JP3983692B2 - Microwave power transmission device, microwave power reception device, microwave power transmission method, and microwave power transmission system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention, microwave power transmitting device that transmits power by the microwave, the microwave power receiving device, the microwave power transmission method and a microwave transmission system.
[0002]
[Prior art]
One concept for obtaining energy from radio waves is the Solar Power Station (SPS) project. This launches a huge satellite with solar panels arranged on the earth's satellite orbit, and sends the power generated there to the earth by microwaves. There are also plans to use microwave power transmission for power transmission to remote islands and mountain peaks where wired power transmission is difficult.
[0003]
[Problems to be solved by the invention]
In microwave power transmission, it is necessary to adjust the power transmission amount in response to power generation fluctuation and load fluctuation. At present, the microwave that is assumed to be used in the SPS plan is a continuous wave. Therefore, the transmission power must be changed in order to adjust the transmission amount. However, the rectifier circuit used in the power receiving device has a characteristic that the rectification efficiency is maximized when the received power is P0 as shown in FIG. Will become bigger.
[0004]
In view of such circumstances, the present invention provides a microwave power transmission method, a microwave power transmission device, and a microwave power reception device that transmit power using a microwave that can adjust the amount of power transmission without impairing rectification efficiency. For the purpose.
[0005]
[Means for Solving the Problems]
In order to solve the above problem, the invention according to claim 1 is a microwave power transmission used in a microwave power transmission method for radiating a microwave from an antenna on the power transmission side, and capturing and rectifying the microwave with the antenna on the power reception side. In the device, the microwave radiated from the antenna is changed to a pulse that is intermittent in time, the duty ratio of the pulse is changed to adjust the amount of power transmission, and the frequency is monotonically lowered within the pulse duration. It is characterized by that.
[0006]
[0007]
Invention of Claim 2 is the microwave power transmission method using the microwave power transmission apparatus of Claim 1, Comprising: The signal is transmitted from the power transmission side to the power receiving side by changing the pulse duration. It is characterized by.
[0008]
[0009]
[0010]
The invention described in claim 3 is a microwave power receiving apparatus that receives and rectifies the microwave from the microwave power transmitting apparatus described in claim 1, and delays the one having a high frequency component prior to rectification. and made to interfere with the intended low frequency components Te, and rectifies the microwave pulses, characterized in that it comprises a secondary battery to charge the electric charges generated on the basis of the microwave pulse.
[0011]
[0012]
[0013]
The invention described in claim 4 is the microwave transmission system comprising a microwave power receiving apparatus for receiving and rectifying the microwave and the microwave transmitting device, from the microwave transmitting device according to claim 1 The microwave power receiving apparatus includes a power receiving antenna, a variable capacitor element capable of changing a tuning frequency with respect to the power receiving antenna, a voltage monitoring circuit unit, and a voltage generation circuit unit, and the voltage monitoring circuit unit outputs an output voltage. It is characterized by monitoring and adjusting the value of the variable capacitor through the voltage generation circuit unit so that the output always takes the maximum value.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
(First embodiment)
FIG. 1 shows a microwave power receiving apparatus of the present invention.
A microwave pulse intermittently transmitted as shown in FIG. 3A is sent to the microwave power receiving device from a power transmitting device (not shown).
[0015]
The microwave pulse is captured by the antenna 1 and sent to the filter 2. This filter 2 is composed of capacitors 3 and 4 and an inductor 5, and blocks the passage of harmonics in order to prevent the harmonics generated in the rectifier circuit 8 at the subsequent stage from being radiated from the antenna 1. The microwave pulse that has passed through the filter 2 is sent to a rectifier circuit 8 including two Schottky barrier diodes (hereinafter referred to as SBDs) 6 and 7. This rectifier circuit 8 is a half-wave / double-voltage rectifier circuit, which can drop only 1D as compared with the 4Di system, can perform full-wave rectification, and outputs a DC pulse as shown in FIG.
[0016]
The DC pulse output from the rectifier circuit 8 is input to a switched capacitor circuit 9 serving as a switch means. The switched capacitor circuit 9 includes a plurality of capacitors C, a switch SW composed of a MOSFET, and an inverter 10. That is, one end of each of the plurality of capacitors C is connected in parallel via the switch SW, and both ends of the parallel connected capacitors C are connected to the rectifier circuit 8 and the storage capacitor 11 via the switch SW.
[0017]
The clock signal CK is input to the gate of the MOSFET constituting the odd-numbered SW, while the inverted clock signal CK bar is input to the gate of the MOSFET constituting the even-numbered SW. Further, the clock signal CK is input to the odd-numbered capacitors C1, C3... Via one inverter 10, while the clocks are input to the even-numbered capacitors C2, C4. A signal CK is input. That is, since the boost voltage is applied to each capacitor C, the voltage is boosted by the number of stages and stored in the storage capacitor 11 at the final stage.
[0018]
When the clock signal CK becomes H level, as shown in FIG. 2A, the odd-numbered switches SW1, SW3,... Are turned on, and the boost voltage is applied to the even-numbered capacitors C2, C4,. The Therefore, the charge flows from the rectifier circuit 6 into the first capacitor C1, and the charges of the even-numbered capacitors C2, C4... Are pumped out to the capacitors C3, C5.
[0019]
When the clock signal CK becomes L level, the even-numbered switches SW2, SW4,... Are turned ON and the boost voltage is applied to the odd-numbered capacitors C1, C3,. The Therefore, the charges of the odd-numbered capacitors C1, C3,... Are pumped out to the capacitors C2, C3,. In this manner, the electric charge of each capacitor C is sequentially pumped out to the capacitor C at the subsequent stage in synchronization with the clock signal CK. The electric charge pumped out from the switched capacitor circuit 9 is temporarily stored in the storage capacitor 11 and supplied from the output terminal 12 to the load.
[0020]
The frequency of the clock signal CK is set higher than the frequency of the output pulse from the rectifier circuit 8 shown in FIG. However, during the period when no pulse is output from the rectifier circuit 8, both the clock signal CK and the inverted clock signal CK bar are set to L level, and all the switches SW are turned OFF.
[0021]
Since a microwave pulse as shown in FIG. 3A is sent to the power receiving apparatus from the power transmitting apparatus, the duty ratio t / T of the microwave pulse may be changed when adjusting the power transmission amount. . Incidentally, since the rectifier circuit 8 has the efficiency characteristics as shown in FIG. 4, the received power is set to Po to maximize the rectification efficiency. In the conventional continuous wave power transmission method, when the amount of power transmission is to be adjusted, the transmitted power must be changed. Therefore, the received power deviates from the value Po at which the maximum efficiency is achieved, and the rectification efficiency deteriorates. . On the other hand, in the pulse power transmission method of the present invention, since the duty ratio t / T of the microwave pulse is changed by PWM modulation, that is, the received power does not change, the rectification efficiency can be kept at the maximum.
[0022]
By the way, when the switched capacitor circuit 9 is omitted and the rectifier circuit 8 and the storage capacitor 11 are directly connected, current flows backward from the storage capacitor 11 to the SBD 6, 7 due to the reverse leakage characteristics of the SBDs 6, 7. FIG. A rectified waveform as shown in FIG. For this reason, during the period when no DC pulse is output from the rectifier circuit 6, the generation of the clock signal CK is stopped and all the SWs are turned OFF, thereby preventing the reverse flow from the capacitor C or the storage capacitor 11 to the SBDs 6 and 7. Thus, the output is prevented from decreasing.
[0023]
Furthermore, since the boost voltage is applied to each capacitor C of the switched capacitor circuit 9 so as to pump out the charge, the charge stored in the storage capacitor increases.
[0024]
The microwave pulse shown in FIG. 3A preferably has a pulse width t of 2 to 18 msec, a period T of 20 msec, and a duty ratio t / T of 10 to 90%. The frequency of the clock signal CK is preferably 10 K to 500 KHz.
[0025]
(Second Embodiment)
FIG. 5 shows a microwave power transmission system.
The power transmission device amplifies the output signal of the frequency sweep signal generator 20 by the amplifier 21 and radiates it from the antenna 22. The frequency sweep signal generator 20 generates a microwave pulse signal as shown in FIG. That is, a signal whose frequency is monotonically lower within the pulse duration t is generated.
[0026]
The power receiving apparatus captures the microwave pulse from the power transmitting apparatus with the antenna 23 and passes it through the delay filter 24. As shown in FIG. 8, the delay filter 24 has a characteristic that the delay time increases as the frequency increases. FIG. 7 shows a waveform change due to the passage of the microwave pulse through the delay filter 24. That is, a waveform having a high frequency is delayed and overlaps with a waveform having a low frequency to interfere with each other, and the pulse width is narrowed to increase the peak value.
[0027]
The microwave pulse that has passed through the delay filter 24 is rectified by the rectifier circuit 25 to become a DC pulse. The DC pulse is supplied to the load 27 via the switched capacitor circuit 26. The rectifier circuit 25 and the switched capacitor circuit 26 are the same as the rectifier circuit 8 and the switched capacitor circuit 9 of the first embodiment.
[0028]
FIG. 9 shows changes in the power spectrum of the microwave. That is, the microwave transmitted from the power transmission device is distributed in a wide band with a small amplitude of the spectrum component (curve in FIG. 3A). On the other hand, the microwave that has passed through the delay filter 24 is distributed in a narrow band with a large amplitude and a spectrum component (curve in FIG. 5B). That is, the spectrum component that has been spread over a wide band on the power transmission side is compressed into a narrow band on the power reception side, thereby increasing the amplitude of the spectrum distribution.
[0029]
In microwave power transmission, considering the influence of microwaves on ecosystems and interference with communication radio waves, there is a limit to increasing the power density of microwaves. That is, there is a limit to the power that can be obtained from the unit module of the power receiving apparatus. However, according to the power transmission method described above, the amplitude of the spectrum distribution is increased by band compression on the power receiving side, so that the transmitted power can be increased without increasing the power density of the microwave.
[0030]
Furthermore, a DC pulse is output from the rectifier circuit 25. Since the switched capacitor circuit 26 is provided at the subsequent stage of the rectifier circuit 25, current leakage to the SBD of the rectifier circuit 25 can be prevented. It helps to prevent the output from decreasing.
[0031]
The frequency generated by the frequency sweep signal generator 20 is preferably changed in a range of about 100 MHz, for example, 2.4 to 2.5 GHz. The pulse duration t is preferably about 10 msec and the duty ratio is 10 to 90%.
[0032]
(Third embodiment)
Next, a case where the microwave power transmission method of the second embodiment is applied to an ID tag system will be described. In addition, the same component as 2nd Embodiment attaches | subjects the same code | symbol, and abbreviate | omits description.
[0033]
FIG. 10 is a block diagram on the reader side.
A circulator 28 is provided between the amplifier 21 and the antenna 22, and a demodulator 29 is connected to the circulator 28 via the amplifier 21. That is, the circulator 28 enables signal transmission from the frequency sweep signal generator 20 to the antenna 22 and signal transmission from the antenna 22 to the demodulator 29. Note that a rectifier circuit 25 may be provided between the circulator 28 and the amplifier 21.
[0034]
FIG. 11 is a block diagram on the tag side.
A load resistor 31 is connected to the rectifier circuit 25 via a load switch 30, and the load switch 30 is opened and closed by a signal from the microcomputer 32. The DC pulse output from the switched capacitor circuit 26 charges the secondary battery 33, and the microcomputer 32 is activated with the secondary battery 33 as a power source.
[0035]
Next, the operation of this ID tag system will be described.
A microwave pulse as shown in FIG. 6 is sent from the reader to the tag. The reader rectifies the microwave pulse by the rectifier circuit 26 and supplies the DC pulse to the secondary battery 33 via the switched capacitor circuit 26. When the voltage of the secondary battery 33 reaches a specified value, the microcomputer 32 is activated to open and close the load switch 30 in synchronization with the microwave pulse. That is, this tag is of a battery-less type that is supplied with power from a reader by microwave power transmission. Note that the load switch 30 is opened and closed corresponding to serial data to be transmitted to the reader side.
[0036]
When the load switch 30 is opened and closed, the current flowing from the rectifier circuit 25 to the load resistor 31 is interrupted. However, as the load switch 30 is opened and closed, the reflectance of the microwave reflected by the tag-side antenna 23 changes. The reflected wave interferes with the incident wave to generate a standing wave, and its peak value also changes depending on the opening / closing of the load switch 30. That is, the VSWR (Voltage Standing Wave Ratio) seen from the reader side changes.
[0037]
This standing wave is received by the antenna 22 on the reader side, and input to the demodulator 29 through the circulator 28 and the amplifier 21. Data transmission from the tag to the reader is performed in this way. FIG. 12A schematically shows a microwave pulse sent from the reader, and FIG. 12B schematically shows a standing wave returning to the reader.
[0038]
In this ID tag system, power is supplied to the tag side by microwave pulses as shown in FIG. 6, so that even if the microwave power density is kept within the allowable range of the Radio Law, large power can be supplied. become. That is, in order to shorten the charging time of the secondary battery 33 on the tag side, when using a microwave pulse as shown in FIG. 3A, the duty ratio must be made as large as possible. When a microwave pulse as shown in FIG. 7 is used, it becomes a pulse anyway after rectification as shown in FIG. 7, and it is not necessary to take a duty ratio as large as possible in order to obtain a large electric power. (10 to 90%) can be varied, and the duty ratio can be small. Digital signal data can be exchanged by modulating the duty ratio.
[0039]
Therefore, the pulse frequency can be increased and the communication speed is increased.
Furthermore, a modulation method other than ASK (Amplitude shift Keying) can be adopted, and the degree of freedom in modulation is increased.
In addition, there is an effect that the reach distance of the radio wave is significantly increased.
[0040]
Although three embodiments have been described above, the present invention is not limited to these embodiments.
For example, as shown in FIG. 13, a plurality of switched capacitor circuits 9 (or 26, hereinafter the same) are arranged in parallel with a backflow prevention diode 41 in the rectifier circuit 8 to control ON / OFF of switching elements. The phase of the signal may be shifted for each switched capacitor circuit 9. For example, there are three switched capacitor circuits in this circuit, so that the balance is good if the phases are shifted by 90 degrees. By doing so, the dead time due to ON / OFF of the switch can be reduced, which is efficient.
[0041]
Moreover, as the switched capacitor circuit 9, what is shown to FIG.14 and FIG.15 may be used. In this switched capacitor circuit 9, SW1 to SW2n are switches, and CPT1 to CPTn are capacitors. 14 and 15, reference numerals 9b and 9c are input terminals, and 9a and 9f are output terminals.
A clock signal for switching the switches SW1 to SW2n to the “1” side (state 1) is applied to the clock input terminal 9d, and an inversion for switching the switches SW1 to SW2n to the “2” side (state 2) to the inverted clock input terminal 9e. Each clock signal is input.
[0042]
The capacitors CPT1 to CPTn are connected in series in the state 1 and inserted between the HV output terminal 9a and the LV output terminal 9f, and are connected in parallel and inserted between the RF input terminals 9b and 9c in the state 2. The switches SW1 to SW2n are connected. The switches SW1 to SW2n are connected between the terminals 9a and 9b so that the capacitors CPT1 to CPTn are connected as described above.
[0043]
The operation of the switched capacitor circuit 9 will be described. In state 1, capacitors CPT1 to CPTn connected in series are connected to the storage capacitor 11 via the HV output terminal 9a and discharged, and in state 2, Are connected to the capacitors CPT1 to CPTn connected in parallel via the RF input terminals 9b and 9c, and stored in the capacitors CPT1 to CPTn.
States 1 and 2 are alternately repeated at a predetermined frequency (cycle) by the switches SW1 to SW2n that are switch-controlled by the clock signal input to the clock input terminal 9d and the inverted clock input terminal 9e and the inverted clock signal. Therefore, the above-described charging / discharging operation of the capacitors CPT1 to CPTn is repeated at a predetermined frequency, and the electric charge is pumped out to the storage capacitor 11.
[0044]
FIG. 15 shows a specific circuit configuration example of the switched capacitor circuit 9 described in FIG. In FIG. 15, NMOS1 to NMOS3n-1 each indicate an N channel type MOSFET. 15, the same reference numerals as those in FIG. 14 denote the same or corresponding parts.
[0045]
FIGS. 16 and 17 show another embodiment. In this embodiment, each capacitor of the switched capacitor circuit 9 is switched by switching the switching element without performing the clock control as described above. The stored charge is directly stored in the storage capacitor. In FIG. 16, 107 is an RF input terminal H, 108 is an RF input terminal C, 1300 is an integrated circuit unit using a one-chip (monolithic) IC, 9 is a switched capacitor circuit, and 1307 and 1308 are reverse current blocking diodes.
[0046]
The switched capacitor circuits 9 and 9 are configured to obtain an RF input from the RF input terminals 107 and 108 and store the voltage output HVOUT in the storage capacitor 11.
The switched capacitor circuits 9 and 9 include an RFH input terminal 9b; an RFL input terminal 9c, an HV output terminal 9a, and an LV output terminal 9f.
The RFH input terminal 9b and the RFL input terminal 9c of the switched capacitor circuits 9 and 9 are so-called stake-connected to the RF input. That is, the RFH input terminal 9b of one switched capacitor circuit 9 and the RFL input terminal 9c of the other switched capacitor circuit 9 are respectively connected to the RF input terminal H108, the RFL input terminal 9b of one switched capacitor circuit 9 and the other. RFH input terminals 9c of the switched capacitor circuit 9 are connected to the RF input terminal 107, respectively.
[0047]
On the other hand, the HV output terminal 9a of the switched capacitor circuit unit 9 is connected to one end of the storage capacitor 11 via the backflow prevention diode 1307, and the HV output terminal 9a of the switched capacitor circuit 9 is connected to the one end of the storage capacitor 11 via the backflow prevention diode 1308. Has been.
The LV output terminal 9 f of one switched capacitor circuit 9 and the LV output terminal 9 f of the other switched capacitor circuit 9 are connected in common and connected to one end of the storage capacitor 11.
[0048]
FIG. 17 shows a specific circuit configuration example of the switched capacitor circuit 9 described with reference to FIG. 16. FIG. 17 has substantially the same configuration as that of FIG. 15, except that there is no switch clock control. In other words, in this embodiment, since the input microwave pulse directly opens and closes the MOS gate, which is a switching element, to open and close the switch, the clock control as described above is not required, so that the charge consumption can be reduced. Efficient. In FIG. 17, the same reference numerals as those in FIG. 15 denote the same or corresponding parts.
[0049]
FIG. 18 is a circuit diagram showing still another embodiment. In this embodiment, each switch is utilized by using the amplitude of the microwave frequency (RF signal) received by the receiving circuit 51 without using the clock signal (CK) used in the first embodiment shown in FIG. SW1, SW2, SW3... Are switched. That is, the microwave RF signal received by the receiving circuit 51 is sent from the full-wave rectifier circuit 53 to one end of each capacitor C1, C2, C3... Of the clock boost circuit 9 and before the full-wave rectifier circuit 53. The other half-wave rectifier circuit 56 is connected to the capacitors C1, C2, C3,... Via the half-wave rectifier circuits 55 and 56. (Rad), that is, shifted by 180 degrees. In this embodiment, since the clock generation circuit is unnecessary, power consumption is unnecessary, and power efficiency can be improved.
[0050]
19 and 20 are circuit diagrams showing still other embodiments, and FIGS. 20A and 20B are specific configuration diagrams of the circuit shown in FIG. 19, respectively. In this embodiment, similarly to the embodiment shown in FIG. 18, each switch SW <b> 1 is made using the amplitude of the microwave frequency (RF signal) received by the receiving circuit 51 without using the clock signal (CK). , SW2, SW3,..., And using the half-phase rectifier circuit 57 of reverse phase without providing the delay circuit 54. Other points are the same as those of the embodiment shown in FIG. Note that D1 to D8 in FIG. 20B are rectified and connected MOSFET transistors.
FIG. 21 is a further specific configuration diagram of the circuit shown in FIG. 19, in which R1 and R2 shown in FIG. 20A are replaced with a MOSFET configuration. According to the circuit shown in FIG. Less power consumption and higher efficiency.
The circuit shown in FIG. 22 shows a circuit of a power receiving device according to still another embodiment. In this circuit, a variable capacitor whose capacitance can be varied with respect to the antenna 1 (capacitance changes with voltage). By adopting a configuration including the element 40, the voltage monitoring circuit unit 44, and the voltage generation circuit unit 44, the voltage monitoring circuit unit 44 monitors the voltage of the output 12, and the value of the variable capacitor is monitored through the voltage generation circuit unit. Is always adjusted so that the output 12 takes the maximum value, and power can be received with the maximum efficiency even if the power receiving frequency of the power receiving apparatus is detuned due to various external factors.
[0051]
【The invention's effect】
According to the first and second aspects of the invention, the amount of power transmission can be adjusted without impairing the rectification efficiency, and the transmission power can be increased without increasing the power density of the microwave.
Furthermore, according to the invention of claim 2, a communication signal can be sent together with power transmission.
[0052]
[0053]
[0054]
According to the invention of claim 3 , in addition to the effect of the invention of claim 1 , energy of the microwave pulse can be stored as electric power.
[0055]
[0056]
[0057]
According to the fourth aspect of the present invention, it is possible to receive power with the maximum efficiency even if the power receiving frequency of the power receiving apparatus is out of synchronization due to various external factors.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a power receiving device according to a first embodiment of the present invention.
FIG. 2 illustrates an operation of a switched capacitor circuit of the power receiving device.
FIG. 3 is a diagram showing a waveform in each part of the power receiving device.
FIG. 4 is a graph showing efficiency characteristics of a rectifier circuit.
FIG. 5 is a block diagram showing a power transmission system according to a second embodiment of the present invention.
FIG. 6 is a view showing an output waveform of a frequency sweep signal generator of the power transmission system.
FIG. 7 is a view showing a waveform change due to a delay filter passing through the power transmission system.
FIG. 8 is a view showing characteristics of the delay filter.
FIG. 9 is a view showing a microwave power spectrum in the power transmission system;
FIG. 10 is a block diagram of a reader in the ID tag system according to the third embodiment of the present invention.
FIG. 11 is a block diagram of a tag of the ID tag system.
FIG. 12 is a diagram for explaining a change in peak value of a standing wave in the ID tag system.
FIG. 13 is a circuit diagram of a microwave power receiving apparatus according to another embodiment of the present invention.
FIG. 14 is a diagram illustrating the operation of a switched capacitor circuit according to another embodiment.
FIG. 15 is a specific circuit diagram of FIG. 14;
FIG. 16 is a circuit diagram of a microwave power receiving apparatus according to another embodiment of the present invention.
FIG. 17 is a specific circuit diagram of FIG. 16;
FIG. 18 is a circuit diagram of a microwave power receiving apparatus according to another embodiment of the present invention.
FIG. 19 is a circuit diagram of a microwave power receiving apparatus according to another embodiment of the present invention.
20A and FIG. 20B are specific circuit diagrams of FIG. 19, respectively.
FIG. 21 is a further specific circuit diagram of FIG. 19;
FIG. 22 is a circuit diagram of a power receiving device according to another embodiment.
[Explanation of symbols]
1 Antenna 2 Filter 6 SBD
7 SBD
8 Rectifier Circuit 9 Switched Capacitor Circuit 10 Inverter 11 Storage Capacitor 12 Output Terminal 20 Frequency Sweep Signal Generator 21 Amplifier 22 Antenna 23 Antenna 24 Delay Filter 25 Rectifier Circuit 26 Switched Capacitor Circuit 27 Load 28 Circulator 29 Demodulator 30 Load Switch 31 Load resistor 32 Microcomputer 33 Secondary battery 40 Variable capacitor element 42 Voltage generation circuit section 44 Voltage monitoring circuit section

Claims (4)

  It is used in a microwave power transmission method that captures and rectifies microwaves with a power receiving antenna, and in a microwave power transmission device that radiates microwaves from an antenna, the microwaves radiated from the antenna are converted into pulses that are intermittent in time, A microwave power transmitting apparatus characterized in that the amount of power transmission is adjusted by changing the duty ratio of a pulse, and the frequency is monotonically lowered within the pulse duration. A microwave power transmission method using the microwave power transmission device according to claim 1, wherein a signal is transmitted from a power transmission side to a power reception side by changing the pulse duration. A microwave power receiving apparatus for receiving and rectifying microwaves from the microwave power transmitting apparatus according to claim 1, wherein, prior to rectification, a high frequency component is delayed to interfere with a low frequency component. and it has, and rectifies the microwave pulses, microwave power receiving apparatus comprising: a secondary battery to charge the electric charges generated on the basis of the microwave pulse. A microwave power transmission system comprising the microwave power transmission device according to claim 1 and a microwave power reception device that receives and rectifies microwaves from the microwave power transmission device, wherein the microwave power reception device is a power reception antenna. And a variable capacitor element that can vary the tuning frequency with respect to the power receiving antenna, a voltage monitoring circuit unit, and a voltage generation circuit unit, the voltage monitoring circuit unit monitors the output voltage, and through the voltage generation circuit unit, A microwave power transmission system in which the value of a variable capacitor is constantly adjusted so that the output takes a maximum value.

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