JP5112192B2 - Antenna and RFID reader - Google Patents

Description

  The present invention relates to an antenna that can communicate with another communication device when close to the communication device, and an RFID reader using the antenna.

Conventionally, various antennas are used in wireless communication, and RF (Radio Frequency) tags using the antennas have also been proposed. Such techniques are disclosed in the following documents, for example.
JP 2007-150654 A

  [Patent Document 1] discloses a technique that uses an RF tag as a sensor device that is arranged near the surface of a sheet-like signal transmission device and transmits various measurement results to the signal transmission device. .

  In addition, as an RF tag, an RFID (RF IDentification) tag that transmits identification information is widely used instead of the sensor information as described above. In addition, RFID readers that read identification information stored in RFID tags are becoming widespread.

  Here, in the RFID reader that is widely used at present, the electromagnetic wave may fly to an unintended region, and may be connected so as to be communicable with other than the target RFID tag. Specifically, there are cases where a plurality of RFID readers interfere with each other, or an RFID reader different from the intended one reads an RFID tag.

  For this reason, the inventors are advancing research and development of a communication device that can communicate only when an antenna is brought close to a communication target.

  At this time, a method of reducing the antenna power of a normal antenna or reducing the antenna gain is also conceivable. However, in these methods, when the antennas are brought close to each other, the VSWR (Voltage Standing Wave Ratio) of the antennas fluctuates or the antenna position slightly changes due to a change in the electric field on the antenna surface. Transmission loss S21 between antennas becomes large. For this reason, stable communication becomes impossible.

  Therefore, only when the antennas are close to each other, there is a strong demand for a system with a small transmission loss S21 and capable of stable communication.

  An object of the present invention is to solve such a problem, and an object of the present invention is to provide an antenna that can communicate with another communication device when close to the communication device, and an RFID reader using the antenna.

  In order to achieve the above object, the following invention is disclosed in accordance with the principle of the present invention.

  The antenna according to the first aspect of the present invention is an antenna to be connected to a communication device that communicates in the frequency band of the electromagnetic wave length λ, and the communication device communicates with other communication devices, and includes a power feeding unit and a line unit. The terminal resistance unit is provided and configured as follows.

  That is, the power feeding unit has a signal terminal and a ground terminal to which the communication device is connected.

  On the other hand, one end of the line portion is connected to the signal terminal of the power feeding portion, and is composed of a conductor wire that is capacitively coupled or electromagnetically coupled in proximity to another antenna connected to the other communication device.

  Furthermore, the termination resistance unit connects between the ground terminal of the power feeding unit and the other end of the line unit.

And, regarding the input impedance Zi between the signal terminal and the ground terminal, the characteristic impedance Zo of the line portion, the impedance Zr of the termination resistor portion,
Zi = Zo = Zr
It is.

  The antenna according to the second aspect of the present invention is an antenna to be connected to a communication device that communicates in the frequency band of the electromagnetic wave length λ, and the communication device communicates with other communication devices, and includes a power feeding unit and a line unit. The terminal resistance unit is provided and configured as follows.

  That is, the power feeding unit has a signal terminal and a ground terminal to which the communication device is connected.

  On the other hand, the line portion is composed of a conductor wire having one end connected to the signal terminal of the power feeding portion and capacitively coupling or electromagnetically coupling in close proximity to another antenna connected to the other communication device.

  Furthermore, the termination resistance unit connects between the ground terminal of the power feeding unit and the other end of the line unit.

And, for the input impedance Zi between the signal terminal and the ground terminal, the impedance Zr of the termination resistor part, the path length L from the one end to the other end of the line part, an integer constant n of 1 or more,
Zi = Zr;
L = nλ / 2
It is.

In the antenna of the present invention, the characteristic impedance Zo of the line portion,
Zi = Zo = Zr
Therefore, the communication device can be configured to communicate with the other communication device in a frequency band other than the electromagnetic wave length λ.

  In the antenna of the present invention, the line portion has a spiral shape, and a termination resistor is connected to one of the ends on the center side and the peripheral side of the spiral, and a power feeding portion is connected to the other end. It can be configured to be connected.

  Further, in the antenna of the present invention, the line portion is a mesh-like conductor having a mesh shape, a power feeding portion is connected to a position where the mesh-like conductor is located, and a termination resistor portion is located at another position of the mesh-like conductor. Can be configured to be connected.

  In the antenna of the present invention, the electromagnetic wave length λ can be configured to be 5 cm to 35 cm.

  An RFID reader according to another aspect of the present invention is connected to the antenna and a power feeding unit of the antenna as a communication device as an RFID (Radio Frequency IDentification) tag that is the other communication device and the electromagnetic wave via the antenna. And an RF communication unit that communicates in the long λ frequency band.

  ADVANTAGE OF THE INVENTION According to this invention, the antenna which can be communicated by making it close to another communication apparatus, and the RFID reader using the said antenna can be provided.

  Embodiments of the present invention will be described below. The embodiments described below are for explanation, and do not limit the scope of the present invention. Therefore, those skilled in the art can employ embodiments in which each of these elements or all of the elements are replaced with equivalent ones, and these embodiments are also included in the scope of the present invention.

  FIG. 1 is an explanatory diagram showing a circuit diagram of the antenna according to the present embodiment. Hereinafter, a description will be given with reference to FIG.

  The antenna 101 includes a power supply unit 102 connected to a communication device, a line unit 103 that performs communication in proximity to another antenna, and a termination resistor unit 104 that adjusts impedance at the end of the line unit 103.

  The power feeding unit 102 includes a signal terminal 111 and a ground terminal 112. The signal terminal 111 plays a role of connecting the signal line of the communication device and one end of the line unit 103, and the ground terminal 112 serves as a ground wire of the communication device. Play the role of grounding.

  Termination resistor 104 adjusts the impedance between one end of line 103 and the ground line of the communication device.

  The line portion 103 is typically made of a linear, strip-like, or net-like conductor, and as described above, one end is connected to the signal terminal 111 of the power feeding portion 102 and the other end is connected to the terminating resistor portion 104, respectively.

Here, the specification of each part shall be defined as follows.
(A) Input impedance Zi between the signal terminal 111 and the ground terminal 112. That is, the impedance of the communication device.
(B) Characteristic impedance Zo of the line portion 103.
(C) The impedance Zr of the termination resistor 104.
(D) A path length L from the one end of the line portion 103 to the other end.
(E) The electromagnetic wave length λ in the frequency band with which the communication device communicates.

If the specifications are determined in this way, the impedance Z of the entire antenna 101 viewed from the power feeding unit 102 can be calculated as follows with j as an imaginary unit.
Z = Zo (Zr + j Zo tan βL) / (Zo + j Zr tan βL);
β = 2π / λ

  In the antenna 101 of this embodiment, while communication is not being performed, reflection of power and resonance are not generated, thereby suppressing radiation of electromagnetic waves and reducing gain, which is completely opposite to a normal antenna. Based on the design.

That is, if any of the following conditions is met:
(1) Zi = Zo = Zr.
(2) Zi = Zr and L = nλ / 2 (n is an integer constant of 1 or more).
Since no impedance mismatch occurs in the power supply unit 102, no reflection or resonance occurs.

  The above condition (1) is similar to the design specification of a beverage antenna used in the field of low frequency communication having an electromagnetic wave length of several hundred meters or more. Here, the beverage antenna is mainly used as a receiving antenna, and in order to increase the reception efficiency, the overall size needs to be about 1 to 3 times the electromagnetic wave length.

  On the other hand, in this embodiment, the electromagnetic wave length in the communication frequency band is assumed to be 50 cm or less, typically about 5 cm to 35 cm, and the size of the antenna is strongly desired to be small.

  That is, if the beverage antenna is simply applied, the overall size is about several hundreds cm, which is not suitable for use in the frequency band of the present embodiment.

  In this embodiment, since the line portion of the antenna 101 has a shape that can be capacitively coupled or electromagnetically inductively coupled with another antenna, electromagnetic waves can be efficiently transmitted and received. Moreover, it is easy to set the overall size of the antenna 101 to about several centimeters to several tens of centimeters. Therefore, it is suitable for actual use.

  Here, the condition (1) is a condition that does not limit the communication frequency band, and the condition (2) is a condition suitable for communication in a specific communication frequency band. Therefore, designing the antenna 101 to satisfy both the conditions (1) and (2) makes the antenna 101 particularly suitable for communication in a specific communication frequency band and also for communication in other communication frequency bands. Can be applied.

  Further, in the case where only communication in a specific communication frequency band is intended, if the condition (2) is adopted, the width, thickness, material, overall shape of the line portion 103, and the substrate on which each portion of the antenna 101 is arranged Therefore, the design of the gain of the antenna 101 can be easily changed.

  In general, when another object is brought close to the antenna, the VSWR (Voltage Standing Wave Ratio) of the antenna changes. However, in the present embodiment, the termination resistance unit 104 is provided, so that Change is smaller. For this reason, there is also an advantage that the operation is stabilized.

  Although the resistance element itself can be used as the termination resistance unit 104, various electronic elements, electronic circuits, electric circuits, and the like may be adopted as long as the impedance has a desired value. For example, when an LED (Light Emitting Diode) is employed as the termination resistor unit 104, the user can easily know whether or not communication is in progress.

  FIG. 2 is an explanatory diagram showing the appearance of the surface of the first mode of the antenna 101. Hereinafter, a description will be given with reference to FIG.

  As shown in the figure, the line portion 103 of the antenna 101 is a conductor wire composed of a microstrip line disposed on the surface of the substrate 151. A conductor foil 152 is disposed on the back surface of the substrate 151 and plays a role of grounding.

  The length L of the line portion 103 is an integral multiple of half of the electromagnetic wave length λ in the communication frequency band, and the line portion 103 in this figure has a linear shape. Is typically about λ / 2.

  In the present embodiment, the coaxial cable connector is disposed on the back surface of the substrate 151, the center line thereof corresponds to the signal terminal 111, passes through the substrate 151, is connected to one end of the line portion 103, and the covered wire is grounded. It corresponds to the terminal 112, is connected to the grounding conductor foil 152 on the back surface, and functions as the power feeding unit 102.

  A terminating resistor is connected between the other end of the line portion 103 and the conductor foil 152 on the back surface of the substrate 151, and functions as the terminating resistor portion 104.

  By changing the width a of the microstrip line, the thickness b of the substrate 151, and the (relative) dielectric constant ε of the substrate 151, the gain of this antenna can be controlled.

  For example, considering the cases of a = 1.0mm, b = 0.5mm, ε = 4, and dielectric loss tangent tanδ = 0.01, the characteristic impedance of the transmission line in the 2.4GHz band is 50Ω, and communication connected to the coaxial cable The impedance Zi of the device and the impedance Zr of the termination resistor 104 can be matched.

  In order to confirm that communication is possible by the antenna 101, in addition to the above specifications, the total length L of the line portion 103 is 50 mm, the size of the substrate 151 is 20 mm × 70 mm, and the line portion 103 is placed at the center of the substrate 151. The transmission loss S21 between the antennas at the communication frequency of 2.45 GHz when the dipole antenna is placed close to the antenna 101 was calculated by simulation.

  For ease of understanding, as shown in the figure, the center of the line portion 103 is the origin, the longitudinal direction of the line portion 103 is the y axis, the direction orthogonal to the line portion 103 is the x axis, and the thickness of the substrate 151 The vertical direction is the z axis.

  FIG. 3 is a graph showing the value of the transmission loss S21 when the center position (x, y, z) of the dipole antenna is x = y = 0 mm of the antenna 101 and the distance z between them is changed.

  FIG. 4 is a graph showing the value of transmission loss S21 when x is changed when the center position (x, y, z) of the dipole antenna is y = 0 mm and z = 0.5 mm of the antenna 101.

  FIG. 5 is a graph showing the value of the transmission loss S21 when y is changed when the center position (x, y, z) of the dipole antenna is x = 0 mm and z = 0.5 mm of the antenna 101.

  FIG. 6 shows the value of the transmission loss S21 when the angle θ formed by the antenna 101 is changed when the center position (x, y, z) of the dipole antenna is x = y = 0 mm and z = 0.5 mm of the antenna 101. It is a graph.

  From these results, it can be seen that communication is sufficiently possible by bringing both close together, and that the communication power increases as the longitudinal directions of the two are arranged in parallel. This is because the mutual inductance between the antennas is large.

  It is known that the transmission loss S21 when both are sufficiently separated can be predicted from the gain and is sufficiently small.

  If an antenna with a shape other than a dipole antenna is used, the performance may be different from these. However, if a loop antenna or the like having a large mutual inductance is used, the value of the transmission loss S21 also increases. Communication is possible enough.

  In the above embodiment, the line portion 103 is a linear microstrip line, but this shape can be arbitrarily changed. Hereinafter, embodiments in which the line portion 103 has various shapes will be described.

  FIG. 7 is an explanatory diagram showing the shape of the spiral line portion 103. Hereinafter, description will be given with reference to this figure (reference numerals are omitted).

  As shown in the figure, the line portion 103 has a spiral shape, and one end thereof is connected to the power feeding portion 102 and the other end is connected to the terminating resistor portion 104 as in the above embodiment.

  With such a spiral shape, it is expected that the mutual inductance with the counterpart antenna will increase. Therefore, in order to confirm this, the transmission loss S21 with the dipole antenna was obtained by simulation.

  FIG. 8 is an explanatory diagram showing the positional relationship between the spiral line portion 103 and the dipole antenna. Hereinafter, description will be given with reference to this figure (reference numerals are omitted).

  As shown in the figure, a dipole antenna is arranged so as to share the center with the spiral line portion 103, and the angle between the two is rotated.

  FIG. 9 is a graph showing the value of the transmission loss S21 with respect to both angles θ. Hereinafter, a description will be given with reference to FIG.

  As shown in this figure, it can be seen that the change in the transmission loss S21 is small even when θ is changed as compared with the above embodiment. Therefore, the angle dependency with the communication partner can be reduced by adopting a spiral shape.

  Hereinafter, other line shapes will be described.

  FIG. 10 is an explanatory diagram showing the shape of the dragon-shaped line portion 103. Hereinafter, a description will be given with reference to FIG.

  A dragon crest is a spiral having a substantially square shape, and can be easily formed by etching a printed circuit board. Even when this shape is adopted, the power feeding unit 102 is connected to one of the end portions 901 of the line portion 103, and the terminating resistor portion 104 is disposed on the other end portion 901.

  FIG. 11 is an explanatory diagram showing the shape of the mesh-shaped line portion 103 and the shape of the terminating resistor portion 104. Hereinafter, a description will be given with reference to FIG.

  As shown in this figure, when a lattice-like mesh or a honeycomb-like mesh is formed of a conductor, it can be regarded as a transmission line. Therefore, if a mesh is disposed on the surface of the substrate, the back surface is a conductor foil, a resistor is disposed so as to surround the entire side surface of the substrate, and the mesh and the conductor foil are connected to each other, the terminal resistor section 104 is caused to function. The power feeding unit 102 can be arranged at an arbitrary location on the mesh.

  Of course, it is also possible to function as the terminating resistance unit 104 by connecting a specific point of the mesh and the back surface thereof with a resistor.

  In addition, a plurality of spiral or dragon-shaped line sections 103 as described above may be arranged in an array.

  An RFID reader can be realized by connecting an RF communication device that communicates with an RFID tag to the power feeding unit 102 of the antenna 101.

  As described above, this RFID reader can communicate with a nearby RFID tag, but since the gain with a separated RFID tag is extremely small, it suppresses the emission of electromagnetic waves and prevents interference and the like from occurring. Can do.

  As described above, according to the present invention, it is possible to provide an antenna that can communicate with another communication device and an RFID reader using the antenna.

It is explanatory drawing which shows the circuit diagram of the antenna which concerns on this embodiment. It is explanatory drawing which shows the external appearance of the surface of the 1st aspect of an antenna. It is a graph which shows the value of the transmission loss S21 when changing the distance z of both in the center position (x, y, z) of a dipole antenna and x = y = 0mm of an antenna. It is a graph which shows the value of the transmission loss S21 when x is changed when the center position (x, y, z) of the dipole antenna is y = 0 mm and z = 0.5 mm of the antenna. It is a graph which shows the value of transmission loss S21 when changing the center position (x, y, z) of a dipole antenna, when x = 0 mm of the antenna and z = 0.5 mm. It is a graph which shows the value of the transmission loss S21 when changing the angle (theta) which both make the center position (x, y, z) of a dipole antenna x = y = 0mm and z = 0.5mm of antenna. It is explanatory drawing which shows the shape of a spiral line part. It is explanatory drawing which shows the positional relationship of a spiral track | line part and a dipole antenna. It is a graph which shows the value of the transmission loss S21 with respect to angle (theta) of a spiral line part and a dipole antenna. It is explanatory drawing which shows the shape of a dragon-shaped track part. It is explanatory drawing which shows the shape of a mesh-shaped track part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Antenna 102 Feed part 103 Line part 104 Termination resistor part 111 Signal terminal 112 Ground terminal 151 Substrate 152 Conductive foil for grounding 901 End part of line part

Claims (5)

An antenna that can be connected to any one of a communication device that communicates in a frequency band of the electromagnetic wave length λ and a communication device that communicates in a frequency band other than the electromagnetic wave length λ, and the communication device connected to the antenna is another Communicate with other communication devices,
A power feeding unit having a signal terminal and a ground terminal to which the communication device is connected;
One end connected to the signal terminal of the power feeding unit, a line unit made of a conductor wire that is capacitively coupled or electromagnetically coupled in proximity to another antenna connected to the other communication device,
A termination resistor for connecting between the ground terminal of the power supply unit and the other end of the line unit;
The input impedance Zi between the signal terminal and the ground terminal, the impedance Zr of the termination resistor unit, the characteristic impedance Zo of the line unit, the path length L from the one end of the line unit to the other end, and an adjustment of 1 or more For the constant n,
Zi = Zr;
L = nλ / 2 ;
Zi = Zo = Zr
An antenna characterized by being. The antenna according to claim 1 ,
The line portion has a spiral shape,
Of the ends on the center side and the peripheral side of the spiral, a termination resistor is connected to one end, and a power feeding unit is connected to the other end. The antenna according to claim 1 ,
The line portion is a mesh conductor having a mesh shape,
An antenna, wherein a power feeding unit is connected to a position where the mesh-shaped conductor is present, and a termination resistor is connected to another position of the mesh-shaped conductor. The antenna according to any one of claims 1 to 3 ,
The electromagnetic wave length λ is 5 cm to 35 cm. The antenna according to any one of claims 1 to 3 ,
An RF communication unit that is connected as a communication device to the power feeding unit of the antenna and communicates in the frequency band of the electromagnetic wave length λ with an RFID (Radio Frequency IDentification) tag that is the other communication device via the antenna;
An RFID reader comprising:

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