Ac device

Abstract

To provide an AC circuit capable of reducing a reflection ratio in a wider power range and a wider frequency range.SOLUTION: An AC device has: a transmission line having output impedance ZC in which one end point is connected to an AC power supply; a plurality of phase shift circuits connected to the other end point of the transmission line; and an AC circuit connected to each of the phase shift circuits. An input transmission path is divided into multiple branch lines and connected to the AC circuit. In each branch line, the phase shift circuit is placed before the AC circuit which is a load. Each phase shift circuit takes impedance matching with signals at a plurality of frequencies or a plurality of powers so as to have a phase shift angle and characteristic impedance in which a real part of synthetic admittance is 1 / ZC and an imaginary part is zero when seen from the other end point for a plurality of conditions on an inputted signal.SELECTED DRAWING: Figure 20

Description

[Technical field]

[0001] The present disclosure relates to alternating current devices. [Background technology]

[0002] Microwave antennas efficiently send signals into the air at the desired frequency by adjusting the size of the antenna and the position of the power feed so that reflection is zero due to the characteristic impedance of the signal source and transmission line.

[0003] In addition, with the spread of electric vehicles and portable devices, there is an increasing demand for contactless power transfer, which transmits power without contact. In contactless power transfer using microwaves, a rectenna circuit, that is, a circuit that converts (rectifies) microwaves, which are alternating current, into direct current, is used.

[0004] In a rectenna circuit that converts AC signals to DC signals, power reflection occurs between the signal source and the rectifier circuit. In an antenna that emits radio waves into the air, reflection occurs at the interface between the signal cable and the antenna. Not only is the reflected power not used effectively, but if the reflected power returns to the power transmission device (power supply), it may destroy the power transmission device.

[0005] In general, to prevent reflection, a matching circuit is placed between devices that generate reflection. It is known that by inserting a matching circuit, if the output impedance of the power transmitting device and the input impedance at the inlet of the matching circuit have a complex conjugate relationship, reflection can be prevented and maximum power can be supplied to the load (for example, Patent Document 1). In other words, to supply maximum power to the load, it is necessary that the output impedance of the power source and the input impedance of the load have the same real value. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 5953603 Summary of the Invention [Problem to be solved by the invention]

[0007] Rectenna circuits, which rectify high-frequency waves, use rectifier diodes that have nonlinear characteristics with respect to the input power. As a result, even if the rectenna circuit is matched at a certain input power value, the input impedance changes when the input power value changes, resulting in reflection loss. Therefore, even if a matching circuit is used, the power range over which the rectenna circuit can achieve high efficiency is narrow. In environments with unstable transmission conditions, such as wireless power transmission, there is a demand for AC circuits that can reduce the reflectance over a wider power range and perform highly efficient AC-DC conversion.

[0008] In addition, because antennas use resonance within the antenna material, the frequency band in which they can transmit efficiently is narrow and limited to one frequency. Therefore, there is a demand for antennas that can transmit over a wider band and at multiple frequencies.

[0009] An object of the present invention is to provide an AC circuit which prevents reflections over a wider power range. [Means for solving the problem]

[0010] In one embodiment of the present disclosure, an AC device has an output impedance Z C a transmission line, a plurality of phase shift circuits connected to terminals of the transmission line, and an AC circuit connected to the phase shift circuits, each of which has a real part of a composite admittance seen from the other terminal for a plurality of conditions of an input signal, the real part being 1 / Z C and the imaginary part is zero. Effect of the Invention

[0011] The present disclosure enables a rectenna circuit to reduce the reflection rate over a wider power range, and an antenna to efficiently emit radio waves at multiple frequencies. [Brief description of the drawings]

[0012] [Figure 1] A diagram showing a circuit that transmits power from a power source to a load using a rectifier circuit. [Diagram 2] A diagram showing a circuit that connects a rectenna using a matching circuit and a harmonic blocking filter to transmit power from a power source to a load. [Diagram 3] A diagram showing a circuit in which the input transmission line is branched at a branch point and an AC circuit is connected in parallel. [Figure 4] A diagram showing an example of an AC circuit acting as a load [Diagram 5] Smith chart display of reflected waves from AC circuits [Figure 6] A diagram showing an example of connecting a matching circuit between the input and the branch point. [Figure 7] The diagram shows a circuit in which an input transmission line is branched into a first line and a second line at a branch point, and a phase shift circuit is connected to the input of the AC circuit of each line. [Figure 8] A diagram showing the rectifier circuit, which is the basic part of a rectenna circuit. [Figure 9] A diagram showing a rectenna circuit with an LPF added to the basic circuit [Figure 10] A diagram showing a rectenna circuit with an LPF and matching circuit added to the basic circuit. [Figure 11] A diagram showing the efficiency and reflectance of RF / DC conversion versus input power in a rectenna circuit. [Figure 12] A diagram showing a circuit that uses the phase difference of the reflected wave between lines to suppress rectenna circuit reflections. [Figure 13] Smith chart display of reflected waves corresponding to input signals [Figure 14] A diagram showing an example of multiple antennas connected in parallel [Figure 15] A diagram showing the reflection characteristics of an antenna with respect to an input signal [Figure 16] Smith chart explaining impedance matching [Figure 17] A diagram showing an example of input branching stacked in multiple stages [Figure 18] A diagram showing an example in which multiple antennas are connected in parallel and a phase shift circuit is provided at the input of each line. [Figure 19] Reflectance when impedance matching is performed for four frequencies [Figure 20] A diagram showing an example in which multiple rectifier circuits are connected in parallel and a phase shift circuit is provided at the input of each rectifier circuit. [Figure 21] A diagram showing the efficiency and reflectance of RF / DC conversion when branched into multiple lines. [Figure 22] Complex representation of admittance at a branch point when the input signal power of each line is changed from 0.1 to 50 W. [Figure 23] A diagram showing a rectenna circuit using an LC matching circuit. [Figure 24] A diagram showing a circuit using an LC circuit as a phase shift circuit for rectenna circuits connected in parallel. [Diagram 25] A graph showing the RF / DC conversion efficiency and reflectance when the input power is changed DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] As described below, in the AC circuit of the present disclosure, reflections can be suppressed for a variety of input signal conditions simply by adjusting the phase shift angle of the phase shift circuit.

[0014] In a rectenna circuit, by combining it with a matching circuit, it is possible to suppress reflections and maintain high efficiency in RF / DC (Radio Frequency / Direct Current) conversion for a wide range of input power or frequency. Also, when used as an antenna, it can radiate signals in multiple bands.

[0015] Alternatively, it is possible to widen the radiation band by arranging multiple bands closely together.

[0016] (Rectenna) Before describing the details of the present invention, a problem with a rectifier circuit will be described. FIG. 1 is a diagram showing a circuit that transmits power from a power source to a load using a rectifier circuit.

[0017] 1 includes a power supply 111, a capacitor 122, a rectifier circuit 120, and a load 130. The load may be a constant voltage load or another type of load, such as a constant resistive load.

[0018] The power supply 111 is understood as an equivalent circuit having an oscillator 112 and a power supply resistor 113 .

[0019] The power source 111 generates microwaves to be transmitted. The frequency of the microwaves generated by the power source 111 is, for example, 5.8 GHz. In wireless power transmission, the power source serves as a power receiving antenna.

[0020] The rectifier circuit 120 has a diode 123 and a diode 124. The anode of the diode 123 is connected to the ground. The cathode of the diode 124 is connected to one side of a load 130. The other side of the load 130 is connected to the ground. The load 130 is a constant resistance load or a constant voltage load. In either case, a constant voltage must be maintained between the cathode of the diode 124 and the ground, so in the case of a load other than a constant voltage load, a smoothing circuit using a capacitor or a stub is connected therebetween.

[0021] One side of capacitor 122 is connected to power supply 111, and the other side of capacitor 122 is connected to the connection point of the cathode of diode 123 and the anode of diode 124 in rectifier circuit 120. In the rectifier circuit, a DC voltage is generated by signal conversion, but capacitor 122 is inserted to separate the DC voltages on the signal source side and the rectenna circuit, and has a sufficiently large value so as not to affect the AC characteristics.

[0022] The rectifier circuit 120 in FIG. 1 is called a voltage doubler circuit.

[0023] The rectifier circuit 120 may be a single shunt circuit using one diode and a λ / 4 line.

[0024] When a microwave signal is input to rectifier circuit 120, reflection occurs at the connection point between the cathode of diode 123 and the anode of diode 124. When viewed from the power transmitting device side, the diode rectifier circuit appears to be a parallel connection of the capacitance of diodes 123 and 124 when they are off and the effective resistance of load 130. When the load is a constant voltage power supply, the effective resistance is determined by the voltage of the power supply and the current flowing in. The complex impedance resulting from this parallel connection of capacitance and resistance creates a mismatch with the impedance of the input transmission line, causing reflection. In a rectenna circuit, reflection is a loss.

[0025] FIG. 2 is a diagram showing a circuit for transmitting power from power source 111 to load 130 by connecting rectenna circuit 220 using matching circuit 226 and harmonic cutoff or low-pass filter 227 (LPF: Low-pass Filter).

[0026] One end of matching circuit 226 is connected to the other end of capacitor 122 , and the other end of matching circuit 226 is connected to one end of LPF 227 .

[0027] The other end of the LPF 227 is connected to the cathode of the diode 123 and the anode of the diode 124 .

[0028] In order to prevent reflection, it is common to use a matching circuit in a high frequency circuit to suppress reflection and prevent a decrease in efficiency, so a matching circuit 226 is connected.

[0029] In addition, since diodes have nonlinear characteristics with respect to the input voltage, even if a sine wave AC signal is input, the reflected wave contains harmonics of the input signal. Since the reflection of harmonics also causes loss, LPF 227 is connected to confine the harmonics generated inside and prevent them from being emitted as reflected waves. As a result, the circuit in Figure 2 can achieve impedance matching because the reflected wave is only the fundamental wave when viewed from matching circuit 226.

[0030] When the load 130 is a constant voltage load, the current flowing to the load changes depending on the input power, so if the load is considered a resistor, the effective resistance value changes depending on the power. When the load 130 is a constant resistance load, the resistance value does not change, but the output DC voltage changes depending on the input power. As a result, the average voltage applied to the diode when it is off changes, and the depletion layer capacitance changes.

[0031] In other words, when the input power changes, the input impedance of the rectenna circuit changes whether it is a constant voltage load or a constant resistance load. This shows that even if matching is performed under certain input conditions to eliminate reflections, reflections will occur when the input power changes. In the end, the high efficiency state with low reflections is limited to a narrow range of impedance-matched input conditions.

[0032] (First embodiment: branching of lines in an RC circuit) Here, a method for suppressing reflections in an AC circuit by using line branches and phase shift circuits, which is the subject of the present invention, will be described using a simple circuit example.

[0033] When a sine wave is input to an AC circuit, the AC circuit will reflect this input signal due to its characteristics.

[0034] When the reflected wave is only the fundamental wave, it is possible to suppress the reflection by controlling the amplitude and phase of the reflected wave using a capacitor and inductor, or a finite-length impedance line and stub, etc. However, when an AC circuit can be configured with two circuits connected in parallel, it is possible to suppress the reflection by inserting a phase-shift circuit into each of the two circuits and controlling the phase delay (phase shift angle) without using a matching circuit.

[0035] Below, we will explain a circuit that branches the input power into two lines at a branch point and suppresses reflections by utilizing the phase difference of the reflected wave between the lines without using a matching circuit.

[0036] FIG. 3 is a diagram showing a circuit in which an input transmission line 330 to which an input terminal 310 is connected is branched at a branch point 320, and an AC circuit A 340 and an AC circuit B 350 are connected in parallel.

[0037] Fig. 4 is a diagram showing an example of an AC circuit that serves as a load in Fig. 3. The AC circuit is formed, for example, of a circuit in which a resistor and a capacitor are connected in parallel.

[0038] Figure 5 is a Smith chart showing the reflected wave for the signal to the circuit of Figures 3 and 4. The normalized impedance is 50 Ω.

[0039] 3 is configured, for example, with a 240 Ω resistor and a 100 pF capacitor connected in parallel. When a signal with a frequency of 10 MHz is applied to this circuit from a signal source with a characteristic impedance of 50 Ω, the reflection coefficient is shown by the white circle reflection coefficient 510 on the Smith chart in FIG.

[0040] 3 is configured, for example, with a 40 Ω resistor and a 200 pF capacitor connected in parallel. When a signal with a frequency of 10 MHz is applied to this circuit from a signal source with a characteristic impedance of 50 Ω, the reflection coefficient is shown by the white square reflection coefficient 520 on the Smith chart in FIG.

[0041] In addition, when a signal having a frequency of 10 MHz is applied from a signal source having a characteristic impedance of 50 Ω to a circuit in which AC circuit A 340 and AC circuit B 350 are connected in parallel as shown in FIG. 3, the reflection coefficient is shown by the reflection coefficient 530 indicated by a black triangle in the Smith chart in FIG. 5.

[0042] As shown in Figure 5, neither circuit is matched to a signal source with a characteristic impedance of 50 Ω.

[0043] For example, impedance matching has conventionally been performed by connecting a matching circuit between input terminal 310 and branch point 320 in Fig. 3. Fig. 6 is a diagram showing an example in which a matching circuit 610 is connected between input terminal 310 and branch point 320.

[0044] 6, when impedance matching is performed at a frequency of 10 MHz for input terminal 310 with an impedance of 50 Ω, by using inductor 611 (L=647 nH) and capacitor 612 (C=329 pF), the coordinate of the reflected wave as seen from input terminal 310 can be set to origin 560, thereby eliminating reflection.

[0045] 3, if the combined admittance seen from the branch point 320 is in a complex conjugate relationship with the signal source impedance, reflection will not occur. In other words, the real part of the combined admittance should be set to the reciprocal of the signal source impedance, i.e., 20mS, and the imaginary part should be set to zero.

[0046] This can also be achieved by connecting a phase-shift circuit to the input of each AC circuit. Each "series of circuits" branched off from branch point 320 and connected in parallel will be called a "line."

[0047] FIG. 7 is a diagram showing a circuit in which an input transmission line 330 is branched at a branch point 320 into a first line 730 and a second line 740, a phase-shift circuit A710 is connected to the input of an AC circuit A340 in the first line 730, and a phase-shift circuit B720 is connected to the input of an AC circuit B350 in the second line 740.

[0048] The reflected wave returning to the branch point 320 from the first line 730 and the second line 740 is a combination of the reflected waves from each line. Since the signal frequency of the reflected wave is the same as that of the incident wave, the combined reflected wave can be uniquely expressed by two parameters, the amplitude and the phase difference with respect to the input signal. In other words, in order to perform impedance matching, it is necessary to optimize the two parameters, the amplitude and the phase difference with respect to the input signal.

[0049] Each phase shift circuit has two parameters, the characteristic impedance and the phase shift angle, so there are four parameters in total for the two phase shift circuits. Here, we will fix the characteristic impedance to 50 Ω and adjust the phase shift angle of each phase shift circuit to achieve matching.

[0050] In the Smith chart of Figure 5, the change in the coordinate (reflection coefficient) of the reflected wave by a phase-shift circuit with a characteristic impedance of 50 Ω corresponds to a movement on a circle centered on the origin.

[0051] If the phase shift angle of the phase shift circuit A710 is 135.5 degrees, the reflected wave moves from the reflection coefficient 510 to the reflection coefficient 540. The reflection coefficient 540 is a reflection corresponding to a load whose admittance is (0.00467-j0.0095)S.

[0052] If the phase shift angle of the phase shift circuit B 720 is 155.8 degrees, the reflected wave moves from the reflection coefficient 520 to the reflection coefficient 550. The reflection coefficient 550 is a reflection whose admittance corresponds to (0.01533+j0.0095)S.

[0053] The combined admittance seen from the branch point 320 is the sum of the two admittances, that is, (0.02+j0)S, and therefore matching can be achieved with a signal source having a characteristic impedance of 50Ω.

[0054] The adjustment range of admittance is limited depending on the original impedance value, so it is not always possible, but accurate adjustment is possible within the adjustable range. When matching is performed in this way, reflection occurs in the first line 730 and the second line 740 connected to the branch point 320, but this reflection remains within each line and does not exit outside the branch point 320 (the input transmission line 330 side).

[0055] (Second embodiment: rectenna circuit) An example will now be described in which the principles of the present invention are applied to suppression of reflections in the rectenna circuit described above. Hereinafter, reflection suppression in a rectenna circuit using a Schottky barrier diode (SBD: Schottky Barrier Diode) made of gallium nitride (GaN) as the diode will be described.

[0056] Figures 8 to 10 are diagrams showing the rectenna circuit used in the calculations. Figure 8 is a diagram showing a rectifier circuit, which is a basic part of the rectenna circuit. Figure 9 is a diagram showing a rectenna circuit in which an LPF 927 is added to the basic part. Figure 10 is a diagram showing a rectenna circuit in which an LPF 927 and a matching circuit 1026 are added to the basic part.

[0057] The output of the power supply 111 is connected to one side of a capacitor 122. The other side of the capacitor 122 is connected to the cathode of an SBD 823 and the anode of an SBD 824. The capacitor 122 separates the DC voltages of the signal source and the rectenna circuit. The anode of the SBD 823 is connected to ground. The cathode of the SBD 824 is connected to a load 130.

[0058] The SBD 823 and the SBD 824 configure a rectifier circuit 820 .

[0059] Both SBD823 and SBD824 are made by connecting 16 dot (small circular) diodes with a diameter of 4 μm in parallel. The capacitance of one dot when it is off is 0.03 pF, the resistance when it is on is 26 Ω, and the constant voltage load is 60 V due to the withstand voltage constraints.

[0060] 9 shows a rectifier circuit 920 in which an LPF 927 is connected to the rectifier circuit 820. The SBD 823 and the SBD 824 are the same as those in FIG.

[0061] The LPF927 is created using a 50 Ω microstrip line on a substrate with a relative dielectric constant of 4.2. The microwave frequency is 5.8 GHz, and the signal wavelength in the microstrip line on the substrate is approximately 28 mm. The LPF927 is composed of a third harmonic cutoff filter (BEF: Band Elimination Filter) 927a and a fifth harmonic BEF927b.

[0062] The BEF927a is an open stub of a microstrip line with L=2.1 mm (0.083λ=1 / 12λ). The BEF927b is an open stub of a microstrip line with L=1.26 mm (0.05λ=1 / 20λ). The BEF927a and the BEF927b are both connected to the other side of the capacitor 122, the cathode of the SBD823, and the anode of the SBD824.

[0063] The LPF 927 may be a filter that removes only the third harmonics, or may be a filter that removes harmonics of more than the fifth harmonics. The LPF 927 may also be configured in other ways. When the frequency is low, an LPF using an LC circuit may be used instead of the BEF 927a and the BEF 927b.

[0064] 10 shows a rectenna circuit 1020 in which a matching circuit 1026 is connected to a rectifier circuit 920. The SBD 823, the SBD 824, and the LPF 927 are the same as those in FIG.

[0065] The matching circuit 1026 is composed of a series connected microstrip line 1026a and an open stub microstrip line 1026b. The matching circuit 1026 may be constructed in other configurations.

[0066] One side of the microstrip line 1026a is connected to the other side of the capacitor 122 and to the microstrip line 1026b, and the other side of the microstrip line 1026a is connected to the cathode of the SBD 823, the anode of the SBD 824, the BEF 927a and the BEF 927b.

[0067] Here, a line with L=0.153λ is used as the microstrip line 1026a, and a stub with L=0.195λ is used as the microstrip line 1026b so that the input power Pin is matched at 3W. FIG. 11 is a diagram showing the efficiency of RF / DC conversion (conversion from microwave power to DC power) and the reflectance to the input side with respect to the input power of the circuit in FIG. 10. The RF / DC conversion efficiency is shown by line 1110 in FIG. 11, and the reflectance (power reflectance) is shown by line 1120. At Pin=3W, the reflectance becomes 0, and the RF / DC conversion efficiency is maximized. However, the RF / DC conversion efficiency becomes high (for example, 90% or more) only when the input signal power is in the range of 2.5 to 4W.

[0068] Fig. 12 shows a circuit that splits the input into two lines and suppresses reflections by utilizing the phase difference of the reflected wave between the lines. In Fig. 12, each line includes a matching circuit, and at Pin=3W, reflections are suppressed by this effect.

[0069] The input transmission line 330 has a characteristic impedance of 25Ω, and the first line 1230 and the second line 1240 have a characteristic impedance of 50Ω.

[0070] The input transmission path 330 includes a power source 1211 and a capacitor 122. One end of the capacitor 122 is connected to the output of the power source 1211, and the other end of the capacitor 122 is connected to the branch point 320.

[0071] The first line 1230 includes a phase shift circuit 1210 and a rectenna circuit 1020a. The rectenna circuit 1020a is the same as the rectenna circuit 1020 in FIG.

[0072] The second line 1240 includes a phase shift circuit 1220 and a rectenna circuit 1020b. The rectenna circuit 1020b is the same as the rectenna circuit 1020a.

[0073] Branch point 320, phase shift circuit 1210, rectenna circuit 1020a, phase shift circuit 1220, and rectenna circuit 1020b constitute rectenna circuit 1250.

[0074] The power supply 1211 has an output impedance of 25Ω.

[0075] When 6 W of power is output from power source 1211, 3 W of power is input to first line 1230 and second line 1240. As described in Fig. 10, rectenna circuit 1020a and rectenna circuit 1020b are matched for an input power of 3 W, so no reflection occurs regardless of the phase shift amount of the phase shift circuit.

[0076] On the other hand, consider the case where 20 W of power is output from the power source 1211. In this case, if there is no reflection in the transmission path, 10 W of power is input to each of the first line 1230 and the second line 1240, but reflection occurs because the matching circuit 1026 is matched at 3 W. Therefore, when 10 W of power is input, the phase shift amount of the phase shift circuit 1210 of the first line 1230 and the phase shift circuit 1220 of the second line 1240 is adjusted so that the composite impedance of the first line 1230 and the second line 1240 is only the real part of 25 Ω.

[0077] Such adjustment of the phase shift circuit 1210 and the phase shift circuit 1220 will be explained using a Smith chart.

[0078] FIG. 13 shows a Smith chart representation of the reflected wave corresponding to the input signal of the circuit of FIG.

[0079] The circuit in Fig. 12 is matched at an input power of 3 W, so the coordinates when the input power is 3 W are the origin 1310. Next, consider the case where 10 W of power is input to each line of the circuit in Fig. 12 in which rectenna circuit 1020a and rectenna circuit 1020b are arranged. Since both rectifier circuits are already matched for Pin=3 W, reflection occurs at 10 W. Taking into account the reflectance, the reflection coefficient when 10 W is input inside the rectifier circuit is equivalent to the case where 13.55 W is input from the outside. The reflection coefficient in this case is reflection coefficient 1320.

[0080] If the phase shift circuits 1210 and 1220 are used to shift the reflection coefficient 1320 to reflection coefficients 1330 and 1340 on an equal conductance circle of 50 Ω, the imaginary parts of the impedances cancel each other out, so the composite impedance will be only the real part of 25 Ω. This makes the impedance equal to 25 Ω of the input transmission line 330, so reflections can be suppressed. If the phase shift angle in the phase shift circuit 1210 is set to 55.44 degrees, the reflection coefficient shifts from 1320 to 1330, and if the phase shift angle in the phase shift circuit 1220 is set to 175.58 degrees, the reflection coefficient shifts from 1320 to 1340.

[0081] For the circuit in Fig. 12, the RF / DC conversion efficiency versus input power is shown by line 1130 in Fig. 11, and the reflectance is shown by line 1140. Here, the horizontal axis indicates the input power to the unit line, and the output power of the power supply in the case of two lines is twice this. The same is true for Figs. 21 and 26 described later. The reflectance shown by line 1140 is close to zero between Pin = 3W and 10W, and the RF / DC conversion efficiency shown by line 1130 is maintained at a value of 90% or more between 1.7W and 13W.

[0082] 12, line 1130 indicates that high efficiency is maintained over a wide input power range compared to line 1110 for the single line case. This shows that highly efficient RF / DC conversion is achieved even if the power of the input signal changes significantly, which is particularly advantageous in applications such as wireless power transmission where fluctuations in transmission power are likely to occur.

[0083] (Third embodiment: antenna) Next, the application of the principles of the present invention to an antenna circuit will be described.

[0084] 14 is a diagram showing an example in which a plurality of antennas are connected in parallel. In the following, matching when the frequency of the input signal changes will be described.

[0085] A power supply 1411 is connected to an input terminal 310, and antennas A 1430 and B 1440 are connected in parallel at a branch point 320 via phase shift circuits A 1410 and B 1420, respectively. Antennas A 1430 and B 1440 are assumed to have the same characteristics.

[0086] For example, the antenna is a patch antenna that has a characteristic impedance of 50 Ω and does not generate reflections when the input signal frequency is 2.45 GHz, that is, it is an antenna that radiates radio waves.

[0087] 15 is a diagram showing the reflection characteristics of the antenna versus the input signal frequency. The reflection coefficient for the input signal at a single antenna is shown as line 1510. Line 1510 shows that the reflection coefficient is 0 at 2.45 GHz, indicating that all of the input signal is emitted from the antenna at this frequency.

[0088] 14, when a phase shift circuit is connected to the input of each antenna and the characteristic impedance of each phase shift circuit is set to 50 Ω, the same as the characteristic impedance of the antenna, the composite impedance at branch point 320 is 25 Ω. By setting the characteristic impedance of input transmission path 330 from input terminal 310 to branch point 320 to 25 Ω, impedance matching is achieved at branch point 320, so no reflection occurs at branch point 320. At an input signal of 2.45 GHz, no reflection occurs at the antenna section either, so no reflection occurs overall.

[0089] Although impedance matching was performed for this antenna when the input signal was 2.45 GHz, it is possible to perform matching for other frequency conditions by utilizing the phase shift angle of each phase shift circuit. For example, it is also possible to perform matching for an input signal of 2.40 GHz.

[0090] Using the Smith chart in FIG. 16, a case where impedance matching for 2.40 GHz is performed using a phase shift circuit will be described.

[0091] Since neither antenna generates a reflection at 2.45 GHz, the reflection coefficient of each antenna when the input signal is 2.45 GHz is the origin 1610. On the other hand, when the input signal is 2.40 GHz, the reflection coefficient of both antennas moves to 1620 due to the change in input frequency.

[0092] When a phase shift circuit with a characteristic impedance of 50 Ω is connected to the antenna, the reflection coefficient moves on a circle centered on the origin. For example, if the phase shift angle of phase shift circuit A 1410 is 36.4 degrees, the reflection coefficient 1620 moves to 1630. If the phase shift angle of phase shift circuit B 1420 is 64.65 degrees, the reflection coefficient 1620 moves to 1640.

[0093] Since the reflected wave passes through the phase shift circuit twice, the shift on the Smith chart corresponds to twice the phase angle caused by the phase shift circuit. Both reflection coefficient 1630 and reflection coefficient 1640 are on an equal conductance circle with an admittance of 20 mS. The imaginary parts of reflection coefficient 1630 and reflection coefficient 1640 have the same absolute value but opposite signs.

[0094] In this case, the real part of the composite admittance seen from the branch point 320 is 40 mS, and the imaginary part is 0. This indicates that impedance matching is achieved when the input signal line is 25 Ω.

[0095] At 2.45 GHz, matching is achieved regardless of the phase shift circuit, so that a circuit that does not generate reflections at the two frequencies of 2.40 GHz and 2.45 GHz can be achieved. This reflection characteristic is shown by line 1520 in FIG.

[0096] As the second matching condition, the reflection characteristics when the input signal is set to 2.449 GHz, which is almost equal to 2.45 GHz, are shown by line 1530 in Fig. 15. Referring to line 1530, it can be seen that the center frequency is 2.45 GHz, which is almost the same as line 1510 in the case of a single antenna, but the band is wider.

[0097] It is important to note that interference occurs because the phase of the signal radiated from the antenna differs between the two antennas due to the phase shift circuit, and that the antennas will have complex directivity depending on the distance between the antennas, their orientation, etc. Antenna directivity can be either an advantage or a disadvantage depending on the application.

[0098] (Fourth embodiment: multi-stage stacking) The reflection suppression circuit that branches into two lines can be stacked in multiple stages. Here, we will explain using a rectenna circuit as an example again.

[0099] In the rectenna circuit of FIG. 12, rectenna circuit 1020a and rectenna circuit 1020b, which suppress reflections for an input power of 3 W, are configured so that phase shift circuit 1210 and phase shift circuit 1220 can also suppress reflections for an input power of 10 W.

[0100] FIG. 17 is a diagram showing a circuit in which two more circuits shown in FIG. 12 are combined.

[0101] The input transmission line 1740 has a characteristic impedance of 12.5Ω, and the first line 330a and the second line 330b have a characteristic impedance of 25Ω.

[0102] The input transmission path 1740 includes a power source 1711 and a capacitor 122. One end of the capacitor 122 is connected to the output of the power source 1711, and the other end of the capacitor 122 is connected to a branch point 1730.

[0103] The first line 330a has a phase shift circuit 1710 and a rectenna circuit 1250a. One end of the phase shift circuit 1710 is connected to the branch point 1730, and the other end of the phase shift circuit 1710 is connected to the rectenna circuit 1250a. The rectenna circuit 1250a is the same as the rectenna circuit 1250 in FIG.

[0104] The second line 330b includes a phase shift circuit 1720 and a rectenna circuit 1250b. One end of the phase shift circuit 1720 is connected to the branch point 1730, and the other end of the phase shift circuit 1420 is connected to the rectenna circuit 1250b. The rectenna circuit 1250b is the same as the rectenna circuit 1250a.

[0105] The branch point 1730 branches the input transmission line 1740 into a first line 330a and a second line 330b.

[0106] As described in FIG. 12, rectenna circuit 1250a and rectenna circuit 1250b are matched for an input power of 6 W or 20 W, so that no reflection occurs regardless of the phase shift amount of phase shift circuits 1710 and 1720.

[0107] On the other hand, when power supply 1711 outputs 4 W of power, 2 W of power is input to first line 330a and second line 330b, respectively, and reflection occurs from rectenna circuit 1250a and rectenna circuit 1250b. Therefore, when power supply 1711 outputs 4 W of power, that is, when 1 W of power is input to the unit rectifier circuit, the phase shift angles of phase shift circuit 1710 of first line 330a and phase shift circuit 1720 of second line 330b are adjusted so that the composite impedance of first line 330a and second line 330b seen at branch point 1730 is 12.5 Ω, which is the real part only.

[0108] To make the real parts of the impedance equal and the absolute values ​​of the imaginary parts of the impedance equal at an input power of 1 W to the unit rectifier circuit, the phase shift angle in phase shift circuit 1710 should be 57.6 degrees and the phase shift angle in phase shift circuit 1720 should be 119.5 degrees.

[0109] By setting the phase shift angles in each phase shift circuit as described above, the composite impedance of the first line 330a and the second line 330b consists only of the real part of 12.5Ω, which is the same as the impedance 12.5Ω of the input transmission line 1740, thereby suppressing reflection.

[0110] In the circuit of FIG. 17, the absolute values ​​of the RF / DC conversion efficiency and the reflectance versus the input power are shown as lines 1150 and 1160 in FIG.

[0111] In FIG. 11, line 1110 shows the RF / DC conversion efficiency when only 3W reflection is suppressed, line 1120 shows the reflectance when only 3W reflection is suppressed, line 1130 shows the RF / DC conversion efficiency when 3W and 10W reflections are suppressed, line 1140 shows the reflectance when 3W and 10W reflections are suppressed, line 1150 shows the RF / DC conversion efficiency when 1W, 3W, and 10W reflections are suppressed, and line 1160 shows the reflectance when 1W, 3W, and 10W reflections are suppressed.

[0112] According to the line 1150, it can be seen that the input power range in which efficiency is high is expanded to 0.8 to 20W.

[0113] (Fifth embodiment: line with three or more branches; antenna) So far, we have explained the method of dividing the line into two, but it is also possible to configure the AC circuit with three or more circuits connected in parallel and perform impedance matching by connecting a phase shift circuit to the input of each circuit. In this case, the number of adjustable parameters increases, making it possible to accommodate more changes in input conditions. Again, an example of transmission at multiple frequencies from an antenna will be described. Fig. 18 shows an example in which multiple lines are connected in parallel to a branch point 1820, and phase shift circuits 1210a to 1210n are provided at the inputs of the lines to connect to an antenna.

[0114] Impedance matching requires control of two parameters, the phase and amplitude of the reflected wave, and therefore, in order to perform impedance matching, two control parameters are required for one input condition (input power or frequency).

[0115] For example, six control parameters are required to perform impedance matching for three frequencies. In this case, six phase shift angles may be controlled by six phase shift circuits with the same characteristic impedance, or three phase shift angles and three characteristic impedances of three phase shift circuits may be used. To use six phase shift circuits, the line may be branched into six at the branch point 1820, and to use three phase shift circuits, the line may be branched into three at the branch point 1820.

[0116] Line 1920 in FIG. 19 shows the reflectance when impedance matching is performed for three frequencies, for example, 2.43 GHz, 2.44 GHz, and 2.46 GHz, in addition to 2.45 GHz, using six of the antennas used in FIG. 14 and six phase-shift circuits, each with a characteristic impedance of 50 Ω.

[0117] Line 1510 in Fig. 19 indicates the reflectance of a single antenna with respect to the input signal. By setting the characteristic impedance of input transmission line 330 to 1 / 6 of 50 Ω, that is, 8.33 Ω, impedance matching is achieved at branch point 1820. In the case of 2.45 GHz, impedance matching is achieved at each antenna, so overall matching is achieved from the perspective of power supply 1811 as well.

[0118] However, this alone does not achieve matching at frequencies other than 2.45 GHz. Therefore, the phase shift angles of the six phase shift circuits are adjusted so that the reflection at 2.43, 2.44, and 2.46 GHz is zero. To do this, the optimization function of the simulator is used, and the six parameters are randomly varied to find the optimal solution. Although it was not possible to completely eliminate the reflection at the three frequencies, it was possible to reduce it to a sufficiently low value of -50 dB. Table 1 shows the phase shift angles of the six phase shift circuits in this case, and the input admittance of each line as viewed from the branch point 1820. In Table 1, Yre indicates the real part of the admittance, and Yim indicates the imaginary part of the admittance.

[0119] [Table 1]

[0120] For all four frequencies, the sum of the real parts of the admittance of the parallel-connected phase-shift circuits is approximately 120mS, and the sum of the imaginary parts is approximately 0mS. This indicates that impedance matching is achieved. Since the phase-shift angle changes the real and imaginary parts of the admittance simultaneously, it is not possible to set the three real and three imaginary parts of the admittance independently, so perfect matching was not achieved, but it can be seen that a sufficiently practical impedance matching is achieved over a wide frequency range.

[0121] Next, in FIG. 18, four antennas are used, and four phase-shift circuits with variable characteristic impedance are used to perform impedance matching for four frequencies, for example, 2.43 GHz, 2.45 GHz, 2.47 GHz, and 2.49 GHz, as shown by line 1930 in FIG.

[0122] In this case, the characteristic impedance of the input transmission line 330 is 1 / 4 of 50Ω, that is, 12.5Ω. Here, the phase shift circuit controls the characteristic impedance as well as the phase shift angle. Impedance lines with various characteristic impedances can be created by changing the line width, etc., of the microstrip line.

[0123] In this case, the characteristic impedance of the phase shift circuit is not necessarily 50 Ω, so there is reflection at the antenna entrance and matching is not necessarily achieved even at 2.45 GHz. In other words, adjustments are required to achieve matching even at 2.45 GHz. The simulator's optimization function was used to adjust the characteristic impedance and phase shift angle of the four phase shift circuits to find the optimal solution. As a result, as shown in 1930 of Figure 19, the reflection is -80 dB or less at four frequencies, and it is clear that matching is sufficient. The input admittance of each line as viewed from the branch point 1820 in this case is shown in Table 2. In Table 2, Yre is the real part of the admittance, and Yim is the imaginary part of the admittance.

[0124] [Table 2]

[0125] Although the admittance of each line varies for all four frequencies, the sum of the real parts of the admittances connected in parallel is approximately 80mS, and the sum of the imaginary parts is approximately 0mS. This matches the characteristic impedance of 12.5Ω, indicating that there is no reflection.

[0126] (Sixth embodiment: Line with three or more branches; Rectenna circuit) The matching method of dividing into three or more lines can also be applied to a rectenna circuit. Fig. 20 shows an example in which a plurality of rectifier circuits 820a to 820n are connected in parallel to a branch point 2020, and phase shift circuits 1210a to 1210n are provided at the inputs of the rectifier circuits.

[0127] Rectifier circuits 820a-820n in the circuit of Fig. 20 are the same as 820 in Fig. 8, and no matching circuit or LPF is connected. A rectenna circuit with a matching circuit or LPF connected may be used, but with multi-line optimization, it is possible to provide the LPF function along with the matching circuit, so that the matching circuit and LPF parts can be omitted, reducing the number of parts and the circuit size.

[0128] The optimization function of the circuit simulator is used to determine the phase shift angle in the phase shift circuit. Although the optimization function of the circuit simulator may not achieve an exact reflectance of 0, it is possible to keep the reflectance below the required condition. On the other hand, the target power value for reflection suppression is specified as a range rather than a point, so the reflectance can be reduced more uniformly as the number of branches increases. On the other hand, an increase in the number of branches also increases the number of components, so the number of branches is determined by taking both factors into consideration and based on the usage conditions.

[0129] Table 3 shows the optimized power range when two, four or eight lines are connected, and the phase shift angle of the phase shift circuit connected to the input of each line.

[0130] [Table 3]

[0131] The RF / DC conversion efficiency when branched into two lines is shown by line 2110 in Fig. 21, and the reflectance is shown by line 2120. Here, optimization was performed to make the reflection zero at 3 W. If the phase shift angles in each phase shift circuit when branched into two lines are set to 41.3 degrees and 87.3 degrees, the reflection at 3 W is suppressed, and even without a matching circuit and LPF, it is possible to obtain efficiency almost the same as in the case of 1110 in Fig. 10, which uses an LPF and matching circuit.

[0132] The RF / DC conversion efficiency when branched into four lines is shown by line 2130 in Fig. 21, and the reflectance is shown by line 2140. Here, optimization was performed to make the reflection zero in the range of 0.8 to 6 W. The phase shift angles in each phase shift circuit were found to be 15.0 degrees, 37.8 degrees, 56.7 degrees, and 85.4 degrees.

[0133] The RF / DC conversion efficiency when branched into eight lines is shown by line 2150 in Fig. 21, and the reflectance is shown by line 2160. Here, optimization was performed so that the reflectance was zero at 0.2 to 12 W. When branched into eight lines, the phase shift angles in each phase shift circuit were found to be 0.0 degrees, 15.8 degrees, 29.5 degrees, 39.4 degrees, 53.2 degrees, 64.3 degrees, 77.6 degrees, and 89.7 degrees.

[0134] Since the reflectance of a rectenna circuit changes according to the power of the input signal, the power received by each line is not uniform, and the ratio of power distributed to each line also changes according to the power of the input signal. Therefore, it is difficult to calculate the admittance of each line individually, as is done with an antenna.

[0135] However, it is possible to find the combined admittance value. The average admittance per line for each line is shown in Figure 22. In Figure 22, the dotted line shows the complex representation of the admittance when the input signal power for each line is changed from 0.1 to 50 W.

[0136] In Fig. 21, cases where the reflectance is 2% or less are indicated by white circles, diamonds, triangles, or squares. In Fig. 22, line 2210 indicates the combined admittance in the case of one line using a matching circuit, line 2220 indicates the combined admittance in the case of two lines of the present invention without connecting a matching circuit, and line 2230 indicates the combined admittance in the case of four lines of the present invention. In the case of eight lines, most of the lines have a reflectance of 2% or less in this power range, and are not shown because they are hidden by the symbols of the other lines.

[0137] In both cases, the average admittance of each line is approximately 20mS in real part and zero in imaginary part. The characteristic impedance Z of the signal source and the input transmission line c For the branch point, the real part of the composite admittance is exactly 1 / Z c Even if the imaginary part is not exactly 0, the reflectance is sufficiently low that it is often not a problem in practice.

[0138] Because suppressing reflections requires adjusting two parameters for one input condition, increasing the number of lines allows for more accurate adjustment, but increases costs. Therefore, the number of divisions is determined by balancing the strictness of the conditions in the control range with the increased cost due to the number of divisions.

[0139] (Seventh embodiment: Phase shift circuit in the low frequency range) In the second to sixth embodiments, the input signal has a microwave frequency of 2.45 GHz or 5.8 GHz, and in addition to an LPF and a matching circuit, an impedance line is used as a phase shift circuit. However, when the input signal has a low frequency, an LC circuit is used as a phase shift circuit.

[0140] 23 is a diagram showing a rectenna circuit using a phase shift circuit with an LC circuit for a 13.56 MHz input signal. The diode is a commercially available silicon Schottky barrier diode. Power supply 2311 is connected to one side of capacitor 2322. The other side of capacitor 2322 is connected to one side of inductor 2326a. The other side of inductor 2326a is connected to one side of inductor 2326b, the cathode of SBD 2323, and the anode of SBD 2324. The other side of inductor 2326b is connected to one side of capacitor 2326c. The other side of capacitor 2326c is connected to ground.

[0141] The anode of the SBD 2323 is connected to ground. The cathode of the SBD 2324 is connected to the load 130.

[0142] Inductor 2326a, inductor 2326b, and capacitor 2326c configure LPF and matching circuit 2326. SBD 2323, SBD 2324, and capacitor 2325 configure rectifier circuit 2320. Rectifier circuit 2320 and LPF and matching circuit 2326 configure rectenna circuit 2340.

[0143] Here, if load 130 is a constant voltage load of 100 V, inductor 2326a has an inductance of 828 nH, inductor 2326b has an inductance of 177 nH, and capacitor 2326c has a capacitance of 86.6 pF, then rectenna circuit 2340 will be matched to an input power of 10 W and no reflection will occur.

[0144] FIG. 24 is a diagram showing a circuit in which two circuits shown in FIG. 23 are connected in parallel.

[0145] An input transmission line 330 to which a power source 2311 is connected is branched at a branch point 320 into a first line 2430 and a second line 2440 .

[0146] The first line 2430 has a phase shift circuit 2410, and the second line 2440 has a phase shift circuit 2420. These phase shift circuits allow matching to be achieved for an input power of 30 W as well as an input power of 10 W on a single line. The output power of the power source 2311 is twice the power input to each line. According to a simulation using a transmission line, in order to achieve matching for an input power of 30 W, the phase shift angle of the phase shift circuit 2410 should be set to 97.7 degrees and the phase shift angle of the phase shift circuit 2420 should be set to 155.1 degrees. Therefore, the inductance of the inductor 2410a is set to 582 nH, the capacitances of the capacitors 2410b and 2410c to 269 pF, the inductance of the inductor 2420a to 247 nH, and the capacitances of the capacitors 2420b and 2420c to 1063 pF. By doing so, the phase shift circuits 2410 and 2420 can achieve their respective desired phase shift angles with an input / output impedance of 50 Ω.

[0147] FIG. 25 is a diagram showing the RF / DC conversion efficiency and the reflectance when the input power is changed in the circuit of FIG. 23 and the circuit of FIG.

[0148] Line 2510 shows the RF / DC conversion efficiency of the single line circuit of Figure 23, and line 2520 shows the reflectance of the single line circuit of Figure 23. Line 2530 shows the RF / DC conversion efficiency of the circuit of Figure 24, and line 2540 shows the reflectance of the circuit of Figure 24.

[0149] It can be seen from FIG. 25 that the multi-line circuit of FIG. 24 maintains high efficiency over a wider range of input power than the single-line circuit of FIG.

[0150] In the second to seventh embodiments, the rectifier circuits (AC circuits) connected to each line have the same characteristics, but they do not necessarily have to be the same. Even if the circuits have different characteristics, reflections can be suppressed by setting the phase shift amount of each line so that the imaginary parts of the impedances of the lines have the same absolute value but opposite signs, and the real part of the composite impedance is equal to the real part of the impedance before branching. This has already been shown in the first embodiment.

[0151] [effect] As described above, according to the present disclosure, by branching into multiple lines and providing a phase shift circuit for each line, it is possible to prevent reflection of high frequency signals in AC devices for multiple different input signals. In an antenna, radio waves of different frequencies can be emitted, and radio waves can be emitted over a wider band. Since the input impedance of a rectenna changes depending on the input power, the present disclosure can prevent reflection over a wide range of input power and achieve high efficiency. It can also be combined with a conventional matching circuit, in which case reflection suppression can be achieved over a wider range.

[0152] The phase shift circuit may be an impedance line or an LC circuit, and the input signal frequency may be in a wide range from kHz to GHz.

[0153] Although the examples of the present disclosure have been described in detail above, the present disclosure is not limited to the specific embodiments described above, and various modifications and variations are possible within the scope of the gist of the present disclosure described in the claims. [Industrial Applicability]

[0154] By using the present disclosure in a rectenna circuit, it is possible to achieve high conversion efficiency and eliminate power waste even when the input power changes significantly in contactless power supply. [Explanation of symbols]

[0155] 111, 1211, 1411, 1711, 1811, 2011, 2311 power supply 112 Oscillator 113 Power supply resistance 120, 820, 2320 rectifier circuit 122, 2322 DC cut capacitor 612, 2326c Matching circuit capacitor 2410b, 2420b Capacitor for phase shift circuit 611, 2326a, 2326b Inductors for matching circuits, 2410a, 2420a Inductors for phase shift circuits 123, 124, 823, 824, 2323, 2324 diodes 130 Load 220, 1020, 2340 Rectenna Circuit 226, 610, 1026, 2326 matching circuit 227, 927 Harmonic cutoff filter (LPF) 310 Input terminal 320, 1730, 1820, 2020 Turning Point 330, 1740, 1830, 2030 Input transmission line 340, 350 AC circuit 710, 720, 1210, 1220, 1410, 1420, 1710, 1720, 2410, 2420 phase shift circuit 730, 740, 1230,1240,2430,2440 tracks 1430, 1440 Antenna

Claims

1. One end point is connected to an AC power source and the output impedance Z Ｃ A transmission line of a plurality of phase shift circuits connected to the other end point of the transmission line; an AC circuit connected to each of the phase shift circuits; having Each phase shift circuit has a real part of a composite admittance from the other end point that is 1 / Z for a plurality of conditions of the input signal. Ｃ and has a phase shift angle and characteristic impedance such that the imaginary part is zero. AC device.

2. Each of the AC circuits connected to each of the phase shift circuits is an antenna.

2. An alternating current device as claimed in claim 1.

3. Each of the AC circuits connected to each of the phase shift circuits is a rectifier circuit.

2. An alternating current device as claimed in claim 1.

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