Radio wave emitting device

Abstract

A radio wave emitting device (1) comprises: a cavity (10); a signal generation unit (2); a signal amplification unit (3); a radio wave emitting unit (4); a control unit (5); a filter circuit (6); and a non-reciprocal circuit (7). The signal generation unit (2) generates a high-frequency signal. The signal amplification unit (3) includes an amplifier (31) and amplifies the high-frequency signal. The radio wave emitting unit (4) emits a radio wave into the cavity (10) on the basis of the amplified high-frequency signal. The control unit (5) controls the signal generation unit (2) and the signal amplification unit (3). The filter circuit (6) is disposed between the amplifier (31) and the radio wave emitting unit (4). The filter circuit (6) passes the amplified high-frequency signal and attenuates unwanted radiation generated in the signal amplification unit (3). The non-reciprocal circuit (7) is disposed between the filter circuit (6) and the radio wave emitting unit (4).

Description

Radio wave emitting device

[0001] The present disclosure relates to radio wave emitting devices.

[0002] Patent Document 1 discloses a power amplifier for a microwave heating device. The power amplifier disclosed in Patent Document 1 includes an input matching circuit, an amplifier circuit, and an output matching circuit. The amplifier circuit is connected to the input matching circuit and amplifies an input signal. The output matching circuit is connected to the amplifier circuit and performs impedance matching. The input matching circuit includes a switch unit and a filter unit and reduces harmonic power.

[0003] Patent Document 2 discloses a microwave oven including a power supply, a controller, a small signal microwave generator, a human-machine interface, one or more bandpass filters, a plurality of power amplifiers, and an RF (Radio Frequency) signal supply device.

[0004] Chinese Patent Application Publication No. 114245508 U.S. Patent No. 10,368,404

[0005] The present disclosure provides a radio wave emitting device capable of improving the signal purity of a high frequency signal transmitted to a radio wave emitting portion.

[0006] A radio wave emitting device according to one aspect of the present disclosure includes a cavity, a signal generating unit, a signal amplifying unit, a radio wave emitting unit, a control unit, a filter circuit, and a non-reciprocal circuit.

[0007] The signal generating unit generates a high-frequency signal. The signal amplifying unit has an amplifier and amplifies the high-frequency signal. The radio wave emitting unit radiates radio waves into the cavity based on the high-frequency signal amplified by the signal amplifying unit. The control unit controls the signal generating unit and the signal amplifying unit.

[0008] The filter circuit is disposed between the amplifier and the radio wave emitting portion, and passes the high-frequency signal amplified by the signal amplifying portion while attenuating unwanted radiation generated by the signal amplifying portion. The non-reciprocal circuit is disposed between the filter circuit and the radio wave emitting portion.

[0009] A radio wave emitting device according to another aspect of the present disclosure includes a cavity, a signal generating unit, a signal amplifying unit, a radio wave emitting unit, a control unit, a filter circuit, and a non-reciprocal circuit.

[0010] The signal generating unit generates a high-frequency signal. The signal amplifying unit has an amplifier and amplifies the high-frequency signal. The radio wave emitting unit radiates radio waves into the cavity based on the high-frequency signal amplified by the signal amplifying unit. The control unit controls the signal generating unit and the signal amplifying unit.

[0011] The filter circuit passes the high-frequency signal amplified by the signal amplifier and attenuates unwanted radiation generated by the signal amplifier. The non-reciprocal circuit reduces fluctuations in the characteristics of the filter circuit.

[0012] The present disclosure can improve the signal purity of a high-frequency signal transmitted to a radio wave emitting portion.

[0013] FIG. 1 is a schematic circuit diagram of a radio wave emitting device according to a first embodiment of the present disclosure. FIG. 2 is a schematic circuit diagram of a signal amplifier (amplifier) ​​in the radio wave emitting device according to the first embodiment. FIG. 3 is a schematic diagram of a filter circuit in the radio wave emitting device according to the first embodiment. FIG. 4 is a schematic diagram of a coupler in the radio wave emitting device according to the first embodiment. FIG. 5 is a schematic diagram of a coupler in the radio wave emitting device according to the first embodiment. FIG. 6 is a graph showing the characteristics of the filter circuit of the radio wave emitting device shown in FIG. 1 for various states of an irradiated object. FIG. 7 is a partially enlarged view of the graph shown in FIG. 6. FIG. 8 is a graph showing the characteristics of the filter circuit of a comparative radio wave emitting device for various states of an irradiated object. FIG. 9 is a partially enlarged view of the graph shown in FIG. 8. FIG. 10 is a graph showing changes in the measured forward power of the radio wave emitting device of FIG. 1 with changes in the state of the irradiated object. FIG. 11 is a graph showing changes over time in the measured forward power of the comparative radio wave emitting device with changes in the state of the irradiated object. FIG. 12 is a schematic circuit diagram of a radio wave emitting device according to a second embodiment of the present disclosure. Fig. 13 is a schematic circuit diagram of a radio wave emitting device according to a third embodiment of the present disclosure. Fig. 14 is a schematic diagram of a first example of a coupler in the radio wave emitting device shown in Fig. 13. Fig. 15 is a schematic diagram of a second example of a coupler in the radio wave emitting device shown in Fig. 13. Fig. 16 is a schematic circuit diagram of a filter circuit of a first modified example. Fig. 17 is a schematic circuit diagram of a filter circuit of a second modified example. Fig. 18 is a schematic circuit diagram of a filter circuit of a third modified example. Fig. 19 is a schematic diagram of a filter circuit of a fourth modified example. Fig. 20 is a schematic circuit diagram of a filter circuit of a fifth modified example.

[0014] [1. Embodiments] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. However, in the following embodiments, for example, detailed descriptions of known matters may be omitted, and identical or substantially identical configurations may be assigned the same reference numerals and redundant descriptions may be omitted.

[0015] [1.1 First Embodiment] [1.1.1 Configuration] Fig. 1 is a schematic circuit diagram of a radio wave emission device 1 according to a first embodiment of the present disclosure. As shown in Fig. 1, the radio wave emission device 1 includes a cavity 10. The cavity 10 is capable of accommodating an irradiation target 11. The irradiation target 11 is an object to which radio waves are irradiated by the radio wave emission device 1.

[0016] In this embodiment, the radio wave emission device 1 is a microwave oven that performs dielectric heating on an irradiation object 11 by irradiating the irradiation object 11 with radio waves. That is, the cavity 10 is a heating chamber, and the irradiation object 11 is, for example, food.

[0017] The cavity 10 confines radio waves (microwaves) within the cavity 10. Therefore, the cavity 10 is made of a material that blocks radio waves so that the radio waves do not leak out of the cavity 10 when the radio waves are irradiated onto the irradiation target 11. Radio wave blocking materials include materials that reflect radio waves, such as metal materials, and materials that absorb radio waves, such as ferrite rubber.

[0018] In addition to the cavity 10, the radio wave emitting device 1 includes a signal generating unit 2, a signal amplifying unit 3, a radio wave emitting unit 4, a control unit 5, a filter circuit 6, and a non-reciprocal circuit 7. The radio wave emitting device 1 also includes a forward wave power measuring unit 8a and a reflected wave power measuring unit 8b. The radio wave emitting device 1 further includes an analog-to-digital conversion circuit (AD conversion circuit) 91, a bias voltage control circuit 92, a DC power supply 93, a latch circuit 94, and a termination circuit 95.

[0019] The signal generating unit 2 generates a high-frequency signal for generating radio waves. The frequency band of the high-frequency signal is, for example, 1 MHz to 10 GHz. The signal generating unit 2 includes an oscillation circuit 21, a matching circuit 22, and a variable amplifier 23.

[0020] The oscillator circuit 21 generates a high-frequency signal. For example, the oscillator circuit 21 may be configured with a PLL (Phase Locked Loop) frequency synthesizer. The matching circuit 22 is disposed between the oscillator circuit 21 and the variable amplifier 23. The matching circuit 22 matches the impedance of the oscillator circuit 21 with the impedance of the variable amplifier 23.

[0021] The signal amplifier 3 amplifies the high-frequency signal from the signal generator 2. The signal amplifier 3 may be composed of a single amplifier or multiple amplifiers. In this embodiment, the signal amplifier 3 includes an amplifier 31a and an amplifier 31b. Hereinafter, the amplifiers 31a and 31b will be collectively referred to as amplifiers 31.

[0022] Fig. 2 is a schematic circuit diagram of the amplifier 31 included in the signal amplification unit 3. As shown in Fig. 2, the amplifier 31 includes a transistor 311, choke circuits 312 and 313, capacitors C11, C12, C13 and C14, and a resistor R11.

[0023] The amplifier 31 further includes a radio frequency input terminal RFin, a radio frequency output terminal RFout, a gate bias terminal Vin, and a power supply terminal Vdd. The radio frequency input terminal RFin is connected to the signal generating unit 2. The radio frequency output terminal RFout is connected to the filter circuit 6 via an output matching circuit 33.

[0024] The transistor 311 is, for example, a field-effect transistor. The transistor 311 is, for example, a normally-on type that is turned on when the gate voltage is 0 V. The source terminal of the transistor 311 is grounded. In other words, the amplifier 31 is a source-grounded circuit. The transistor 311 amplifies a high-frequency signal input to the gate terminal and outputs the amplified high-frequency signal from the drain terminal.

[0025] The amplifier 31 includes a circuit including a capacitor C11, a choke circuit 312, and a resistor R11, which are arranged in the gate bias path. In Fig. 2, a series circuit including the choke circuit 312 and the resistor R11 is connected between the gate bias terminal Vin and the gate terminal of the transistor 311. The capacitor C11 is connected between the gate bias terminal Vin, the choke circuit 312, and ground.

[0026] Capacitor C11 functions as a bypass capacitor to reduce power supply noise. Choke circuit 312 is composed of a transmission line with a length that is one-fourth the wavelength of the high-frequency signal. The combination of choke circuit 312 and capacitor C11 increases the impedance of the bias circuit with respect to the high-frequency signal. This prevents the high-frequency signal from leaking to the bias circuit.

[0027] Resistor R11 suppresses abnormal oscillation caused by noise in the gate bias. Capacitor C13 is disposed between the gate of transistor 311 and radio frequency input terminal RFin, and cuts the DC component of the bias voltage.

[0028] The amplifier 31 has a circuit configured with a capacitor C12 and a choke circuit 313 arranged in the drain bias path. In Fig. 2, the choke circuit 313 is connected between the power supply terminal Vdd and the drain terminal of the transistor 311. The capacitor C12 is connected between the power supply terminal Vdd, the choke circuit 313, and ground. The capacitor C12 functions as a bypass capacitor that reduces power supply noise.

[0029] Like choke circuit 312, choke circuit 313 is configured with a transmission line having a length that is one-fourth the wavelength of the high-frequency signal. The combination of choke circuit 313 and capacitor C12 increases the impedance of the bias circuit with respect to the high-frequency signal, thereby preventing leakage of the high-frequency signal to the bias circuit side.

[0030] The capacitor C14 is disposed between the drain of the transistor 311 and the radio frequency output terminal RFout, and cuts the DC component of the power supply voltage.

[0031] 1, the signal amplifier 3 is a multi-stage amplifier configured by connecting an amplifier 31a and an amplifier 31b in series. The amplifier 31a is a driver stage (input stage) amplifier, and the amplifier 31b is a final stage (output stage) amplifier.

[0032] The multistage amplifiers stepwise amplify the minute high-frequency signal from the signal generating unit 2. For example, the amplifier 31a amplifies a 0.1 mW high-frequency signal to a 10 W high-frequency signal, and the amplifier 31b amplifies the 10 W high-frequency signal to a 250 W high-frequency signal.

[0033] A multistage amplifier can reduce heat density by dispersing heat generation points using multiple heat-generating elements. Therefore, a multistage amplifier can dissipate heat with a simple cooling structure. In this embodiment, the signal amplification unit 3 constitutes a high power amplifier.

[0034] The signal amplifier 3 further includes an input matching circuit 32 disposed in the input path of the high-frequency signal, and an output matching circuit 33 disposed in the output path of the high-frequency signal. The input matching circuit 32 is disposed between the signal generator 2 and the amplifier 31a (particularly, the high-frequency input terminal RFin (see FIG. 2)).

[0035] The output matching circuit 33 is disposed between the filter circuit 6 and the amplifier 31b (particularly, the radio frequency output terminal RFout (see FIG. 2)). The output matching circuit 33 matches the impedance of the transistor 311 (see FIG. 2) of the amplifier 31b with the impedance on the filter circuit 6 side.

[0036] The input matching circuit 32 matches the impedance of the transistor 311 (see FIG. 2) of the amplifier 31a with the impedance of the signal generating unit 2. Note that an additional matching circuit may be disposed between the amplifiers 31a and 31b to match the impedance of the amplifiers 31a and 31b.

[0037] The radio wave emitting unit 4 emits radio waves into the cavity 10 based on the high-frequency signal amplified by the signal amplifier 3. The radio wave emitting unit 4 is, for example, an antenna. The radio wave emitting unit 4 is disposed, for example, inside the cavity 10 and emits radio waves into the cavity 10.

[0038] The filter circuit 6 is disposed between the amplifier 31 (particularly, amplifier 31b) of the signal amplifier 3 and the radio wave emitting unit 4. The filter circuit 6 passes the high-frequency signal amplified by the signal amplifier 3 and attenuates unwanted radiation generated by the signal amplifier 3. In this embodiment, the amplifier 31 of the signal amplifier 3 operates in a saturation region, which will be described later.

[0039] This generates harmonics whose fundamental wave is the high-frequency signal generated by the signal generating unit 2. The unwanted radiation attenuated by the filter circuit 6 includes harmonics of the high-frequency signal amplified by the signal amplifying unit 3. In other words, the filter circuit 6 attenuates harmonics that are generated when the amplifier 31 of the signal amplifying unit 3 operates in the saturation region.

[0040] Fig. 3 is a schematic diagram of the filter circuit 6. As shown in Fig. 3, the filter circuit 6 includes band elimination filters 61 and 62. The band elimination filters 61 and 62 attenuate harmonics of the high frequency signal amplified by the signal amplifier 3. The band elimination filters 61 and 62 are distributed constant circuits.

[0041] A distributed constant circuit is a circuit that assumes that circuit elements with line constants per unit length are distributed along a transmission line. Distributed constant circuits can be used when the wavelength of the signal propagating through the transmission line cannot be considered sufficiently large compared to the circuit shape. With distributed constant circuits, filters can be constructed using only wiring such as microstrip lines.

[0042] The band-elimination filters 61 and 62 are arranged on the circuit board 30 of the signal amplifier 3. For example, the circuit board 30 includes a transmission line 301 and grounds 302 and 303. The transmission line 301 transmits the high-frequency signal amplified by the signal amplifier 3.

[0043] The band-elimination filter 61 is a short stub that attenuates the second harmonic of the high-frequency signal amplified by the signal amplifier 3. The band-elimination filter 61 is configured, for example, by a microstrip line that extends from the transmission line 301 to the ground 302 and is connected to the ground 302.

[0044] If the length of the short stub is L1 and the wavelength of the signal propagating through the transmission line 301 is λ, then when L1 < λ / 4, the short stub functions as an inductor. When L1 = λ / 4, the short stub has an open impedance. When λ / 4 < L1 < λ / 2, the short stub functions as a capacitor. When L1 = λ / 2, the short stub has a short-circuit impedance.

[0045] The length L1 of the short stub is set based on ¼ of the wavelength λ of the high-frequency signal amplified by the signal amplifier 3. Therefore, the short stub has an open impedance for the high-frequency signal amplified by the signal amplifier 3. On the other hand, the short stub has a short-circuit impedance for the second harmonic of the high-frequency signal amplified by the signal amplifier 3.

[0046] As a result, the band-elimination filter 61 passes the high-frequency signal amplified by the signal amplifier 3 and attenuates the second harmonic of the high-frequency signal amplified by the signal amplifier 3. For example, if the frequency of the high-frequency signal amplified by the signal amplifier 3 is 2450 MHz, the frequency of the second harmonic is 4900 MHz.

[0047] The line impedance is determined by the line width of the short stub, which can change the Q value of the band-elimination filter 61 and adjust the attenuation band somewhat.

[0048] The line impedance may be increased by making the line width of the short stub sufficiently smaller than the width of the transmission line 301. The line impedance may be decreased by making the line width of the short stub larger than the width of the transmission line 301. The line width of the short stub may be changed partially or continuously to design the shape of the short stub according to the desired attenuation characteristics.

[0049] The band-elimination filter 62 is an open stub that attenuates the third harmonic of the high-frequency signal amplified by the signal amplifier 3. The band-elimination filter 62 is configured, for example, by a microstrip line that extends from the transmission line 301 toward the ground 303 but is not connected to the ground 303.

[0050] If the length of the open stub is L2 and the wavelength of the signal propagating through the transmission line 301 is λ, then when L2 < λ / 4, the open stub functions as a capacitor. When L2 = λ / 4, the open stub has a short-circuit impedance. When λ / 4 < L2 < λ / 2, the open stub functions as an inductor. When L2 = λ / 2, the open stub has an open-circuit impedance.

[0051] The length L2 of the open stub is set based on ¼ of the wavelength λ of the third harmonic of the high-frequency signal amplified by the signal amplifier 3. Therefore, the open stub functions as a capacitor for the high-frequency signal amplified by the signal amplifier 3. On the other hand, the open stub has a short-circuit impedance for the third harmonic of the high-frequency signal amplified by the signal amplifier 3.

[0052] As a result, the band-elimination filter 62 passes the high-frequency signal amplified by the signal amplifier 3 and attenuates the third harmonic of the high-frequency signal amplified by the signal amplifier 3. For example, if the frequency of the high-frequency signal amplified by the signal amplifier 3 is 2450 MHz, the frequency of the third harmonic is 7350 MHz.

[0053] The line impedance is determined by the line width of the open stub, which allows the Q value of the band-elimination filter 62 to be changed and the attenuation band to be adjusted somewhat.

[0054] The line impedance may be increased by making the line width of the short stub sufficiently smaller than the width of the transmission line 301. The line impedance may be decreased by making the line width of the short stub larger than the width of the transmission line 301. The line width of the short stub may be changed partially or continuously to design the shape of the short stub according to the desired attenuation characteristics.

[0055] In this way, the filter circuit 6 passes the high-frequency signal with a frequency of 2450 MHz amplified by the signal amplifier 3, and attenuates the unwanted radiation generated by the signal amplifier 3 (the second harmonic with a frequency of 4900 MHz and the third harmonic with a frequency of 7350 MHz).

[0056] Returning to Fig. 1, the non-reciprocal circuit 7 is disposed between the filter circuit 6 and the radio wave emitting unit 4. The non-reciprocal circuit 7 includes a first transmission line 71 and a second transmission line 72 that are insulated from each other, and separates a traveling wave from a reflected wave. The first transmission line 71 transmits the traveling wave to the radio wave emitting unit 4. The second transmission line 72 transmits the reflected wave to the termination circuit 95. The non-reciprocal circuit 7 is, for example, a circulator.

[0057] The traveling wave is a high-frequency signal amplified by the signal amplifier 3. That is, the traveling wave is a high-frequency signal supplied to the radio wave emitting portion 4 to radiate radio waves into the cavity 10.

[0058] The reflected wave is a high-frequency signal that flows backward from the radio wave emitting portion 4. The reflected wave is generated by radio waves that are not emitted from the radio wave emitting portion 4 into the cavity 10 due to, for example, an impedance mismatch. Alternatively, the reflected wave is generated by radio waves that are emitted into the cavity 10 by the radio wave emitting portion 4 but are not absorbed by the irradiation target 11 and are reflected within the cavity 10 and return to the radio wave emitting portion 4.

[0059] The forward wave power measuring unit 8a measures the power of a forward wave on the first transmission line 71. The forward wave power measuring unit 8a includes a detection circuit 81 and a coupler 82. The reflected wave power measuring unit 8b measures the power of a reflected wave on the second transmission line 72. The reflected wave power measuring unit 8b includes a detection circuit 81 and a coupler 83.

[0060] In the radio wave emission device 1, the detection circuit 81 functions as both the forward wave power measurement section 8a and the reflected wave power measurement section 8b. Hereinafter, the power of the forward wave and the power of the reflected wave will be referred to as the forward wave power and the reflected wave power, respectively.

[0061] The coupler 82 is disposed between the filter circuit 6 and the non-reciprocal circuit 7 and detects a traveling wave. In other words, the coupler 82 is disposed on the first transmission line 71. Fig. 4 is a schematic diagram of the coupler 82. The coupler 82 shown in Fig. 4 is a directional coupler. The coupler 82 includes an input port 82a, an output port 82b, a coupled port 82c, a termination resistor 82d, a first line 821, and a second line 822.

[0062] The first line 821 is arranged between the input port 82 a and the output port 82 b. The second line 822 is arranged between the coupled port 82 c and the termination resistor 82 d. The second line 822 is electromagnetically coupled to the first line 821, partially in parallel with the first line 821.

[0063] The traveling wave S11 is input to the input port 82a and propagates through the first line 821. The coupler 82 outputs a part of the traveling wave S11 as a traveling-wave coupled signal S12 from the coupled port 82c via the second line 822. The magnitude of the traveling-wave coupled signal S12 is proportional to the power of the traveling wave S11.

[0064] The coupler 83 is disposed between the non-reciprocal circuit 7 and the termination circuit 95 and detects the reflected wave. In other words, the coupler 83 is disposed on the second transmission line 72. FIG. 5 is a schematic diagram of the coupler 83. The coupler 83 shown in FIG. 5 is a directional coupler. The coupler 83 includes an input port 83a, an output port 83b, a coupled port 83c, a termination resistor 83d, a first line 831, and a second line 832.

[0065] The first line 831 is arranged between the input port 83 a and the output port 83 b. The second line 832 is arranged between the coupled port 83 c and the termination resistor 83 d. The first line 832 is partially parallel to the first line 831 and is electromagnetically coupled to the first line 831.

[0066] The reflected wave S21 is input to the input port 83a and propagates through the first line 831. The coupler 83 outputs a portion of the reflected wave S21 as a reflected wave coupled signal S22 from the coupled port 83c via the second line 832. The magnitude of the reflected wave coupled signal S22 is proportional to the power of the reflected wave S21.

[0067] The couplers 82 and 83 are disposed on the first transmission line 71 and the second transmission line 72, respectively, which are electrically insulated from each other, so that the forward wave and the reflected wave are insulated from each other. Therefore, the couplers 82 and 83 do not require strict directivity. Therefore, the couplers 82 and 83 can be easily formed. For example, the couplers 82 and 83 can be easily formed by patterns on a printed circuit board.

[0068] The detection circuit 81 measures the forward wave power and the reflected wave power. Specifically, the detection circuit 81 generates a forward wave power measurement signal, which is an analog signal corresponding to the forward wave power, based on the forward wave coupled signal S12 from the coupler 82. The forward wave power measurement signal is sent to the AD conversion circuit 91 and the latch circuit 94.

[0069] The detection circuit 81 generates a reflected wave power measurement signal, which is an analog signal corresponding to the reflected wave power, based on the reflected wave coupled signal S22 from the coupler 83. The reflected wave power measurement signal is sent to an AD conversion circuit 91 and a latch circuit 94.

[0070] The AD conversion circuit 91 converts the forward wave power measurement signal into a digital signal and transmits the digital signal to the control unit 5. The AD conversion circuit 91 converts the reflected wave power measurement signal into a digital signal and transmits the digital signal to the control unit 5.

[0071] A DC power supply 93 supplies a bias voltage to the drain terminal of the transistor 311 (see FIG. 2) of the amplifier 31a and the drain terminal of the transistor 311 of the amplifier 31b. A bias voltage control circuit 92 controls these bias voltages.

[0072] The bias voltage control circuit 92 includes a first switch element and a second switch element. The first switch element is arranged between the DC power supply 93 and the drain terminal of the transistor 311 (more specifically, the power supply terminal Vdd in FIG. 2 ). The second switch element is arranged between the DC power supply 93 and the drain terminal of the transistor 311 (more specifically, the power supply terminal Vdd in FIG. 2 ). These switch elements are, for example, transistors.

[0073] The bias voltage for amplifier 31a and the bias voltage for amplifier 31b may differ depending on the power levels output by amplifiers 31a and 31b and the type of transistor 311. For example, the bias voltage for amplifier 31a, which has a relatively low power level, may be 30 V, and the bias voltage for amplifier 31b, which has a relatively high power level, may be 48 V.

[0074] The DC power supply 93 generates one or more predetermined DC voltages from the AC voltage of a commercial AC power supply. The DC voltages from the DC power supply 93 are used as bias voltages for the amplifiers 31 a and 31 b and as drive power sources for the signal generating unit 2, the control unit 5, the bias voltage control circuit 92, etc.

[0075] The latch circuit 94 controls the bias voltage control circuit 92. When the magnitude of the forward wave power measurement signal or the magnitude of the reflected wave power measurement signal exceeds a threshold, the latch circuit 94 turns off the bias voltage control circuit 92. In other words, when the forward wave or the reflected wave reaches a predetermined magnitude, the latch circuit 94 turns off the bias voltage control circuit 92.

[0076] When the latch circuit 94 receives a reset signal from the control unit 5, it turns on the bias voltage control circuit 92. When the bias voltage control circuit 92 is turned on, the first and second switch elements are turned on. In this case, a bias voltage is supplied from the DC power supply 93 to the drain terminal of the transistor 311. This causes the amplifiers 31a and 31b to operate, causing the radio wave emitting unit 4 to emit radio waves.

[0077] When the bias voltage control circuit 92 is turned off, the first and second switch elements are turned off. In this case, the bias voltage is not supplied to the drain terminal of the transistor 311 from the DC power supply 93. This stops the amplifiers 31 a and 31 b, and the radio wave radiation from the radio wave radiation unit 4 stops.

[0078] The reflected wave separated by the non-reciprocal circuit 7 reaches the termination circuit 95 via the coupler 83. The termination circuit 95 includes a termination resistor and dissipates the reflected wave as heat.

[0079] The control unit 5 controls the signal generating unit 2 and the signal amplifying unit 3. This causes radio waves to be emitted from the radio wave emitting unit 4 into the cavity 10. In this embodiment, the control unit 5 operates the transistors 311 included in the amplifiers 31 a and 31 b in the saturation region. This improves the power efficiency of the amplifiers 31 a and 31 b.

[0080] When the amplifier 31 operates in the saturation region, the signal waveform is distorted. This generates harmonics whose fundamental wave is the high-frequency signal generated by the signal generating unit 2. As described above, the filter circuit 6 attenuates unwanted radiation. The unwanted radiation includes harmonics of the high-frequency signal amplified by the signal amplifying unit 3. In other words, the filter circuit 6 attenuates harmonics that are generated when the amplifier 31 operates in the saturation region.

[0081] The control unit 5 receives the forward wave power measurement signal and the reflected wave power measurement signal converted into digital signals by the AD conversion circuit 91. The control unit 5 may control the signal generating unit 2 and the signal amplifying unit 3 based on the forward wave power indicated by the forward wave power measurement signal and the reflected wave power indicated by the reflected wave power measurement signal.

[0082] The control unit 5 may cause the signal generating unit 2 and the signal amplifying unit 3 to perform normal operation based on the forward wave power indicated by the forward wave power measurement signal. In normal operation, the control unit 5 may control the signal generating unit 2 and the signal amplifying unit 3 so that the forward wave power becomes the target power.

[0083] The control unit 5 may control the power of the radio waves emitted by the radio wave emission unit 4 by causing the signal generation unit 2 to adjust the magnitude of the high-frequency signal. The control unit 5 may control the output of the radio waves emitted by the radio wave emission unit 4 by changing the amplification factor of the signal amplification unit 3, changing the voltage of an internal power supply connected to the signal amplification unit 3, etc. The control unit 5 may cause the variable amplifier 23 to adjust the magnitude of the high-frequency signal.

[0084] The control unit 5 may control the frequency of the radio waves emitted by the radio wave emission unit 4 by causing the signal generation unit 2 to adjust the frequency of the high-frequency signal. The frequency of the radio waves emitted by the radio wave emission unit 4 may be appropriately selected from a frequency band that can be used for dielectric heating of the irradiation target 11.

[0085] The control unit 5 may cause the signal generating unit 2 and the signal amplifying unit 3 to perform a protective operation based on the reflected wave power indicated by the reflected wave power measurement signal. For example, the control unit 5 may determine whether protection of the signal amplifying unit 3 is necessary based on the reflected wave power. The control unit 5 may determine whether protection of the signal amplifying unit 3 is necessary depending on whether the reflected wave power is equal to or greater than a threshold. When the control unit 5 determines that the reflected wave power is equal to or greater than the threshold, it executes a protective operation.

[0086] In the protection operation, the control unit 5 may stop at least one of the signal generating unit 2 and the signal amplifying unit 3. In the present embodiment, the latch circuit 94 stops the operation of the signal amplifying unit 3 by turning off the bias voltage control circuit 92 before the control unit 5 does. When the control unit 5 determines that protection of the signal amplifying unit 3 is not necessary, it may output a reset signal to the latch circuit 94 to terminate the protection operation.

[0087] The control unit 5 determines whether or not a corrective operation is required for the signal generating unit 2 and the signal amplifying unit 3 based on the reflected wave power. If the control unit 5 determines that a corrective operation is required, the control unit 5 executes the corrective operation. For the corrective operation, the control unit 5 controls the signal generating unit 2 or the signal amplifying unit 3, taking into account the reflected wave power, so that the forward wave power supplied to the irradiation target 11 becomes a target value.

[0088] The generation of reflected wave power may cause the forward wave power supplied to the irradiation object 11 to deviate from the target value. In this case, the control unit 5 adjusts the high-frequency signal output from at least one of the signal generating unit 2 and the signal amplifying unit 3 to correct the power of the radio waves radiated by the radio wave radiating unit 4. In this way, the control unit 5 adjusts the amount of power supplied to the irradiation object 11 so that it falls within the target range.

[0089] The control unit 5 may be configured by a microcontroller having one or more microprocessors and a memory, or may be configured by, for example, an FPGA (Field-Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit).

[0090] 1, the filter circuit 6 is disposed between the signal amplifier 3 and the radio wave emitter 4. The filter circuit 6 passes the high-frequency signal amplified by the signal amplifier 3 and attenuates unwanted radiation generated by the signal amplifier 3. The filter circuit 6 is usually designed with a predetermined load impedance and maintains optimal characteristics for the predetermined load impedance.

[0091] However, the electrical properties (e.g., relative dielectric constant) of the irradiation object 11 change depending on the state of the irradiation object 11 in the cavity 10 (e.g., the type of the irradiation object 11, the heating state, etc.). That is, the load impedance of the irradiation object 11 differs depending on the type of the irradiation object 11 and also changes during the heating process.

[0092] A change in the state of the irradiation object 11, i.e., a change in the load impedance of the irradiation object 11, changes the characteristics of the filter circuit 6. The characteristics of the filter circuit 6 are those that allow the high-frequency signal amplified by the signal amplifier 3 to pass and attenuate unwanted radiation generated by the signal amplifier 3.

[0093] The radio wave emitting device 1 includes a non-reciprocal circuit 7 disposed between the filter circuit 6 and the radio wave emitting unit 4. The non-reciprocal circuit 7 transmits signals from the filter circuit 6 to the radio wave emitting unit 4, while blocking signals from the radio wave emitting unit 4 to the filter circuit 6.

[0094] The non-reciprocal circuit 7 substantially makes the impedance of the non-reciprocal circuit 7 seen from the filter circuit 6 less susceptible to fluctuations in the load impedance. Therefore, the filter circuit 6 is less susceptible to changes in the state of the irradiation object 11 in the cavity 10.

[0095] That is, since the non-reciprocal circuit 7 is disposed after the filter circuit 6, the characteristics (signal passing characteristics) of the filter circuit 6 are kept constant regardless of the state of the irradiation object 11. This makes it possible to maintain the characteristics of the filter circuit 6 almost unchanged. That is, the filter circuit 6 can maintain the optimal signal passing characteristics for a determined load impedance.

[0096] In this way, the radio wave emission device 1 can suppress fluctuations in the characteristics of the filter circuit 6 due to the state of the irradiation target 11. This stabilizes the characteristics of the filter circuit 6 and improves the signal purity of the high frequency signal transmitted to the radio wave emission unit 4. In other words, the filter circuit 6 can stably remove unwanted radiation from the high frequency signal transmitted to the radio wave emission unit 4.

[0097] Furthermore, the non-reciprocal circuit 7 keeps the characteristics of not only the filter circuit 6 but also the signal amplifier 3 constant regardless of the state of the irradiation object 11. This stabilizes the power efficiency of the signal amplifier 3.

[0098] The following are the results of a simulation evaluating the characteristics of the filter circuit 6 for the radio wave emission device 1 and a comparative radio wave emission device when the state of the object to be irradiated 11 is different. The comparative radio wave emission device has the same configuration as the radio wave emission device 1 in Fig. 1 except that it does not include the non-reciprocal circuit 7. This makes it possible to confirm the effect of the non-reciprocal circuit 7 in the radio wave emission device 1.

[0099] Fig. 6 is a graph showing the characteristics of the filter circuit 6 of the radio wave emission device 1 for various states of the irradiation object 11. Fig. 7 is a partially enlarged view of the frequency band of 2400 MHz to 2500 MHz in Fig. 6.

[0100] Fig. 8 is a graph showing the characteristics of the filter circuit 6 of the radio wave emission device of the comparative example for various states of the irradiation object 11. Fig. 9 is a partially enlarged view of the frequency band of 2400 MHz to 2500 MHz of Fig. 8.

[0101] 6 to 9, the horizontal axis represents frequency [MHz], and the vertical axis represents loss (insertion loss) [dB]. In Fig. 6 and Fig. 7, graphs G11, G12, and G13 represent cases where the load impedance is 60Ω, 100Ω, and 150Ω, respectively. In Fig. 8 and Fig. 9, graphs G21, G22, and G23 represent cases where the load impedance is 60Ω, 100Ω, and 150Ω, respectively.

[0102] In this embodiment, the filter circuit 6 passes a high-frequency signal having a frequency of 2450 MHz and attenuates unwanted radiation generated in the signal amplifier 3. In this case, the unwanted radiation is a second harmonic having a frequency of 4900 MHz and a third harmonic having a frequency of 7350 MHz.

[0103] As shown in Figures 6 and 8, the loss is small near a frequency of 2450 MHz, and large near frequencies of 4900 MHz and 7350 MHz. As shown in Figure 6, graphs G11, G12, and G13 are almost the same. As shown in Figure 7, in the frequency band from 2400 MHz to 2500 MHz, the loss is about -1 dB when the load impedance is 60 Ω, 100 Ω, or 150 Ω.

[0104] That is, in the radio wave emission device 1, the filter circuit 6 is insulated from the irradiation target 11 (load) by the non-reciprocal circuit 7, so that the characteristics of the filter circuit 6 are less susceptible to the effects of fluctuations in load impedance, thereby reducing the effect on the power loss of the radio wave emission device 1.

[0105] Graphs G21, G22, and G23 shown in Fig. 8 are different from those shown in Fig. 6. From Fig. 9, in the frequency band (2400 MHz to 2500 MHz) of the high-frequency signal amplified by the signal amplifier 3, the loss [dB] at each of the load impedances of 60 Ω, 100 Ω, and 150 Ω for each of the frequencies of 2400 MHz, 2450 MHz, and 2500 MHz is as shown in Table 1.

[0106]

[0107] When the input power is 250 W, the power loss [W] in the filter circuit 6 for each frequency of 2400 MHz, 2450 MHz, and 2500 MHz is as shown in Table 2 below.

[0108]

[0109] 8 and 10, in the radio wave emission device of the comparative example, the filter circuit 6 is not insulated from the target 11 (load), and the characteristics of the filter circuit 6 are affected by fluctuations in the load impedance. That is, as the load impedance increases, the loss in the filter circuit 6 increases. As a result, the power loss in the filter circuit 6 increases (see Table 2).

[0110] In this way, the radio wave emission device 1 can suppress fluctuations in the characteristics of the filter circuit 6 due to the state of the irradiation target 11 by using the non-reciprocal circuit 7 .

[0111] As described above, in the radio wave emission device 1, the non-reciprocal circuit 7 includes the first transmission line 71 and the second transmission line 72, which are insulated from each other. The first transmission line 71 transmits a traveling wave to the radio wave emission unit 4, and the second transmission line 72 transmits a reflected wave to the termination circuit 95. The traveling wave power measurement unit 8a measures the traveling wave power in the first transmission line 71, and the reflected wave power measurement unit 8b measures the reflected wave power in the second transmission line 72.

[0112] This allows the forward wave power measuring unit 8a to measure the forward wave power without being affected by the reflected wave, thereby improving the accuracy of the radio wave emission device 1 in measuring the forward wave power and the reflected wave power.

[0113] The following are simulation results of changes in measured forward wave power with changes in the state of the object to be irradiated, for the radio wave emitting device 1 and a comparative radio wave emitting device. By evaluating these results, the effectiveness of the radio wave emitting device 1 was confirmed. The comparative radio wave emitting device differs from the radio wave emitting device 1 in FIG. 1 in that it does not include the non-reciprocal circuit 7.

[0114] Fig. 10 is a graph showing the change in the measured value of forward wave power in response to the change in the state of the irradiation object 11 in the radio wave emission device 1. Fig. 11 is a graph showing the change in the measured value of forward wave power in response to the change in the state of the irradiation object 11 in the radio wave emission device of the comparative example.

[0115] 10 and 11, the horizontal axis represents the load phase [°], and the vertical axis represents the measured value of the forward wave power [dBm]. The load phase is a parameter according to the state of the object 11 to be irradiated, and is the phase difference that occurs between the forward wave and the reflected wave due to a change in the state of the object 11 to be irradiated.

[0116] 10 and 11, the radio wave emission device 1 exhibits smaller fluctuations in the measured value of forward wave power than the radio wave emission device of the comparative example. The radio wave emission device of the comparative example does not include the non-reciprocal circuit 7, so the reflected wave S21 is coupled to the forward wave S11 in the coupler 82. This causes the reflected wave S21 to fluctuate the forward wave coupled signal S12. In other words, the detection accuracy of the forward wave coupled signal S12 deteriorates.

[0117] 11, the phase difference between the traveling wave S11 and the reflected wave S21 changes due to leakage of the reflected wave S21 from the first line 831 to the second line 832. This change in phase difference causes an error of about ±2 dBm in the measurement value.

[0118] On the other hand, since the radio wave emission device 1 includes the non-reciprocal circuit 7, the first transmission line 71 and the second transmission line 72 are insulated from each other. Therefore, leakage of the reflected wave S21 from the first line 831 to the second line 832 is extremely small. As a result, as shown in Fig. 10, almost no error occurs in the measurement value due to a change in the phase difference between the forward wave S11 and the reflected wave S21. In other words, the radio wave emission device 1 can improve the accuracy of measuring the forward wave power.

[0119] [1.1.3 Effects, etc.] The radio wave emission device 1 according to this embodiment includes a cavity 10, a signal generating unit 2, a signal amplifying unit 3, a radio wave emission unit 4, a control unit 5, a filter circuit 6, and a non-reciprocal circuit 7.

[0120] The signal generating unit 2 generates a high-frequency signal. The signal amplifying unit 3 has an amplifier 31 and amplifies the high-frequency signal. The radio wave emitting unit 4 emits radio waves into the cavity 10 based on the high-frequency signal amplified by the signal amplifying unit 3. The control unit 5 controls the signal generating unit 2 and the signal amplifying unit 3.

[0121] The filter circuit 6 is disposed between the amplifier 31 and the radio wave emitting unit 4, and passes the high-frequency signal amplified by the signal amplifying unit 3, while attenuating unwanted radiation generated by the signal amplifying unit 3. The non-reciprocal circuit 7 is disposed between the filter circuit 6 and the radio wave emitting unit 4.

[0122] This configuration can suppress variations in the characteristics of the filter circuit 6 due to the state of the irradiation target 11. Therefore, the signal purity of the high frequency signal transmitted to the radio wave emitting portion 4 can be improved.

[0123] In the radio wave emission device 1, the control unit 5 operates the amplifier 31 of the signal amplification unit 3 in the saturation region. This configuration can improve the power efficiency of the signal amplification unit 3.

[0124] In the radio wave emitting device 1, unwanted radiation includes harmonics of the high frequency signal generated when the amplifier 31 of the signal amplifying unit 3 operates in a saturated region. This configuration can improve the signal purity of the high frequency signal transmitted to the radio wave emitting unit 4.

[0125] The radio wave emission device 1 further includes a forward wave power measurement unit 8a and a reflected wave power measurement unit 8b. The forward wave power measurement unit 8a measures forward wave power. The forward wave power is the power of a forward wave, and a forward wave is a high-frequency signal amplified by the signal amplifier 3. The reflected wave power measurement unit 8b measures reflected wave power. The reflected wave power is the power of a reflected wave, and a reflected wave is a high-frequency signal that flows backward from the radio wave emission unit 4.

[0126] The non-reciprocal circuit 7 includes a first transmission line 71 and a second transmission line 72 that are insulated from each other. The first transmission line 71 transmits a traveling wave to the radio wave emitting unit 4. The second transmission line 72 transmits a reflected wave to the termination circuit 95. The traveling wave power measuring unit 8a measures the traveling wave power in the first transmission line 71. The reflected wave power measuring unit 8b measures the reflected wave power in the second transmission line 72.

[0127] The control unit 5 controls the signal generating unit 2 and the signal amplifying unit 3 based on the forward wave power and the reflected wave power. This configuration can improve the accuracy of the measurement of the forward wave power and the measurement of the reflected wave power.

[0128] In the radio wave emission device 1, the filter circuit 6 includes band-elimination filters 61 and 62, which are distributed constant circuits. The band-elimination filters 61 and 62 are disposed on the circuit board 30 of the signal amplifier 3. This configuration makes it possible to reduce the size of the radio wave emission device 1. This configuration is suitable for a radio wave emission device that can handle high-frequency power of 10 W or more.

[0129] In the radio wave emission device 1, the filter circuit 6 includes band-elimination filters 61 and 62. The band-elimination filters attenuate harmonics of the high-frequency signal. This configuration allows for the miniaturization of the filter circuit 6. This configuration is suitable for a radio wave emission device capable of handling high-frequency power of 10 W or more.

[0130] In the radio wave emission device 1, each of the band-elimination filters 61, 62 includes a short stub and an open stub. The short stub attenuates the second harmonic of the radio frequency signal. The open stub attenuates the third harmonic of the radio frequency signal. This configuration enables the filter circuit 6 to be miniaturized. This configuration is suitable for a radio wave emission device capable of handling radio frequency power of 10 W or more.

[0131] A radio wave emitting device 1 according to another embodiment includes a cavity 10, a signal generating section 2, a signal amplifying section 3, a radio wave emitting section 4, a control section 5, a filter circuit 6, and a non-reciprocal circuit 7.

[0132] The signal generating unit 2 generates a high-frequency signal. The signal amplifying unit 3 has an amplifier 31 and amplifies the high-frequency signal. The radio wave emitting unit 4 emits radio waves into the cavity 10 based on the high-frequency signal amplified by the signal amplifying unit 3. The control unit 5 controls the signal generating unit 2 and the signal amplifying unit 3.

[0133] The filter circuit 6 passes the high-frequency signal amplified by the signal amplifier 3 and attenuates unwanted radiation generated by the signal amplifier 3. The non-reciprocal circuit 7 reduces fluctuations in the characteristics of the filter circuit 6. This configuration can improve the signal purity of the high-frequency signal transmitted to the radio wave emitter 4.

[0134] [1.2 Second Embodiment] [1.2.1 Configuration] Fig. 12 is a schematic circuit diagram of a radio wave emission device 1A according to a second embodiment of the present disclosure. As shown in Fig. 12, the radio wave emission device 1A includes a signal generating unit 2, a signal amplifying unit 3, a radio wave emission unit 4, a control unit 5, a filter circuit 6, and a non-reciprocal circuit 7A. The radio wave emission device 1A also includes a forward wave power measuring unit 8A. Furthermore, the radio wave emission device 1A includes an AD conversion circuit 91, a bias voltage control circuit 92, a DC power supply 93, and a latch circuit 94.

[0135] The non-reciprocal circuit 7A is disposed between the filter circuit 6 and the radio wave emitting portion 4. The non-reciprocal circuit 7A transmits the traveling wave from the filter circuit 6 to the radio wave emitting portion 4, but does not transmit the reflected wave from the radio wave emitting portion 4 to the filter circuit 6. The non-reciprocal circuit 7A is, for example, an isolator.

[0136] The non-reciprocal circuit 7A includes a circulator 70A and a termination circuit 73A. The circulator 70A includes a first transmission line 71A and a second transmission line 72A. The termination circuit 73A is connected to the second transmission line 72A. The first transmission line 71A transmits a traveling wave to the radio wave emitting portion 4, and the second transmission line 72A transmits a reflected wave to the termination circuit 73A.

[0137] The forward wave power measuring unit 8A measures the forward wave power. In this embodiment, the forward wave power measuring unit 8A is disposed on the first transmission line 71A between the filter circuit 6 and the non-reciprocal circuit 7A, and measures the forward wave power.

[0138] This allows the forward wave power measuring unit 8A to measure the forward wave power without being affected by the reflected wave, thereby improving the accuracy of the forward wave power measurement of the radio wave emission device 1A.

[0139] The traveling wave power measuring unit 8A includes a detection circuit 81 and a coupler 82. The coupler 82 detects the traveling wave. The coupler 82 is disposed between the filter circuit 6 and the non-reciprocal circuit 7A. The coupler 82 is a directional coupler.

[0140] The detection circuit 81 measures the forward power. In this embodiment, the detection circuit 81 receives the forward coupled signal S12 (see FIG. 4 ) from the coupler 82 and generates a forward power measurement signal, which is an analog signal corresponding to the forward power, based on the forward coupled signal S12. In this embodiment, the detection circuit 81 transmits the forward power measurement signal to the AD conversion circuit 91 and the latch circuit 94.

[0141] The AD conversion circuit 91 converts the forward power measurement signal from the detection circuit 81 into a digital signal, and transmits the digital signal to the control unit 5 .

[0142] The latch circuit 94 controls the bias voltage control circuit 92. For example, when the forward wave power measurement signal from the detection circuit 81 exceeds a threshold value, the latch circuit 94 turns off the bias voltage control circuit 92. When the latch circuit 94 receives a reset signal from the control unit 5, it turns on the bias voltage control circuit 92.

[0143] The control unit 5 controls the signal generating unit 2 and the signal amplifying unit 3 to cause the radio wave emitting unit 4 to emit radio waves into the cavity 10. In this embodiment, the control unit 5 operates the amplifier 31 of the signal amplifying unit 3 in the saturation region, thereby improving the power efficiency of the amplifier 31.

[0144] The control unit 5 receives the forward power measurement signal converted into a digital signal by the AD conversion circuit 91. The control unit 5 may control the signal generating unit 2 and the signal amplifying unit 3 based on the forward power indicated by the forward power measurement signal.

[0145] For example, the control unit 5 may control the signal generating unit 2 and the signal amplifying unit 3 based on the forward wave power indicated by the forward wave power measurement signal to cause the radio wave emitting device 1A to perform normal operation. In normal operation, the control unit 5 may control the signal generating unit 2 and the signal amplifying unit 3 to adjust the forward wave power to a target power.

[0146] [1.2.2 Effects, etc.] As described above, the radio wave emission device 1A includes a forward wave power measurement unit 8A. The forward wave power measurement unit 8A is disposed between the signal amplification unit 3 and the radio wave emission unit 4, and measures the forward wave power. The control unit 5 controls the signal generation unit 2 and the signal amplification unit 3 based on the forward wave power. This configuration can improve the accuracy of measuring the forward wave power.

[0147] [1.3 Third Embodiment] [1.3.1 Configuration] Fig. 13 is a schematic circuit diagram of a radio wave emission device 1B according to a third embodiment of the present disclosure. As shown in Fig. 13, the radio wave emission device 1B includes a signal generating unit 2, a signal amplifying unit 3, a radio wave emission unit 4, a control unit 5, a filter circuit 6, and a non-reciprocal circuit 7A. The radio wave emission device 1B also includes a power measuring unit 8B. Furthermore, the radio wave emission device 1B includes an AD conversion circuit 91, a bias voltage control circuit 92, a DC power supply 93, and a latch circuit 94.

[0148] The power measurement unit 8B measures the forward wave power and the reflected wave power. The power measurement unit 8B includes a detection circuit 81 and a coupler 84. The coupler 84 detects the forward wave and the reflected wave. The coupler 84 is disposed between the non-reciprocal circuit 7A and the radio wave emitting unit 4.

[0149] Fig. 14 is a schematic diagram of a coupler 84A, which is a first example of the coupler 84. As shown in Fig. 14, the coupler 84A is a bidirectional coupler. The coupler 84A includes a first input / output port 84a, a second input / output port 84b, a first coupled port 84c, a second coupled port 84d, a first line 841, and a second line 842.

[0150] The first input / output port 84a is connected to the non-reciprocal circuit 7A, and the second input / output port 84b is connected to the radio wave emitting unit 4. The first line 841 is disposed between the first input / output port 84a and the second input / output port 84b. The second line 842 is disposed between the first coupled port 84c and the second coupled port 84d, and is electromagnetically coupled to the first line 841 in a partially parallel manner.

[0151] The traveling wave S11 is input to the first input / output port 84a and propagates through the first line 841. The coupler 84A outputs a part of the traveling wave S11 as a traveling-wave coupled signal S12 from the first coupled port 84c via the second line 842. The magnitude of the traveling-wave coupled signal S12 is proportional to the power of the traveling wave S11.

[0152] The reflected wave S21 is input to the second input / output port 84b and propagates through the first line 841. The coupler 84A outputs a part of the reflected wave S21 as a reflected wave coupled signal S22 from the second coupled port 84d via the second line 842. The magnitude of the reflected wave coupled signal S22 is proportional to the power of the reflected wave S21.

[0153] 15 is a schematic diagram of a coupler 84B, which is a second example of the coupler 84. As shown in Fig. 15, the coupler 84B is a dual directional coupler. The coupler 84B includes a first input / output port 84a, a second input / output port 84b, a first coupled port 84c, a second coupled port 84d, a first termination resistor 84e, a second termination resistor 84f, a first line 841, a second line 842, and a third line 843.

[0154] The first input / output port 84a is connected to the non-reciprocal circuit 7A, and the second input / output port 84b is connected to the radio wave emitting unit 4. The first line 841 is arranged between the first input / output port 84a and the second input / output port 84b. The second line 842 is arranged between the first coupled port 84c and the first termination resistor 84e, and is electromagnetically coupled to the first line 841 in a partially parallel manner.

[0155] The third line 843 is disposed between the second coupled port 84d and the second termination resistor 84f, and is electromagnetically coupled to the first line 841 in a partially parallel manner.

[0156] The traveling wave S11 is input to the first input / output port 84a and propagates through the first line 841. The coupler 84B outputs a part of the traveling wave S11 as a traveling-wave coupled signal S12 from the first coupled port 84c via the second line 842. The magnitude of the traveling-wave coupled signal S12 is proportional to the power of the traveling wave S11.

[0157] The reflected wave S21 is input to the second input / output port 84b and propagates through the first line 841. The coupler 84B outputs a part of the reflected wave S21 as a reflected wave coupled signal S22 from the second coupled port 84d via the third line 843. The magnitude of the reflected wave coupled signal S22 is proportional to the power of the reflected wave S21.

[0158] Both the coupler 84A shown in Fig. 14 and the coupler 84B shown in Fig. 15 can detect forward and reflected wave power. However, unlike the coupler 84A, the coupler 84B has a first coupled port 84c and a second coupled port 84d arranged on a second line 842 and a third line 843, respectively. That is, the first coupled port 84c is arranged on a line different from the line on which the second coupled port 84d is arranged.

[0159] This configuration allows coupler 84B to have higher directivity and isolation characteristics than coupler 84A. Also, coupler 84B is less likely than coupler 84A to have a mismatch in one of the two lines affect the other line.

[0160] 13 , the control unit 5 controls the signal generating unit 2 and the signal amplifying unit 3 to cause the radio wave emitting unit 4 to emit radio waves into the cavity 10. In this embodiment, the control unit 5 operates the amplifier 31 of the signal amplifying unit 3 in the saturation region, thereby improving the power efficiency of the amplifier 31.

[0161] The control unit 5 receives the forward wave power measurement signal and the reflected wave power measurement signal converted into digital signals by the AD conversion circuit 91. The control unit 5 may control the signal generating unit 2 and the signal amplifying unit 3 based on the forward wave power indicated by the forward wave power measurement signal and the reflected wave power indicated by the reflected wave power measurement signal.

[0162] [1.3.2 Effects, etc.] As described above, radio wave emission device 1B includes power measurement unit 8B. Power measurement unit 8B is disposed between non-reciprocal circuit 7A and radio wave emission unit 4, and measures forward wave power and reflected wave power. Control unit 5 controls signal generation unit 2 and signal amplification unit 3 based on the forward wave power and reflected wave power.

[0163] [2. Modifications] The present disclosure is not limited to the above-described embodiments. Various modifications may be made to the above-described embodiments as necessary as long as the object of the present disclosure can be achieved. Modifications of the above-described embodiments are listed below.

[0164] 16 is a schematic circuit diagram of a filter circuit 6C according to a first modification. The filter circuit 6C can be used in place of or in addition to the filter circuit 6 in any of the first to third embodiments.

[0165] 16 , the filter circuit 6C includes a band-elimination filter 63. The band-elimination filter 63 is, for example, a short stub that attenuates the second harmonic of the high-frequency signal amplified by the signal amplifier 3. The band-elimination filter 63 is formed, for example, by a microstrip line that extends from the transmission line 301 to the ground 303 and is connected to the ground 303.

[0166] If the length of the band-elimination filter 63 is L63 and the wavelength of the signal propagating through the transmission line 301 is λ, then when L63<λ / 4, the band-elimination filter 63 functions as an inductor. When L63=λ / 4, the band-elimination filter 63 has an open impedance. When λ / 4<L63<λ / 2, the band-elimination filter 63 functions as a capacitor. When L63=λ / 2, the band-elimination filter 63 has a short-circuit impedance.

[0167] The length L63 of the band elimination filter 63 is set based on ¼ of the wavelength λ of the high frequency signal amplified by the signal amplifier 3. Therefore, the band elimination filter 63 functions as an open impedance for the high frequency signal amplified by the signal amplifier 3. On the other hand, the band elimination filter 63 functions as a short-circuit impedance for the second harmonic of the high frequency signal amplified by the signal amplifier 3.

[0168] As a result, the band-elimination filter 63 passes the high-frequency signal amplified by the signal amplifier 3, and attenuates the second harmonic of the high-frequency signal amplified by the signal amplifier 3. For example, if the frequency of the high-frequency signal amplified by the signal amplifier 3 is 2450 MHz, the frequency of the second harmonic is 4900 MHz.

[0169] 17 is a schematic circuit diagram of a filter circuit 6D according to a second modification. The filter circuit 6D can be used in place of or in addition to the filter circuit 6 according to the first to third embodiments.

[0170] 17, the filter circuit 6D includes band-elimination filters 64 and 65. The band-elimination filters 64 and 65 are, for example, short stubs that attenuate the second harmonic of the high-frequency signal amplified by the signal amplifier 3.

[0171] The band-elimination filter 64 is configured, for example, by a microstrip line that extends from the transmission line 301 to the ground 302 and is connected to the ground 302. The band-elimination filter 65 is configured, for example, by a microstrip line that extends from the transmission line 301 to the ground 303 and is connected to the ground 303.

[0172] If the length of the band-elimination filter 64 is L64 and the wavelength of the signal propagating through the transmission line 301 is λ, then when L64<λ / 4, the band-elimination filter 64 functions as an inductor. When L64=λ / 4, the band-elimination filter 64 has an open impedance. When λ / 4<L64<λ / 2, the band-elimination filter 64 functions as a capacitor. When L64=λ / 2, the band-elimination filter 64 has a short-circuit impedance.

[0173] If the length of the band-elimination filter 65 is L65 and the wavelength of the signal propagating through the transmission line 301 is λ, then when L65<λ / 4, the band-elimination filter 65 functions as an inductor. When L65=λ / 4, the band-elimination filter 65 has an open impedance. When λ / 4<L65<λ / 2, the band-elimination filter 65 functions as a capacitor. When L65=λ / 2, the band-elimination filter 65 has a short-circuit impedance.

[0174] The lengths L64 and L65 are set based on ¼ of the wavelength λ of the high-frequency signal amplified by the signal amplifier 3. As a result, the band-elimination filters 64 and 65 function as open impedances for the high-frequency signal amplified by the signal amplifier 3. On the other hand, the band-elimination filters 64 and 65 function as short-circuit impedances for the second harmonic of the high-frequency signal amplified by the signal amplifier 3.

[0175] In this embodiment, the lengths L64 and L65 are different from each other. Specifically, L65≦λ / 4≦L64. This causes the stop bands of the band-elimination filters 64 and 65 to partially overlap, widening the stop band of the filter circuit 6.

[0176] 17 includes band-elimination filters 64 and 65. The band-elimination filters 64 and 65 are multiple distributed constant circuits whose rejection bands partially overlap. This configuration widens the rejection band of the filter circuit 6, thereby improving the signal purity of the high-frequency signal transmitted to the radio wave emitting portion 4.

[0177] 17, the band elimination filters 64 and 65 are configured as separate bodies. However, the band elimination filters 64 and 65 may also be configured as an integrated unit. The band elimination filters 64 and 65 may be configured to share a connection point with the transmission line 301 and have paths that branch at the portion connected to the ground 303, so that L64 and L65 are different from each other.

[0178] Each of the band elimination filters 64 and 65 includes a short stub. However, the length of the short stub included in the band elimination filter 64 is different from the length of the short stub included in the band elimination filter 65. This configuration allows the filter circuit 6 to be made smaller.

[0179] 18 is a schematic circuit diagram of a filter circuit 6E according to a third modification. The filter circuit 6E can be used in place of or in addition to the filter circuit 6 according to the first to third embodiments.

[0180] 18, the filter circuit 6E includes a low-pass filter 66. The low-pass filter 66 is a lumped constant circuit. The low-pass filter 66 attenuates signals with frequencies higher than the frequency of the high-frequency signal amplified by the signal amplifier 3. The low-pass filter 66 includes an input terminal 66a, an output terminal 66b, inductors L21 and L22, and capacitors C21 and C22.

[0181] Inductors L21 and L22 are connected in series between input terminal 66a and output terminal 66b. Capacitor C21 is arranged between ground and the midpoint between input terminal 66a and inductor L21. Capacitor C22 is arranged between ground and the midpoint between inductors L21 and L22.

[0182] The low-pass filter 66 functions as a matching circuit (e.g., the output matching circuit 33 in FIG. 1 ) for the amplifier 31 of the signal amplification unit 3. More specifically, the low-pass filter 66 is configured using an inductor and a capacitor, as described above. The inductor and the capacitor are used to set the output impedance of the amplifier 31 to a predetermined impedance (e.g., 50Ω).

[0183] Therefore, the low-pass filter 66 functions as a matching circuit, more specifically, as the output matching circuit 33 in Fig. 1. From another perspective, the output matching circuit 33 in Fig. 1 functions as a filter for the filter circuit 6. The output matching circuit of the signal amplifier 3 that handles high power is configured by a distributed constant circuit.

[0184] As described above, the filter circuit 6E includes the low-pass filter 66 that functions as a matching circuit for the amplifier 31 of the signal amplifier 3. This configuration makes it possible to reduce the size of the radio wave emission device 1. This configuration is suitable when the radio wave emission device 1 handles large high-frequency power.

[0185] 19 is a schematic circuit diagram of a filter circuit 6F according to a fourth modification. The filter circuit 6F can be used in place of or in addition to the filter circuit 6 in any of the first to third embodiments.

[0186] 19, the filter circuit 6F includes a band-pass filter 67. The band-pass filter 67 is a distributed constant circuit. The band-pass filter 67 passes high-frequency signals in a frequency band that includes the frequency of the high-frequency signal amplified by the signal amplifier 3.

[0187] The bandpass filter 67 has microstrip lines 671, 672, 673, and 674 that form part of the transmission line 301. The microstrip lines 671, 672, 673, and 674 are formed by conductor patterns formed on a printed circuit board.

[0188] The microstrip line 671 functions as an inductor inserted into the transmission line 301. The microstrip line 672 functions as a capacitor between the transmission line 301 and the ground. The microstrip line 673 functions as a capacitor inserted into the transmission line 301. The microstrip line 674 functions as an inductor between the transmission line 301 and the ground.

[0189] The inductance of the microstrip lines 671 and 674 and the capacitance of the microstrip lines 672 and 673 allow high frequency signals in a frequency band that includes the frequency of the high frequency signal amplified by the signal amplifier 3 to pass.

[0190] 20 is a schematic circuit diagram of a filter circuit 6G according to a fifth modification. The filter circuit 6G can be used in place of or in addition to the filter circuit 6 in any of the first to third embodiments.

[0191] As shown in Figure 20, the filter circuit 6G includes a bandpass filter 68. The bandpass filter 68 is a lumped constant circuit. A lumped constant circuit can be used when the wavelength of a high-frequency signal is sufficiently large relative to the circuit shape and the shapes of the circuit elements (circuit components). In this case, the lines connecting the circuit elements are sufficiently short compared to the wavelength, and phase differences can be ignored, so the voltage and current are considered to be constant at any position on the line.

[0192] In a lumped constant circuit, the constant values ​​concentrated at a single point of a circuit element can be used as they are, i.e., the resistance of a resistor, the capacitance of a capacitor, and the inductance of an inductor can be used as they are.

[0193] The bandpass filter 68 passes high-frequency signals in a frequency band that includes the frequency of the high-frequency signal amplified by the signal amplifier 3. The bandpass filter 68 includes an input terminal 68a, an output terminal 68b, capacitors C41 and C42, and inductors L41 and L42.

[0194] Capacitor C41 is arranged between ground and the midpoint between input terminal 68a and output terminal 68b. Inductor L41 is arranged between input terminal 68a and capacitor C41. Capacitor C42 is arranged between capacitor C41 and output terminal 68b. Inductor L42 is arranged between ground and the midpoint between capacitor C42 and output terminal 68b.

[0195] [2.6 Other Modifications] The configurations of the signal generating unit 2, the signal amplifying unit 3, and the radio wave emitting unit 4 are not limited to those in the above embodiment. The signal generating unit 2 may generate a plurality of high-frequency signals with different frequencies. In the signal amplifying unit 3, at least one of the plurality of amplifiers may be an amplifier 31 having a transistor. The number of signal generating units 2, the number of signal amplifying units 3, and the number of radio wave emitting units 4 is also not particularly limited.

[0196] The operation of the control unit 5 is not limited to that of the above embodiment. The control unit 5 does not have to operate all of the amplifiers 31 a, 31 b of the signal amplification unit 3 in the saturation region. The operation of the control unit 5 described in the above embodiment is merely an example, and the control unit 5 may perform various well-known operations.

[0197] The filter circuit 6 is arranged between the amplifier 31 (particularly, amplifier 31b) of the signal amplifier 3 and the radio wave emitter 4, and passes the high-frequency signal amplified by the signal amplifier 3 while attenuating unwanted radiation generated by the signal amplifier 3.

[0198] The filter circuit 6 includes one or more filters. Each filter may be a distributed constant circuit or a lumped constant circuit. The filter circuit 6 includes at least one of a distributed constant circuit and a lumped constant circuit. This configuration can improve the signal purity of the high-frequency signal transmitted to the radio wave emitting unit 4.

[0199] The filter circuit 6 includes at least one of a band-pass filter, a band-elimination filter, and a low-pass filter. This configuration can improve the signal purity of the high-frequency signal transmitted to the radio wave emitting portion 4.

[0200] The non-reciprocal circuit 7 is disposed between the filter circuit 6 and the radio wave emitting portion 4 and reduces fluctuations in the characteristics of the filter circuit 6. The non-reciprocal circuit 7 is formed, for example, by a circulator or an isolator. However, the non-reciprocal circuit 7 is not limited to these and may be any circuit as long as it can connect the filter circuit 6 and the radio wave emitting portion 4 so that the load impedance seen from the filter circuit 6 does not substantially change.

[0201] The configurations of the forward wave power measuring unit 8 a, the reflected wave power measuring unit 8 b, the forward wave power measuring unit 8 A, and the power measuring unit 8 B are not limited to those in the above embodiment. For example, it is not essential that any of a directional coupler, a bidirectional coupler, and a dual coupler be used.

[0202] In the first embodiment, the forward wave power measuring unit 8a is arranged between the filter circuit 6 and the non-reciprocal circuit 7. However, the forward wave power measuring unit 8a may be arranged between the signal amplifier 3 and the non-reciprocal circuit 7. In other words, the forward wave power measuring unit 8a may be arranged in the upstream stage of the filter circuit 6.

[0203] The AD conversion circuit 91, the bias voltage control circuit 92, the DC power supply 93, and the latch circuit 94 are optional elements.

[0204] The radio wave emission device 1 may include an additional processing means. The processing means may be a heating means or a radio wave emission means. The heating means is, for example, a heater. In this case, a process can be performed by combining the heater and the radio wave emission unit 4. The radio wave emission means is, for example, a magnetron. In this case, a process can be performed by combining the magnetron and the radio wave emission unit 4.

[0205] [3. Aspects] A radio wave emitting device (1; 1A; 1B) according to a first aspect includes a cavity (10), a signal generating unit (2), a signal amplifying unit (3), a radio wave emitting unit (4), a control unit (5), a filter circuit (6; 6C; 6D; 6E; 6F; 6G), and a non-reciprocal circuit (7; 7A).

[0206] The signal generating unit (2) generates a high-frequency signal. The signal amplifying unit (3) has an amplifier (31) and amplifies the high-frequency signal. The radio wave emitting unit (4) emits radio waves into the cavity (10) based on the high-frequency signal amplified by the signal amplifying unit (3). The control unit (5) controls the signal generating unit (2) and the signal amplifying unit (3).

[0207] The filter circuits (6; 6C; 6D; 6E; 6F; 6G) are arranged between the amplifier (31) and the radio wave emitting section (4) to pass the high frequency signal amplified by the signal amplifying section (3) and attenuate unwanted radiation generated by the signal amplifying section (3). The non-reciprocal circuits (7; 7A) are arranged between the filter circuits (6; 6C; 6D; 6E; 6F; 6G) and the radio wave emitting section (4).

[0208] According to this aspect, the signal purity of the high frequency signal transmitted to the radio wave emitting portion (4) can be improved.

[0209] In the radio wave emission device (1; 1A; 1B) according to the second aspect, based on the first aspect, the control unit (5) operates the amplifier (31) of the signal amplification unit (3) in a saturation region. According to this aspect, the power efficiency of the signal amplification unit (3) can be improved.

[0210] In the radio wave emitting device (1; 1A; 1B) according to the third aspect, the unwanted radiation includes harmonics of the high frequency signal generated when the amplifier (31) of the signal amplifying unit (3) operates in a saturated region. According to this aspect, the signal purity of the high frequency signal transmitted to the radio wave emitting unit (4) can be improved.

[0211] A radio wave emission device (1; 1A; 1B) according to a fourth aspect is based on any one of the first to third aspects and further includes a forward wave power measurement unit (8a) and a reflected wave power measurement unit (8b). The forward wave power measurement unit (8a) measures forward wave power, which is the power of a forward wave that is a high-frequency signal amplified by the signal amplifier (3). The reflected wave power measurement unit (8b) measures reflected wave power, which is the power of a reflected wave that flows back from the radio wave emission unit (4).

[0212] The non-reciprocal circuit (7) includes a first transmission line (71) and a second transmission line (72) that are insulated from each other. The first transmission line (71) transmits a traveling wave to the radio wave emitting portion (4). The second transmission line (72) transmits a reflected wave to the termination circuit (95).

[0213] The forward wave power measuring unit (8a) measures the forward wave power on the first transmission line (71). The reflected wave power measuring unit (8b) measures the reflected wave power on the second transmission line (72). The control unit (5) controls the signal generating unit (2) and the signal amplifying unit (3) based on the forward wave power and the reflected wave power. According to this aspect, the accuracy of measuring the forward wave power and the reflected wave power can be improved.

[0214] A radio wave emission device (1A) according to a fifth aspect is based on any one of the first to third aspects and further includes a forward wave power measurement unit (8A). The forward wave power measurement unit (8A) is disposed between the signal amplification unit (3) and the radio wave emission unit (4) and measures forward wave power, which is the power of a forward wave that is a high-frequency signal amplified by the signal amplification unit (3).

[0215] The control unit (5) controls the signal generating unit (2) and the signal amplifying unit (3) based on the forward power. According to this aspect, the accuracy of measurement of the forward power can be improved.

[0216] A radio wave emission device (1B) according to a sixth aspect is based on any one of the first to third aspects and further includes a power measurement unit (8B). The power measurement unit (8B) is disposed between the non-reciprocal circuit (7A) and the radio wave emission unit (4) and measures forward wave power, which is the power of a forward wave that is a high-frequency signal amplified by the signal amplifier (3), and reflected wave power, which is the power of a reflected wave that flows back from the radio wave emission unit (4).

[0217] The control unit (5) controls the signal generating unit (2) and the signal amplifying unit (3) based on the forward wave power and the reflected wave power. According to this aspect, the accuracy of measurement of the forward wave power and the reflected wave power can be improved.

[0218] In a radio wave emission device (1; 1A; 1B) according to a seventh aspect, based on any one of the first to sixth aspects, the filter circuit (6; 6C; 6D; 6E; 6F; 6G) includes at least one of a band-pass filter (67, 68), a band-elimination filter (61, 62, 63, 64, 65), and a low-pass filter (66). According to this aspect, the signal purity of a high-frequency signal transmitted to the radio wave emission unit (4) can be improved.

[0219] In a radio wave emitting device (1; 1A; 1B) according to an eighth aspect, based on any one of the first to seventh aspects, the filter circuit (6; 6C; 6D; 6E; 6F; 6G) includes at least one of a distributed constant circuit (61, 62, 63, 64, 65, 66, 67) and a lumped constant circuit (68). According to this aspect, the signal purity of a high frequency signal transmitted to the radio wave emitting unit (4) can be improved.

[0220] In a radio wave emission device (1; 1A; 1B) according to a ninth aspect, based on any one of the first to eighth aspects, the filter circuit (6; 6C; 6D; 6E; 6F) includes distributed constant circuits (61, 62, 63, 64, 65, 66, 67). The distributed constant circuits (61, 62, 63, 64, 65, 66, 67) are arranged on a circuit board (300) of the signal amplifier section (3). According to this aspect, the radio wave emission device (1; 1A; 1B) can be miniaturized.

[0221] In a radio wave emission device (1; 1A; 1B) according to a tenth aspect, based on any one of the first to ninth aspects, the filter circuit (6E) includes a low-pass filter (66) that functions as a matching circuit for the amplifier (31) of the signal amplification section (3). According to this aspect, the radio wave emission device (1; 1A; 1B) can be made smaller.

[0222] In a radio wave emission device (1; 1A; 1B) according to an eleventh aspect, based on any one of the first to tenth aspects, the filter circuit (6D) includes a plurality of band elimination filters (64, 65). The plurality of band elimination filters (64, 65) are a plurality of distributed constant circuits (64, 65) whose elimination bands partially overlap.

[0223] According to this aspect, the rejection band of the filter circuit (6D) can be widened, and the signal purity of the high frequency signal transmitted to the radio wave emitting portion (4) can be improved.

[0224] In the radio wave emission device (1; 1A; 1B) according to the twelfth aspect, based on the eleventh aspect, the plurality of distributed constant circuits (64, 65) include a plurality of short stubs (64, 65) each having a different length. According to this aspect, the filter circuit (6D) can be miniaturized.

[0225] In a radio wave emission device (1; 1A; 1B) according to a thirteenth aspect, based on any one of the first to twelfth aspects, the filter circuit (6) includes distributed constant circuits (61, 62) constituting a band-elimination filter that attenuates harmonics of a high-frequency signal. According to this aspect, the filter circuit (6) can be made smaller.

[0226] In a radio wave emission device (1; 1A; 1B) according to a fourteenth aspect, based on the thirteenth aspect, the distributed constant circuit (61, 62) includes a short stub (61) and an open stub (62). The short stub (61) attenuates the second harmonic of the high frequency signal. The open stub (62) attenuates the third harmonic of the high frequency signal. According to this aspect, the filter circuit (6) can be miniaturized.

[0227] The radio wave emitting device (1; 1A; 1B) according to the fifteenth aspect comprises a cavity (10), a signal generating unit (2), a signal amplifying unit (3), a radio wave emitting unit (4), a control unit (5), a filter circuit (6; 6C; 6D; 6E; 6F; 6G), and a non-reciprocal circuit (7; 7A).

[0228] The signal generating unit (2) generates a high-frequency signal. The signal amplifying unit (3) has an amplifier (31) and amplifies the high-frequency signal. The radio wave emitting unit (4) emits radio waves into the cavity (10) based on the high-frequency signal amplified by the signal amplifying unit (3). The control unit (5) controls the signal generating unit (2) and the signal amplifying unit (3).

[0229] The filter circuits (6; 6C; 6D; 6E; 6F; 6G) pass the high-frequency signals amplified by the signal amplifier section (3) and attenuate unwanted radiation generated by the signal amplifier section (3). The non-reciprocal circuits (7; 7A) reduce fluctuations in the characteristics of the filter circuits (6; 6C; 6D; 6E; 6F; 6G).

[0230] According to this aspect, the signal purity of the high frequency signal transmitted to the radio wave emitting portion (4) can be improved.

[0231] The second to fourteenth aspects are not essential and are optional, and can be appropriately combined with the fifteenth aspect.

[0232] The present disclosure is applicable to a radio wave emitting device that emits radio waves based on a high frequency signal amplified by a signal amplifier.

[0233] REFERENCE SIGNS LIST 1, 1A, 1B Radio wave emitting device 2 Signal generating section 21 Oscillator circuit 22 Matching circuit 23 Variable amplifier 3 Signal amplifying section 30 Circuit board 301 Transmission line 302, 303 Ground 31, 31a, 31b Amplifier 311 Transistor 312, 313 Choke circuit 32 Input matching circuit 33 Output matching circuit 4 Radio wave emitting section 5 Control section 6, 6C, 6D, 6E, 6F, 6G Filter circuit 61, 62, 63, 64, 65 Band-stop filter (distributed constant circuit) 66 Low-pass filter (lumped constant circuit) 66a Input terminal 66b Output terminal 67 Band-pass filter (distributed constant circuit) 671, 672, 673, 674 Microstrip line 68 Band-pass filter (lumped constant circuit) 68a Input terminal 68b Output terminal 7, 7A Non-reciprocal circuit 70A Circulator 71, 71A First transmission line 72, 72A Second transmission line 73A, 95 Termination circuit 8a Forward wave power measurement unit 8b Reflected wave power measurement unit 8A Forward wave power measurement unit 8B Power measurement unit 81 Detector circuit 82, 83, 84, 84A, 84B Couplers 821, 822, 831, 832, 841, 842, 843 Lines 82a, 83a Input port 82b, 83b Output port 82c, 83c, 84c, 84d Coupled port 82d, 83d, 84e, 84f Termination resistor 84a, 84b Input / output port 91 AD conversion circuit 92 Bias voltage control circuit 93 DC power supply 94 Latch circuit 10 Cavity 11 Irradiation object

Claims

1. A radio wave emitting device comprising: a cavity; a signal generating unit configured to generate a high-frequency signal; a signal amplifying unit having an amplifier and configured to amplify the high-frequency signal; a radio wave emitting unit configured to radiate radio waves into the cavity based on the high-frequency signal amplified by the signal amplifying unit; a control unit configured to control the signal generating unit and the signal amplifying unit; a filter circuit arranged between the amplifier and the radio wave emitting unit, configured to pass the high-frequency signal amplified by the signal amplifying unit and to attenuate unwanted radiation generated in the signal amplifying unit; and a non-reciprocal circuit arranged between the filter circuit and the radio wave emitting unit.

2. The radio wave emitting device according to claim 1, wherein the control section is configured to operate the amplifier of the signal amplifying section in a saturation region.

3. The radio wave emitting device according to claim 2, wherein the unwanted radiation includes harmonics of the high frequency signal generated when the amplifier of the signal amplifying section operates in a saturated region.

4. The radio wave emitting device of claim 1, further comprising: a forward wave power measuring unit configured to measure forward wave power, which is the power of a forward wave, which is the high-frequency signal amplified in the signal amplifier; and a reflected wave power measuring unit configured to measure reflected wave power, which is the power of a reflected wave flowing back from the radio wave emitting unit, wherein the non-reciprocal circuit includes a first transmission line and a second transmission line insulated from each other, the first transmission line transmits the forward wave to the radio wave emitting unit, and the second transmission line transmits the reflected wave to a termination circuit, the forward wave power measuring unit is configured to measure the forward wave power in the first transmission line, and the reflected wave power measuring unit is configured to measure the reflected wave power in the second transmission line, and the control unit is configured to control the signal generating unit and the signal amplifying unit based on the forward wave power and the reflected wave power.

5. The radio wave emitting device of claim 1, further comprising a forward wave power measuring unit disposed between the signal amplifier and the radio wave emitting unit for measuring forward wave power, which is the power of a forward wave that is the high frequency signal amplified by the signal amplifier, and the control unit configured to control the signal generating unit and the signal amplifier based on the forward wave power.

6. The radio wave emitting device according to claim 1, further comprising a power measuring unit disposed between the non-reciprocal circuit and the radio wave emitting unit for measuring forward wave power, which is the power of the forward wave that is the high frequency signal amplified by the signal amplifying unit, and reflected wave power, which is the power of the reflected wave flowing back from the radio wave emitting unit, and wherein the control unit controls the signal generating unit and the signal amplifying unit based on the forward wave power and the reflected wave power.

7. The radio wave emitting device according to claim 1, wherein said filter circuit includes at least one of a band pass filter, a band elimination filter, and a low pass filter.

8. The radio wave emitting device according to claim 1, wherein said filter circuit includes at least one of a distributed constant circuit and a lumped constant circuit.

9. The radio wave emitting device according to claim 1, wherein the filter circuit includes a distributed constant circuit, and the distributed constant circuit is disposed on a circuit board of the signal amplifier section.

10. The radio wave emitting device according to claim 1, wherein said filter circuit includes a low-pass filter that functions as a matching circuit for said amplifier of said signal amplifying section.

11. The radio wave emitting device according to claim 1, wherein the filter circuit includes a plurality of band elimination filters, the plurality of band elimination filters being a plurality of distributed constant circuits whose elimination bands partially overlap each other.

12. The radio wave radiating device according to claim 11, wherein said plurality of distributed constant circuits includes a plurality of short stubs each having a different length.

13. The radio wave emitting device according to claim 1, wherein said filter circuit includes a distributed constant circuit constituting a band-elimination filter for attenuating harmonics of said high-frequency signal.

14. The radio wave radiating device according to claim 13, wherein the distributed constant circuit includes: a short stub that attenuates a second harmonic of the high frequency signal; and an open stub that attenuates a third harmonic of the high frequency signal.

15. A radio wave emitting device comprising: a cavity; a signal generating unit configured to generate a high-frequency signal; a signal amplifying unit having an amplifier and configured to amplify the high-frequency signal; a radio wave emitting unit configured to radiate radio waves into the cavity based on the high-frequency signal amplified by the signal amplifying unit; a control unit configured to control the signal generating unit and the signal amplifying unit; a filter circuit configured to pass the high-frequency signal amplified by the signal amplifying unit and to attenuate unwanted radiation generated in the signal amplifying unit; and a non-reciprocal circuit configured to reduce fluctuations in the characteristics of the filter circuit.