JP2008199857A - Rectenna equipment - Google Patents

Abstract

Output power is efficiently obtained even when incorporated in a moving body.
When a microwave is received by an antenna, a switch change control unit switches the changeover switch to a second rectenna substrate. The output voltage of the second rectenna substrate 22 is detected by the output voltage detection unit 25, and the output voltage detection result is input to the switch switching control unit 27. The switch switching control unit 27 obtains microwave input power based on the output voltage detection result and the data table 50. The switch switching control unit 27 selects the rectenna board having the highest conversion efficiency based on the microwave input power and the data table 50, and switches the changeover switch 20 to the selected rectenna board. In particular, when it is built in a mobile body, output power can be obtained efficiently even if the microwave transmission / reception distance changes.
[Selection] Figure 3

Description

  The present invention relates to a rectenna device that converts a microwave received by an antenna into DC power by a rectifier circuit.

  A rectenna device that converts microwaves received by an antenna into DC power by a rectifier circuit is known (see Patent Document 1). This rectenna device is a space solar satellite (SPS) project that sends power generated by an artificial satellite equipped with a solar panel to the earth by microwaves, and a micro that can be used for remote islands and mountaintops where wired power transmission is difficult. It is expected to be used for wave transmission plans.

  In recent years, a rectenna apparatus has also been built in a responder such as an RFID (Radio Frequency Identification) tag (see Patent Document 2). When the RFID tag approaches the interrogator, microwaves are transmitted from the interrogator to the RFID tag. In the RFID tag, the microwave transmitted from the interrogator is converted into drive power by the rectenna device, and thereby the RFID tag is activated. Information stored in advance in the RFID tag is returned to the interrogator as a response signal.

In such a rectenna apparatus, various proposals have been made in order to realize highly efficient and stable power supply. For example, when the input power of a microwave received by an RFID tag decreases, a method is known in which the output on the interrogator side is increased by notifying the interrogator side that the input power has decreased (Patent Document). 3). Moreover, the conversion efficiency (output power) is increased as much as possible by separately incorporating a rectenna device for harmonic conversion that converts harmonics generated when microwaves are converted into DC power into DC power. A method is also known (see Patent Document 4).
JP 2002-84585 A JP 2001-86666 A JP 2003-348773 A Japanese Patent Laid-Open No. 11-69667

  By the way, the conversion efficiency with which the rectenna device converts microwaves into DC power varies according to the input power of the microwaves. The conversion efficiency increases in a specific input power range, and decreases in other input power ranges (see FIG. 6A). For this reason, when the input power of the microwave changes, the output power of the rectenna device may be significantly reduced.

  When the rectenna device is built in a moving body such as an RFID tag, the transmission / reception distance of microwaves changes unlike the transmission / reception of microwaves between fixed points such as the SPS described above. When the transmission / reception distance is long, the microwave input power (reception power) is low, and conversely, when the transmission / reception distance is short, the microwave input power is high (see FIG. 2). Even if the transmission / reception distance is short, the input power of the microwave is reduced when the transmission / reception direction is changed. For this reason, if the transmission / reception distance becomes long or the transmission / reception direction changes, the rectenna apparatus may not be able to obtain the power necessary to drive the RFID tag.

  Such a problem cannot be solved by the methods described in Patent Documents 3 and 4 above. In the method described in Patent Document 3, when the input power of the microwave is extremely reduced or when the change of the input power is large, the power required to drive the RFID tag cannot be obtained, and the interrogator side There is a possibility that the information notifying that the input power has decreased is not transmitted.

  Even if the harmonics are converted into DC power as described in Patent Document 4, the conversion efficiency basically improves only by a few percent (less than 10%). For this reason, when input power falls or fluctuates, there exists a possibility that the electric power required for driving an RFID tag may not be obtained.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a rectenna device that can efficiently obtain output power even when incorporated in a mobile object such as an RFID tag.

  The present invention includes an antenna that receives microwaves, a plurality of rectifier circuits that convert the microwaves to DC power, a changeover switch that selectively connects any of the plurality of rectifier circuits to the antenna, and the switching A switch switching control unit that controls the operation of the switch; and a voltage detection unit that detects an output voltage of the DC power, wherein the plurality of rectifier circuits have conversion efficiencies of the DC power with respect to the input power by the microwaves. The switch switching control unit selects a rectification circuit that maximizes the conversion efficiency from the plurality of rectification circuits based on the detection result of the output voltage, and the selected rectification circuit The changeover switch is operated so as to be connected to the antenna.

  Each of the plurality of rectifier circuits includes a storage unit that stores the relationship between the input power, the conversion efficiency, and the output voltage, and the switch switching control unit includes the input power, the conversion efficiency, It is preferable that the input power corresponding to the detection result is obtained by referring to the relationship between the output voltage and the rectifier circuit that maximizes the conversion efficiency at the obtained input power.

  The switch switching control unit compares the detection result with an upper limit value and a lower limit value of the output voltage that are set in advance for each of the plurality of rectifier circuits and have a higher conversion efficiency than other rectifier circuits. When the voltage detection result is within the range between the upper limit value and the lower limit value, the rectifier circuit selected by the changeover switch at that time is selected, and the detection result is the upper limit value, or When the lower limit value is exceeded, it is preferable to select a rectifier circuit in which the upper limit value and the lower limit value range are set high, or a rectifier circuit in which the upper limit value and the lower limit value range are set low.

  The switch switching control unit preferably compares the detection results of the plurality of rectifier circuits and selects a rectifier circuit having the largest detection result.

  The switch switching control unit preferably operates the selector switch so that a rectifier circuit having the highest conversion efficiency with the lowest input power among the plurality of rectifier circuits is connected to the antenna at the time of startup. .

  When the detection result exceeds a rated voltage, the switch switching control unit is connected to the antenna with a rectifier circuit having the same input power and lower conversion efficiency than the rectifier circuit selected by the selector switch at that time. It is preferable to operate the changeover switch so as to operate.

  The plurality of rectifier circuits are preferably provided on a plurality of substrates each having the same circuit pattern.

  It is preferable that a plurality of diode mounting portions having different numbers of diodes for converting the microwaves into DC power are formed in the circuit pattern.

  The diode mounting part is preferably formed so that the diodes are connected in series with the common anode.

  The plurality of substrates are preferably stacked.

  The present invention selects a rectifier circuit having the maximum conversion efficiency from a plurality of rectifier circuits based on detection results of DC power (output power) output from a plurality of rectifier circuits, and the selected rectifier circuit is used as an antenna. Because it is connected, even when the input power (transmission / reception distance and transmission / reception direction) of the microwave changes, especially when the rectenna device is built in the mobile body, the output power can be obtained efficiently. it can.

  Further, by storing the relationship between input power, conversion efficiency, and output voltage for each of the plurality of rectifier circuits, based on the result of detecting any one output voltage of the plurality of rectifier circuits, The selection of the rectifier circuit can be performed quickly and reliably. Furthermore, it is not necessary to detect all output voltages of the plurality of rectifier circuits.

  In addition, by setting the upper limit value and the lower limit value of the output voltage in advance for each of the plurality of rectifier circuits, the range of the upper limit value and the lower limit value corresponding to the detection result of the output power of each rectifier circuit, respectively. Similarly, the selection of the rectifier circuit can be surely executed based on whether or not it is within.

  In addition, since the detection results of the output voltages of the plurality of rectifier circuits are compared and the rectifier circuit having the largest detection result is selected, the selection of the rectifier circuit can be executed in a similar manner.

  In addition, since the rectifier circuit with the highest conversion efficiency at the lowest input power among the multiple rectifier circuits is connected to the antenna at startup, the rectenna device can be securely connected even when the microwave input power is low. Can be operated.

  In addition, when the output voltage detection result exceeds the rated voltage, a rectifier circuit with the same input power and lower conversion efficiency than the rectifier circuit selected by the changeover switch is connected to the antenna. The output voltage is prevented from exceeding the breakdown voltage of a capacitor or a diode mounted on the rectifier circuit.

  Further, since the circuit patterns of the plurality of rectifier circuits are made common, it is not necessary to design rectifier circuits having different conversion efficiencies each time. As a result, the manufacturing cost can be reduced.

  In addition, since a plurality of diode mounting portions having different numbers of mounted diodes are formed in the circuit pattern, the number of diodes mounted in each circuit pattern of each rectifier circuit can be changed by simply changing the number of diodes mounted on each rectifier circuit. Mutual conversion efficiency can be made different. As a result, similarly, it is not necessary to design rectifier circuits with different conversion efficiencies each time, and the manufacturing cost can be reduced.

  Further, since the substrates are stacked, the wiring length between the substrates can be shortened. Thereby, the loss at the time of converting a microwave into direct-current power can be suppressed. Further, the rectenna device can be downsized.

  As shown in FIG. 1, an RFID tag 10 corresponding to the rectenna device of the present invention is incorporated in a mobile body such as a portable electronic device or a card (not shown), and is roughly divided into an antenna 11 and a direction. The coupler 12, the rectifier circuit 13, the changeover switch 14, the power supply stabilization circuit 15, the load circuit 16, the demodulation circuit 17, and the modulation circuit 18.

  The antenna 11 receives the microwave transmitted from the interrogator when the RFID tag 10 approaches the interrogator (not shown). Note that the fundamental frequency of the microwave used in the present embodiment is the 2.45 GHz band that is an ISM (Industry Science Medical) band. The microwave received by the antenna 11 is input to the directional coupler 12.

  The directional coupler 12 outputs a part of the microwave (for example, about −10 dB) input from the antenna 11 to the rectifier circuit 13 for driving power, and outputs the rest to the changeover switch 14 as a question signal. The rectifier circuit 13 converts the input microwave into DC power and outputs it. The DC power output from the rectifier circuit 13 is input to the load circuit 16 through the power supply stabilization circuit 15. The power supply stabilization circuit 15 suppresses voltage fluctuation and noise of the DC power output from the rectifier circuit 13.

  The changeover switch 14 outputs the microwave (question signal) input from the directional coupler 12 toward the demodulation circuit 17 and the microwave (response signal) input from the modulation circuit 18 to the directional coupler 12. Output toward. The demodulation circuit 17 demodulates the modulated microwave (question signal). The demodulated interrogation signal is input to the load circuit 16.

  The load circuit 16 operates using DC power input through the power supply stabilization circuit 15 as drive power. When an interrogation signal is input, the load circuit 16 inputs a response signal stored in advance to the modulation circuit 18. The modulation circuit 18 modulates the response signal into a microwave. The modulated microwave is output from the antenna 11 via the changeover switch 14 and the directional coupler 12.

  The interrogator (not shown) receives the microwave (response signal) transmitted from the RFID tag 10 and demodulates the mobile object in which the RFID tag 10 is incorporated or a person who owns this mobile object. recognize.

  As shown in FIG. 2, when the transmission / reception distance between the RFID tag 10 (moving body) and the interrogator (not shown) changes, the input power of the microwave input through the antenna 11 also changes. As described above, the input power increases as the transmission / reception distance decreases, and the input power decreases as the transmission / reception distance increases. Moreover, although illustration is abbreviate | omitted, input power changes also when a transmission / reception direction changes. When the RFID tag 10 is incorporated in a moving body, the transmission / reception distance and the transmission / reception direction are not constant, so that the microwave input power is not constant. For this reason, in this embodiment, output power is efficiently obtained by the above-described rectifier circuit 13 regardless of microwave input power.

  As shown in FIG. 3, the rectifier circuit 13 according to the first embodiment of the present invention includes a changeover switch 20, first to third rectenna substrates 21 to 23 corresponding to a plurality of rectifier circuits of the present invention, and a power storage function unit. 24, an output voltage detection unit 25, and a switch switching control unit 27.

  As the changeover switch 20, a high-frequency switch such as an SP3T (single pole three throw) type GaAs MMIC (monolithic microwave integrated circuit) switch used for a triple mode mobile phone such as CDMA / PCS / GPS is used. A changeover switch including a diode, a field effect transistor (FET), a MEMS (Micro Electro Mechanical Systems), or the like may be used. The changeover switch 20 includes an input port 28 to which a microwave is input from the directional coupler 12 and first to third output ports 30a to 30c. The changeover switch 20 is switch-controlled by the switch changeover control unit 27 and selectively outputs the input microwave from any one of the output ports 30a to 30c.

  The first to third output ports 30a to 30c of the changeover switch 20 are connected to the first to third rectenna boards 21 to 23, respectively. Therefore, the rectenna substrate to which the microwave is input can be switched by switching the switch 20 described above. The changeover switch 20 is adjusted so that impedance matching with the rectenna substrates 21 to 23 can be achieved in order to suppress microwave power loss.

  As shown in FIG. 4, the first to third rectenna boards 21 to 23 are circuit boards of the same size that convert input microwaves into DC power, and the third rectenna board 23 → second rectenna board from below. The layers 22 are stacked in the order of the first rectenna substrate 21. Note that the order of stacking the rectenna substrates 21 to 23 is not particularly limited.

  As shown in FIGS. 5A to 5C, the same circuit pattern 31 is formed on each of the first to third rectenna substrates 21 to 23. The circuit pattern 31 includes a microwave input unit 32, a capacitor mounting unit 33, first to third diode mounting units 35 a to 35 c, a low-pass filter (LPF) 36, and a DC power output unit 37. They are formed in order from the input side. The microwave input unit 32 is connected to output ports 30a to 30c (see FIG. 3) corresponding to the rectenna substrates 21 to 23, respectively.

  The capacitor mounting portion 33 is mounted with a direct current (DC) cut capacitor 38. In this embodiment, a chip ceramic capacitor (10 pF) is used as the capacitor 38. The capacitor 38 prevents the DC power rectified by the diode (rectifier element) 39 from being output to the changeover switch 20 side (antenna 11 side). The capacitor 38 preferably has a sufficiently low impedance so that the input microwave harmonic signal is efficiently transmitted to the diode 39.

  A diode 39 that rectifies microwaves and converts them into direct current is mounted on the first to third diode mounting portions 35a to 35c. In the present embodiment, a UHF band high-frequency detection / mixing Schottky barrier diode is used as the diode 39. One to three diodes 39 are mounted on each of the diode mounting portions 35a to 35c. The diodes 39 mounted on the rectenna substrates 21 to 23 may all be the same type, or different types may be mixed.

  The second diode mounting portion 35b is mounted so as to form a diode row 40 (see FIG. 5B) in which two diodes 39 are connected in series with a common anode. Similarly, the third diode mounting portion 35c is mounted so as to form a diode row 41 (see FIG. 5C) in which three diodes 39 are connected in series with a common anode.

  Further, in the present embodiment, the circuit pattern 31 so that the diode 39 mounted on each of the diode mounting portions 35a to 35c and the anode side of the diode arrays 40 and 41 are grounded via the via (plated through hole) 42. Is formed. The cathode side of the diode 39 and the diode arrays 40 and 41 is connected to a line between the microwave input unit 32 and the DC power output unit 37. As a result, a potential is generated between the anode and the cathode, and the diode 39 is switched by this potential difference to perform rectification.

  In the first rectenna substrate 21, one diode 39 is mounted only on the first diode mounting portion 35a (see FIG. 5A). In the second rectenna substrate 22, two diodes 39 are mounted only on the second diode mounting portion 35b (see FIG. 5B). In the third rectenna substrate 23, three diodes 39 are mounted only on the third diode mounting portion 35c (see FIG. 5C). That is, in this embodiment, the circuit pattern 31 of each rectenna board | substrate 35a-35c is made common, and the mounting number of the diode 39 is changed by which of each diode mounting part 35a-35c mounts the diode 39. FIG.

  In this way, by changing the number of diodes 39 mounted on each of the rectenna boards 35a to 35c, as will be described in detail later, the conversion efficiency for converting microwaves to DC power (hereinafter simply referred to as conversion efficiency) is varied. (See FIG. 6A).

  The LPF 36 is formed by an open stub of the circuit pattern 31. The LPF 36 blocks the fundamental frequency signal leaking from the output of the diode 39 (diode arrays 40 and 41) and the harmonic component signal generated during rectification to prevent the harmonic signal from flowing into the load circuit 16. To do. The LPF 36 smoothes the direct current rectified by the diode 39. The DC power smoothed by the LPF 36 is output from the DC power output unit 37. In the present embodiment, the case where the input filter is not provided in the circuit pattern 31 of each rectenna substrate 21 to 23 has been described as an example, but the present invention is not limited to this, and the circuit An input filter may be provided in the pattern 31.

  As shown in FIG. 3, the first rectenna substrate 21 is connected to the power storage function unit 24 via the first wiring 45a, and the output voltage detection unit via the first wiring 45b branched from the first wiring 45a. 25. The second rectenna substrate 22 is connected to the first wiring 45 b (the power storage function unit 24 and the output voltage detection unit 25) via the second wiring 46. The third rectenna substrate 23 is connected to the first wiring 45 a (the power storage function unit 24 and the output voltage detection unit 25) via the third wiring 47.

  The DC power output from each of the rectenna substrates 21 to 23 is output to the power supply stabilization circuit 15 (see FIG. 1) via the power storage function unit 24. The power storage function unit 24 includes, for example, a capacitor, and suppresses voltage fluctuations of the DC power output from the rectifier circuit 13 when the changeover switch 20 is switched.

  Next, a method for selecting / switching the rectenna substrate according to the input power of the microwave will be described. As described above, since the number of diodes 39 mounted on each rectenna substrate 21 to 23 is different, the conversion efficiency of each rectenna substrate 21 to 23 is also different.

  For example, as shown in FIG. 6A, the conversion efficiency of each rectenna substrate 21 to 23 changes so as to draw a substantially parabola according to the input power of the microwave. As the number of mounted diodes 39 increases, the peak height of the conversion efficiency decreases and the peak position shifts toward the higher input power value. The conversion efficiency (marked with ●) of the first rectenna substrate 21 has a peak (about 65%) around an input power of 10 mW. The conversion efficiency (▲) of the second rectenna substrate 22 has a peak (about 50%) around the input power of 50 mW. Further, the conversion efficiency (x mark) of the third rectenna substrate 23 has a peak (about 43%) around the input power of 100 mW.

  In this way, the rectenna substrates 21 to 23 have different microwave input powers at which the conversion efficiency peaks. Therefore, when the microwave input power is within the range W1, the conversion efficiency of the first rectenna substrate 21 is the highest, and when the input power is within the range W2, the conversion efficiency of the second rectenna substrate 22 is the highest. Thus, when the input power is within the range W3, the conversion efficiency of the third rectenna substrate 23 is the highest. Therefore, the one having the maximum conversion efficiency is selected from the rectenna substrates 21 to 23 in accordance with the input power of the microwave.

When selecting the one having the maximum conversion efficiency from among the rectenna substrates 21 to 23, the selection is performed based on the voltage detection result of the DC power output from the rectenna substrate. Here, when the load resistance of each of the rectenna substrates 21 to 23 is RL, the microwave input power PinRF, the conversion efficiency η (× 100%), the DC power PoutDC, and the DC power voltage (hereinafter, The relationship with VoutDC (simply called output voltage) is expressed by the following equation (1).
Η = PoutDC / PinRF = {(VoutDC) ² / RL} / PinRF

  Based on the relationship of the above equation (1), the relationship between the conversion efficiency (%) and the output voltage (V) is shown in FIG. 6B in which the vertical axis in FIG. 6A is replaced with “output voltage (V)”. Indicated by

  As shown in FIG. 6B, the output voltage of each rectenna substrate 21 to 23 also changes according to the microwave input power. Similar to the above-described conversion efficiency, when the microwave input power is within the range W1, the output voltage of the first rectenna substrate 21 is the highest, and when the input power is within the range W2, the second rectenna substrate 22 When the output voltage is the highest and the input power is within the range W3, the output voltage of the third rectenna substrate 23 is the highest.

  As described above, the relationship between the input power of the microwave and the output voltage from each rectenna substrate 21 to 23 is expressed, and by detecting the output voltage of each rectenna substrate 21 to 23, the micro voltage is detected. Wave input power can be determined. Then, based on the relationship between the microwave input power as shown in FIG. 6A and the conversion efficiency of each of the rectenna substrates 21 to 23, the conversion efficiency is maximized with the current microwave input power. A rectenna substrate can be selected. In this embodiment, based on the voltage detection result of the DC power output from the second rectenna substrate 22, the microwave input power and the selection / switching of the rectenna substrate that maximizes the conversion efficiency are performed.

  As shown in FIG. 3, the output voltage of the second rectenna substrate 22 is detected by an output voltage detection unit 25 equipped with a voltage detection circuit (A / D circuit or the like) not shown. Since the output voltage detection unit 25 is connected in parallel with the power storage function unit 24, the output voltage of each rectenna substrate 21 to 23 can be detected. When the rectifier circuit 13 is activated by the microwave input, the changeover switch 20 is switched to the second rectenna substrate 22 to output DC power from the second rectenna substrate 22. At this time, the output voltage detection unit 25 detects the output voltage of the second rectenna substrate 22 and inputs the output voltage detection result to the switch switching control unit 27.

  As the switch switching control unit 27, for example, a CPU or a comparator is used. The switch switching control unit 27 collates (compares) the input output voltage detection result with the data table 50 stored in advance.

  As shown in FIG. 7, the data table 50 represents the relationship between the microwave “input power”, “conversion efficiency”, and “output voltage” for each of the rectenna substrates 21 to 23. For example, it is created based on the above-described FIGS. In this figure, only five typical input powers (1.0 mW, 10.0 mW, 30.0 mW, 100 mW, and 200 mW) are stored as “input power”, but in actuality, every few mW. Input power may be stored.

  The switch switching control unit 27 obtains the current microwave input power based on the voltage detection result by the output voltage detection unit 25 and the data table 50. For example, if the output voltage of the second rectenna substrate 22 is 2.14 V, the microwave input power is 30 mW.

  Next, the switch switching control unit 27 selects a rectenna substrate having the highest conversion efficiency from the rectenna substrates 21 to 23 based on the obtained microwave input power and the data table 50. For example, when the output voltage of the second rectenna substrate 22 is 1.12 V, the input power is 10.0 mW. Therefore, the first rectenna substrate 21 (66%) having the maximum conversion efficiency when the input power is 10 mW. ) Is selected. As a result, as shown in FIG. 6A described above, the first rectenna substrate 21 is selected if the microwave input power is within the above-described range W1, and the second is selected if the input power is within the range W2. If the rectenna substrate 22 is selected and the input power is within the range W3, the third rectenna substrate 23 is selected.

  Next, the switch change control unit 27 switches the changeover switch 20 to the selected rectenna board. Thereby, a microwave can be converted into direct-current power using the rectenna board | substrate from which the conversion efficiency becomes the maximum with the input power of the present microwave among each rectenna board | substrates 21-23.

  Next, the selection / switching process of the rectenna substrate will be described with reference to the flowchart of FIG. When the microwave is received by the antenna 11 and the rectifier circuit 13 is activated by the microwave input from the antenna 11 (directional coupler 12), the switch switching control unit 27 sets the changeover switch 20 to the second rectenna substrate 22. Switch. Thereby, the microwave input to the rectifier circuit 13 is rectified and smoothed by the second rectenna substrate 22 and converted to DC power.

  The DC power converted by the second rectenna substrate 22 is input to the power storage function unit 24 through the second wiring 46, the first wiring 45b, and the first wiring 45a. At the same time, the output voltage detection unit 25 detects the output voltage of the second rectenna substrate 22, and the output voltage detection result is input to the switch switching control unit 27.

  The switch switching control unit 27 first obtains microwave input power based on the input output voltage detection result and the data table 50. Next, the switch switching control unit 27 selects a rectenna substrate having the maximum conversion efficiency with the current microwave input power, based on the obtained microwave input power and the data table 50.

  When the “first rectenna substrate 21” is selected, the switch switching control unit 27 switches the changeover switch 20 to the first rectenna substrate 21. Further, when the “second rectenna substrate 22” is selected, the changeover switch 20 is maintained in the state of being switched to the second rectenna substrate 22, and when the “third rectenna substrate 23” is selected, the changeover switch 22 is switched to the third rectenna substrate 23. . Thereby, the microwave is converted into DC power by the selected rectenna substrate. The converted DC power is output to the power supply stabilization circuit 15 (load circuit 16) via the power storage function unit 24.

  The output voltage detection unit 25 detects the output voltage of the newly switched rectenna board and inputs it to the switch switching control unit 27. The switch switching control unit 27 constantly or periodically monitors the microwave input power based on the output voltage detection result input from the output voltage detection unit 25 and the data table 50. Then, the switch switching control unit 27 selects a new rectenna substrate according to the above-described procedure based on the microwave input power. These series of processes (output voltage measurement, input power derivation, rectenna board selection, and switch switching) are repeated repeatedly until no microwave is received.

  As described above, in the present embodiment, the output voltage of any one of the rectenna substrates 21 to 23 (in this embodiment, the second rectenna substrate 22) is detected, and based on the output voltage detection result and the data table. Since the rectenna substrate having the maximum conversion efficiency with the current microwave input power is selected, and the changeover switch 20 is switched to the selected rectenna substrate, the microwave input power (transmission / reception distance) like the RFID tag 10 is selected. The output power can be obtained efficiently even with a mobile object whose transmission / reception direction is not constant.

  Further, by storing in advance a data table 50 representing the relationship between the “input power”, “conversion efficiency”, and “output voltage” of the microwave for each of the rectenna substrates 21 to 23, each rectenna. Based on the result of detecting any one of the output voltages of the substrates 21 to 23, the rectenna substrate having the maximum conversion efficiency with the current input power can be selected quickly and reliably. Furthermore, there is an advantage that the output voltages of all the rectenna substrates 21 to 23 need not be detected.

  Also, the conversion efficiency can be easily changed by simply changing the number of diodes 39 (the number of series connections) mounted on each of the rectenna substrates 21 to 23 by sharing the circuit pattern 31 of each of the rectenna substrates 21 to 23. A rectenna substrate is obtained. This eliminates the need to design rectenna substrates with different conversion efficiencies each time. As a result, the manufacturing cost can be reduced.

  Further, by stacking the rectenna substrates 35a to 35c, the wiring length between the substrates can be made shorter than when each rectenna substrate is formed by a single substrate. Thereby, the loss at the time of converting a microwave into direct-current power can be suppressed. Further, the rectenna substrates 35a to 35c can be stacked to reduce the size. Thereby, it can be incorporated in a small responder such as the RFID tag 10.

  In the above embodiment, the case where the output voltage of the second rectenna substrate 22 is first detected has been described as an example, but the present invention is not limited to this. For example, based on the output voltage detection result of the first rectenna substrate 21 or the third rectenna substrate 23 and the data table 50, a rectenna substrate having the maximum conversion efficiency with the current input power may be selected.

  Moreover, in the said embodiment, although it is made to memorize | store beforehand the data table 50 showing the relationship between the input power of microwave, conversion efficiency, and an output voltage with respect to each of each rectenna board | substrates 21-23, The present invention is not limited to this. For example, an arithmetic expression representing the relationship among microwave input power, conversion efficiency, and output voltage may be stored instead of the data table 50.

  Next, the rectifier circuit 60 according to the second embodiment of the present invention will be described with reference to FIG. The rectifier circuit 60 has basically the same configuration as the rectifier circuit 13 of the first embodiment described above. However, the rectifier circuit 60 is provided with a switch switching control unit 61 different from the switch switching control unit 27. In the following description, the same components as those of the rectifier circuit 13 described above are denoted by the same reference numerals and description thereof is omitted.

The switch switching control unit 61 outputs, for each of the rectenna boards 21 to 23, an output voltage range V _N th (N = 1 to 3) in which the output voltage is higher than the other rectenna boards with the same microwave input power. Is remembered. The output voltage range V _N th of each rectenna substrate 21 to 23 is obtained, for example, from FIG. 6B described above.

The output voltage range V ₁ th (see FIG. 6B) of the first rectenna substrate 21 is when the microwave input power is within the range W1, that is, the conversion efficiency of the first rectenna substrate 21 is another rectenna substrate. The lower limit value V ₁ thmin is the minimum value for the load circuit 16 to operate, and the upper limit value upper limit value V ₁ thmax is the boundary between the input power ranges W1 and W2. It becomes the value of. Similarly, the output voltage range V ₂ th of the second rectenna substrate 22 has a lower limit value V ₂ thmin that is the same as V ₁ thmax, and an upper limit value V ₂ thmax of the input power ranges W2 and W3. It becomes a boundary. The output voltage range V ₃ th of the third rectenna substrate 23 has a lower limit value V ₃ thmin that is the same as V ₂ thmax, and an upper limit value V ₃ thmax that is the rated voltage of the RFID tag 10.

Switch control unit 61, when the changeover switch 20 is switched to the first rectenna substrate 21, the output voltage detection result V ₁ is output voltage range V ₁ of the first rectenna substrate 21 by the output voltage detection unit 25 of the above It is determined whether it is within the range of th. Then, when it is judged to be within the output voltage range V ₁ th, the input power of the microwave is within the range W1. For this reason, the switch switching control unit 61 selects the first rectenna substrate 21 as the rectenna substrate having the maximum conversion efficiency.

Further, if it is determined that the output voltage detection result _{V 1} is the output voltage range _V 1 th range of _{(V 1> V 1 thmax)} , the input power of the microwave is in the range W1 outside. Accordingly, the switch change control unit 61 switches the changeover switch 20 to the second rectenna substrate 22. Note that when V ₁ <V ₁ thmax, the load circuit 16 (RFID tag 10) does not operate, so the changeover switch 20 is not switched.

When it is determined that the output voltage detection result V ₂ of the second rectenna substrate 22 is within the output voltage range V ₂ th when the changeover switch 20 is switched to the second rectenna substrate 22, the microwave Input power is within the range W2. At this time, the switch switching control unit 61 selects the second rectenna substrate 22 as the rectenna substrate having the maximum conversion efficiency.

Further, the output voltage detection result V ₂ is the case where it is determined that the lower limit V ₂ thmin the input power of the microwave has a value lower than the range W2. When the reversed output voltage detection result V ₂ is determined to exceed the upper limit value V ₂ thmax has a higher value than the input power range W2 of the microwave. Thus, switch control unit 61, when the output voltage detection result _{V 2} is less than the lower limit _V 2 thmin switches the changeover switch 20 to the first rectenna substrate 21, the output voltage detection result _{V 2} is the upper limit value _{V 2} When it exceeds thmax, the changeover switch 20 is switched to the third rectenna substrate 23.

Once Similarly, when the changeover switch 20 is switched to the third rectenna substrate 23, the third output voltage detection result V ₃ rectenna substrate 23 is determined to be within the range of the output voltage range V ₃ th, The input power of the microwave is within the range W3. At this time, the switch switching control unit 61 selects the third rectenna substrate 23 as the rectenna substrate having the maximum conversion efficiency.

Further, the output When the voltage detection result _{V 3} is determined to be the output voltage range _V 3 th range of _{(V 3 <V 3 thmin)} , the input power of the microwave is in the range W3 outside. Accordingly, the switch change control unit 61 switches the changeover switch 20 to the second rectenna substrate 22. When V ₃ > V ₃ thmax, the rated voltage is exceeded and the operation of the rectifier circuit 13 is stopped. Further, as will be described later, the changeover switch 20 may be switched to the second rectenna substrate 22 (see FIG. 13).

Thus, based on the output voltage detection results V _{1 to} V _{3 of the} rectenna substrates 21 to 23 and the output voltage ranges V ₁ th to V ₃ th, conversion efficiency is selected from the rectenna substrates 21 to 23. It is possible to select a rectenna substrate that maximizes. In the present embodiment, when the microwave is input, the changeover switch 20 is first switched to the second rectenna substrate 22. Accordingly, it is possible to select a rectenna substrate that maximizes the conversion efficiency with one voltage detection.

Next, the selection / switching process of the rectenna substrate in the second embodiment of the present invention will be described using the flowchart of FIG. When the microwave is received by the antenna 11 and the rectifier circuit 60 is activated by the microwave input from the antenna 11, the switch switching control unit 61 switches the changeover switch 20 to the second rectenna substrate 22. Accordingly, as described above, the output voltage V ₂ of the DC power converted by the second rectenna substrate 22 is detected by the output voltage detection unit 25, and the output voltage detection result V ₂ is input to the switch switching control unit 61. The

Switch control unit 61 determines, within the range of the output voltage detection result _{V 2} which is input the output voltage range _V 2 th, that _is, whether or not satisfy V ₂ thmin _<V 2 <V 2 thmax. If it is determined that the output voltage detection result V ₂ is within the output voltage range V ₂ th, the switch switching control unit 61 maximizes the conversion efficiency of the second rectenna substrate 22 with the current microwave input power. Select as rectenna board. The switch control unit 27 maintains the changeover switch 20 in a state where the changeover switch 20 is switched to the second rectenna substrate 22.

Further, when the switch switching control unit 61 determines that V ₂ <V ₂ thmin, the switch 20 is switched to the first rectenna substrate 21. In the case of V ₂ <V ₂ thmin, the microwave input power is within the range W1, so that the conversion efficiency of the first rectenna substrate 21 is maximized.

Conversely, when the switch switching control unit 61 determines that V ₂ > V ₂ thmax, the switch switching control unit 27 switches the changeover switch 20 to the third rectenna substrate 23. When V ₂ > V ₂ thmax, the microwave input power is within the range W 3, so that the conversion efficiency of the third rectenna substrate 23 is maximized.

Note that the switch switching control unit 61 constantly or periodically monitors whether or not the output voltage detection result of the newly switched rectenna board is within the corresponding output voltage range. When the output voltage detection result is outside the corresponding output voltage range, a new rectenna substrate is selected by the above-described procedure. A series of these processes (output voltage measurement, monitoring whether the output voltage is within the range, switch switching) is repeated until microwaves are not received.

As described above, in the second embodiment of the present invention, by setting the lower limit value and the upper limit value (output voltage range) of the output voltage in advance for each of the rectenna substrates 21 to 23, each rectenna substrate is set. Based on whether the output voltage detection results V _{1 to} V _{3 of} 21 to 23 are within the corresponding output voltage ranges V ₁ th to V ₃ th, the conversion efficiency is the current microwave input power. The largest rectenna substrate can be selected reliably. As a result, similarly to the first embodiment described above, output power can be obtained efficiently regardless of microwave input power (transmission / reception distance and transmission / reception direction).

  Further, in the present embodiment, when the microwave is input, the changeover switch 20 is first switched to the second rectenna substrate 22, so that the rectenna substrate having the highest conversion efficiency can be quickly selected by one voltage detection. be able to. It is to be noted that the rectenna having the maximum conversion efficiency is detected by sequentially detecting the output voltage from the rectenna substrate having the lowest or highest voltage range and determining whether or not the output voltage detection result is within the corresponding output voltage range. A substrate may be selected.

  Next, the rectifier circuit 65 according to the third embodiment of the present invention will be described with reference to FIG. The rectifier circuit 65 has basically the same configuration as the rectifier circuit 13 of the first embodiment described above. However, the rectifier circuit 65 is provided with a switch switching control unit 66 different from the switch switching control units 27 and 61. The switch switching control unit 66 stores the output voltage measurement results of the rectenna substrates 21 to 23 and selects the rectenna substrate having the highest output voltage.

  When the microwave received by the antenna 11 is input to the rectifier circuit 65, the switch switching control unit 66 sequentially switches the changeover switch 20 from the first rectenna substrate 21 to the second rectenna substrate 22 to the third rectenna substrate 23. Thereby, the output voltage of each rectenna substrate 21 to 23 is sequentially detected by the output voltage detection unit 25. These output voltage detection results are stored in the switch switching control unit 66.

  The switch switching control unit 66 compares the stored output voltage measurement results of the rectenna substrates 21 to 23. At this time, the output voltage of the rectenna substrate having the maximum conversion efficiency is the highest (see FIGS. 6A and 6B). Accordingly, the switch switching control unit 66 selects the rectenna board having the highest output voltage from the rectenna boards 21 to 23, and switches the changeover switch 20 to the selected rectenna board.

  Next, the selection / switching process of the rectenna substrate according to the third embodiment of the present invention will be described with reference to the flowchart of FIG. When the microwave is received by the antenna 11 and the rectifier circuit 65 is activated by the microwave input from the antenna, the switch switching control unit 66 switches the switch 20 to the first rectenna substrate 21. As a result, the output voltage of the DC power converted by the first rectenna substrate 21 is detected by the output voltage detector 25. This output voltage detection result is stored in the switch switching control unit 66.

  Next, the switch change control unit 66 switches the changeover switch 20 to the second rectenna substrate 22. Similarly, the output voltage of the second rectenna substrate 22 is detected, and the output voltage detection result is stored in the switch switching control unit 66. When the switch change control unit 66 switches the changeover switch 20 to the third rectenna substrate 23, the output voltage detection result of the third rectenna substrate 23 is stored in the switch change control unit 66.

  The switch switching control unit 66 compares the output voltage measurement results of the rectenna substrates 21 to 23, selects the rectenna substrate having the highest output voltage, and switches the changeover switch 20 to the selected rectenna substrate. Thereby, the changeover switch 20 is switched to the rectenna substrate having the highest output voltage, that is, the maximum conversion efficiency, with the current microwave input power.

  The switch switching control unit 66 periodically switches the changeover switch 20 to each of the rectenna boards 21 to 23 periodically. As a result, new output voltage measurement results of the rectenna substrates 21 to 23 are detected and overwritten on the previously stored output voltage measurement results. Then, the switch switching control unit 67 selects the rectenna substrate having the highest output voltage based on the newly stored output voltage measurement result. A series of these processes (output voltage measurement / comparison of each rectenna board, switch switching) is continuously repeated until microwaves are not received.

  As described above, in the third embodiment of the present invention, the output voltage measurement results of the rectenna substrates 21 to 23 are compared, and the rectenna substrate having the highest output voltage is selected from the rectenna substrates 21 to 23. Thus, it is possible to select a rectenna substrate that maximizes the conversion efficiency with the current microwave input power. As a result, similarly to the first embodiment described above, output power can be obtained efficiently regardless of microwave input power (transmission / reception distance and transmission / reception direction). In this case, since it is necessary to sequentially detect the output voltage of each rectenna substrate 21 to 23, it is preferable to apply the first and second embodiments of the present invention, more preferably the first embodiment.

  In the first to third embodiments, when the microwave is input (when the microwave is received by the antenna 11), the changeover switch 20 switches to any of the first to third rectenna substrates 21 to 23. There is no particular limitation as to whether or not it is. For this reason, when the input power of the microwave received first is low, if the changeover switch 20 is switched to the second and third rectenna boards 22 and 23, the DC power necessary for the operation of the load circuit 16 is increased. The RFID tag 10 itself may not operate. Therefore, when microwaves are input, the changeover switch 20 switches to the first rectenna substrate 21 (see FIG. 6A) that has the highest conversion efficiency at the lowest input power among the rectenna substrates 21 to 23. Initialize as possible.

  As an example of this initial setting method, in the first to third embodiments, when the load circuit 16 operates and a microwave (response signal) is output, the switch switching control units 27, 61, and 66 The changeover switch 20 is switched to the first rectenna substrate 21 before the processing of the tag 10 is closed. Thereby, when microwaves are input, the changeover switch 20 is switched to the first rectenna substrate 21.

  As described above, when microwaves are input (at start-up), microwave input is performed by initial setting so that the selector switch is switched to the rectenna board that maximizes conversion efficiency with the lowest input power. Even if the power is low, the load circuit 16 (RFID tag 10) can be reliably operated.

In the first to third embodiments, when the output voltage of the DC power becomes too high, the withstand voltage of the capacitor 38 and the diode 39 (see FIGS. 5A to 5C) mounted on the rectenna substrate is reduced. May be a problem. Therefore, each switch switching control unit 27, 61, 66 stores the upper limit value V ₃ thmax of the output voltage of the third rectenna substrate 23, that is, the rated voltage of the RFID tag 10.

  As shown in FIG. 13, when the microwave is received and the changeover switch 20 is switched to the third rectenna substrate 23, the output voltage detection unit 25 always detects the output voltage of the third rectenna substrate 23 and outputs it. The voltage detection result is input to the switch switching control units 27, 61, and 66. Then, when the output voltage detection result exceeds the rated voltage, the switch switching control units 27, 61, and 66 switch to the second rectenna substrate 22 having a lower conversion efficiency than the third rectenna substrate 23 with the current microwave input power. Switch 20 is switched.

  As described above, when the output voltage of the third rectenna board 23 exceeds the rated voltage, the changeover switch 20 is switched to the rectenna board having a low conversion efficiency, so that the output voltage exceeds the breakdown voltage of the capacitor or the diode. Is prevented.

  In the first embodiment (the same applies to the second and third embodiments), the second rectenna substrate 22 is connected to the output voltage detection unit 25 via the first wiring 45b, and the third rectenna substrate 23 is Although connected to the output voltage detection unit 25 via the first wirings 45a and 45b, the present invention is not limited to this.

  Therefore, as in the rectifier circuit 70 shown in FIG. 14, the second rectenna substrate 22 is connected to the first wiring 45a (the power storage function unit 24) via the second wiring 71a and is branched from the second wiring 71a. The output voltage detection unit 25 may be connected via the two wires 71b. Similarly, even if the third rectenna substrate 23 is connected to the first wiring 45a (the power storage function unit 24) via the third wiring 72a, it is connected to the output voltage detection unit 25 via the third wiring 72b. Good. Also in this case, the output voltage of each rectenna substrate 21 to 23 can be detected by the output voltage detection unit 25 as in the above-described rectifier circuit 13.

  Further, as another embodiment of the rectifier circuit 70 described above, a changeover switch 76 different from the changeover switch 20 may be provided, for example, as a rectifier circuit 75 shown in FIG. The changeover switch 76 includes three first to third switch portions 76a to 76c of SPST type that are connected in parallel to each other and can be individually turned on and off.

  The first to third switch portions 76a to 76c are connected to the first to third rectenna substrates 21 to 23, respectively. Then, by individually turning on / off each of the switch sections 76a to 76c, a microwave can be selectively input to any one of the rectenna substrates 21 to 23 in the same manner as the changeover switch 20 described above. Furthermore, microwaves can be input to any two or all of the rectenna substrates 21 to 23 as necessary.

  In each rectifier circuit unit described above, only one changeover switch 20 is provided on the microwave input side of each rectenna substrate 21 to 23, but the present invention is not limited to this. For example, like the rectifier circuit 78 shown in FIG. 16, a changeover switch 79 may be provided on the DC power output side of each rectenna substrate 21 to 23.

  The changeover switch 79 includes first to third input ports 80 a to 80 c to which DC power output from the rectenna boards 21 to 23 is input, and an output port 81. The changeover switch 79 is integrated with a power storage function unit 82 having the same function as the power storage function unit 24.

  The first to third rectenna substrates 21 to 23 are connected to the first to third input ports 80a to 80c through first to third wirings 83, 84a, and 85, respectively. In the rectifier circuit 78, only the second rectenna substrate 22 is connected to the output voltage detection unit 25 via the second wiring 84b branched from the second wiring 84a.

  The switch change control unit 27 switches both the changeover switches 20 and 79 in conjunction with each other. For example, at the same time when the changeover switch 20 is switched to the first rectenna substrate 21, the changeover switch 79 is also switched to the first rectenna substrate 21. Similarly, when the changeover switch 20 is switched to the second and third rectenna boards 22 and 23, the changeover switch 79 is switched to the second and third rectenna boards 22 and 23. Therefore, similarly to the rectifier circuit 13, any one of the rectenna substrates 21 to 23 can be selectively connected to the directional coupler 12 (antenna 11) and the power supply stabilization circuit 15 (load circuit 16).

  In the rectifier circuit 78 described above, only the second rectenna substrate 22 is connected to the output voltage detector 25. For this reason, since the output voltages of the first and third rectenna substrates 21 and 23 cannot be detected, the rectifier circuit 78 cannot be used in the second and third embodiments. Therefore, for example, like the rectifier circuit 87 shown in FIG. 17, all output voltages of the rectenna substrates 21 to 23 may be detected. When the rectifier circuit 78 is used in the first embodiment, the switch switching control unit 27 switches the changeover switch 20 to the second rectenna substrate 22 at regular time intervals to perform the above-described series of processing (output voltage measurement, Input power derivation, rectenna board selection and switch switching).

  The rectifier circuit 87 has basically the same configuration as the rectifier circuit 78. However, in the rectifier circuit 87, the first rectenna substrate 21 and the first input port 80a are connected via the first wiring 88a, and the third rectenna substrate 23 and the third input port 80c connect the third wiring 89a. Connected through. The first rectenna substrate 21 is connected to the output voltage detector 25 via the first wiring 88b branched from the first wiring 88a, and the third rectenna substrate 23 is connected to the third wiring 89b branched from the third wiring 89a. Is connected to the output voltage detection unit 25. Thereby, since the output voltage of each rectenna board | substrate 21-23 can be detected by the output voltage detection part 25, the rectifier circuit 87 can be used for the said 1st-3rd embodiment.

  Further, as another embodiment of the rectifier circuit 87, for example, as in the rectifier circuit 91 shown in FIG. 18, the above-described selector switch 76 is provided instead of the selector switch 20, and the selector switch 92 is provided instead of the selector switch 79. It may be provided.

  The changeover switch 92 is basically the same as the changeover switch 76 except that the power storage function unit 82 is integrated. The changeover switch 92 includes a first switch portion 92a connected to the first rectenna substrate 21 via the first wiring 89a, and a second switch portion 92b connected to the second rectenna substrate 22 via the second wiring 84a. And a third switch portion 92c connected to the third rectenna substrate 23 via the third wiring 89a.

  The switch switching control unit 27 turns ON / OFF the switch units 76a to 76c of the switch 76 and the switch units 92a to 92c of the switch 92 in conjunction with each other. As a result, any one of the rectenna substrates 21 to 23 can be selectively connected to the directional coupler 12 (antenna 11) and the power supply stabilization circuit 15 (load circuit 16). Further, if necessary, any two or all of the rectenna substrates 21 to 23 can be simultaneously connected to the directional coupler 12 and the power supply stabilization circuit 15.

  In the above embodiment, the case where three rectenna substrates (first to third rectenna substrates 21 to 23) are provided in each rectifier circuit has been described as an example, but the present invention is limited to this. The rectifier circuit may be provided with two or four or more rectenna substrates. In this case, diode mounting portions corresponding to the number of rectenna substrates are formed in the circuit pattern 31.

  In the above-described embodiment, the rectenna substrate that maximizes the conversion efficiency at the current input power is selected. However, the present invention is not limited to this, and a predetermined conversion efficiency that is set in advance is used. A rectenna substrate that matches or is close to may be selected.

  In the above embodiment, the RFID tag 10 has been described as an example of the rectenna apparatus of the present invention. However, the present invention is not limited to this, and the direct current is received by receiving microwaves such as microwaves. The present invention can be applied to various rectenna devices that convert power.

It is the block diagram which showed the electrical structure of the RFID tag. It is a graph showing an example of the relationship between the transmission / reception distance between the RFID tag and the interrogator and the input power of the microwave. It is a block diagram which shows the electric constitution of the rectifier circuit of 1st Embodiment. It is an external appearance perspective view which shows the laminated | stacked 1st-3rd rectenna board | substrate. (A) is a top view of the first rectenna substrate, (B) is a top view of the second rectenna substrate, and (C) is a top view of the third rectenna substrate. (A) is a graph showing an example of the relationship between microwave input power and conversion efficiency, and (B) is a graph showing an example of the relationship between microwave input power and output voltage. It is a table | surface for demonstrating an example of a data table. It is a flowchart for demonstrating the rectenna board | substrate selection and switching process in 1st Embodiment. It is a block diagram which shows the electric constitution of the rectifier circuit of 2nd Embodiment. It is a flowchart for demonstrating the rectenna board | substrate selection and switching process in 2nd Embodiment. It is a block diagram which shows the electric constitution of the rectifier circuit of 3rd Embodiment. It is a flowchart for demonstrating the rectenna board | substrate selection and switching process in 3rd Embodiment. 10 is a flowchart for explaining a rectenna substrate selection / switching process by a rectifier circuit capable of preventing an output voltage from exceeding a withstand voltage of a capacitor or a diode. It is a block diagram of the rectifier circuit of other embodiment from which the connection of each rectenna board | substrate and an output voltage detection part differs. It is a block diagram of the rectifier circuit of other embodiment provided with a different changeover switch. It is a block diagram of the rectifier circuit of other embodiment provided with two changeover switches. The rectifier circuit of FIG. 16 is a block diagram of a rectifier circuit of another embodiment in which the connection between each rectenna substrate and the changeover switch is different. It is a block diagram of the rectifier circuit of other embodiment provided with the changeover switch different from the rectifier circuit of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 RFID tag 11 Antenna 13,60,65,70,75,78,87,91 Rectifier circuit 20,76,79,92 Changeover switch 21 1st rectenna board | substrate 22 2nd rectenna board | substrate 23 3rd rectenna board | substrate 24 Electric storage function part 25 Output voltage detection unit 27, 61, 66 Switch switching control unit 31 Circuit pattern 35a to 35c First to third diode mounting unit 39 Diode 50 Data table

Claims (10)

An antenna for receiving microwaves;
A plurality of rectifier circuits for converting the microwaves into DC power;
A selector switch that selectively connects any of the plurality of rectifier circuits to the antenna;
A switch change control unit for controlling the operation of the changeover switch;
A voltage detector for detecting an output voltage of the DC power,
The plurality of rectifier circuits are configured such that conversion efficiency of the DC power with respect to input power by the microwave is different from each other.
The switch switching control unit selects a rectifier circuit that maximizes the conversion efficiency from the plurality of rectifier circuits based on the detection result of the output voltage, and the selected rectifier circuit is connected to the antenna. A rectenna device for operating the changeover switch. For each of the plurality of rectifier circuits, a storage unit storing the relationship between the input power, the conversion efficiency, and the output voltage is provided.
The switch switching control unit obtains input power corresponding to the detection result with reference to the relationship between the input power, the conversion efficiency, and the output voltage, and the conversion efficiency is maximized in the obtained input power. The rectenna device according to claim 1, wherein a rectifier circuit is selected.   The switch switching control unit compares the detection result with an upper limit value and a lower limit value of the output voltage that are set in advance for each of the plurality of rectifier circuits and have a higher conversion efficiency than other rectifier circuits. When the voltage detection result is within the range between the upper limit value and the lower limit value, the rectifier circuit selected by the changeover switch at that time is selected, and the detection result is the upper limit value, or When the lower limit value is exceeded, the rectifier circuit in which the upper limit value and the range of the lower limit value are set high or the rectifier circuit in which the upper limit value and the range of the lower limit value are set low is selected. The rectenna device according to claim 1.   The rectenna device according to claim 1, wherein the switch switching control unit compares the detection results of the plurality of rectifier circuits and selects a rectifier circuit having the largest detection result.   The switch switching control unit operates the changeover switch so that a rectifier circuit having the highest conversion efficiency with the lowest input power among the plurality of rectifier circuits is connected to the antenna at the time of startup. The rectenna device according to any one of claims 1 to 4.   When the detection result exceeds a rated voltage, the switch switching control unit is connected to the antenna with a rectifier circuit having the same input power and lower conversion efficiency than the rectifier circuit selected by the selector switch at that time. The rectenna device according to claim 1, wherein the changeover switch is operated as described above.   The rectenna device according to claim 1, wherein the plurality of rectifier circuits are provided on a plurality of substrates each having the same circuit pattern.   8. The rectenna device according to claim 7, wherein a plurality of diode mounting portions having different numbers of diodes for converting the microwaves into DC power are formed in the circuit pattern.   9. The rectenna device according to claim 7, wherein the diode mounting portion is formed so that the diodes are connected in series in common with the anode.   The rectenna device according to claim 7, wherein the plurality of substrates are stacked.

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