JP7485329B2 - Circuit having microwave amplifier circuit and impedance matching circuit, and microwave heating device using the same - Google Patents

Description

The present invention relates to a circuit having a microwave amplifier circuit and an impedance matching circuit that perform impedance matching by sweeping frequencies in the high frequency range of the microwave region, and to a microwave heating device using the same.

Microwave amplifier circuits that operate in the microwave frequency range are used in various devices such as microwave heating devices (for example, microwave cooking devices such as microwave ovens and microwave surgical devices such as microwave forceps). In high-frequency circuits such as microwave amplifier circuits, it is necessary to use an impedance matching circuit to match the impedance (load impedance) of the load in order to efficiently transmit power to the load. However, depending on the load, the load impedance often changes during operation, and it is not uncommon for the impedance of the impedance matching circuit to be unable to be fixed to a specific value. In many cases, a varactor diode is used in the impedance matching circuit, and impedance matching is performed by changing the variable capacitance value of the varactor diode while monitoring whether or not it is matched. However, circuits using varactor diodes have high losses, and it is not easy to increase the power resistance.

On the other hand, another method of impedance matching is known, which uses an impedance matching circuit whose impedance changes depending on the frequency, and performs impedance matching by changing the frequency within a range usable by devices such as microwave heating devices (for example, a 100 MHz bandwidth from 2.4 GHz to 2.5 GHz) and selecting the optimal frequency.

For example, Patent Document 1 discloses a high-frequency heating device that includes an impedance matching circuit that includes an impedance detection unit and an impedance adjustment unit, which detect the impedance of the power supply to the heating chamber and control the oscillation frequency of the solid-state oscillator. Here, the load impedance to be matched is considered to be the impedance of the load that includes the heating chamber and the non-heated object. Non-Patent Document 1 also discloses an impedance matching circuit that includes a first transmission line member and a second transmission line member, and uses a long coaxial cable for the second transmission line member. When the frequency is swept from 2.4 GHz to 2.5 GHz, this impedance matching circuit can draw a spiral impedance locus starting from the origin of the Smith chart and cover the entire surface of the Smith chart evenly.

Japanese Patent Application Laid-Open No. 59-165399

Asako Suzuki and 5 others, "Frequency Sweep Impedance Matching Circuit Drawing a Spiral Locus on the Smith Chart", IEICE Technical Report, Institute of Electronics, Information and Communication Engineers, 2019, Vol. 118, No. 506, MW2018-164, pp. 43-48

However, since the impedance matching circuit disclosed in Patent Document 1 does not disclose details, it is unclear whether impedance matching is possible over the entire area to be matched (in other words, the entire surface of the Smith chart), and it is also unclear whether it is small or large. In addition, since the second transmission line component of the impedance matching circuit disclosed in Non-Patent Document 1 is a long line, it is quite large in volume and the loss is also likely to be large.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a circuit having a microwave amplifier circuit and an impedance matching circuit which can draw an impedance locus when the frequency is swept to cover the entire surface of the Smith chart evenly, and which can be made compact and have low loss.

In order to achieve the above object, the circuit having a microwave amplifier circuit and an impedance matching circuit according to claim 1 is a circuit having a microwave amplifier circuit and an impedance matching circuit, the impedance matching circuit having a first terminal to which an output of the microwave amplifier circuit is input and a second terminal connected to a load, the impedance matching circuit comprising: a transmission line having the first terminal as one end and the second terminal as the other end; and a plurality of resonators, the resonant frequencies of the resonators being set to be different from each other within the predetermined frequency range in which the frequency sweep is performed, the plurality of resonators being connected to the transmission line at intervals from each other, the microwave amplifier circuit having a signal source having a variable frequency and capable of sweeping the frequency within a predetermined frequency range, and when the frequency sweep is performed, a reflected wave at the first terminal is extracted and monitored with respect to the load impedance of the load, and the signal source can be set to a frequency showing a state in which the reflected wave is the smallest .

The circuit having a microwave amplifier circuit and an impedance matching circuit according to claim 2 is the circuit having a microwave amplifier circuit and an impedance matching circuit according to claim 1, characterized in that the impedance matching circuit has a filter characteristic that blocks the passage of signals at the resonant frequencies of the plurality of resonators.

The circuit having a microwave amplifier circuit and an impedance matching circuit according to claim 3 is the circuit having a microwave amplifier circuit and an impedance matching circuit according to claim 1 or 2, characterized in that the plurality of resonators are connected to the transmission line at intervals from each other, and a capacitor and an inductor are connected in series to resonate at the resonant frequency.

The circuit having a microwave amplifier circuit and an impedance matching circuit according to claim 4 is characterized in that in the circuit having a microwave amplifier circuit and an impedance matching circuit according to claim 1 or 2, the plurality of resonators are connected to the transmission line at intervals from each other, and a capacitance and a distributed constant line resonator are connected in series to resonate at the resonant frequency.

The circuit having a microwave amplifier circuit and an impedance matching circuit according to claim 5 is characterized in that, in the circuit having a microwave amplifier circuit and an impedance matching circuit according to claim 4, the distributed constant line resonator is a quarter-wave ceramic coaxial resonator.

A microwave heating device according to a sixth aspect of the present invention uses a circuit having the microwave amplifier circuit according to any one of the first to fifth aspects and an impedance matching circuit.

According to the circuit having the microwave amplifier circuit and the impedance matching circuit of the present invention, when the frequency is swept, an impedance locus is drawn, so that the entire surface of the Smith chart can be covered uniformly, and further, miniaturization and low loss can be achieved. According to the microwave heating device of the present invention, miniaturization and low loss can be achieved.

1 is a schematic plan view of an impedance matching circuit according to an embodiment of the present invention; FIG. 2 is a circuit diagram of the impedance matching circuit of the embodiment. FIG. 4 is another circuit diagram of the impedance matching circuit shown in FIG. FIG. 4 is a circuit diagram showing the distributed constant line resonator of the impedance matching circuit of FIG. 3 in an equivalent lumped constant circuit. 4A and 4B are diagrams illustrating an example of the impedance matching circuit according to the embodiment of the present invention, corresponding to the circuit diagram of FIG. 3, in which FIG. 4A is a plan view and FIG. 4B is a cross-sectional view taken along the plane indicated by AA in FIG. FIG. 4 is a circuit diagram for simulation of the impedance matching circuit shown in FIG. 3 . FIG. 4 is a characteristic diagram of the impedance matching circuit of the embodiment. 4 is a characteristic diagram showing the characteristics of the impedance matching circuit of the embodiment on a Smith chart, which shows the reflection characteristics of a first terminal. 4 is a characteristic diagram showing the characteristics of the impedance matching circuit of the embodiment on a Smith chart, which shows the reflection characteristics of the second terminal. FIG. 2 is a circuit diagram showing a microwave amplifier circuit using the impedance matching circuit of the above embodiment.

The following describes an embodiment of the present invention with reference to the drawings. The impedance matching circuit 1 according to the embodiment of the present invention is configured to match the impedance of a connected load by frequency sweeping, as will be described in detail later.

As shown in FIG. 1, the impedance matching circuit 1 includes a transmission line 10 and multiple (four in FIG. 1) resonators 11, 12, 13, and 14. The multiple resonators 11, 12, 13, and 14 have different resonant frequencies. The multiple resonators 11, 12, 13, and 14 are connected to the transmission line 10 at intervals. One end of the transmission line 10 is a first terminal 10a, and the other end is a second terminal 10b. The transmission line 10 extends linearly.

The impedance matching circuit 1 can be designed to have filter characteristics that block the passage of signals at the resonant frequencies of the multiple resonators 11, 12, 13, and 14 (see S12 in Figure 7, described later).

For this purpose, as shown in Fig. 2, the multiple resonators 11, 12, 13, and 14 can be a series-connected capacitance 11a and inductor 11b, a series-connected capacitance 12a and inductor 12b, a series-connected capacitance 13a and inductor 13b, and a series-connected capacitance 14a and inductor 14b. The series-connected capacitance 11a and inductor 11b, the series-connected capacitance 12a and inductor 12b, the series-connected capacitance 13a and inductor 13b, and the series-connected capacitance 14a and inductor 14b resonate at different resonant frequencies. The inductors 11b, 12b, 13b, and 14b are lumped constant elements. In Fig. 2 (and Fig. 3, etc., which will be described later), the transmission line 10 is divided and shown as transmission lines ₁₀₁ , ₁₀₂ , ₁₀₃ , ₁₀₄ , and ₁₀₅ .

Alternatively, as shown in Fig. 3, the resonators 11, 12, 13, and 14 can be respectively a series-connected capacitance 11a and a distributed constant line resonator 11c, a series-connected capacitance 12a and a distributed constant line resonator 12c, a series-connected capacitance 13a and a distributed constant line resonator 13c, and a series-connected capacitance 14a and a distributed constant line resonator 14c. The series-connected capacitance 11a and the distributed constant line resonator 11c, the series-connected capacitance 12a and the distributed constant line resonator 12c, the series-connected capacitance 13a and the distributed constant line resonator 13c, and the series-connected capacitance 14a and the distributed constant line resonator 14c resonate at different resonant frequencies. When the distributed constant line resonators 11c, 12c, 13c, and 14c are expressed by equivalent lumped constants, as shown in Figure 4, they become a parallel resonator of capacitance component 11ca and inductance component 11cb connected in parallel, a parallel resonator of capacitance component 12ca and inductance component 12cb connected in parallel, a parallel resonator of capacitance component 13ca and inductance component 13cb connected in parallel, and a parallel resonator of capacitance component 14ca and inductance component 14cb connected in parallel. Therefore, in this case, the resonant frequencies of resonators 11, 12, 13, and 14 are determined by the capacitance value determined by capacitance 11a and capacitance component 11ca and the inductance value of inductance component 11cb, the capacitance value determined by capacitance 12a and capacitance component 12ca and the inductance value of inductance component 12cb, the capacitance value determined by capacitance 13a and capacitance component 13ca and the inductance value of inductance component 13cb, and the capacitance value determined by capacitance 14a and capacitance component 14ca and the inductance value of inductance component 14cb.

The distributed constant line resonators 11c, 12c, 13c, and 14c can easily obtain the required inductance value by changing the physical size, etc. Therefore, the distributed constant line resonators 11c, 12c, 13c, and 14c can easily obtain better characteristics in the microwave frequency range than the inductors 11b, 12b, 13b, and 14b.

The distributed constant line resonators 11c, 12c, 13c, and 14c can be ceramic coaxial resonators. These ceramic coaxial resonators are usually quarter-wave ceramic coaxial resonators, but other ceramic coaxial resonators can also be used.

5(a) and (b) are plan and cross-sectional views of the impedance matching circuit 1 corresponding to the circuit diagram of FIG. 3. In the impedance matching circuit 1, a strip line transmission line 10 is formed on one surface of a printed circuit board 1a, and chip-type capacitors 11a, 12a, 13a, and 14a and distributed constant line resonators 11c, 12c, 13c, and 14c of a quarter-wave ceramic coaxial resonator are mounted. On the other surface of the printed circuit board 1a, a ground electrode 1b is formed on the entire surface and is wired to the one surface of the printed circuit board 1a through a plurality of through holes 1c. As shown in FIG. 5(b), the distributed constant line resonator 11c of the quarter-wave ceramic coaxial resonator has a ground electrode _11c2 formed on the outer peripheral surface of a ceramic body _11c1 having a hollow portion in the axial direction, and an electrode rod _11c3 inserted into the hollow portion of the ceramic body _11c1 . The electrode rod _11c3 is connected to the capacitor 11a by a jumper wiring 1d. The distributed constant line resonators 12c, 13c, and 14c are similar to the distributed constant line resonator 11c.

Next, the characteristics of the impedance matching circuit 1 will be described based on the results of a simulation of the circuit. The impedance matching circuit 1 here is shown in the circuit diagram of FIG. 3, and in the simulation, as shown in FIG. 6, 50 Ω resistors 1A and 1B are connected to the first terminal 10a and the second terminal 10b of the impedance matching circuit 1, respectively. The distributed constant line resonators 11c, 12c, 13c, and 14c are quarter-wave ceramic coaxial resonators.

The resonant frequencies of the four resonators 11, 12, 13, and 14 are set to be different from each other between 2.4 GHz and 2.5 GHz. For this purpose, the characteristic impedance of the transmission line 10 is set to 50Ω, and the electrical lengths of the divided transmission lines ₁₀₁ , ₁₀₂ , ₁₀₃ , ₁₀₄ , and ₁₀₅ are set to 90.00 degrees, 46.65 degrees, 42.15 degrees, 37.65 degrees, and 90.00 degrees at a frequency of 2.45 GHz. The capacitances of the capacitances 11a, 12a, 13a, and 14a are set to 0.092 pF, 0.074 pF, 0.076 pF, and 0.082 pF, respectively.

The electrical lengths of the distributed constant line resonators 11c, 12c, 13c, and 14c are 86.42 degrees, 87.92 degrees, 89.05 degrees, and 89.74 degrees at a frequency of 2.45 GHz, respectively, and the characteristic impedance is 25 Ω. When expressed in terms of equivalent lumped constants, the capacitance components 11ca, 12ca, 13ca, and 14ca of the distributed constant line resonators 11c, 12c, 13c, and 14c are 2.094 pF, 2.059 pF, 2.008 pF, and 1.958 pF, respectively, and the inductance components 11cb, 12cb, 13cb, and 14cb are 2.0 nH, 2.0 nH, 2.0 nH, and 2.0 nH.

In FIG. 7, S11 and S22 shown by dashed lines respectively indicate the reflection characteristics of the first terminal 10a and the second terminal 10b, and are overlapped. In FIG. 7, S12 shown by a solid line indicates the transmission characteristics from the first terminal 10a to the second terminal 10b. As shown in FIG. 7, the impedance matching circuit 1 has frequency characteristics with stop bands near the resonant frequencies of the four resonators 11, 12, 13, and 14 (approximately 2.408 GHz, approximately 2.430 GHz, approximately 2.462 GHz, and approximately 2.493 GHz).

When the frequency of such an impedance matching circuit 1 is swept from 2.4 GHz to 2.5 GHz, as shown in Figures 8 and 9, a trajectory is drawn in which a circle is drawn by changing the position near the periphery between near the center and near the periphery of the Smith chart for each resonant frequency of the resonators 11, 12, 13, and 14, as many times as there are resonators 11, 12, 13, and 14, so that the entire surface of the Smith chart is covered evenly. Note that in Figures 8 and 9, 2.4 GHz is indicated by a circle, and 2.5 GHz is indicated by a black circle.

Therefore, by setting either frequency, good impedance matching can be achieved with respect to the impedance of the load connected to the second terminal 10b. The same is true when a load is connected to the first terminal 10a. In addition, to improve the accuracy of impedance matching, the number of resonators 11, 12, 13, and 14 can be increased (for example, more than four) to approach the ideal impedance matching value.

In this way, the impedance matching circuit 1 can draw an impedance locus and cover the entire surface of the Smith chart evenly when the frequency is swept, so that good impedance matching can be performed for the impedance of the load connected to the second terminal 10b (or the first terminal 10a). Moreover, since the impedance matching circuit 1 does not use a long line like the impedance matching circuit disclosed in Non-Patent Document 1, it can simultaneously achieve miniaturization and low loss. Furthermore, if each of the resonators 11, 12, 13, and 14 is a quarter-wave ceramic coaxial resonator as described above, further miniaturization and low loss are possible.

The impedance matching circuit 1 described above can be used in a microwave amplifier circuit 2 as shown in FIG. 10. The impedance matching circuit 1 is provided between the output of the microwave amplifier circuit 2 and a load 3. In FIG. 10, the first terminal 10a of the impedance matching circuit 1 is connected to the output of the microwave amplifier circuit 2, and the second terminal 10b is connected to the load 3. When the microwave amplifier circuit 2 is used in a microwave heating device, the load 3 is a load that combines a microwave radiation mechanism and a non-heated object.

The microwave amplifier circuit 2 can be composed of a signal source 21, a power amplifier 22, a reflected wave extractor 23, and a reflected wave detection circuit 24. The signal source 21 has a variable frequency. A signal is input from the signal source 21 to the power amplifier 22. The output of the power amplifier 22 is connected to the reflected wave detection circuit 24 via the reflected wave extractor 23. The output of the power amplifier 22 becomes the output of the microwave amplifier circuit 2.

The reflected wave extractor 23 is capable of extracting the reflected wave from the impedance matching circuit 1 (i.e., the reflected wave reflected by the load 3), and may be, for example, a directional coupler. The reflected wave detection circuit 24 is a circuit that outputs a DC voltage according to the power of the reflected wave, and may be, for example, a commercially available RF power detector. The reflected wave detection circuit 24 can indicate the state in which the reflected wave is least (i.e., the impedance matching state of the impedance matching circuit) when sweeping the frequency as described below, by using the DC voltage it outputs.

In the microwave amplifier circuit 2, a frequency sweep (e.g., a sweep from 2.4 GHz to 2.5 GHz) is performed on the load impedance of the load 3 by changing the frequency of the signal source 21, and the output of the reflected wave detection circuit 24 is monitored. Then, the signal source 21 is set to a frequency that indicates the impedance matching state of the impedance matching circuit from the output of the reflected wave detection circuit 24, and the impedance of the impedance matching circuit is set to a matching state.

The impedance matching circuit according to the embodiment of the present invention, and the microwave amplifier circuit and microwave heating device using the same have been described above, but the present invention is not limited to the above-described embodiment, and various design modifications are possible within the scope of the claims. For example, the impedance matching circuit according to the embodiment of the present invention can be used in high-frequency circuits other than microwave amplifier circuits.

1 impedance matching circuit 1a printed circuit board 1b ground electrode 1c through hole in printed circuit board 1d jumper wiring 1A, 1B resistor 10 transmission line 10 ₁ , 10 ₂ , 10 ₃ , 10 ₄ , 10 ₅ divided transmission line 10a first terminal 10b second terminal 11, 12, 13, 14 resonator 11a, 12a, 13a, 14a capacitance 11b, 12b, 13b, 14b inductor 11c, 12c, 13c, 14c distributed constant line resonator 11ca, 12ca, 13ca, 14ca capacitance component of distributed constant line resonator 11cb, 12cb, 13cb, 14cb inductance component of distributed constant line resonator 11c ₁ ceramic body of distributed constant line resonator 11c ₂ Ground electrode of distributed constant line resonator 11c ₃ Electrode rod of distributed constant line resonator 2 Microwave amplifier circuit 21 Signal source 22 Power amplifier 23 Reflected wave extractor 24 Reflected wave detection circuit 3 Load

Claims (6)

Microwave amplifier circuitImpedance Matching CircuitA circuit havingAnd,
The impedance matching circuit includes:
a first terminal to which an output of the microwave amplifier circuit is input and a second terminal to be connected to a load;
A transmission line having the first terminal as one end and the second terminal as the other end;
A number of resonators,
Equipped with
The resonant frequencies of the resonators are set to be different from each other within the predetermined frequency range in which the frequency sweep is performed,
The plurality of resonators are connected to the transmission line at intervals.And,
The microwave amplifier circuit includes:
A signal source having a variable frequency and capable of sweeping the frequency within a predetermined frequency range,
When the frequency sweep is performed, a reflected wave at the first terminal is extracted and monitored with respect to the load impedance of the load, and the signal source can be set to a frequency that shows the smallest reflected wave.Characterized byMicrowave amplifier circuitImpedance Matching Circuit A circuit having. 2. A circuit having a microwave amplifier circuit and an impedance matching circuit according to claim 1,
A circuit having a microwave amplifier circuit and an impedance matching circuit, wherein the impedance matching circuit has a filter characteristic that blocks the passage of signals at the resonance frequencies of the plurality of resonators. 3. A circuit having the microwave amplifier circuit and the impedance matching circuit according to claim 1,
The circuit having a microwave amplifier circuit and an impedance matching circuit, wherein the plurality of resonators are connected to the transmission line at intervals from one another, and a capacitance and an inductor are connected in series to resonate at the resonant frequency. 3. A circuit having the microwave amplifier circuit and the impedance matching circuit according to claim 1,
The plurality of resonators are connected to the transmission line at intervals from one another, and a capacitance and a distributed constant line resonator are connected in series to resonate at the resonant frequency. 5. A circuit having a microwave amplifier circuit and an impedance matching circuit according to claim 4,
1. A circuit having a microwave amplifier circuit and an impedance matching circuit, wherein the distributed constant line resonator is a quarter-wave ceramic coaxial resonator. A microwave heating device using a circuit having the microwave amplifier circuit and an impedance matching circuit according to any one of claims 1 to 5.

Images