JP7685228B2 - Transmitting device and transmitting system - Google Patents

Description

The present invention relates to a transmitting device that performs wireless transmission and a transmitting system that includes the same.

In recent years, many sensors, cameras, IoT devices, etc. have been installed in factories, facilities, etc. As a technology for supplying power to such equipment, microwave power transmission, especially retrodirective power transmission, has attracted attention. In this method, a pilot signal emitted from a target is generally received, and the direction of the target is estimated using the pilot signal, and a power transmission beam is formed that faces the direction of the target, thereby controlling the power transmission beam in the direction of the target.

Patent Document 1 discloses a wireless power transmission system that uses the difference in arrival time of beacon signals in a multipath environment to wirelessly supply power to a client device. This wireless power transmission system receives a beacon signal from a client device with an array antenna, and transmits a transmission signal from the array antenna with the start of transmission shifted based on the inversion of the arrival time of the beacon signal. This allows the transmission signals to arrive at the client device at approximately the same time even if they travel along paths with different propagation delays.

Patent Document 2 discloses a microwave power transmission system that transmits power from multiple separately configured power transmission units to a target device. Each power transmission unit includes a receiving antenna, a power transmission antenna, a phase locking circuit, a conjugate phase generating circuit, and a microwave generating device. The phase locking circuit generates a phase synchronization signal based on the phase difference between pilot signals received by each power transmission unit and transmitted between each power transmission unit. The conjugate phase generating circuit superimposes the pilot signal received by the power transmission unit and the phase synchronization signal generated by the phase locking circuit to generate a conjugate phase wave. The microwave generating device corrects the phase of the conjugate phase wave and supplies the generated microwave to the power transmitting antenna. With this configuration, phase synchronization control between multiple separately configured power transmission units is performed.

Special Publication No. 2021-507663 JP 2004-7932 A

The power transmission systems disclosed in Patent Documents 1 and 2 use the same frequency for the pilot signal and the power transmission signal. This may result in interference between the pilot signal and the power transmission signal, reducing the accuracy of target direction estimation.

Similarly, in communication systems that use pilot signals to form communication beams, there is a risk that the pilot signal and communication signal will interfere with each other, reducing the accuracy of target direction estimation.

The object of the present invention is to provide a transmission device that suppresses interference between a pilot signal and a transmission signal, and a transmission system equipped with the same.

The transmitting device of the present invention comprises an array antenna having a plurality of receiving antenna elements and a plurality of transmitting antenna elements, and a plurality of phase conjugation circuits respectively connected to the plurality of receiving antenna elements and the plurality of transmitting antenna elements, each of the phase conjugation circuits receiving a pilot signal received by the receiving antenna element and outputting a transmission signal supplied to the transmitting antenna element, the frequency of the transmission signal output from each of the phase conjugation circuits being equal to 1/2 the frequency of the pilot signal input to each of the phase conjugation circuits, and the phase difference of the transmission signal output from each of the phase conjugation circuits with respect to the transmission signal output from any one of the plurality of phase conjugation circuits being equal to -1/2 the phase difference of the pilot signal input to each of the phase conjugation circuits with respect to the pilot signal input to the any one of the phase conjugation circuits.

The transmission system of the present invention comprises a transmission device of the present invention and a receiving device having a rectenna, and the rectenna generates the pilot signal by reflecting a portion of the transmission signal that reaches the rectenna as a second harmonic.

The present invention can suppress interference between pilot signals and transmission signals, improving the accuracy of target direction estimation.

FIG. 1 is a conceptual diagram of a power transmission system 10 according to an embodiment of the present invention. FIG. 2 is a block diagram of the rectenna 31 provided in the power receiving device 30. As shown in FIG. FIG. 3 is a block diagram of a main part of the power transmitting device 20. As shown in FIG. 4A and 4B are conceptual diagrams for explaining the formation of a power transmission beam. FIG. 5 is a block diagram of the phase conjugation circuit 40. As shown in FIG.

The following describes several embodiments for implementing the present invention. Each embodiment is an example, and partial substitution or combination of configurations shown in different embodiments is possible. In each embodiment, differences from those described in the previous embodiment are described. In particular, similar effects resulting from similar configurations will not be mentioned in each embodiment.

The transmission system according to an embodiment of the present invention may be a retrodirective power transmission system.

Figure 1 is a conceptual diagram of a power transmission system 10 according to an embodiment of the present invention. The power transmission system 10 includes a power transmission device 20 and a power receiving device 30. The power transmission device 20 is an example of a "transmitting device" of the present invention. The power receiving device 30 is an example of a "receiving device" of the present invention. The power transmission system 10 operates as follows.

The power transmission device 20 first radiates a transmission signal of frequency f at a wide angle or isotropically for a short period of time. The frequency of the transmission signal radiated by the power transmission device 20 is, for example, 2.45 GHz. The transmission signal radiated by the power transmission device 20 is an example of a "transmission signal" in the present invention.

The power receiving device 30 generates a pilot signal of frequency 2f by reflecting a part of the transmission signal that reaches the power receiving device 30 as a second harmonic. The frequency of the pilot signal is, for example, 4.9 GHz. The power transmitting device 20 uses the phase of the pilot signal that reaches the power transmitting device 20 to orient itself in the direction from which the pilot signal arrives and form a transmission beam of frequency f that reproduces the path from which the pilot signal arrives. In other words, the power transmitting device 20 radiates a transmission signal of frequency f toward the direction from which the pilot signal arrives. As a result, the power receiving device 30 continues to radiate the pilot signal, and the power transmitting device 20 continues to radiate the transmission signal.

The power transmission device 20 may stop transmitting power after a predetermined time has elapsed since the start of power transmission, or may stop transmitting power in response to a stop command received from the power receiving device 30.

In addition, the power transmission device 20 may emit the initial power transmission signal so as to scan the surroundings of the power transmission device 20.

When the power receiving device 30 moves, the arrival path of the pilot signal changes. The power transmitting device 20 forms a power transmission beam that reproduces the arrival path of the changed pilot signal. In this way, the power transmitting device 20 can automatically track the power receiving device 30 and transmit power to the power receiving device 30.

Figure 2 is a block diagram of the rectenna 31 provided in the power receiving device 30. The rectenna 31 includes an antenna 32 and a rectifier circuit 33. The rectifier circuit 33 is connected between the antenna 32 and the load and is composed of a shunt-connected diode. The rectenna 31 does not include a filter that is provided in typical rectennas to prevent re-radiation of harmonics. Therefore, harmonics generated during rectification by the rectifier circuit 33 are radiated from the antenna 32. As a result, the rectenna 31 reflects a portion of the transmission signal that reaches the rectenna 31 as a second harmonic.

Figure 3 is a block diagram of the main parts of the power transmission device 20. The power transmission device 20 includes an array antenna 21 and multiple phase conjugation circuits 40. The array antenna 21 includes multiple receiving antenna elements 22 and multiple transmitting antenna elements 23. The transmitting antenna element 23 is an example of a "transmitting antenna element" of the present invention. The receiving antenna element 22 operates at a frequency 2f of the pilot signal, and the transmitting antenna element 23 operates at a frequency f of the transmitting signal. The receiving antenna element 22 and the transmitting antenna element 23 function to separate reception and transmission. The phase conjugation circuits 40 are connected to the pair of receiving antenna element 22 and transmitting antenna element 23, respectively. The phase conjugation circuits 40 receive the pilot signal received by the receiving antenna element 22, respectively, and output a transmitting signal to be supplied to the transmitting antenna element 23. The power transmission device 20 further includes a local oscillator 24 connected to each phase conjugation circuit 40. The local oscillator 24 is shared by each of the phase conjugation circuits 40 and supplies a common reference signal to each of the phase conjugation circuits 40. The power transmission device 20 further includes a general transmission circuit (not shown) provided separately from the circuit shown in FIG. 3 to radiate the initial power transmission signal.

In addition, the power transmission device 20 may be provided with an antenna element that operates at two frequencies and is used for both reception and transmission, instead of the receiving antenna element 22 and the transmitting antenna element 23. In this case, the antenna element that is used for both reception and transmission is an example of the "receiving antenna element" of the present invention, and is also an example of the "transmitting antenna element" of the present invention.

The frequency of the power transmission signal output from each phase conjugate circuit 40 is equal to 1/2 times the frequency of the pilot signal input to each phase conjugate circuit 40. The phase difference of the power transmission signal output from each phase conjugate circuit 40 with respect to the power transmission signal output from any one of the multiple phase conjugate circuits 40 is equal to -1/2 times the phase difference of the pilot signal input to each phase conjugate circuit 40 with respect to the pilot signal input to the any one of the phase conjugate circuits 40.

That is, the frequency of the power transmission signal is f, and the frequency of the pilot signal is 2f. Also, when the phase of the pilot signal acquired by the nth receiving antenna element 22 and input to the nth phase conjugate circuit 40 at time t is 2(ωt-θ _n ), the phase of the power transmission signal output from the nth phase conjugate circuit 40 and input to the nth power transmitting antenna element 23 is ωt+α+θ _n . Here, 2ω is the angular frequency of the pilot signal. -2θ _n is the phase difference of the pilot signal input to the nth phase conjugate circuit 40 with respect to the pilot signal input to the first phase conjugate circuit 40. α is the phase of the power transmission signal output from the first phase conjugate circuit 40 at time t=0.

The order of the receiving antenna element 22, the power transmitting antenna element 23, and the phase conjugate circuit 40 is for convenience in distinguishing between the receiving antenna element 22, the power transmitting antenna element 23, and the phase conjugate circuit 40.

4A and 4B are conceptual diagrams for explaining the formation of a power transmission beam. As illustrated in FIG. 4A, it is assumed that the phase of a pilot signal of frequency 2f acquired by the nth receiving antenna element 22 lags behind the phase of a pilot signal acquired by the first receiving antenna element 22 by 2θ _n . In that case, as illustrated in FIG. 4B, if the phase of a power transmission signal of frequency f input to the nth power transmission antenna element 23 leads the phase of a power transmission signal of frequency f input to the first power transmission antenna element 23 by θ _n , the equiphase surface of the radio waves or microwaves of the power transmission signals radiated from each power transmission antenna element 23 faces the arrival direction of the pilot signal. Therefore, if the frequency of the pilot signal is 2f and the phase of the pilot signal acquired by the nth receiving antenna element 22 is 2(ωt- _θn ), if the frequency of the transmission signal is f and the phase of the transmission signal input to the nth transmitting antenna element 23 is ωt+α+ _θn , a transmission beam pointing in the direction of arrival of the pilot signal is formed.

Figure 5 is a block diagram of the phase conjugation circuit 40. The phase conjugation circuit 40 has a high-pass filter 41, a low-noise amplifier 42, a mixer 43, a frequency divider 44, a low-pass filter 45, and a power amplifier 46, which are connected in series or cascade between the input terminal and the output terminal. The high-pass filter 41 is an example of the "second filter" of the present invention. The low-pass filter 45 is an example of the "first filter" of the present invention.

The high-pass filter 41 is connected to the input side of the mixer 43, passes the pilot signal input to the phase conjugate circuit 40, and blocks the transmission signal input to the phase conjugate circuit 40 without being blocked by the receiving antenna element 22. This increases the separation between reception and transmission, and further suppresses interference between the pilot signal and the transmission signal.

The mixer 43 mixes the pilot signal amplified by the low noise amplifier 42 with the reference signal generated by the local oscillator 24. The reference signal has a frequency twice the frequency of the pilot signal and has the same phase in each phase conjugation circuit 40. That is, the reference signal has a frequency of 4f and a phase of 2 (2ωt+θ _LO ), where 2θ _LO is the phase of the reference signal at time t=0. The mixer 43 outputs a signal having a frequency of 6f and a phase of 2 (3ωt+θ _LO -θ _n ) and a signal having a frequency of 2f and a phase of 2 (ωt+θ _LO +θ _n ).

The frequency divider 44 divides the frequency of the signal output from the mixer 43 and transmitted by a factor of 2. Therefore, when a signal having a frequency 2f and a phase 2(ωt+θ _LO +θ _n ) is input to the frequency divider 44, the frequency divider 44 outputs a signal having a frequency f and a phase ωt+θ _LO +θ _n .

Note that although the frequency divider 44 may operate on an input signal of frequency 6f, it is preferable that it does not operate on an input signal of frequency 6f.

The low-pass filter 45 passes the signal with the lower frequency of the two signals with different frequencies output from the mixer 43 and transmitted. That is, the low-pass filter 45 passes the signal of frequency f output from the mixer 43 and transmitted through the frequency divider 44. In addition, when the frequency divider 44 operates on an input signal of frequency 6f, or when the frequency divider 44 operates unexpectedly on an input signal of frequency 6f, the low-pass filter 45 blocks the signal of frequency 3f output from the mixer 43 and transmitted through the frequency divider 44.

The power amplifier 46 has a predetermined gain in a frequency range including frequency f, and amplifies the signal that passes through the low-pass filter 45 and supplies it to the power transmission antenna element 23.

Therefore, when a pilot signal having a frequency 2f and a phase 2(ωt-θ _n ) is input, the nth phase conjugator 40 outputs a power transmission signal having a frequency f and a phase ωt+θ _LO +θ _n .

The phase conjugate circuit 40 may have a band-pass filter instead of the high-pass filter 41, and may have a band-pass filter instead of the low-pass filter 45.

In addition, instead of or together with the low-pass filter 45, the phase conjugate circuit 40 may have a low-pass filter connected between the mixer 43 and the frequency divider 44, which passes signals of frequency 2f and blocks signals of frequency 6f.

In addition, the phase conjugate circuit 40 performs mixing and then frequency division, but mixing may also be performed after frequency division.

In addition, each phase conjugation circuit 40 may use a reference signal generated by doubling the pilot signal received by any one of the receiving antenna elements 22 instead of the reference signal generated by the local oscillator 24.

In addition, the phase conjugate circuit 40 does not require the high-pass filter 41 and the low-noise amplifier 42.

According to this embodiment, the power transmitting device 20 generates a power transmission signal by converting the frequency of the pilot signal using the phase conjugate circuit 40, and the power receiving device 30 generates a pilot signal by reflecting a part of the power transmission signal as a second harmonic. This makes it possible to use a pilot signal and a power transmission signal with different frequencies. This makes it possible to suppress interference between the pilot signal and the power transmission signal and to improve the accuracy of the direction estimation of the power receiving device 30. In wireless power transmission, the strength of the power transmission signal is much stronger than the strength of the pilot signal, so interference between the pilot signal and the power transmission signal is a particular problem. Also, in wireless power transmission, the power transmission beam needs to have high directional accuracy. For this reason, the effect of this embodiment described above is particularly remarkable.

The power transmission system 10 is a hardware retrodirective power transmission system, and the phase conjugate circuit 40 is composed of an analog circuit. Therefore, in the power transmission system 10, the response time from detecting the direction of the power receiving device 30 to transmitting the beam is shorter than in a software retrodirective power transmission system. This enables high-speed automatic tracking, making it easier to supply power to mobile objects such as smartphones, drones, and EVs.

In addition, the phase conjugate circuit 40 has a much simpler configuration than a software retrodirective phase conjugate circuit, and is almost as simple as a general hardware retrodirective phase conjugate circuit. Furthermore, a software retrodirective phase conjugate circuit requires an expensive phase shifter to achieve phase conjugation. In contrast, the phase conjugate circuit 40 is a hardware retrodirective phase conjugate circuit and does not have a phase shifter. Therefore, the power transmission system 10 can be manufactured at low cost, which is advantageous for practical use.

In addition, in a typical retrodirective power transmission system, the power receiving device emits a pilot signal using a battery provided in the power receiving device. Therefore, the power receiving device needs a power source to emit the pilot signal. Also, if the battery of the power receiving device is dead before the start of power transmission, the power transmitting device cannot start power transmission. According to this embodiment, the power transmitting device 20 first emits a power transmission signal at a wide angle, and forms a power transmission beam when it receives a pilot signal. The power receiving device 30 generates a pilot signal by reflecting a part of the power transmission signal as a second harmonic. Therefore, the power receiving device 30 does not need a power source to emit a pilot signal. Also, even if the battery of the power receiving device 30 is dead before the start of power transmission, the power transmitting device 20 can start power transmission. Therefore, the power transmission system 10 is a system that does not depend on the remaining battery capacity of the power receiving device 30, and has a wide range of applications.

In addition, if there are multiple power receiving devices 30 within the vicinity of the power transmitting device 20 from which power can be transmitted, the power transmitting device 20 can transmit power to the multiple power receiving devices 30 simultaneously.

Thus, the power transmission system 10 has many advantages despite being simple to manufacture.

The power transmission system 10 can be used, for example, for wireless charging of smartphones, IoT devices, etc., wireless charging of flying objects such as drones, and wireless charging of AGVs, EVs, etc. operating in factories.

In addition, in another embodiment of the present invention, the power receiving device may generate a pilot signal using a power source provided in the power receiving device instead of generating a pilot signal by reflecting a transmission signal.

A transmission system according to yet another embodiment of the present invention may be a retrodirective communications system equipped with a phase conjugate circuit as described above. When a transmitter in this communications system receives a pilot signal of frequency 2f emitted from a target, it forms a communications beam of frequency f that faces the direction from which the pilot signal is coming.

The phase conjugation circuit of this communication system may include a power amplifier, but a power amplifier is not required.

Finally, the above description of the embodiments is illustrative in all respects and is not restrictive. Those skilled in the art may make appropriate modifications and changes. The scope of the present invention is indicated by the claims, not by the above embodiments. Furthermore, the scope of the present invention includes modifications from the embodiments within the scope of the claims and the scope equivalent thereto.

10... Power transmission system 20... Power transmission device 21... Array antenna 22... Receiving antenna element 23... Power transmission antenna element 24... Local oscillator 30... Power receiving device 31... Rectenna 32... Antenna 33... Rectifier circuit 40... Phase conjugation circuit 41... High-pass filter 42... Low-noise amplifier 43... Mixer 44... Frequency divider 45... Low-pass filter 46... Power amplifier

Claims (5)

an array antenna having a plurality of receiving antenna elements and a plurality of transmitting antenna elements;
a plurality of phase conjugation circuits respectively connected to the plurality of receiving antenna elements and the plurality of transmitting antenna elements;
each of the phase conjugation circuits receives a pilot signal received by the receiving antenna element, and outputs a transmission signal to be supplied to the transmitting antenna element;
the frequency of the transmission signal output from each of the phase conjugation circuits is equal to 1/2 the frequency of the pilot signal input to each of the phase conjugation circuits,
a phase difference of a transmission signal output from each of the phase conjugation circuits with respect to a transmission signal output from any one of the phase conjugation circuits is equal to -1/2 times a phase difference of a pilot signal input to each of the phase conjugation circuits with respect to the pilot signal input to the any one of the phase conjugation circuits. The phase conjugation circuits each include
a mixer for mixing the pilot signal with a reference signal having a frequency twice the frequency of the pilot signal and having the same phase in each of the phase conjugation circuits;
a frequency divider that divides the frequency of the signal output from the mixer and transmitted by a factor of two;
2. The transmitting device according to claim 1, further comprising: a first filter that passes a signal having a lower frequency out of two signals having different frequencies output from the mixer and transmitted. The transmitting device according to claim 2, wherein the phase conjugation circuits each have a power amplifier that amplifies a signal output from a circuit including the mixer, the frequency divider, and the first filter and supplies the amplified signal to the transmitting antenna element. The transmitting device according to claim 2 or 3, wherein each of the phase conjugate circuits has a second filter connected to the input side of the mixer, passing the pilot signal and blocking the transmission signal. A transmitting device according to any one of claims 1 to 4,
A receiving device having a rectenna;
Equipped with
A transmission system in which the rectenna generates the pilot signal by reflecting a portion of the transmission signal that reaches the rectenna as a second harmonic.

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