11e at a position closer to the opening tip portion 11ea than the opening central portion 11c in a plan view. The second straight line portion 13ba intersects the second elongated hole 11f at a position closer to the opening tip portion 11fa than the opening central portion 11c in a plan view. Usually, a stronger magnetic field is generated around the opening tips 11ea and 11fa than around the opening center 11c. With the above configuration, a stronger magnetic field is coupled to the microstrip line 13. Therefore, the current flowing through the microstrip line 13 becomes larger. As a result, the incident wave and the reflected wave can be separated and detected with higher accuracy.

In the directional coupler 6 according to the present embodiment, the first straight line portion 13aa is orthogonal to the first elongated hole 11e in a plan view. With this configuration, the transmission direction of the microwave indicated by the solid arrow M1 generated at the first coupling point P1 is made the same as the rotation direction 32 of the microwave radiated from the cross opening 11. As a result, the amount of microwaves indicated by the solid arrow M1 can be further increased.

The transmission direction of the microwave indicated by the solid arrow M3 generated at the first coupling point P1 is reversed from the rotation direction 32 of the microwave radiated from the cross opening 11. As a result, the amount of microwaves indicated by the solid arrow M3 can be made smaller. As a result, the incident wave and the reflected wave can be separated and detected with higher accuracy.

In the directional coupler 6 according to the present embodiment, the second straight line portion 13ba is orthogonal to the second elongated hole 11f in a plan view. With this configuration, the transmission direction of the microwave indicated by the solid arrow M2 generated at the second coupling point P2 is made the same as the rotation direction 32 of the microwave radiated from the cross opening 11. As a result, the amount of microwaves indicated by the solid arrow M2 can be further increased.

The transmission direction of the microwave indicated by the solid arrow M4 generated at the second coupling point P2 is reversed from the rotation direction 32 of the microwave radiated from the cross opening 11. As a result, the amount of microwaves indicated by the solid arrow M4 can be made smaller. As a result, the incident wave and the reflected wave can be separated and detected with higher accuracy.

In the directional coupler 6 according to the present embodiment, the microstrip line 13 has a first straight line portion 13aa, a second straight line portion 13ba, a third straight line portion 13ab, and a fourth straight line portion 13bb. The first straight line portion 13aa and the third straight line portion 13ab adjacent to each other are connected so as to form an obtuse angle. The second straight line portion 13ba and the fourth straight line portion 13bb adjacent to each other are connected so as to form an obtuse angle.

With this configuration, it is possible to reduce the number of places where the microstrip line 13 bends at a right angle. As a result, it is possible to suppress the obstruction of the current flow in the coupling line. As a result, the incident wave and the reflected wave can be separated and detected with higher accuracy.

In the directional coupler 6 according to the present embodiment, the total distance between the first transmission line 13a and the second transmission line 13b, which are farther from the tube axis L1 than the virtual straight line L3, is 1/4 of the _{effective length λ re.} Set. With this configuration, the incident wave and the reflected wave can be separated and detected with higher accuracy. The total distance, if it is set to approximately 1/4 of the effective length lambda _re, need not necessarily be set to 1/4 of the effective length lambda _re.

In the directional coupler 6 according to the present embodiment, the total distance between the first transmission line 13a and the second transmission line 13b, which are farther from the pipe axis L1 than the parallel line L4, is halved of the _{effective length λ re.} Set. With this configuration, the incident wave and the reflected wave can be separated and detected with higher accuracy. The total distance, if it is set to approximately 1/2 of the effective length lambda _re, need not necessarily be set to 1/2 of the effective length lambda _re.

As shown in FIG. 8, in the present embodiment, one end of the first transmission line 13a and one end of the second transmission line 13b are connected so as to form a right angle. However, this disclosure is not limited to this. It suffices that one end of the first transmission line 13a is connected to one end of the second transmission line 13b at a position outside the region of the cross opening 11 in a plan view. In this region, the influence of the magnetic field is large.

12 to 17 are plan views showing first modification to sixth modification of the microstrip line 13, respectively. As shown in FIG. 12, the first transmission line 13a and the second transmission line 13b are bent so that the connection point between one end of the first transmission line 13a and one end of the second transmission line 13b is separated from the opening central portion 11c. You may be doing it.

As shown in FIG. 13, the first transmission line 13a and the second transmission line 13b are bent so that the connection point between one end of the first transmission line 13a and one end of the second transmission line 13b approaches the opening center portion 11c. You may be doing it. As shown in FIG. 14, the first transmission line 13a and the second transmission line 13b are curved so that the connection point between one end of the first transmission line 13a and one end of the second transmission line 13b approaches the opening central portion 11c. You may be doing it.

In the present embodiment, the first straight line portion 13aa and the second straight line portion 13ba correspond to the first crossing line portion and the second crossing line portion, respectively. However, this disclosure is not limited to this. As shown in FIG. 15, the first crossing line portion and the second crossing line portion may be the arc-shaped portion 13ac and the arc-shaped portion 13bc, respectively.

In the present embodiment, the third straight line portion 13ab and the fourth straight line portion 13bb are parallel to the perpendicular line L2. However, this disclosure is not limited to this. As shown in FIG. 16, the third straight line portion 13ab and the fourth straight line portion 13bb may be parallel to the parallel line L4.

In the present embodiment, the first transmission line 13a and the second transmission line 13b have a plurality of linear portions. However, this disclosure is not limited to this. As shown in FIG. 17, the first transmission line 13a and the second transmission line 13b may each be composed of one straight line portion.

In the present embodiment, the cross opening 11 is formed line-symmetrically with respect to the perpendicular line L2. The perpendicular line L2 is orthogonal to the pipe axis L1 and passes through the central portion 11c of the opening. However, this disclosure is not limited to this. The cross opening 11 does not have to be formed line-symmetrically with respect to the perpendicular line L2. For example, the first elongated hole 11e and the second elongated hole 11f may intersect at positions deviated from the central portion in the longitudinal direction of each. The length of the first elongated hole 11e and the length of the second elongated hole 11f may be different from each other.

In these cases, the opening intersection where the first elongated hole 11e and the second elongated hole 11f intersect is displaced from the opening central portion 11c. The cross opening 11 may be formed line-symmetrically with respect to a straight line slightly inclined with respect to the perpendicular line L2 in a plan view.

(New discoveries regarding the arrangement of standing waves in the pipe and reflected wave detectors)
FIG. 19 is a plan view of the orthogonal waveguide 251 for checking the detection accuracy of the reflected wave depending on the position of the reflected wave detection unit. As shown in FIG. 19, the orthogonal waveguide 251 has a main waveguide 252 and a sub-guide 253. The sub-waveguide 253 is orthogonal to the main waveguide 252 and is coupled to the main waveguide 252 via an X-shaped opening 254 and 255.

In order to quantitatively measure the reflected wave using a network analyzer, the terminal 256 of the main waveguide 252 is closed and short-circuited. Microwave 257 incident from port Q (not shown) of the network analyzer is completely reflected at the termination 256.

Part of the reflected wave returns to port Q. The remaining reflected wave is transmitted to the sub-waveguide 253 via the openings 254 and 255 and is divided into microwave 258 and microwave 259 within the sub-waveguide 253. Microwave 258 is transmitted to port S (not shown) of the network analyzer, and microwave 259 is transmitted to port T (not shown) of the network analyzer.

Both the main waveguide 252 and the sub-guide tube 253 have a symmetrical shape. The openings 254 and 255 have the same shape. The openings 254 and 255 are arranged symmetrically with respect to both the main waveguide 252 and the sub-waveguide 253. Therefore, the amount of microwave 258 and the amount of microwave 259 are equivalent.

The main waveguide 252 and the sub-guide 253 have a waveguide width (usually referred to as a dimension) of about 100 mm. The in-tube wavelength λg of microwaves in the main waveguide 252 and the sub-guide tube 253 is about 154 mm.

The S-parameters actually observed are general observation values of a network analyzer. Specifically, the ratio S31 of the microwave 258 transmitted to the port S to the microwave 257 incident from the port Q and the ratio S41 of the microwave 259 transmitted to the port T to the microwave 257 incident from the port Q. And are observed with a network analyzer. The ratios S31 and S41 may be considerably smaller than 1, and are generally expressed in decibels.

Using microwaves having a frequency of 2450 to 2500 MHz, the ratios S31 and S41 are measured while changing the distance Lsf from the terminal 256 of the main waveguide 252 to the openings 254 and 255. FIG. 20 is a graph of the results. The horizontal axis represents the distance Lsf [mm], and the vertical axis represents the ratios S31 and S41 [dB]. Consider this result.

In the main waveguide 252, a node of an in-tube standing wave is generated at the closed end 256, and a node is generated from the end 256 every 1/2 (= 77 mm) of the in-tube wavelength λg. Therefore, when the distance Lsf is 154 mm, the openings 254 and 255 are arranged at the nodes.

Since a belly is generated at a position deviated from the node by λg / 4 (= 38.5 mm), when the distances Lsf are 115.5 mm (= λg × 3/4) and 192.5 mm (= λg × 5/4). , Openings 254 and 255 are arranged at the abdominal position. The present inventors have found the following two features from this characteristic diagram.

The first feature is related to sensitivity. When the opening is at the node position (distance Lsf = 154 mm), the ratios S31 and S41 are -12 to -21 dB. When the opening is at the abdominal position (distance Lsf = 115.5 mm, 192.5 mm), the ratios S31 and S41 are -4 to -8 dB. Therefore, the ratios S31 and S41 are larger when the opening is arranged at the abdominal position than when the opening is arranged at the node position.

That is, the present inventors have found that when an opening is arranged in the abdomen, the reflected wave detected from the opening becomes large and the sensitivity is improved. Comparing the average values of the six graphs shown in FIG. 20, the difference between the ratio when the opening is in the node (about -16 dB) and the ratio when the opening is in the abdomen (about -6 dB) is 10 dB. That is, when the opening is arranged at the abdominal position, the sensitivity is 10 times higher than when the opening is arranged at the node position.

The second feature is frequency stability. When the opening is at the node position (distance Lsf = 154 mm), the ratios S31 and S41 observed according to the change in frequency are -12 to -21 dB. When the opening is at the abdominal position (distance Lsf = 115.5 mm, 192.5 mm), the ratios S31 and S41 observed according to the change in frequency are -4 to -8 dB.

Therefore, the fluctuation range (about 4 dB) of the ratios S31 and S41 when the opening is in the abdominal position is smaller than the fluctuation range (about 9 dB) of the ratios S31 and S41 when the opening is in the node position. That is, the present inventors have found that placing an opening in the abdomen improves the stability of the reflected wave detected from the opening with respect to the frequency.

As described above, by detecting the reflected wave at the antinode of the standing wave in the tube, the sensitivity and the stability with respect to the frequency can be improved. As a result, the state of the object to be heated 1 can be detected more accurately.

Next, the case where the opening is arranged at the position between the position of the belly (distance Lsf = 115.5 mm, 192.5 mm) and the position of the node (distance Lsf = 154 mm) will be considered.

As shown in FIG. 20, the ratios S31 and S41 when the opening is arranged at the intermediate position of the abdomen and the node (distance Lsf = 134.75 mm, 173.25 mm) are the positions of the node (distance Lsf = 154 mm). Not as bad as when placed in. The ratios S31 and S41 in this case are rather close to the case where the opening is arranged at the abdominal position (distance Lsf = 115.5 mm, 192.5 mm), which is quite good.

That is, the measurement result is extremely poor only when the opening is arranged near the position of the node (distance Lsf = 154 mm). Therefore, as long as the opening is not arranged at the node position, the detection accuracy of the reflected wave can be improved to some extent.

More safely, the accuracy of the reflected wave detection can be improved by arranging the opening closer to the abdomen than the intermediate position between the abdomen and the node (distance Lsf = 134.75 mm, 173.25 mm). These positions are separated from the exact antinode position (or the position of the center of the two nodes) of the standing wave in the tube by 1/8 or less of the wavelength λg in the tube before and after.

Specifically, the ratios S31 and S41 at these positions are approximately in the range of -5 to -9 dB. With respect to sensitivity, the average value of the six graphs shown in FIG. 20 is about -16 dB when the opening is placed at the node position and about -6 dB when the opening is placed at the belly position, between the belly and the node. When the opening is arranged at the position, it is -7 dB.

That is, the ratios S31 and S41 when the opening is arranged at the intermediate position between the abdomen and the node are 9 dB better than when the opening is arranged at the node position, and the difference from the case where the opening is arranged at the abdomen position is 1 dB. Not too much.

With respect to frequency stability, the fluctuation range of the six graphs shown in FIG. 20 is about 9 dB when the opening is placed at the node position and about 2 dB when the opening is placed at the belly position. When the opening is arranged at the intermediate position, it is about 4 dB.

That is, the ratios S31 and S41 when the opening is arranged at the intermediate position between the abdomen and the node are considerably better than when the opening is arranged at the node position, and are rather close to the case where the opening is arranged at the abdominal position. .. Therefore, the detection accuracy of the reflected wave can be improved by arranging the opening at a position separated from the position of the abdomen (or the position of the center of the two nodes) by 1/8 or less of the in-tube wavelength λg.

(Each aspect and action / effect of the present disclosure)
With reference to FIG. 21, the positional relationship between the standing wave in the pipe and the arrangement of the reflected wave detection unit, and each aspect of the present disclosure will be described. FIG. 21 is an enlarged view of the periphery of the waveguide 10 in FIG.

As shown in FIG. 21, the microwave heating device of one aspect of the present disclosure includes a heating chamber 2 for accommodating an object to be heated, a magnetron 3 for generating microwaves, a waveguide 10, and a directional coupler 6. And.

The waveguide 10 transmits the microwave generated by the magnetron 3 to the heating chamber. The directional coupler 6 is arranged in the vicinity of the antinode 302 of the in-tube standing wave 301 generated in the waveguide 10. The directional coupler 6 includes a reflected wave detection unit that detects a part of the reflected wave that is a microwave returning from the heating chamber 2 to the magnetron 3.

The antinode 302 and the node 303 of the in-tube standing wave 301 appear alternately every 1/4 of the in-tube wavelength λg.

With this configuration, the reflected wave can be detected in the vicinity of the antinode 302 of the standing wave 301 in the pipe. Thereby, the detection accuracy of the reflected wave can be improved, and the state of the object to be heated 1 can be detected more accurately.

In the microwave heating device of one aspect of the present disclosure, the reflected wave detection unit is provided by arranging the central portion of the rectangular region E1 circumscribing the cross opening 11 between the two nodes 303 of the standing wave 301 in the pipe. The including directional coupler 6 is arranged in the vicinity of the antinode 302 of the in-tube standing wave 301.

With this configuration, the reflected wave can be detected in the vicinity of the antinode 302 of the standing wave 301 in the pipe. Thereby, the detection accuracy of the reflected wave can be improved, and the state of the object to be heated 1 can be detected more accurately.

It is difficult to determine the position of the antinode 302 of the invisible invisible standing wave 301. The directional coupler 6 can be easily positioned by using the position between two adjacent nodes 303 as a guide.

In the microwave heating device of one aspect of the present disclosure, the rectangular region E1 circumscribing the cross opening 11 is arranged so as not to overlap the two nodes 303 of the standing wave 301 in the pipe, so that the reflected wave detection unit is included. The directional coupler 6 is arranged in the vicinity of the antinode 302 of the in-tube standing wave 301.

With this configuration, the reflected wave can be detected at a position closer to the antinode 302 of the standing wave 301 in the pipe. Thereby, the detection accuracy of the reflected wave can be improved, and the state of the object to be heated 1 can be detected more accurately.

In the microwave heating device of one aspect of the present disclosure, the directional coupler 6 including the reflected wave detection unit is 1/8 or less of the in-tube wavelength λg in the front-rear direction from the central position of the two nodes 303 of the in-tube standing wave 301. By being arranged only apart from each other, it is arranged in the vicinity of the antinode 302 of the standing wave 301 in the pipe.

As described with reference to FIG. 20, the reflected wave can be detected with a certain degree of accuracy if the position is separated from the antinode 302 by 1/8 or less of the in-tube wavelength λg. Thereby, the detection accuracy of the reflected wave can be improved, and the state of the object to be heated 1 can be detected more accurately.

In the microwave heating device of one aspect of the present disclosure, the directional coupler 6 including the reflected wave detection unit is an odd multiple of 1/4 of the in-tube wavelength λg from the terminal 304 of the waveguide 10 (3 times in FIG. 21). By arranging them apart by the distance of, they are arranged in the vicinity of the antinode 302 of the standing wave 301 in the pipe.

With this configuration, the reflected wave can be detected in the vicinity of the antinode 302 of the standing wave 301 in the pipe. Thereby, the detection accuracy of the reflected wave can be improved, and the state of the object to be heated 1 can be detected more accurately.

The microwave heating device of one aspect of the present disclosure further includes a standing wave stabilizing portion 5 for stabilizing the position of the standing wave 301 in the tube generated in the waveguide 10. The directional coupler 6 including the reflected wave detection unit is arranged at a distance of an odd number of 1/4 (1 time in FIG. 21) of the wavelength λg in the tube from the standing wave stabilizing unit 5 to determine the inside of the tube. It is arranged in the vicinity of the antinode 302 of the standing wave 301.

With this configuration, the reflected wave can be detected in the vicinity of the antinode 302 of the standing wave 301 in the pipe. Thereby, the detection accuracy of the reflected wave can be improved, and the state of the object to be heated 1 can be detected more accurately.

In the microwave heating device of one aspect of the present disclosure, the standing wave stabilizing portion 5 is composed of a protruding portion protruding into the waveguide 10.

In this configuration, a node 303 of the standing wave 301 in the pipe is generated at the position of the protrusion. The directional coupler 6 including the reflected wave detection unit is arranged at a distance of an odd multiple of 1/4 of the in-tube wavelength λg from the protrusion, and detects the reflected wave in the vicinity of the antinode 302 of the in-tube standing wave 301. .. Thereby, the detection accuracy of the reflected wave can be improved, and the state of the object to be heated 1 can be detected more accurately.

In the microwave heating device of one aspect of the present disclosure, even if the waveguide 10 has an L-shaped bent portion 10b (see FIG. 3) and the standing wave stabilizing portion is composed of the bent portion 10b. Good.

In this configuration, a node 303 of the standing wave 301 in the pipe is generated at the position of the bent portion 10b. The directional coupler 6 including the reflected wave detection unit is arranged at a distance of an odd multiple of 1/4 of the in-tube wavelength λg from the bent portion 10b, and detects the reflected wave at the position of the antinode 302 of the in-tube standing wave 301. To do. Thereby, the detection accuracy of the reflected wave can be improved, and the state of the object to be heated 1 can be detected more accurately.

In the microwave heating device of one aspect of the present disclosure, the directional coupler 6 including the reflected wave detection unit is an integral multiple of 1/2 of the in-tube wavelength λg from the coupling position 305 of the magnetron 3 and the waveguide 10 (FIG. By arranging them at a distance of (twice as much as 21), they are arranged near the antinode 302 of the standing wave 301 in the pipe.

In this configuration, the antinode 302 of the in-tube standing wave 301 is generated at the coupling position 305. The directional coupler 6 including the reflected wave detection unit is arranged at a distance of an integral multiple of 1/2 of the in-tube wavelength λg from the coupling position 305, and detects the reflected wave in the vicinity of the antinode 302 of the in-tube standing wave 301. To do. Thereby, the detection accuracy of the reflected wave can be improved, and the state of the object to be heated 1 can be detected more accurately.

The microwave heating device of one aspect of the present disclosure has an antenna 4 that radiates microwaves transmitted by the waveguide 10 to the heating chamber 2. The directional coupler 6 including the reflected wave detection unit is arranged at a distance of an integral multiple (1 time in FIG. 21) of 1/2 of the in-tube wavelength λg from the coupling position 306 of the antenna 4 and the waveguide 10. As a result, it is arranged in the vicinity of the antinode 302 of the standing wave 301 in the pipe.

In this configuration, the antinode 302 of the in-tube standing wave 301 is generated at the coupling position 306. The directional coupler 6 including the reflected wave detection unit is arranged at a distance of an integral multiple of 1/2 of the in-tube wavelength λg from the coupling position 306, and detects the reflected wave in the vicinity of the antinode 302 of the in-tube standing wave 301. To do. Thereby, the detection accuracy of the reflected wave can be improved, and the state of the object to be heated 1 can be detected more accurately.

In the microwave heating device of one aspect of the present disclosure, the directional coupler 6 including the reflected wave detection unit has a cross opening 11 provided in the waveguide 10 and a coupling line facing the cross opening 11 (see FIG. 8). ) And. The cross opening 11 is arranged in the vicinity of the antinode 302 of the standing wave 301 in the pipe.

With this configuration, the reflected wave can be detected at the position of the antinode 302 of the standing wave 301 in the pipe. Thereby, the detection accuracy of the reflected wave can be improved, and the state of the object to be heated 1 can be detected more accurately.

In the microwave heating device of one aspect of the present disclosure, the cross opening 11 includes a first elongated hole 11e and a second elongated hole 11f that intersect each other (see FIGS. 7 and 8), and the waveguide 10 is viewed in a plan view. It is installed at a position that does not intersect with the pipe axis of. The opening intersection (see FIGS. 7 and 8) where the first elongated hole 11e and the second elongated hole 11f intersect is arranged in the vicinity of the antinode 302 of the standing wave 301 in the pipe.

With this configuration, the microwave transmitted by the waveguide 10 is radiated to the heating chamber 2 as a circularly polarized microwave whose direction of the electric field rotates around the aperture intersection. With respect to the circularly polarized microwave, since the incident wave and the reflected wave have opposite rotation directions, the incident wave and the reflected wave can be easily separated. In addition to this, in this configuration, the reflected wave is detected in the vicinity of the antinode 302 of the standing wave in the tube. Thereby, the detection accuracy of the reflected wave can be improved, and the state of the object to be heated 1 can be detected more accurately.

The present disclosure is applicable to consumer or commercial microwave heating devices.

1 Heated object 2 Heating chamber 2a Mounting stand 3 Magnetron 4 Antenna 5 Standing wave stabilizer 6, 60 Directional coupler 7 Control unit 7a Signal 8 Drive power supply 9 Motor 10 Waveguide 10a Wide surface 10b Bending part 10d Magnetic field distribution 11 Cross opening 11c Opening center 11d Width 11e 1st slot 11ea, 11fa Opening tip 11f 2nd slot 11w Length 12 Printed board 12a Board surface 12b Board back side 13 Microstrip line 13a 1st transmission line 13aa 1st straight line Part 13ab 3rd straight part 13ac, 13bc Arc-shaped part 13b 2nd transmission line 13ba 2nd straight part 13bb 4th straight part 14 Support part 15 1st waveguide 16 2nd waveguide 18 1st waveguide 18a, 19a Connector 19 2nd detection output unit 50 Microwave heating device 131 1st output unit 132 2nd output unit 141, 142 Groove 251 Orthogonal waveguide 252 Main waveguide 253 Sub-waveguide 254, 255 Opening 256, 304 Termination 257, 258 259 Microwave 301 In-tube standing wave 302 Abdominal 303 Section 305, 306 Connection position E1 Rectangular region L1 Tube axis L2 Vertical line L3 Virtual straight line L4 Parallel line P1 First connection point P2 Second connection point P3 Third connection point P4 Fourth Bonding point P5 5th coupling point

Claims (12)

A heating chamber configured to accommodate the object to be heated,
A microwave generator configured to generate microwaves,
A waveguide configured to transmit the microwave generated by the microwave generator to the heating chamber, and a waveguide configured to transmit the microwave to the heating chamber.
A reflected wave arranged in the vicinity of the antinode of the stationary wave in the tube generated in the waveguide and configured to detect a part of the reflected wave which is the microwave returning from the heating chamber to the microwave generating portion. A microwave heating device including a detector. The microwave heating device according to claim 1, wherein the reflected wave detection unit is arranged between two nodes of the in-tube standing wave so as to be arranged in the vicinity of the antinode of the in-tube standing wave. .. The micro according to claim 2, wherein the reflected wave detection unit is arranged in the vicinity of the antinode of the in-tube standing wave by arranging so as not to overlap the two nodes of the in-tube standing wave. Wave heating device. The reflected wave detection unit is arranged in front of and behind the center position of the two nodes of the standing wave in the tube so as to be separated from the standing wavelength in the tube by 1/8 or less of the wavelength in the tube. The microwave heating device according to claim 3, which is arranged in the vicinity of the antinode of the wave. By arranging the reflected wave detection unit at a distance of an odd multiple of 1/4 of the in-tube wavelength of the in-tube standing wave from the end of the waveguide, the vicinity of the antinode of the in-tube standing wave The microwave heating device according to claim 1, which is arranged in. It further has a standing wave stabilizing section configured to stabilize the position of the standing wave in the tube, and the reflected wave detecting section is from the standing wave stabilizing section to 1 / of the in-tube wavelength of the standing wave in the tube. The microwave heating device according to claim 1, wherein the microwave heating device is arranged in the vicinity of the antinode of the standing wave in the pipe by being arranged at a distance of an odd multiple of 4. The microwave heating device according to claim 6, wherein the standing wave stabilizing portion is composed of a protruding portion protruding into the waveguide. The microwave heating device according to claim 6, wherein the waveguide has an L-shaped bent portion, and the standing wave stabilizing portion is composed of the bent portion. The reflected wave detection unit is arranged at a distance of an integral multiple of 1/2 of the in-tube wavelength of the in-tube standing wave from the coupling position between the microwave generation unit and the waveguide. The microwave heating device according to claim 1, which is arranged in the vicinity of the antinode of the informal standing wave. Further having a microwave emitting unit configured to radiate the microwave transmitted by the waveguide to the heating chamber, the reflected wave detecting unit includes the microwave emitting unit and the waveguide. The first aspect of the present invention, wherein the standing wave in the tube is arranged in the vicinity of the antinode of the standing wave in the tube by being arranged at a distance of an integral multiple of 1/2 of the wavelength in the tube of the standing wave in the tube. Microwave heating device. The reflected wave detection unit has an opening provided in the waveguide and a coupling line facing the opening, and the opening is arranged in the vicinity of the antinode of the standing wave in the tube. The microwave heating device according to claim 1. The opening includes a first elongated hole and a second elongated hole that intersect each other, and is provided at a position that does not intersect the tube axis of the waveguide in a plan view. The first elongated hole and the second elongated hole are provided. The microwave heating device according to claim 11, wherein the opening intersection where the waves intersect with each other is arranged in the vicinity of the antinode of the standing wave in the pipe.

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