JP2009017284A - Antenna device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an antenna device which is suitably made compact, is capable of expanding a communication distance and is also suitable for high-speed communication. <P>SOLUTION: The antenna device includes a first conductor 12, a power feeding section 13 connected to the first conductor 12, and a second conductor 14 at least a part of which is disposed away from a connection part of the first conductor 12 with the power feeding section 13 a distance such that the second conductor 14 can be capacitively coupled to the first conductor 12, wherein the first conductor 12 and the second conductor 14 are disposed in parallel while facing each other. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an antenna device, and more particularly to an antenna device that can achieve high-speed communication and expansion of a communication distance.

  In recent years, various antenna devices have been developed and used for various devices. As such an antenna device, for example, an antenna device described in Patent Document 1 is known.

As shown in FIG. 7A, the antenna device 101 is formed on the same substrate 101 with a loop conductor 102 constituting a loop antenna formed on the substrate 101, and one tip portion feeds the loop conductor 102. A balanced / unbalanced transformer (balun) 103 connected at the junction point Q and a high-frequency power source 104 are provided.
Japanese Patent No. 3334079

  However, in this antenna device 101, as shown in FIG. 7B, in order to feed a high-frequency current from a high-frequency power source 104 to the antenna built in the equipment with a coaxial cable 201 or the like, matching is performed. Need to take. Therefore, the above-described balanced / unbalanced transformer (balun) 103 is necessary, which is not convenient from the viewpoint of miniaturization and cost.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an antenna device that is suitable for miniaturization, can increase the communication distance, and is also suitable for high-speed communication.

  The antenna device according to the present invention includes a first conductor, a power supply unit connected to the first conductor, and a distance at least a part of which can be capacitively coupled from a connection point of the first conductor with the power supply unit. And a second conductor spaced apart from each other.

  The first conductor and the second conductor are preferably arranged in parallel.

  Moreover, it is preferable that the at least part of the second conductor is disposed to face the first conductor.

  Further, the first conductor may be configured such that the third conductor and the fourth conductor constituting the first conductor intersect each other.

  Moreover, it is preferable that the 5th conductor and 6th conductor which comprise the said 1st conductor cross | intersect the said 2nd conductor.

  In addition, the first conductor, the second conductor, and the power feeding unit may be formed on the same surface of the circuit board.

  The first conductor may be formed on the same surface of the circuit board, and the second conductor may be disposed adjacent to the circuit board.

  The first conductor and the power feeding unit may be formed on a first surface of a circuit board, and the second conductor may be formed on a second surface of the circuit board.

  Therefore, according to the present invention, the first conductor, the power feeding portion connected to the first conductor, and at least a part thereof are separated from the connection portion of the first conductor with the power feeding portion by a distance capable of capacitive coupling. Therefore, it is suitable for miniaturization because it does not require a balun, and it is possible to provide an antenna device that can increase the communication distance and is also suitable for high-speed communication. .

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
(First embodiment)
1 and 2 show an antenna device 10 constituting an antenna part of an RFID tag according to a first embodiment of the present invention. The antenna device 10 includes a printed board 11 constituting a substrate, A first conductor 12 constituting a power feeding element attached to one surface of the printed circuit board 11 (hereinafter referred to as a surface 11A), a power feeding unit 13 comprising a high frequency power source provided on the surface 11A which is the same surface of the printed circuit board 11, A second conductor 14 constituting a parasitic element provided on the opposite surface (hereinafter referred to as back surface 11B) of the printed circuit board 11 and a ground plate 15 as GND are provided.

In the case of this embodiment, the printed board 11 has a longitudinal (Y direction) length Gy of 55 mm, a lateral (X direction) length Gx of 85 mm, and a thickness of 0.8 mm. The printed board 11 uses, for example, a glass epoxy board, which is a board in which a glass fiber knitted cloth is impregnated with an epoxy resin, as a base substrate, and has a dielectric constant (ε _r ) of 4.3 to 3. 4.7 is used.

  The first conductor 12 is formed in an L shape that bends in the X and Y directions. The first conductor 12 intersects with each other (hereinafter referred to as “X conductor portion 121”) and the fourth conductor (hereinafter referred to as “X conductor portion 121”). And is connected to the power feeding unit 13 via the microstrip line 123, and has a total length of about 80 mm. That is, the first conductor 12 has a frequency band used in the RFID of the present embodiment of UHF of 950 MHz and is set to about ¼ with respect to its center wavelength (λ) of 315 mm. The first conductor 12 and the second conductor 14 to be described later are installed so that the outer edge portion is located at a distance D of 5 mm from the edge portion of the printed circuit board 11, and the inner edge portion is the ground plane 15. It arrange | positions so that the distance E from the outer edge part may be located in the place of 6 mm.

Among these, the X conductor portion 121 has a one end 121 </ b> A serving as a connection portion with the microstrip line 123. The X conductor portion 121 of the present embodiment has a length L _1x of 38 mm and a width W _1x of 5 mm, and a copper plate (or copper foil) formed along the X direction on the surface 11A of the printed board 11 or the like. Consists of.

One end portion of the Y conductor portion 122 is connected to the other end portion of the X conductor portion 121 opposite to the one end portion 121A. The Y conductor portion 122 of the present embodiment has a length L _1y of 46 mm and a width W _1y of 5 mm, and is a copper plate (or copper foil) formed along the Y direction on the surface 11A of the printed board 11. ) Etc.

Since the microstrip line 123 is electrically connected to the X conductor 121, the microstrip line 123 that is integrally formed with the X conductor 121 and made of a copper plate (or copper foil) or the like along the Y direction on the surface 11 </ b> A of the printed board 11. Is formed. Incidentally, the microstrip line 123 of the present embodiment, the length _{C y} is 6 mm, the width _{C x} is formed in 1.5 mm.

  The first conductor 12 is configured by the X conductor portion 121 and the Y conductor portion 122 that intersect with each other so as to be orthogonal to each other, so that polarized waves in two directions can be efficiently transmitted or received. That is, when the printed circuit board 11 is arranged to stand up with respect to the direction in which gravity acts (for example, in FIG. 1, the -Y direction is set up to be the direction of gravity acceleration), an RFID tag reader (not shown) is shown. Can be efficiently captured by the X conductor portion 121 and the vertical polarization by the Y conductor portion 122, respectively. As a result, a response can be efficiently transmitted to the RFID tag reader.

  The second conductor 14 is formed in a substantially L shape along the X and Y directions. The second conductor 14 intersects with each other with a fifth conductor (hereinafter referred to as “X conductor portion 141”) and a sixth conductor ( (Hereinafter referred to as “Y conductor portion 142”), and is disposed at a distance capable of capacitive coupling with the first conductor 12 (particularly, the X conductor portion 121) via the printed circuit board 11. ing. The second conductor 14 is also formed to have a length of about ¼ with respect to the wavelength (λ) 315 mm used in the RFID of the present embodiment.

Among these, the X conductor portion 141 is a place where a fixed point 141A near one end is connected to the microstrip line 123 in high frequency. The X conductor portion 141 of the present embodiment has a length L _2x of 45 mm and a width W _2x of 5 mm, and is a copper plate (or copper foil) formed along the X direction on the back surface 11B of the printed circuit board 11. Consists of. The X conductor portion 141 is partially overlapped and capacitively coupled with the X conductor portion 121 of the first conductor 12 with the printed circuit board 11 interposed therebetween. In the present embodiment, the capacitive coupling portion A The superposition | polymerization area | region B which comprises is formed about 8 mm.

One end of the Y conductor 142 is connected to the other end opposite to the one end of the X conductor 141. The Y conductor portion 122 of the present embodiment has a length L _2y of 46 mm and a width W _2y of 5 mm, and is the same as the X conductor portion 141 formed along the Y direction on the back surface 11B of the printed board 11. It consists of a copper plate (or copper foil).

  In the present invention, due to the overlapping portion B constituting the capacitive coupling portion A, the physical position shift between the X conductor portion 121 of the first conductor 12 and the X conductor portion 141 of the second conductor 14 (in other words, A phase shift occurs in the induced current between the two X conductors 121 and 141 by forming the overlap with the printed board 11 interposed therebetween, thereby constituting an alternative means of the balun. For this reason, the superposition | polymerization area | region B electrically comprises the capacitive coupling part A, Since the frequency (f) uses 950 MHz of UHF band in this embodiment, the wavelength band ( Is set to about 1/40 of the center wavelength λ (315 mm), and is set to about 8 mm.

  Next, capacitive coupling between the X conductor portion 121 of the first conductor 12 and the X conductor portion 141 of the second conductor 14 will be described.

FIG. 3 shows an equivalent circuit of the antenna device 10 of the present embodiment, and based on this, the capacitance value between both the X conductor portions 121 and 141 is theoretically calculated.
Assuming that a parallel plate capacitor is formed between the X conductor portions 121 and 141, the capacitance C of the parallel plate capacitor can be generally calculated from the following equation.
C = ε _r · ε ₀ · S / d (1)
However, ε ₀ ; dielectric constant of air (= 8.85 × 10 ⁻¹² ) [F / m],
ε _r ; dielectric constant [F / m] of printed circuit board (glass epoxy board),
S: Area of flat plate (polymerization region = (15 × 10 ⁻³ ) · (5 × 10 ⁻³ )) [m ² ],
d: Distance between flat plates (thickness of printed circuit board = 0.8 × 10 ⁻³ ) [m].

Here, the dielectric constant ε _r of the glass epoxy substrate is difficult to determine uniquely because it depends on the material thickness and other various parameters. Therefore, in the present embodiment, when defined in the following range, ε _r = 4.3 to 4.7 [F / m], the capacitance value between the X conductor portions 121 and 141 is (1) From the equation, C = 3.6 to 3.9 [pF].

  On the other hand, in the actual measurement, it has been confirmed that the capacitance C between the X conductor portion 121 of the first conductor 12 and the X conductor portion 141 of the second conductor 14 is C = 2 to 5 [pF]. . As a result, the above-described theoretical value is within a range that approximately agrees with the actually measured value, and therefore, for the antenna device 10 of the present invention, it is proved that this equivalent circuit (model) is theoretically correct. Is obtained. Therefore, according to the antenna device 10 of the present embodiment, the first conductor 12 and the second conductor 14 are installed on the same surface of the printed circuit board 11, and a capacitor of about 5 [pF] is provided between them. The antenna characteristic can be obtained to the same extent as that of the connected one (however, a frequency band for communication of 950 MHz is used).

  Note that the base plates 15 on both sides are connected to each other through through holes not shown.

  Therefore, according to the present embodiment, the X conductor portion 141 of the second conductor 14 constituting the parasitic element is printed by the overlapping portion B in the vicinity of the microstrip line 123 of the first conductor 12 constituting the feeder element. By superimposing via the substrate 11, the antenna device 10 side and the circuit side (not shown) can be matched without the need for a balun. As a result, the mounting volume on the printed circuit board 11 can be reduced by the amount of the balun, and the antenna device 10 can be reduced in size. Thus, design freedom increases and manufacturing cost can be reduced.

  Furthermore, the communication distance generally varies depending on the wavelength, bandwidth and substrate dielectric constant, and the communication distance increases even if there is a superposition part B that becomes capacitive coupling, and the radiation gain is improved. At the same time, since no balun is required, there is no reactance component, so high-speed communication is possible. In other words, RFID load modulation (the amount of radio waves arriving at the antenna is reflected and emitted again, or / and is replaced with a transmission circuit by controlling the phase) has less balun than when there is a balun. Since the switch characteristics are better, high-speed response of the switch, that is, high-speed communication can be realized.

  Further, as described above, since both the X conductor portions 121 and 141 are capacitively coupled via the printed circuit board 15 which is a dielectric, the wavelength is shortened by the dielectric constant (the square of the effective dielectric constant of the dielectric). Therefore, the electrical length of the second conductor 14 which is a parasitic element can be shortened, and the antenna device 10 can be further downsized.

  In addition, in this embodiment, the X conductor portions 121 and 141 and the Y conductor portions 122 and 142 of the first conductor 12 and the second conductor 14 intersect at an angle of 90 degrees, respectively. Thus, radio waves in two types of polarization states, ie, vertical polarization, can be reliably captured, and the communication range is expanded. That is, according to the simulation performed by the inventor according to the present invention, it has been confirmed that 200 MHz having a good VSWR 2 or less as a communication characteristic can be secured for a center frequency of 1 GHz. This means that a broadband of about 20% can be realized compared to the conventional one.

  Furthermore, since it is not necessary to use a loop antenna as in the prior art, the casing of the antenna device 10 and thus the casing (case) of the RFID tag main body incorporating the antenna device 10 can be particularly thinned. It becomes like this.

(Second Embodiment)
Next, a second embodiment of the present invention will be described. In the present embodiment, the same parts as those in the first embodiment are denoted by the same reference numerals to avoid redundant description.
FIG. 4 shows an antenna device 20 constituting an antenna part of an RFID tag according to the second embodiment of the present invention. In this antenna device 20, unlike the first embodiment, a first conductor is shown. 21 and the second conductor 22 are arranged on the same surface of the printed board 11 (in this case, the surface 11A), parallel to each other, and facing each other. In the antenna device 20, the first conductor 21 is wider than the second conductor 22 and has a straight shape.

The first conductor 21 has a length L _1x in the X direction of 70 mm and a length L _1y in the Y direction of 20 mm, and is substantially along the X and Y directions on the surface 11A of the printed board 11. It consists of a copper plate (or copper foil) formed in an L shape.

The second conductor 22 is formed in an approximately L shape along the X and Y directions, and has a length L _2x in the X direction (X conductor portion 221) and a length in the Y direction (Y conductor portion 222). _Each of L _2y has a size of 46 mm, and is made of a copper plate (or copper foil) formed on the surface 11A of the printed circuit board 11 or the like. In addition, the length of the superposition | polymerization part B which comprises the capacitive coupling part A is 9 mm.

  Therefore, according to the present embodiment, the length of the conductor corresponds to the communication frequency, but in the first conductor 21 and the second conductor 22 of the present embodiment, the first conductor 12 of the first embodiment and Since it is the same length as 157 mm which is the length of the second conductor 14 (the length of the line connecting the intermediate points of the widths of the first conductor 12 and the second conductor 14 respectively), the communication frequency Is almost the same.

(Third embodiment)
Next, a third embodiment of the present invention will be described. In the present embodiment, the same parts as those in the first embodiment are denoted by the same reference numerals to avoid redundant description.

  FIG. 5 shows an antenna device 30 constituting an antenna portion of an RFID tag according to the third embodiment of the present invention. This antenna device 30 is different from the first embodiment in that it is a second conductor. 32 is attached to the outer surface of the casing (case) 5 of the RFID tag main body. The housing 5 includes a printed circuit board 11, a first conductor 31, a high frequency power supply 13, and a ground plane 15 inside.

The first conductor 31 is slightly larger than that of the first embodiment, the length L _{1x in} the X direction (X conductor portion 311) is 37 mm, and the length L _{1y in} the Y direction (Y conductor portion 312) is 50 mm. And a copper plate (or copper foil) formed along the X and Y directions on the surface 11A of the printed board 11. The first conductor 31 has a distance Ex of 5 mm between the X conductor portion 311 and the ground plane 15 and a distance Ey between the Y conductor portion 312 and the ground plane 15 of 7 mm. The distance is slightly different from the form.

The second conductor 32 is formed in an approximately L shape along the X and Y directions, and is slightly larger than that of the first embodiment, and the length L _{2x in} the X direction (X conductor portion 321) is 46 mm. The length L _2y in the Y direction (Y conductor portion 322) is 52 mm, and a copper plate (or copper foil) or the like is attached to a predetermined position on the outer surface of the housing 5. In addition, the second conductor 31 has a 9 mm-long overlapping portion B that forms a capacitive coupling portion A with the first conductor 31.

  The housing 5 is formed of a material that can ensure capacitive coupling between the first conductor 31 and the second conductor 32 inside and outside, for example, an appropriate resin material having a thickness t as thin as about 1 mm. Yes. In addition, in order to ensure this capacitive coupling, the first conductor 31 is disposed at an outer edge portion 1 mm away from the inner surface of the housing 5, in other words, close to and disposed via a 1 mm gap (d). .

  Therefore, according to the present embodiment, since the second conductor 32 is attached to the outer surface of the casing (case) 5 of the RFID tag main body, compared with the antenna devices 10 and 20 of the first and second embodiments. As a result, the size can be further reduced, or the outer element can be moved even after the product is assembled, so that it is easy to adjust the product.

  Also in this embodiment, the first conductor 31 and the second conductor 32 are slightly larger than the lengths of the first conductor 12 and the second conductor 14 of the first embodiment, and the wavelength depending on the dielectric constant. The communication frequency can be set substantially the same by appropriately setting the arrangement and length of the elements. Further, according to the present embodiment, the first conductor 31 and the second conductor 32 of the present embodiment have substantially the same area as the areas of the first conductor 12 and the second conductor 14 of the first embodiment. Therefore, the same gain can be obtained.

(Fourth embodiment)
Next, a fourth embodiment of the present invention will be described. In the present embodiment, the same parts as those in the first to third embodiments are denoted by the same reference numerals to avoid redundant description.

  FIG. 6 shows an antenna device 40 constituting an antenna part of an RFID tag according to the fourth embodiment of the present invention. This antenna device 40 is different from the third embodiment in that it is a second conductor. 42 is attached to the inner surface of the housing (case) 6 of the RFID tag main body in which the antenna device 40 is accommodated. The housing 6 includes a printed board 11, a first conductor 41, a high frequency power supply 13, and a ground plane 15 inside.

  The first conductor 41 has the same shape as the first conductor 31 of the third embodiment and is formed with the same dimensions, and the printed circuit board 11 as in the first to third embodiments. Is formed on one surface (in this case, the upper surface 11A). In addition, the first conductor 41 has a distance Ex between the X conductor portion 411 and the ground plane 15 of 5 mm and a distance Ey between the Y conductor portion 412 and the ground plane 15 as in the case of the third embodiment. The distance is 7 mm, which is slightly different from the first embodiment.

  Also, the second conductor 42 has the same shape and the same size as the second conductor 32 of the third embodiment, but as described above, instead of the printed circuit board 11, It is affixed to the inner surface of the casing (case) 6 of the RFID tag main body.

  Moreover, between the 1st conductor 41 and the 2nd conductor 42, it has the overlap part B of 8 mm in length which comprises the capacitive coupling part A. As shown in FIG.

  The housing (case) 6 is formed of a non-conductive and non-magnetic material that does not generate an electromagnetic shielding action, and is formed of an appropriate resin material in the present embodiment.

  Therefore, according to the present embodiment, since the second conductor 42 is attached to the inner surface of the casing (case) 6 of the RFID tag main body, compared with the antenna devices 10 and 20 of the first and second embodiments. Thus, since the substrate can be made small, an effect that the manufacturing cost can be suppressed is obtained.

  Also in the present embodiment, the first conductor 41 and the second conductor 42 have substantially the same length as the lengths of the first conductor 12 and the second conductor 14 of the first embodiment. The communication frequency can be set substantially the same by devising the arrangement and shape of each part. Further, according to the present embodiment, the first conductor 41 and the second conductor 42 of the present embodiment have substantially the same area as the areas of the first conductor 12 and the second conductor 14 of the first embodiment. Therefore, the same gain can be obtained.

  The present invention is not limited to the embodiment described above, and can be implemented in various forms without departing from the gist of the present invention. That is, for example, the second conductor that is not in contact with the power feeding unit may be installed in a place other than the substrate, or may be placed anywhere inside or outside the housing (case) 6 of the RFID tag main body. Further, the first and second conductors can be applied to a copper plate, a metal rod, a thin plate, a wide surface, or various appropriate shapes attached to the substrate. In addition, the first and second conductors can be attached to the inner surface of the housing, attached to the outer surface, simply placed on the housing without being attached, and shared with external equipment and components, and also shared with other internal components. Various correspondences are possible. Furthermore, it is good also as a structure which handles a human body as an element. Further, as shown in FIG. 4, the power supply side element, that is, the first conductor can be appropriately changed to various shapes such as a bar, a plate, and a surface.

  As described above, according to the present invention, it is not necessary to use a balun. Therefore, the present invention is suitable for downsizing, can increase the communication distance and can perform high-speed communication, and can be combined with an RFID tag reader. It is suitable for application to an IC tag to be used (for example, attached to a product as a tag for a logistics department, etc.) or an IC card.

It is a block diagram which shows a state when the antenna apparatus which concerns on the 1st Embodiment of this invention is seen from one surface of a printed circuit board. The block diagram which shows the state when the antenna device is seen from the opposite surface of the printed circuit board It is explanatory drawing which shows the equivalent circuit of the antenna device. The antenna apparatus which concerns on the 2nd Embodiment of this invention is shown, (A) is the block diagram, (B) is explanatory drawing which shows the magnitude | size of each element. The antenna apparatus which concerns on the 3rd Embodiment of this invention is shown, (A) is the block diagram, (B) is explanatory drawing which shows the magnitude | size of each element. The antenna apparatus which concerns on the 4th Embodiment of this invention is shown, (A) is the block diagram, (B) is explanatory drawing which shows the magnitude | size of each element. (A) is a block diagram which shows the conventional antenna apparatus, (B) is explanatory drawing which shows the principle.

Explanation of symbols

10, 20, 30, 40 Antenna device 11 Printed circuit board (board)
11A Front surface 11B Back surface 12, 21, 31, 41 First conductor (feeding element)
121 X conductor (third conductor)
122 Y conductor (fourth conductor)
123 Microstrip line 13 Feed section 14, 22, 32, 42 Second conductor (parasitic element)
141 X conductor (fifth conductor)
142 Y conductor (sixth conductor)
15 Ground plate (GND)
A Capacitance coupling part B Superposition part 5, 6 Case (case) of RFID tag main body

Claims (8)

A first conductor;
A power supply connected to the first conductor;
At least a portion of the second conductor disposed at a distance capable of capacitive coupling from a connection portion of the first conductor with the power feeding unit;
An antenna device comprising: The antenna device according to claim 1,
The first conductor and the second conductor are arranged in parallel;
Antenna device. The antenna device according to claim 2, wherein
The second conductor is disposed so that at least a part of the second conductor faces the first conductor;
Antenna device. The antenna device according to any one of claims 1 to 3,
In the first conductor, the third conductor and the fourth conductor constituting the first conductor intersect.
Antenna device. The antenna device according to any one of claims 1 to 4,
In the second conductor, the fifth conductor and the sixth conductor constituting the first conductor intersect with each other.
Antenna device. The antenna device according to any one of claims 1 to 5,
The first conductor, the second conductor, and the power feeding unit are formed on the same surface of the circuit board.
Antenna device. The antenna device according to any one of claims 1 to 5,
The first conductor is formed on the same surface of the circuit board, and the second conductor is disposed adjacent to the circuit board;
Antenna device. The antenna device according to any one of claims 1 to 5,
The first conductor and the power feeding unit are formed on a first surface of a circuit board, and the second conductor is formed on a second surface of the circuit board.
Antenna device.

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