JP5991269B2 - Loop antenna - Google Patents

Description

  The present invention relates to a loop antenna capable of transmitting and receiving radio waves of a plurality of frequencies.

  Conventionally, in loop antennas used for RFID tags, etc., a loop antenna that can transmit and receive multiple frequencies by changing the inductance of the loop antenna by connecting a capacitive element with an appropriate value in the middle of the loop has been proposed. (For example, refer to Patent Document 1).

JP 2009-278550 A

  However, the conventional loop antenna transmits radio waves on the assumption that it is used in a radio circuit that operates according to a change in magnetic flux density of radio waves applied from the outside, such as an RFID tag (that is, only reception). I do not assume that. Therefore, when the loop antenna is used for radio wave transmission, if there is a metal such as a battery inside the loop, there is a problem in that loss occurs during radio wave transmission and transmission efficiency is deteriorated.

  The present invention has been made in view of these problems, and an object thereof is to provide a loop antenna that can efficiently transmit and receive radio waves of a plurality of frequencies.

  In this column, in order to facilitate understanding of the invention, the reference numerals used in the “Mode for Carrying Out the Invention” column are attached as necessary, which means that the scope of claims is limited by this reference numeral. is not.

The has been made to solve the problems described in the "INVENTION Problems to be Solved" invention, the first loop antenna (10), and a second loop antenna (20) and connected hand stage. Furthermore, the invention described in claim 1 includes a battery for a circuit that is disposed outside the loop of the loop antenna and inside the loop of the second loop antenna, and for supplying a transmission radio wave to the first loop antenna. In the invention according to claim 5, the connecting means is a switch.

  The first loop antenna (10) is excited at a first resonance frequency, and the second loop antenna (20) has an inductance greater than that of the first loop antenna (10) at the first resonance frequency, and the first resonance Excited at a second resonance frequency that is lower than the frequency.

  Further, the connecting means (30) is configured so that the second loop antenna (20) and the first loop antenna (10) can be excited as one loop antenna by forming one electrical loop. The loop antenna (20) and the first loop antenna (10) are electrically connected at two points.

  In such a loop antenna, the first loop antenna (10) and the second loop antenna (20) are connected at two points by the connecting means (30), and the second loop antenna (20) and the first loop antenna (10). Can be excited as one loop antenna by forming one electric loop.

  The second loop antenna (20) has an inductance larger than that of the first loop antenna (10) at the first resonance frequency, and is excited at a second resonance frequency that is lower than the first resonance frequency.

  Therefore, when externally applied at a second resonance frequency that is lower than the first resonance frequency, the first loop antenna (10) and the second loop antenna (20) operate as one loop antenna. Therefore, the area formed by the loop is a large loop antenna in which the loop areas of the first loop antenna (10) and the second loop antenna (20) are combined.

  Then, when used as an antenna for an externally applied radio wave, for example, an RFID tag, the second loop antenna (20) even if there is a metal such as a battery inside the second loop antenna (20). The reception efficiency can be improved as compared with the case of using only one.

  On the other hand, when transmitting radio waves at the first resonance frequency, the inductance of the second loop antenna (20) is higher than the inductance of the first loop antenna (10), so the current flowing through the second loop antenna (20) is Thus, the second loop antenna (20) does not operate as a loop antenna, and radio waves are transmitted only from the first loop antenna (10).

  Therefore, even if a metal such as a battery for a circuit for supplying transmission radio waves to the first loop antenna (10) is arranged inside the second loop antenna (20), the battery will not be lost. , Transmission efficiency can be improved.

  By the way, the connection means (30) only needs to be able to change the connection form between the case where the loop antenna is excited at the first resonance frequency and the case where the loop antenna is excited at the second resonance frequency, that is, the first loop antenna (10). Since the second loop antenna (20) may be electrically connected to form one loop or not, the gap between the first loop antenna (10) and the second loop antenna (20) It may be such that it can be electrically connected or disconnected. Therefore, as long as it is inductive, as long as it is inductive.

  That is, for example, when the first loop antenna (10) and the second loop antenna (20) are connected using an inductive element such as a coil, the element, the first loop antenna (10), and the second loop antenna are connected. (20) and a low-pass filter are formed respectively.

  Therefore, if the cut-off characteristics of the low-pass filter with respect to the first resonance frequency and the second resonance frequency can be made different, that is, the first loop antenna (10) and the second loop antenna (20). If it is possible to make a difference in inductance with respect to the first resonance frequency and the second resonance frequency, the first loop antenna (10) and the second loop antenna (20) are electrically connected at the first resonance frequency and the second resonance frequency. Since this is the same as connecting or blocking the antenna, the structure of the loop antenna can be simplified.

Further, if the inductive connecting means (30) is a coil as described in claim 3, the inductive connecting means (30) can be easily configured.
Further, when the coil is a chip inductor as described in claim 4, for example, when the loop antenna is configured with a substrate pattern on the printed circuit board (40), the loop antenna can be reduced in size.

By the way, since the connection means (30) only needs to electrically connect the first loop antenna (10) and the first loop antenna (20) at two points. As described above, the switches (100, 102) may be used.

  If it does in this way, a 1st loop antenna (10) and a 2nd loop antenna (20) can be electrically connected by a simple structure by turning ON / OFF a switch (100,102).

Further, as described in claim 6, when the first loop antenna (10) is formed by a loop of a plurality of turns, the efficiency at the time of radio wave transmission can be further improved.
Further, as described in claim 7, when the second loop antenna (20) is formed of a loop of a plurality of turns, the efficiency at the time of receiving radio waves can be further improved.

  By the way, there are various methods for constructing the first loop antenna (10), such as an air-core antenna and a bar antenna, and the printed circuit board (40) has a substrate mounted thereon as described in claim 8. When mounted as a pattern, the size can be reduced.

Further, as described in claim 9, the second loop antenna (20) can also be reduced in size by being mounted as a board pattern on the printed board (40).
Further, as described in claim 10, when the second loop antenna (20) includes a capacitor (80) that forms a low-pass filter with an inductive component of the second loop antenna (20), When transmitting radio waves from the first loop antenna (10), the current flowing through the second loop antenna (20) is blocked by the low-pass filter. Therefore, since no current flows through the second loop antenna (20), it is possible to suppress a decrease in transmission power.

  Further, as recited in claim 11, when exciting at the first resonance frequency in the loop antenna, it is excited by an electric signal supplied from an external circuit connected to the first loop antenna (10), and As described in claim 12, if the first resonance frequency is a frequency used in a remote system of an automobile, for example, a loop antenna may be incorporated in the interior of the automobile key. Can be made small.

  Here, the automobile remote system means a system that controls the automobile by radio waves using devices such as keys used by the driver, such as keyless entry and keyless engine start.

  In addition, as described in claim 13, when excited at the second resonance frequency, it is excited by a radio wave applied from the outside, and further, as described in claim 14, the second resonance frequency is an RFIC tag. For example, a loop antenna can be incorporated in the key of an automobile, so that a key with high power efficiency can be made small.

It is a figure which shows the schematic structure of the loop antenna of 1st Embodiment. It is a circuit diagram of the equivalent circuit of the loop antenna of 1st Embodiment. It is a figure which shows the output characteristic of the loop antenna of 1st Embodiment. It is a figure which shows the input characteristic of the loop antenna of 1st Embodiment. It is a figure which shows the schematic structure of the loop antenna of 2nd Embodiment. It is a circuit diagram of the equivalent circuit of the loop antenna of 2nd Embodiment. It is a figure which shows the schematic structure of the loop antenna of 3rd Embodiment. It is a circuit diagram of the equivalent circuit of the loop antenna of 3rd Embodiment. It is a circuit diagram of the equivalent circuit of the loop antenna of 4th Embodiment.

Embodiments to which the present invention is applied will be described below with reference to the drawings. The embodiment of the present invention is not limited to the following embodiment, and can take various forms as long as they belong to the technical scope of the present invention.
[First Embodiment]
(Configuration of loop antenna 1)
FIG. 1 is a diagram showing a schematic configuration of a loop antenna 1 to which the present invention is applied. As shown in FIG. 1, the loop antenna 1 includes a first loop antenna 10, a second loop antenna 20, and a connection unit 30.

  The first loop antenna 10 is a loop antenna excited at a first resonance frequency (314 [MHz] used in the keyless entry system in this embodiment), and the second loop antenna 20 is a first resonance frequency. In FIG. 5, the first loop antenna 10 is excited at a second resonance frequency (13.56 [MHz] used in the RFIC tag) that is lower than the first resonance frequency. Loop antenna.

The first loop antenna 10 and the second loop antenna 20 are mounted on the printed board 40 as a board pattern.
A transmission IC 50 and a reception IC 60 are arranged on the printed circuit board 40. Among these, the transmission IC 50 is an integrated circuit whose output portion is connected to the first loop antenna 10 and outputs radio waves of 314 [MHz] from the first loop antenna 10.

  The receiving IC 60 is an integrated circuit for an RFID tag. The input portion is connected to the second loop antenna 20, receives 13.56 [MHz] radio waves applied to the second loop antenna 20 from the outside, It is an integrated circuit that operates by the power of received radio waves.

  In addition, a battery 70 for supplying power to the transmission IC 50 is disposed inside the loop of the second loop antenna 20 and outside the first loop antenna 10 (in the lower right of the printed circuit board 40 in FIG. 1). Has been.

  The connection unit 30 includes the second loop antenna 20 and the first loop antenna so that the second loop antenna 20 and the first loop antenna 10 can be excited as one loop antenna by forming one electrical loop. 10 is a part that is electrically connected to two points.

Further, chip capacitors 80, 82, 84, 86 (not shown in FIG. 2) are mounted on the printed circuit board 40 (shown in FIG. 2).
(Operation and characteristics of loop antenna 1)
Next, the operation and characteristics of the loop antenna 1 will be described with reference to FIGS.

  The loop antenna 1 having the above configuration is represented by an equivalent circuit diagram as shown in FIG. That is, the first loop antenna 10 is connected in series to the transmission IC 50, the second loop antenna 20 is connected in parallel to the first loop antenna 10, and the reception IC 60 is connected in series to the second loop antenna 20.

However, in FIG. 2, the first loop antenna 10 and the second loop antenna 20 are replaced with coils (inductors).
In addition, the capacitor 80 is connected to the transmission IC 50 in parallel with the first loop antenna 10, the capacitors 82 and 84 are connected in series to both ends of the first loop antenna 10, and the capacitor 86 is connected to the reception IC 60 in the second state. The loop antenna 20 is connected in parallel.

Note that these capacitors 80, 82, 84, and 86 are mounted on the printed circuit board 40 as discrete components such as chip capacitors.
Since the inductance of the second loop antenna 20 and the capacitance of the capacitor 86 form an LC filter, when transmitting radio waves from the transmission IC 50, the current flowing through the reception IC 60 is blocked by the LC filter. Therefore, almost no current flows through the receiving IC 60, so that a decrease in transmission power can be suppressed.

  In order to confirm this transmission power suppression effect, in the circuit shown in FIG. 2, an AC power source is connected instead of the transmission IC 50, and the results of measuring the outputs of the first loop antenna 10 and the second loop antenna 20 are shown in FIG. Shown in

  Here, the inductances of the first loop antenna 10 and the second loop antenna 20 are 31 [nH] and 1.43 [μH], respectively, and the capacitances of the capacitors 80 to 86 are 24 [pF] and 24, respectively. [PF], 13 [pF], and 95 [pF].

  In FIG. 3, the frequency of the output of the AC power supply is shown on the horizontal axis, and the output is shown on the vertical axis. Further, the output of the first loop antenna 10 of the circuit of the loop antenna 1 shown in FIG. 2 is indicated by a solid line, and the output of the second loop antenna 20 is indicated by a broken line.

As shown in FIG. 3A, it can be seen that the outputs of the first loop antenna 10 and the second loop antenna 20 resonate at a frequency of 314 [MHz].
Further, as shown in FIG. 3B in which the vicinity of the frequency 314 “MHz” in FIG. 3A (the range surrounded by the ellipse in FIG. 3A) is enlarged, the second loop is obtained at the frequency 314 [MHz]. The output of the antenna 20 is 33.2 [dB] lower than the output of the first loop antenna 10 (about 1/45).

  That is, at the frequency 314 [MHz], almost no current flows through the second loop antenna 20, in other words, no current flows through the receiving IC 60, so that no power is consumed in the receiving IC 60. Accordingly, a decrease in transmission power can be suppressed, so that transmission efficiency can be improved.

  On the other hand, FIG. 4 shows the result of measuring the outputs of the first loop antenna 10 and the second loop antenna 20 by connecting an AC power supply instead of the receiving IC 60 in the circuit shown in FIG.

  In FIG. 4, the frequency of the output of the AC power supply is shown on the horizontal axis, and the output is shown on the vertical axis. Further, the output of the first loop antenna 10 of the circuit of the loop antenna 1 shown in FIG. 2 is indicated by a solid line, and the output of the second loop antenna 20 is indicated by a broken line.

As shown in FIG. 4A, it can be seen that the outputs of the first loop antenna 10 and the second loop antenna 20 resonate at a frequency of 13.56 [MHz].
Further, as shown in FIG. 4B in which the vicinity of the frequency 13.56 [MHz] in FIG. 4B (the range surrounded by the ellipse in FIG. 4A) is enlarged, the frequency 13.56 [MHz] is used. The output of the first loop antenna 10 is 49 [dB] lower than the output of the second loop antenna 20 (about 1/9000).

  That is, at a frequency of 13.56 [MHz], almost no current flows through the transmission IC 50 in the first loop antenna 10, and a decrease in received power can be suppressed. Therefore, reception efficiency can be improved.

  As described above, since the first loop antenna 10 and the second loop antenna 20 operate as one loop antenna when externally applied at the second resonance frequency that is lower than the first resonance frequency, the loop Is a large loop antenna in which the loop areas of the first loop antenna 10 and the second loop antenna 20 are combined.

  Therefore, when used as an antenna for an externally applied radio wave, for example, an RFID tag, even if there is a metal such as a battery inside the second loop antenna 20, it is more than the case of the second loop antenna 20 alone. Can also improve the reception efficiency.

  On the other hand, when radio waves are transmitted at the first resonance frequency, the current flowing through the second loop antenna 20 decreases, and the second loop antenna 20 does not operate as a loop antenna, and radio waves are transmitted only from the first loop antenna 10. Will be.

  Therefore, even if a metal such as a battery for a circuit for supplying a transmission radio wave to the first loop antenna 10 is disposed inside the second loop antenna 20, the battery is not lost, so the transmission efficiency is improved. Can be improved.

The loop antenna 1 can be reduced in size because the first loop antenna 10 and the second loop antenna 20 are mounted on the printed circuit board 40 as a substrate pattern.
In addition, since the second loop antenna 20 includes a capacitor 80 that forms a low-pass filter with the inductive component of the second loop antenna 20, when transmitting radio waves from the first loop antenna 10, The current flowing through the two-loop antenna 20 is blocked by the low-pass filter. Therefore, no current flows through the second loop antenna 20), so that a decrease in transmission power can be suppressed.

Further, since the capacitor 80 is a chip capacitor, the loop antenna 1 can be reduced in size.
[Second Embodiment]
Next, the loop antenna 2 according to the second embodiment in which an inductor is added to the loop antenna 1 according to the first embodiment will be described with reference to FIGS. 5 and 6.

  The loop antenna 2 is obtained by adding an inductor to the loop antenna 1 in the first embodiment, and other configurations are the same as those of the loop antenna 1. Is omitted.

  As shown in FIG. 5, in the loop antenna 2, two chip inductors 30 and 32 are arranged on the printed circuit board 40 as the connection portion 30, and the second loop is interposed via the two chip inductors 30 and 32. An antenna 20 is connected to the first loop antenna 10.

  The loop antenna 2 having such a configuration is represented by an equivalent circuit as shown in FIG. That is, two chip inductors 30 and 32 are connected in series to the second loop antenna 20 with the receiving IC 60 interposed therebetween.

Such a loop antenna 2 can improve transmission efficiency and reception efficiency more than the loop antenna 1 in the first embodiment.
That is, in the case of the loop antenna 1 according to the first embodiment, depending on the configuration of the wiring, the second loop antenna 20 mounted as a board pattern on the printed board 40 may have a parasitic capacitance. In that case, the cutoff characteristic of the LC filter formed by the second loop antenna 20 is deteriorated.

  In this case, like the loop antenna 2 in the second embodiment, an inductor is added as the connection portion 30 so that the LC filter formed by the second loop antenna 20 can have a sufficient cutoff characteristic. Become.

  Then, power is not consumed in the reception IC 60 when radio waves are transmitted from the transmission IC 50, and power is not consumed in the transmission IC 50 when radio waves are received by the reception IC 60, so that transmission efficiency and reception efficiency can be improved.

In addition, since the chip inductors 30 and 32 are used, the inductive connection 30 can be easily configured, and the loop antenna can be reduced in size.
[Third Embodiment]
Next, the loop antenna 3 in which the first loop antenna 10 and the second loop antenna 20 in the second embodiment are formed into a plurality of loops will be described with reference to FIGS. 7 and 8.

  As shown in FIGS. 7 and 8, the loop antenna 3 has the first loop antenna 10 and the second loop antenna 20 in the second embodiment as a loop of a plurality of turns (in this third embodiment, two turns). .

  The inner peripheral side (first loop antenna 10b) of the first loop antenna 10 is connected in series to the transmission IC 50 via capacitors 82 and 84, and the outer peripheral side (first loop antenna 10a) is connected to the inner side via capacitors 92 and 94. The peripheral loop antenna 10b is connected in parallel.

  One end on the outer peripheral side (second loop antenna 20a) of the second loop antenna 20 is connected to one end of the first loop antenna 10b on the inner peripheral side via the chip inductor 34, and the other end is connected to the outer peripheral side via the chip inductor 36. Is connected to one end of the first loop antenna 10a.

  One end of the inner circumference side (second loop antenna 20b) of the second loop antenna 20 is connected to the outer circumference side first loop antenna 10a via the chip inductor 30 on the side where the outer circumference side second loop antenna 20a is not connected. The other end of the first loop antenna 10b on the inner peripheral side is connected to the side on which the second loop antenna 20a on the outer peripheral side is not connected via the chip inductor 32.

In such a loop antenna 3, compared with the loop antenna 2 in the second embodiment, the first loop antenna 10 and the second loop antenna 20 are each configured by a plurality of loops, so that reception efficiency and transmission efficiency are improved. Can do.
[Fourth Embodiment]
Next, the loop antenna 4 in the fourth embodiment in which the inductor in the loop antenna 2 of the second embodiment is changed to a switch will be described with reference to FIG.

  The loop antenna 4 is obtained by changing the inductor of the loop antenna 2 in the second embodiment to a switch, and other configurations are the same as those of the loop antenna 2. Therefore, the same components are denoted by the same reference numerals, The description is omitted.

  The configuration of the loop antenna 4 is the same as that of the loop antenna 2 of the second embodiment shown in FIG. 5 simply by replacing the chip inductors 30 and 32 with the switches 100 and 102, and thus the configuration diagram is omitted.

In the loop antenna 4, two switches 100 and 102 are arranged on the printed circuit board 40 as the connection portion 30, and the second loop antenna 20 is connected to the first loop antenna 10 through the two switches 100 and 102. It is connected.

  The loop antenna 2 having such a configuration is represented by an equivalent circuit as shown in FIG. That is, two switches 100 and 102 are connected in series to the second loop antenna 20 with the receiving IC 60 interposed therebetween.

  The switches 100 and 102 are switches composed of SPST (Single Pole / Single Throw) switches. If the first loop antenna 10 or the second loop antenna 20 is a loop having a plurality of turns, the number of SPST poles may be increased in accordance with the number of loop turns.

  The switches 100 and 102 are controlled to be turned on / off by the control IC 104. The control IC 104 is mounted on the printed circuit board 40, and when the radio waves are transmitted by the first loop antenna 10, the switches 100 and 102 are turned off, and when the radio waves are received by the second loop antenna 20, The switches 100 and 102 are turned on.

  In such a loop antenna 4, electrical connection between the first loop antenna 10 and the second loop antenna 20 can be easily turned on / off by a simple structure in which the switches 100 and 102 are provided.

  1, 2, 3 ... Loop antenna 10, 10a, 10b ... First loop antenna 20, 20a, 20b ... Second loop antenna 30 ... Connection (chip inductor) 32, 34, 36 ... Chip inductor 40 ... Printed circuit board 50 ... Transmission IC 60 ... Reception IC 70 ... Battery 80, 82, 84, 86, 92, 94 ... Capacitor 100, 102 ... Switch 104 ... Control IC.

Claims (14)

A first loop antenna (10) excited at a first resonance frequency;
A second loop antenna (20) having an inductance greater than that of the first loop antenna at the first resonance frequency and excited at a second resonance frequency that is lower than the first resonance frequency;
Two points of the second loop antenna and the first loop antenna are formed so that the second loop antenna and the first loop antenna can be excited as one loop antenna by forming one electrical loop. A connection means (30) for electrical connection with;
A battery for a circuit for supplying a transmission radio wave to the first loop antenna, disposed outside the loop of the first loop antenna and inside the loop of the second loop antenna;
A loop antenna (1), comprising: The loop antenna according to claim 1, wherein
The loop antenna is characterized in that the connecting means has inductivity. The loop antenna according to claim 2,
The loop antenna characterized in that the inductive connection means is a coil. The loop antenna according to claim 3,
The loop antenna, wherein the coil is a chip inductor. A first loop antenna (10) excited at a first resonance frequency;
A second loop antenna (20) having an inductance greater than that of the first loop antenna at the first resonance frequency and excited at a second resonance frequency that is lower than the first resonance frequency;
Two points of the second loop antenna and the first loop antenna are formed so that the second loop antenna and the first loop antenna can be excited as one loop antenna by forming one electrical loop. Connecting means for electrical connection with,
The loop antenna characterized in that the connection means is a switch (100, 102). In the loop antenna according to any one of claims 1 to 5,
The first loop antenna is a loop antenna formed by a plurality of loops; The loop antenna according to any one of claims 1 to 6,
A loop antenna, wherein the second loop antenna is formed of a plurality of loops; The loop antenna according to any one of claims 1 to 7,
The first loop antenna is mounted on a printed circuit board (40) as a substrate pattern. In the loop antenna according to any one of claims 1 to 8,
The loop antenna, wherein the second loop antenna is mounted on a printed circuit board as a substrate pattern. The loop antenna according to any one of claims 1 to 9,
The loop antenna according to claim 2, further comprising a capacitor (80) that forms a low-pass filter with an inductive component of the second loop antenna. The loop antenna according to any one of claims 1 to 10,
When excited at the first resonance frequency, the loop antenna is excited by an electric signal supplied from an external circuit connected to the first loop antenna. The loop antenna according to claim 11, wherein
The loop antenna according to claim 1, wherein the first resonance frequency is a frequency used for a remote system of an automobile. The loop antenna according to any one of claims 1 to 12,
When excited at the second resonance frequency, the loop antenna is excited by a radio wave applied from outside. The loop antenna according to claim 13,
The second resonance frequency is a frequency used in an RFIC tag.