JP7454770B2 - Directional coupler and microwave heating device equipped with it - Google Patents

Description

The present disclosure relates to a directional coupler that detects the power level of microwaves propagating in a waveguide, and a microwave heating device equipped with the same.

A directional coupler is known as a device for detecting the power level of microwaves propagating in a waveguide. A directional coupler separates a traveling wave and a reflected wave propagating through a waveguide and detects each.

As a conventional directional coupler, for example, a directional coupler described in Patent Document 1 is known. The directional coupler of Patent Document 1 includes an opening disposed on the wall surface of a waveguide and a coupling line disposed outside the waveguide. The opening is disposed at a position that does not intersect the tube axis of the waveguide in plan view, and is formed to radiate circularly polarized microwaves. The coupled line includes a first transmission line and a second transmission line that cross the opening in plan view. The first transmission line and the second transmission line are arranged to face each other across the center of the opening, and are connected to each other at a position outside the area vertically above the opening.

According to the directional coupler of Patent Document 1, the rotating direction of the circularly polarized traveling wave emitted from the aperture is opposite to that of the circularly polarized reflected wave. Utilizing such a difference in the rotation direction of the circularly polarized microwave, it is possible to separate the traveling wave and the reflected wave and detect each one.

Patent No. 6176540

However, in the conventional directional coupler described above, there is still room for improvement in terms of separating and detecting the traveling wave and the reflected wave with higher accuracy.

Therefore, an object of the present disclosure is to provide a directional coupler that can separate and detect traveling waves and reflected waves with higher accuracy, and a microwave heating device equipped with the same.

In order to solve the conventional problems, the directional coupler in the present disclosure includes:
Directionality that includes an opening disposed in a wall surface of a waveguide and a coupling line disposed outside the waveguide, and separates and detects a traveling wave propagating in the waveguide and a reflected wave. A coupler,
The opening has a first elongated hole and a second elongated hole that intersect with each other and are arranged at a position that does not intersect with the tube axis of the waveguide in a plan view,
The coupled line includes a first transmission line and a second transmission line,
The first transmission line and the second transmission line are connected,
The first transmission line has a first crossing line part, and the first crossing line part is an opening crossing part where the first elongated hole and the second elongated hole intersect from one end side of the tube axis in a plan view. extending away from the tube axis as it approaches a perpendicular line perpendicular to the tube axis, intersecting the first elongated hole at a position farther from the tube axis than the opening intersection,
The second transmission line has a second intersection line portion, and the second intersection line portion extends away from the tube axis as it approaches the perpendicular line from the other end side of the tube axis in plan view, It is configured to intersect with the second elongated hole at a position farther from the tube axis than the opening intersection.

According to the directional coupler of the present disclosure, a traveling wave and a reflected wave can be separated and detected with higher accuracy.

FIG. 1 is a perspective view of a directional coupler according to an embodiment of the present disclosure. FIG. 2 is a perspective view of the directional coupler according to the embodiment with the printed circuit board removed. FIG. 2 is a plan view of a waveguide according to an embodiment. FIG. 3 is a circuit configuration diagram of a printed circuit board provided in the directional coupler according to the embodiment. FIG. 3 is a diagram for explaining the principle of circularly polarized microwaves being radiated from a cross aperture. FIG. 3 is a diagram for explaining the direction and amount of microwaves that propagate through a microstrip line and change over time. FIG. 3 is a diagram for explaining the direction and amount of microwaves that propagate through a microstrip line and change over time. It is a top view which shows the 1st modification of a microstrip line. It is a top view which shows the 2nd modification of a microstrip line. It is a top view which shows the 3rd modification of a microstrip line. It is a top view which shows the 4th modification of a microstrip line. It is a top view which shows the 5th modification of a microstrip line. It is a top view which shows the 6th modification of a microstrip line. 1 is a schematic diagram of a microwave heating device according to an embodiment.

The inventors of the present invention have made extensive studies to separate and detect traveling waves and reflected waves with higher accuracy, and have obtained the following findings.

In conventional directional couplers, the coupled line is constructed by connecting multiple lines parallel to the tube axis in plan view and multiple lines perpendicular to the tube axis in plan view at right angles as a single line. be done. With this configuration, the influence of the impedance of the load connected to the waveguide can be alleviated, and the traveling wave and the reflected wave can be separated with high accuracy.

The present inventors have discovered that where the coupled line bends at a right angle (or an acute angle), the magnetic field concentrates and the flow of current (microwaves) in the coupled line is obstructed, resulting in a degree of separation between the traveling wave and the reflected wave. We found that it affects The present inventors have found that in conventional directional couplers, there are many places where the coupling line is bent at right angles, and these bends greatly affect the degree of separation between the traveling wave and the reflected wave. The present inventors have proposed that by moving the bending point of the coupled line away from the area in the vertical direction of the opening where the influence of the magnetic field is strong, the current flow within the coupled line is prevented from being obstructed. I found out.

Based on these findings, the present inventors discovered the following invention. The present inventors have confirmed that these inventions improve the directionality (degree of separation between traveling waves and reflected waves) by 5 dB or more (approximately 3 times or more) compared to conventional directional couplers.

A directional coupler according to a first aspect of the present disclosure includes an opening disposed in a wall surface of a waveguide and a coupling line disposed outside the waveguide, and includes a traveling wave propagating in the waveguide. and the reflected wave are separated and detected.

The opening has a first elongated hole and a second elongated hole that intersect with each other and are arranged at a position that does not intersect with the tube axis of the waveguide in a plan view. The coupled line includes a first transmission line and a second transmission line, and the first transmission line and the second transmission line are connected.

The first transmission line has a first crossing line portion. The first intersection line portion moves away from the tube axis as it approaches a perpendicular line perpendicular to the tube axis, passing through the opening intersection where the first elongated hole and the second elongated hole intersect from one end of the tube axis in plan view. It extends and intersects with the first elongated hole at a position farther from the tube axis than the opening intersection.

The second transmission line has a second crossing line portion. The second intersection line portion extends away from the tube axis as it approaches the perpendicular line from the other end of the tube axis in plan view, and forms a second elongated hole at a position farther from the tube axis than the opening intersection. intersect.

In the directional coupler of the second aspect of the present disclosure, in addition to the first aspect, the first transmission line and the second transmission line are located outside a rectangular area circumscribing the opening in plan view, and They are connected to each other at a position farther from the tube axis than the rectangular area.

In the directional coupler according to the third aspect of the present disclosure, in addition to the first aspect, at least one of the first intersecting line part and the second intersecting line part is connected to the corresponding first elongated hole or the second intersecting line part in plan view. It intersects the elongated hole at a position closer to the opening tip than the opening intersection.

In the directional coupler according to the fourth aspect of the present disclosure, in addition to the first aspect, at least one of the first intersecting line portion and the second intersecting line portion is connected to the corresponding first elongated hole or the second intersecting line portion in plan view. Perpendicular to the long hole.

In the directional coupler according to the fifth aspect of the present disclosure, in addition to the first aspect, the coupling line has a plurality of straight portions including a first intersecting line portion and a second intersecting line portion. Two adjacent straight parts of the plurality of straight parts are connected to form an obtuse angle.

In the directional coupler according to the sixth aspect of the present disclosure, in addition to the fifth aspect, the plurality of straight sections include a straight section connecting the other end of the first intersecting line section and the first output section; It includes a straight line part that connects the two crossing line parts and the second output part.

In a directional coupler according to a seventh aspect of the present disclosure, in addition to the first aspect, the first coupling point and the second intersection line are the intersections of the first intersection line and the first elongated hole in plan view. The total distance between the first transmission line and the second transmission line, which is further away from the tube axis than a virtual straight line passing through the second connection point, which is the intersection of the line and the second elongated hole, is set to 1/4 of the effective length. Ru.

In a directional coupler according to an eighth aspect of the present disclosure, in addition to the first aspect, a first directional coupler that passes through the opening intersection in plan view and is further away from the tube axis than a parallel line that is parallel to the tube axis. The total distance between the transmission line and the second transmission line is set to 1/2 of the effective length.

A microwave heating device according to a ninth aspect of the present disclosure includes the directional coupler according to the first aspect.

(Embodiment)
Hereinafter, a directional coupler and a microwave heating device including the same according to an embodiment of the present disclosure will be described with reference to the drawings.

FIG. 1 is a perspective view of a directional coupler 5 according to an embodiment of the present disclosure. FIG. 2 is a perspective view of the directional coupler 5 with the printed circuit board 12 removed. FIG. 3 is a plan view of the waveguide 3. FIG. 4 is a circuit diagram of the printed circuit board 12 provided in the directional coupler 5. As shown in FIG.

As shown in FIGS. 1 to 3, the directional coupler 5 is placed on the wall of the waveguide 3 that transmits microwaves. The waveguide 3 is a rectangular waveguide. A cross section of the waveguide 3 perpendicular to the tube axis L1 has a rectangular shape. The tube axis L1 is the central axis of the waveguide 3 in the width direction.

The directional coupler 5 includes a cross opening 11, a printed circuit board 12, and a support section 14. The cross opening 11 is an X-shaped opening disposed on a wide plane 3a of the waveguide 3. The printed circuit board 12 is arranged outside the waveguide 3 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 3 .

As shown in FIG. 3, the cross opening 11 is arranged at a position that does not intersect with the tube axis L1 of the waveguide 3 in plan view. The opening center portion 11c of the cross opening 11 is spaced apart from the tube axis L1 of the waveguide 3 by a distance D1 in plan view. The dimension D1 is, for example, 1/4 of the width of the waveguide 3. The cross opening 11 radiates the microwave propagating through the waveguide 3 toward the printed circuit board 12 as a circularly polarized microwave.

The aperture shape of the cross aperture 11 depends on the width and height of the waveguide 3, the power level and frequency band of the microwave propagating through the waveguide 3, and the power level of the circularly polarized microwave radiated from the cross aperture 11. It is determined according to the following conditions.

For example, the width of the waveguide 3 is 100mm, the height is 30mm, the wall thickness of the waveguide 3 is 0.6mm, the maximum power level of the microwave propagating through the waveguide 3 is 1000W, and the frequency band is 2450MHz. When the maximum power level of the circularly polarized microwave emitted from the cross aperture 11 is approximately 10 mW, the length 11w and width 11d of the cross aperture 11 are set to 20 mm and 2 mm, respectively.

As shown in FIG. 4, the cross opening 11 includes a first elongated hole 11e and a second elongated hole 11f that intersect with each other. The opening center 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 perpendicular to the tube axis L1 and passes through the opening center portion 11c.

In this 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 thereto. 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 center portion 11c of the cross opening 11 is arranged at a position overlapping the tube axis L1 in a plan view, the electric field does not rotate but reciprocates along the microwave transmission direction. In this case, the cross aperture 11 emits linearly polarized microwaves.

If the opening center portion 11c deviates even slightly from the tube axis L1, the electric field rotates. However, when the opening center portion 11c is closer to the tube axis L1 (the closer the dimension D1 is to 0 mm), an electric field with distorted rotation 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 3. In this case, a rotating electric field having a substantially perfect circular shape is generated. The cross aperture 11 emits a substantially perfectly circularly polarized microwave. Therefore, the rotation direction of the circularly polarized microwave becomes clearer. As a result, the traveling wave and the reflected wave can be separated and detected with high accuracy.

The printed circuit board 12 has a back surface 12b facing the cross opening 11 and a front surface 12a opposite to the 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 a microwave reflecting member. This copper foil prevents the circularly polarized microwaves emitted from the cross opening 11 from passing through the printed circuit board 12.

As shown in FIG. 4, a microstrip line 13, which is an example of a coupled line, is arranged on the back surface 12b of the substrate. The microstrip line 13 is, for example, a transmission line having a characteristic impedance of approximately 50Ω. The microstrip line 13 is arranged so as to surround the opening center portion 11c of the cross opening 11.

The effective length λre of the microstrip line 13 will be explained below. When 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 dielectric constant of the printed circuit board is εr, the effective length λre of the microstrip line 13 is It is expressed by the following formula. The effective length λre is the wavelength of electromagnetic waves propagating through 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 portion 13aa which is an example of a first intersecting line portion. The first straight portion 13aa intersects with the first elongated hole 11e at a position farther from the tube axis L1 than the opening center portion 11c in plan view. The first straight portion 13aa extends away from the tube axis L1 as it approaches the perpendicular line L2.

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

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

The first straight portion 13aa is orthogonal to the first elongated hole 11e in plan view. The second straight portion 13ba intersects with the second elongated hole 11f at a position closer to the opening tip portion 11fa than the opening center portion 11c in plan view. The second straight portion 13ba is orthogonal to the second elongated hole 11f in 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 with the cross opening 11 in plan view. One end of the first linear portion 13aa is connected to one end of the second linear portion 13ba outside the rectangular area E1 circumscribing the cross opening 11.

The first connection point P1 is a point where the first straight portion 13aa and the first elongated hole 11e intersect with each other in plan view. The second connection point P2 is a point where the second straight portion 13ba and the second elongated hole 11f intersect with each other in plan view. A straight line connecting the first connecting point P1 and the second connecting point P2 is defined as a virtual straight line L3. In this 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 λre.

A parallel line L4 is a line that passes through the opening center portion 11c in plan view and is parallel to the tube axis L1. In this 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 parallel line L4, is set to 1/2 of the effective length λre.

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

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

The first output section 131 and the second output section 132 are arranged outside the support section 14 (see FIGS. 1 and 2) in plan view. The first detection circuit 15 is connected to the first output section 131 . The first detection circuit 15 detects the level of the microwave signal and outputs the detected level of the microwave signal as a control signal. The second detection circuit 16 is connected to the second output section 132 . The second detection circuit 16 detects the level of the microwave signal and outputs the detected level of the microwave signal as a control signal.

In this embodiment, the first detection circuit 15 and the second detection circuit 16 each include a smoothing circuit (not shown) configured with a chip resistor and a Schottky diode. The first detection circuit 15 rectifies the microwave signal from the first output section 131 and converts the rectified microwave signal into a DC voltage. The converted DC voltage is output to the first detection output section 18.

Similarly, the second detection circuit 16 rectifies the microwave signal from the second output section 132 and converts the rectified microwave signal into a DC voltage. The converted DC voltage is output to the second detection output section 19.

The printed circuit board 12 has four holes (holes 20a, 20b, 20c, and 20d) for attaching the printed circuit board 12 to the waveguide 3. 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 this copper foil is formed has the same potential as the substrate surface 12a.

The printed circuit board 12 is fixed to the waveguide 3 by screwing it to the support part 14 with screws 201a, 201b, 201c, and 201d (see FIG. 1) through the holes 20a, 20b, 20c, and 20d.

As shown in FIG. 2, the support portion 14 has threaded portions 202a, 202b, 202c, and 202d for screwing screws 201a, 201b, 201c, and 201d, respectively. The threaded portions 202a, 202b, 202c, and 202d are formed on a flange portion provided on the support portion 14.

The support part 14 has conductivity and is arranged so as to surround the cross opening 11 in a plan view. The support part 14 functions as a shield to prevent circularly polarized microwaves emitted from the cross opening 11 from leaking outside the support part 14 .

The support part 14 has a groove 141 and a groove 142 through which the third straight part 13ab and the fourth straight part 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 extraction portions for extracting microwave signals propagating through the microstrip line 13 to the outside of the support portion 14 . The grooves 141 and 142 can be formed by recessing the flange portion of the support portion 14 away from the printed circuit board 12.

1 and 2 illustrate a connector 18a and a connector 19a connected to the first detection output section 18 and the second detection output section 19 shown in FIG. 4, respectively.

Next, the operation and effect of the directional coupler 5 will be explained.

First, with reference to FIG. 5, the principle by which circularly polarized microwaves are radiated from the cross aperture 11 will be explained. In FIG. 5, the magnetic field distribution 3d generated within the waveguide 3 is shown by dotted concentric ellipses. The direction of the magnetic field of the magnetic field distribution 3d is indicated by an arrow. The magnetic field distribution 3d moves in the microwave transmission direction A1 within the waveguide 3 over time.

At time t=t0 shown in FIG. 5(a), a magnetic field distribution 3d 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 time t=t0+t1 shown in FIG. 5(b), the magnetic field shown by the broken line arrow B2 excites the second elongated hole 11f of the cross opening 11.

At time t=t0+T/2 (T is the cycle of the microwave wavelength in the tube) shown in FIG. At time t=t0+T/2+t1 shown in FIG. 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, circularly polarized microwaves rotating counterclockwise (microwave rotation direction 32) are radiated out of the waveguide 3 from the cross opening 11.

Here, if the microwave propagating along the arrow 30 shown in FIG. 3 is a traveling wave, and the microwave propagating along the arrow 31 is a reflected wave, the traveling wave will be directed in the same direction as the transmission direction A1 shown in FIG. propagate. Therefore, as described above, the counterclockwise rotating circularly polarized microwave is radiated out of the waveguide 3 from the cross opening 11.

On the other hand, the reflected wave propagates in the opposite direction to the transmission direction A1 shown in FIG. Therefore, circularly polarized microwaves rotating clockwise are radiated out of the waveguide 3 from the cross opening 11.

The circularly polarized microwave radiated outside the waveguide 3 is coupled to the microstrip line 13 facing the cross opening 11. The microstrip line 13 outputs most of the microwaves emitted from the cross aperture 11 by traveling waves propagating along the arrow 30 to the first output section 131 .

On the other hand, the microstrip line 13 outputs most of the microwaves emitted from the cross aperture 11 by reflected waves propagating along the arrow 31 to the second output section 132. Thereby, the traveling wave and the reflected wave can be separated and detected with higher accuracy. This will be explained in more detail with reference to FIG.

FIG. 6 is a diagram for explaining the direction and amount of microwaves propagating through the microstrip line 13 and changing over 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 it takes for the microwave to propagate through this gap. However, for convenience, it is assumed here that this time delay does not exist.

Here, the area where the cross opening 11 and the microstrip line 13 intersect in plan view is called a coupling area. The first coupling point P1 is approximately at 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 at the center of the coupling region where the second elongated hole 11f and the microstrip line 13 intersect.

In FIG. 6, the amount of microwaves propagating through the microstrip line 13 (current flowing due to interlinkage of magnetic fields) is expressed by the thickness of the solid arrow line. That is, when the amount of microwaves propagating through the microstrip line 13 is large, the line is thick, and when the amount of microwaves propagating through the microstrip line 13 is small, the line is thin.

At time t=t0 shown in (a) of FIG. 6, the magnetic field shown by the broken line arrow B1 excites the first elongated hole 11e of the cross opening 11, and the microwave shown by the thick solid line arrow M1 is applied to the first coupling point P1. arise. This microwave propagates through the microstrip line 13 toward the second coupling point P2.

At time t=t0+t1 shown in FIG. 6(b), the magnetic field shown by the broken line arrow B2 excites the second elongated hole 11f of the cross opening 11, and the microwave shown by the thick solid line arrow M2 is generated at the second coupling point P2. arise.

When the effective propagation time of the microwave through the microstrip line 13 between the first connection point P1 and the second connection point P2 is set to time t1, a wave occurs at the first connection point P1 at the time shown in (a) of FIG. The microwave propagates to the second coupling point P2 at the time shown in FIG. 6(b). That is, at the time shown in FIG. 6(b), a microwave indicated by a solid arrow M1 and a microwave indicated by a solid arrow M2 are generated at the second coupling point P2.

Therefore, the two microwaves are added together, propagate through the microstrip line 13 toward the second output section 132, and are output to the second output section 132 after a predetermined period of time has elapsed. In this embodiment, since the effective propagation time is set to 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 equal to the effective length λre. It is set to 1/4. With this configuration, the microstrip line 13 can be easily designed.

At time t=t0+T/2 shown in FIG. 6(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 connecting point P1 is exposed to the microscopic field indicated by the thin solid line arrow M3. A wave is created. This microwave propagates through the microstrip line 13 toward the first output section 131, and is output to the first output section 131 after a predetermined period of time has elapsed.

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

At the time shown in (a) of FIG. 6, the microwave shown by the solid arrow M1 generated at the first coupling point P1 propagates in substantially the same direction as the rotational direction of the microwave radiated from the cross aperture 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. 6(c), the microwave shown by the solid arrow M3 generated at the first coupling point P1 propagates in a direction substantially opposite to the rotational direction of the microwave radiated from the cross aperture 11. Therefore, the energy of the coupled microwaves is reduced. Therefore, the amount of microwaves indicated by solid arrow M3 is smaller than the amount of microwaves indicated by solid arrow M1.

At time t=t0+T/2+t1 shown in FIG. 6(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 connecting point P2 is exposed to the microscopic field indicated by the thin solid line arrow M4. A wave is created. This microwave propagates toward the first coupling point P1. The reason for reducing the thickness of the solid arrow M4 is the same as the reason for reducing the thickness of the solid 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, similar to the time t=t0 shown in FIG. In this case, a microwave indicated by a thin solid arrow M4, which was not explained at the time shown in FIG. 6(a), is present 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 out and disappears, and is not output to the first output section 131.

Strictly speaking, the amount of microwaves propagating from the first coupling point P1 at time t=t0 is the difference between the amount of microwaves shown by the thick solid arrow M1 and the amount of microwaves shown by the thin solid arrow M4 (M1 -M4). Therefore, the amount of microwaves output to the second output section 132 is the amount (M1+M2-M4) that is the sum of the amount of microwaves propagating from the second coupling point P2 and the amount of microwaves indicated by the thick solid arrow M2. Become.

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

The amount of microwaves emitted from the cross aperture 11 relative to the amount of microwaves propagating through the waveguide 3 is determined by the shapes and dimensions of the waveguide 3 and the cross aperture 11. For example, when the shape and dimensions are set as described above, the amount of microwaves emitted from the cross aperture 11 is approximately 1/100,000 (approximately −50 dB) relative to the amount of microwaves propagating through the waveguide 3.

Next, in this embodiment, the first transmission line 13 is further away from the tube axis L1 than the parallel line L4.
The reason why the total distance between a and the second transmission line 13b is set to 1/2 of the effective length λre will be explained.

FIG. 7 is a diagram for explaining the direction and amount of microwaves propagating through the microstrip line 13 and changing over time. (a) to (d) in FIG. 7 are diagrams showing the state in which a time t1/2 has passed from (a) to (d) in FIG. 6, respectively.

Although not described above, the magnetic field distribution 3d moves in the microwave transmission direction A1 within the waveguide 3 over time. Therefore, as shown in FIGS. 7A to 7D, magnetic fields indicated by broken line arrows B12, B23, B34, and B41 excite the first elongated hole 11e and the second elongated hole 11f. Thereby, the circularly polarized microwave radiated outside the waveguide 3 is 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 plan view is referred to as a coupling region. The third coupling point P3 is approximately at the center of the coupling region where the perpendicular line L2 and the microstrip line 13 intersect. The fourth coupling point P4 is approximately at the center of the coupling region where the parallel line L4 and the first transmission line 13a intersect. The fifth coupling point P5 is approximately at the center of the coupling region where the parallel line L4 and the second transmission line 13b intersect.

At time t=t0+t1/2 shown in FIG. 7A, the magnetic field indicated by the broken line arrow B12 excites the cross aperture 11, and a microwave indicated by the thick solid line arrow M11 is generated at the third coupling point P3. This microwave propagates through the microstrip line 13 toward the fifth coupling point P5.

At time t=t0+t1+t1/2 shown in FIG. 7(b), the magnetic field shown by the broken line arrow B23 excites the cross aperture 11. A microwave indicated by a thick solid arrow M12a is generated at the fifth coupling point P5, and a microwave indicated by a thin solid arrow M12b is produced at the fourth coupling point P4. 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 through the microstrip line 13 between the third connection point P3 and the fifth connection point P5 is set to time t1, a signal is generated at the third connection point P3 at the time shown in (a) of FIG. The microwave propagates to the fifth coupling point P5 at the time shown in FIG. 7(b). That is, at the time shown in FIG. 7(b), a microwave indicated by a thick solid arrow M11 and a microwave indicated by a thick solid arrow M12a are generated at the fifth coupling point P5.

Therefore, the two microwaves are added together, propagate through the microstrip line 13 toward the second output section 132, and are output to the second output section 132 after a predetermined period of time has elapsed. In order to set the effective propagation time to time t1, in this embodiment, the distance of the first transmission line 13a that is farther from the tube axis L1 than the parallel line L4 is set to 1/4 of the effective length λre. 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 section 131, and is output to the first output section 131 after a predetermined period of time has elapsed.

At time t=t0+T/2+t1/2 shown in FIG. 7(c), a magnetic field indicated by a broken line arrow B34 excites the cross aperture 11, and a microwave indicated by a thin solid line arrow M13b is generated at the third coupling point P3. This microwave propagates through the microstrip line 13 toward the first output section 131 . The reason for reducing the thickness of the solid arrow M13b is the same as the reason for reducing the thickness of the solid arrow M3 described above.

At time t=t0+T/2+t1+t1/2 shown in FIG. 7(d), broken line arrow B41
A magnetic field indicated by excites the cross aperture 11. A microwave indicated by a thin solid arrow M14b is generated at the fifth coupling point P5, and a microwave indicated by a thick solid arrow M14a is produced at the fourth coupling point P4. 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 arrow M14b is the same as the reason for reducing the thickness of the solid 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. If the effective propagation time of the microwave through the microstrip line 13 between the third connection point P3 and the fourth connection point P4 is set to time t1, a signal is generated at the third connection point P3 at the time shown in (c) of FIG. The microwave propagates to the fourth coupling point P4 at the time shown in FIG. 7(d).

That is, at the time shown in FIG. 7(d), a microwave indicated by a thin solid arrow M13b and a microwave indicated by a thick solid arrow M14a are generated at the fourth coupling point P4. In order to set the effective propagation time to time t1, in this embodiment, the distance of the second transmission line 13b that is farther from the tube axis L1 than the parallel line L4 is set to 1/4 of the effective length λre.

That is, 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 parallel line L4, is set to 1/2 of the effective length λre. 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 arrow M13b is canceled out and disappears, and is not output to the first output section 131.

At time t=t0+T+t1/2, the magnetic field shown by the broken line arrow B12 excites the cross aperture 11, similar to the time t=t0+t1/2 shown in FIG. 7(a). In this case, a microwave indicated by a thin solid arrow M14b, which was not explained at the time shown in FIG. 7(a), is present 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 microwaves indicated by the thick solid arrow M11 and the thick solid arrow M14a. Therefore, the microwave indicated by the thin solid arrow M14b is canceled and disappears, and is not output to the first output section 131.

Strictly speaking, the amount of microwaves propagating from the third coupling point P3 at time t=t0+t1/2 is calculated by subtracting the amount of microwaves shown by thin solid arrow M14b from the amount of microwaves shown by thick solid arrows M11 and M14a. The amount is (M11+M14a-M14b). Therefore, the amount of microwaves output to the second output section 132 is equal to the amount of microwaves propagating from the third coupling point P3 plus the amount of microwaves indicated by the thick solid arrow M12a (M11+M12a+M14a-M14b). Become.

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

The directional coupler 5 has a cross opening 11 disposed at a position that does not intersect the tube axis L1 of the waveguide 3 in a plan view and emits circularly polarized microwaves. With this configuration, the rotating directions of the circularly polarized microwaves emitted from the cross aperture 11 are opposite to each other for the traveling wave and the reflected wave. By utilizing the difference in the rotation direction of this circularly polarized microwave, it is possible to separate and detect the traveling wave and the reflected wave.

In the directional coupler 5, the first transmission line 13a includes a first straight portion 13aa, and the second transmission line 13b includes a second straight portion 13ba. With this configuration, the number of locations where the microstrip line 13 is bent can be reduced compared to the conventional structure. It is possible to eliminate the need to bend the microstrip line 13 at right angles. The bending portion of the microstrip line 13 can be separated from the vertical region of the cross opening 11. As a result, the traveling wave and the reflected wave can be separated and detected with higher accuracy.

In the directional coupler 5, the first transmission line 13a and the second transmission line 13b are connected to each other at a position outside the rectangular area E1 and away from the tube axis L1 in plan view. With this configuration, the bending portion of the microstrip line 13 can be further separated from the vertical region of the cross opening 11. The first straight portion 13aa and the second straight portion 13ba can be made longer, and the current flow within the microstrip line 13 can be prevented from being obstructed. As a result, the traveling wave and the reflected wave can be separated and detected with even higher accuracy.

In the directional coupler 5, the first linear portion 13aa intersects with the first elongated hole 11e at a position closer to the opening tip portion 11ea than the opening center portion 11c in plan view. The second straight portion 13ba intersects the second elongated hole 11f at a position closer to the opening tip portion 11fa than the opening center portion 11c in plan view. Normally, a stronger magnetic field is generated around the opening tips 11ea and 11fa than around the opening center portion 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 increases. As a result, the traveling wave and the reflected wave can be separated and detected with even higher accuracy.

In the directional coupler 5, the first straight portion 13aa is orthogonal to the first elongated hole 11e in plan view. With this configuration, the transmission direction of the microwave generated at the first coupling point P1, indicated by the solid arrow M1, is made the same as the rotation direction 32 of the microwave radiated from the cross aperture 11. Thereby, the amount of microwaves indicated by the solid arrow M1 can be increased.

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

In the directional coupler 5, the second straight portion 13ba is orthogonal to the second elongated hole 11f in plan view. With this configuration, the transmission direction of the microwave generated at the second coupling point P2, indicated by the solid arrow M2, is made the same as the rotation direction 32 of the microwave radiated from the cross aperture 11. Thereby, the amount of microwaves indicated by the solid arrow M2 can be increased.

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

In the directional coupler 5, the microstrip line 13 has a first straight section 13aa, a second straight section 13ba, a third straight section 13ab, and a fourth straight section 13bb. The first linear portion 13aa and the third linear portion 13ab that are adjacent to each other are connected to form an obtuse angle. The second straight portion 13ba and the fourth straight portion 13bb that are adjacent to each other are connected to form an obtuse angle.

With this configuration, the number of right-angled bends in the microstrip line 13 can be reduced. Thereby, it is possible to suppress the flow of current in the coupled line from being inhibited. As a result, the traveling wave and the reflected wave can be separated and detected with even higher accuracy.

In the directional coupler 5, 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 λre. With this configuration, the traveling wave and the reflected wave can be separated and detected with even higher accuracy. The total distance does not necessarily need to be set to 1/4 of the effective length λre, as long as it is set to approximately 1/4 of the effective length λre.

In the directional coupler 5, 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 parallel line L4, is set to 1/2 of the effective length λre. With this configuration, the traveling wave and the reflected wave can be separated and detected with even higher accuracy. The total distance does not necessarily need to be set to 1/2 of the effective length λre, as long as it is set to approximately 1/2 of the effective length λre.

As shown in FIG. 4, in this embodiment, one end of the first transmission line 13a and one end of the second transmission line 13b are connected to form a right angle. However, the present disclosure is not limited thereto. It is sufficient 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 area of the cross opening 11 in plan view. In this region, the influence of the magnetic field is large.

8A to 8D are plan views showing first to sixth modifications of the microstrip line 13, respectively. As shown in FIG. 8A, 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 away from the opening center part 11c. You may do so.

As shown in FIG. 8B, the first transmission line 13a and the second transmission line 13b are bent such 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 do so. As shown in FIG. 8C, 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 center portion 11c. You may do so.

In this embodiment, the first straight portion 13aa and the second straight portion 13ba correspond to the first intersecting line portion and the second intersecting line portion, respectively. However, the present disclosure is not limited thereto. As shown in FIG. 8D, the first intersecting line portion and the second intersecting line portion may be an arcuate portion 13ac and an arcuate portion 13bc, respectively.

In this embodiment, the third straight portion 13ab and the fourth straight portion 13bb are parallel to the perpendicular line L2. However, the present disclosure is not limited thereto. As shown in FIG. 8E, the third straight portion 13ab and the fourth straight portion 13bb may be parallel to the parallel line L4.

In this embodiment, the first transmission line 13a and the second transmission line 13b have a plurality of straight portions. However, the present disclosure is not limited thereto. As shown in FIG. 8F, both the first transmission line 13a and the second transmission line 13b may be composed of one straight portion.

In this embodiment, the cross opening 11 is formed line-symmetrically with respect to the perpendicular line L2. Perpendicular L
2 is perpendicular to the tube axis L1 and passes through the opening center portion 11c. However, the present disclosure is not limited thereto. 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 a position offset from their respective longitudinal centers. 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 shifted from the opening center portion 11c. The cross opening 11 may be formed symmetrically with respect to a straight line that is slightly inclined with respect to the perpendicular line L2 in plan view.

Hereinafter, with reference to FIG. 9, the configuration of the microwave heating device 10 according to the present embodiment will be described. As shown in FIG. 9, the microwave heating device 10 includes a heating chamber 1, a microwave generator 2, a waveguide 3, and a microwave radiator 4.

The heating chamber 1 accommodates an object to be heated. The microwave generator 2 generates microwaves. The waveguide 3 propagates the microwaves generated by the microwave generator 2 . The microwave radiation section 4 is disposed below the bottom surface 1a of the heating chamber 1, and radiates microwaves propagating through the waveguide 3 into the heating chamber 1. A directional coupler 5 is arranged on the wide surface 3a (see FIGS. 1 and 2) of the waveguide 3 between the microwave generator 2 and the microwave radiator 4.

The directional coupler 5 detects a detection signal 5a according to the traveling wave propagating through the waveguide 3 from the microwave generator 2 toward the microwave radiator 4. The directional coupler 5 detects a detection signal 5b according to the reflected wave propagating through the waveguide 3 from the microwave radiation section 4 toward the microwave generation section 2. Directional coupler 5 transmits detection signals 5a and 5b to control section 6.

The control unit 6 receives the signal 8 in addition to the detection signals 5a and 5b. The signal 8 includes heating conditions set by an input section (not shown) of the microwave heating device 10, and the weight of the object to be heated and the amount of steam detected by a sensor (not shown). The control unit 6 controls the drive power source 7 and the motor 9 based on the detection signals 5a, 5b and the signal 8. The drive power source 7 supplies the microwave generator 2 with power for generating microwaves. The motor 9 rotates the microwave radiator 4 . In this way, the microwave heating device 10 heats the object housed in the heating chamber 1 using the microwaves supplied to the heating chamber 1 .

As the heated object is heated, the heated object physically changes. The amount of reflected waves changes in accordance with this physical change. By detecting changes in the amount of reflected waves using the directional coupler 5, the microwave heating device 10 can grasp the progress of heating the object to be heated. The microwave heating device 10 can also grasp changes in the state inside the object to be heated, as well as the type and amount of the object to be heated. Therefore, according to this embodiment, a highly convenient microwave heating device can be provided.

The directional coupler according to the present disclosure can be applied to a microwave heating device for consumer use or business use.

1 Heating chamber 1a Bottom surface 2 Microwave generation section 3 Waveguide 3a Wide surface 3d Magnetic field distribution 4 Microwave radiation section 5 Directional coupler 5a, 5b Detection signal 6 Control section 7 Drive power source 8 Signal 9 Motor 10 Microwave heating device 11 Cross opening 11c Opening center 11d Width 11e First elongated hole 11ea, 11fa Opening tip 11f Second elongated hole 11w Length 12 Printed circuit board 12a Board surface 12b Board back surface 13 Microstrip line 13a First transmission line 13aa First straight line Part 13ab Third straight part 13ac, 13bc Arc part 13b Second transmission line 13ba Second straight part 13bb Fourth straight part 14 Support part 15 First detection circuit 16 Second detection circuit 18 First detection output part 18a, 19a Connector 19 Second detection output section 20a Hole 30 Arrow 31 Arrow 131 First output section 132 Second output section 141, 142 Groove 201a Screw 202a Thread section E1 Rectangular area L1 Tube axis L2 Perpendicular line L3 Virtual straight line L4 Parallel line P1 First connection point P2 Second connection point P3 Third connection point P4 Fourth connection point P5 Fifth connection point

Claims (9)

Directionality that includes an opening disposed in a wall surface of a waveguide and a coupling line disposed outside the waveguide, and separates and detects a traveling wave propagating in the waveguide and a reflected wave. A coupler,
The opening has a first elongated hole and a second elongated hole that intersect with each other and are arranged at a position that does not intersect with the tube axis of the waveguide in a plan view,
The coupled line includes a first transmission line and a second transmission line,
The first transmission line and the second transmission line are electrically connected,
The first transmission line has a first crossing line part, and the first crossing line part is an opening crossing part where the first elongated hole and the second elongated hole intersect from one end side of the tube axis in a plan view. extending away from the tube axis as it approaches a perpendicular line perpendicular to the tube axis, intersecting the first elongated hole at a position farther from the tube axis than the opening intersection,
The second transmission line has a second intersection line portion, and the second intersection line portion extends away from the tube axis as it approaches the perpendicular line from the other end side of the tube axis in plan view, intersects the second elongated hole at a position farther from the tube axis than the opening intersection;
Directional coupler. The first transmission line and the second transmission line are connected to each other outside a rectangular area circumscribing the opening in plan view and at a position farther from the tube axis than the rectangular area. The directional coupler according to item 1. At least one of the first intersecting line portion and the second intersecting line portion intersects the corresponding first elongated hole or the second elongated hole at a position closer to the opening tip than the opening intersecting portion in plan view. , The directional coupler according to claim 1. The directional coupler according to claim 1, wherein at least one of the first intersecting line portion and the second intersecting line portion is orthogonal to the corresponding first elongated hole or the second elongated hole in plan view. The coupled line has a plurality of straight parts including the first crossing line part and the second crossing line part, and two adjacent straight parts of the plurality of straight parts form an obtuse angle. The directional coupler according to claim 1, wherein the directional coupler is connected. The plurality of straight line portions include a straight line portion connecting the other end of the first intersecting line portion and the first output portion, and a straight portion connecting the second intersecting line portion and the second output portion. The directional coupler according to claim 5. An imaginary that passes through a first connection point that is the intersection of the first intersection line and the first long hole and a second connection point that is the intersection of the second intersection line and the second long hole in plan view. The directional coupler according to claim 1, wherein a total distance of the first transmission line and the second transmission line that are farther from the tube axis than in a straight line is set to 1/4 of the effective length. The total distance of the first transmission line and the second transmission line passing through the opening intersection in plan view and further away from the tube axis than a parallel line parallel to the tube axis is 1 of the effective length. The directional coupler according to claim 1, wherein the directional coupler is set to /2. A microwave heating device comprising the directional coupler according to claim 1.