JP5336873B2 - High surface impedance structure, antenna device, and RFID tag - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high surface-impedance structure capable of reducing thickness and losses. <P>SOLUTION: In a sheet-like structure in which unit structures are arranged repeatedly in an x direction, a capacity upper electrode 21 is formed at an upper-surface side of a dielectric layer 10. At a lower-surface side of the dielectric layer 10, a rectangular-frame-shaped ground electrode 31, a capacity lower electrode 32 disposed opposite to the capacity upper electrode 21, a center electrode 33 disposed at the center of a lower surface to connect the capacity lower electrode 32, and an inductance section 34 for connecting the center electrode 33 to the ground one 31 in a y direction are formed. A slit is formed in the capacity lower electrode 32, thus increasing an inductance component. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a sheet-like structure having a high surface impedance, an antenna device using the same, and an RFID (Radio Frequency Identification) tag.

  With recent miniaturization of devices, for example, the distance between a metal surface such as a ground plane and an antenna is shortened, and there is a concern about deterioration of antenna characteristics due to this. It is also known that when an RFID tag is attached to a metal surface, the characteristics of an antenna included in the RFID tag are remarkably deteriorated and the RFID tag does not function properly. These problems are all due to the low surface impedance of the metal surface. On the other hand, it is known that when an element having a high surface impedance is disposed in the vicinity of the antenna, the energy incident on the impedance surface is reflected in the same phase by the high surface impedance and the antenna performance is improved.

  As a sheet-like structure having a high impedance, a sheet-like structure having a so-called mushroom-like conductor having a via is conventionally known (for example, see Patent Document 1). On the other hand, a left-handed medium that is not limited to an antenna use and that does not require a via and has scalability exceeding the limit of via density (for example, see Patent Document 2) has been proposed.

US Pat. No. 6,538,621 JP 2006-245984 A

  When the inductance component or the capacitance component is increased, the region exhibiting high surface impedance or the signal / noise transmission blocking region can be shifted to the low frequency side. As understood by considering the scaling law, the fact that the characteristic can be shifted to the low frequency side means that the sheet-like structure can be miniaturized. Therefore, there is a demand for a large inductance component or capacitance component in any application.

  Accordingly, an object of the present invention is to provide a sheet-like structure in which a physical structure / geometric structure is devised in order to increase an inductance component or a capacitance component, and an antenna device and an RFID tag using the sheet-like structure. To do.

  When trying to shift the characteristics to the low frequency side by devising the structure, it is easier to increase the capacitance component than to increase the inductance component. Therefore, many proposals have been made for increasing the capacitance component.

  On the other hand, the inventors of the present invention have found that a better characteristic can be obtained incidentally when the characteristic is shifted to the low frequency side by increasing the inductance component. The present invention has been made on the basis of such findings, and has the following characteristics.

According to a first aspect of the invention,
A sheet-like structure that enhances the surface impedance for a specific frequency band by a periodic structure in which unit structures are repeatedly arranged in a predetermined direction, thereby reflecting in-phase incident waves having frequencies belonging to the specific frequency band,
The unit structure includes a dielectric layer having first and second main surfaces, a first conductor layer formed on the first main surface, and a first layer formed on the second main surface. 2 conductor layers,
The first conductor layer includes a first predetermined number of capacitive upper electrodes,
The second conductor layer is connected to the frame-shaped ground electrode having the same outer shape as the second main surface, a central electrode disposed at a central portion of the second main surface, and the central electrode. And a second predetermined number of capacitor lower electrodes arranged corresponding to the capacitor upper electrode, and a plurality of inductance portions connecting the center electrode and the ground electrode,
A sheet-like structure in which a slit for increasing the inductance component is provided in the capacitor lower electrode is obtained.

According to a second aspect of the invention,
The first predetermined number and the second predetermined number are both 2,
The capacitor upper electrode is disposed so as to be separated from each other in the predetermined direction, and is disposed so as to be in contact with an edge of the first main surface intersecting the predetermined direction.
The sheet-like structure described in the first aspect is obtained.

According to a third aspect of the invention,
Each of the first and second main surfaces has a first square shape composed of two sides extending in the predetermined direction and two sides extending in a direction orthogonal to the predetermined direction.
Each of the capacitor upper electrodes has a second rectangular shape having an area smaller than half of the area of the first square, and shares one of the sides extending in the orthogonal direction with the first square. Are arranged like this,
The ground electrode is a square frame having an outer shape that matches the first square.
Each of the capacitor lower electrodes has a third rectangular shape having an area smaller than half of the area of the first square, and is disposed apart from the ground electrode.
The central electrode has a fourth rectangular shape smaller than the third rectangular shape, and is disposed on a center point of the first square;
Each of the inductance portions connects the center electrode and the ground electrode on a line that passes through the center point of the first square and extends in the orthogonal direction.
The sheet-like structure described in the second aspect is obtained.

According to a fourth aspect of the invention,
The first predetermined number and the second predetermined number are both 4,
The capacitor upper electrodes are disposed so as to be spaced apart from each other, and are disposed so as to be in contact with an edge of the first main surface.
The sheet-like structure described in the first aspect is obtained.

According to a fifth aspect of the present invention,
Each of the first and second main surfaces has a first square shape with one side having a first predetermined length;
Each of the capacitor upper electrodes has a first right isosceles triangle shape having a base of a second predetermined length shorter than the first predetermined length,
The four first right-angled isosceles triangles are arranged such that the base is arranged on each side of the first square while the vertex is directed to the center point of the first square,
The ground electrode is a quadrangular frame having an outer shape that matches the first square and has a predetermined width,
The center electrode has a second square shape smaller than the first square, and is arranged on the center point of the first square in a state rotated by 45 degrees around the center point. Yes,
Each of the capacitor lower electrodes has a second right-angled isosceles triangle shape arranged so as to be separated from any one of the four inner sides of the square frame by a predetermined distance, with the vertex at the center portion. The sheet-like structure according to the fourth aspect having a second right-angled isosceles triangle shape connected to any one of the four vertices is obtained.

According to a sixth aspect of the present invention,
The sheet-like structure according to any one of the first to fifth aspects, in which slits are formed so as to extend from one side of the capacitor lower electrode toward the inner surface, is obtained.

According to a seventh aspect of the present invention,
Each of the slits is a sheet-like structure according to any one of the first to fifth aspects having a linear shape, a curved shape, or a combination thereof.

According to an eighth aspect of the present invention,
An antenna comprising the sheet-like structure according to any one of the first to seventh aspects, an antenna layer having an antenna pattern, and a dielectric formed on the first conductor layer of the sheet-like structure. An antenna device including a support layer is obtained.

According to a ninth aspect of the present invention,
The antenna device according to the eighth aspect, further including a shield layer made of a conductor having a solid pattern and a shield support layer made of a dielectric formed on the second conductor layer of the sheet-like structure. .

According to a tenth aspect of the present invention,
An RFID (100) comprising the antenna device according to any of the eighth and ninth aspects and an IC connected to the antenna pattern on the antenna support layer, wherein the sheet-like structure is a part of a tag base. Radio Frequency Identification) tag.

  According to the present invention, the inductance in the unit structure is increased. This means that the resonance frequency of the LC parallel resonance circuit, which is an equivalent circuit when the unit structure is viewed from the direction perpendicular to the main surface, is lowered. Therefore, the sheet-like structure can be miniaturized as understood by considering the scaling rule.

  In addition, when the resonance frequency is the same, the larger the inductance component and the smaller the capacitance component, the larger the surface impedance and the wider the frequency range in which in-phase reflection can be obtained.

It is a side view which shows roughly the unit structure in the sheet-like structure by the 1st Embodiment of this invention. 2A is a top view showing the dielectric layer and the first conductor layer shown in FIG. 1, and FIG. 2B shows the dielectric layer and the second conductor layer shown in FIG. It is a bottom view shown. It is a figure which shows an example which provided the slit in the capacity | capacitance lower electrode of 1st Embodiment. It is a figure which shows an example which provided the slit in the capacity | capacitance lower electrode of 1st Embodiment. It is a figure which shows an example which provided the slit in the capacity | capacitance lower electrode of 1st Embodiment. It is a figure which shows the equivalent circuit at the time of seeing the unit structure shown by FIG. 1 from upper direction. FIG. 4 is a diagram illustrating an equivalent circuit that can be replaced with the equivalent circuit of FIG. 3. It is a figure for demonstrating that the broadband of a high impedance area | region can be achieved by increasing an inductance. It is a figure which shows the conditions on the equivalent circuit for making a high impedance area | region into a broadband. It is a figure which shows the example which applied the sheet-like structure shown by FIG. 1 to the RFID tag. FIG. 8 is a top view of the RFID tag shown in FIG. 7. It is a top view of the sheet-like structure included in the RFID tag shown in FIG. It is a bottom view of the sheet-like structure contained in the RFID tag shown in FIG. It is a side view which shows roughly the unit structure in the sheet-like structure by the 2nd Embodiment of this invention. FIG. 15A is a top view showing the dielectric layer and the first conductor layer shown in FIG. 1, and FIG. 15B shows the dielectric layer and the second conductor layer shown in FIG. It is a bottom view shown. It is a figure which shows an example which provided the slit in the capacity | capacitance lower electrode of 2nd Embodiment.

(First embodiment)
The sheet-like structure having a high surface impedance according to the first embodiment of the present invention has a surface impedance for a specific frequency band due to a periodic structure in which unit structures as shown in FIG. 1 are repeatedly arranged in at least one direction. In this way, incident waves having frequencies belonging to the specific frequency band are reflected in phase.

  As shown in FIG. 1 and FIGS. 2A and 2B, the unit structure according to the present embodiment includes a dielectric layer 10, and a first conductor layer 20 formed on the upper surface of the dielectric layer 10. And a second conductor layer 30 formed on the lower surface of the dielectric layer 10. Here, as understood from FIGS. 2A and 2B, the upper surface and the lower surface of the unit structure in the present embodiment are both square. Hereinafter, this square is referred to as a first square.

  As shown in FIG. 2A, the first conductor layer 20 is composed of two capacitor upper electrodes 21 arranged so as to be separated from each other in the x direction. Each capacitor upper electrode 21 has a rectangular shape having an area smaller than half of the area of the first square. Hereinafter, this square is referred to as a second square. Each of the second squares in the present embodiment is a rectangle in which the side in the y direction is approximately twice as long as the side in the x direction. The capacitor upper electrode 21 is arranged so as to share the long side of the second square, that is, one of the sides extending in the y direction, with the side extending in the y direction of the first square. When juxtaposed in the x direction, adjacent capacitor upper electrodes 21 having unit structures are connected to each other.

  As shown in FIG. 2B, the second conductor layer 30 includes a square frame-shaped ground electrode 31 having the same outer shape as the first square, and two capacitance lower portions corresponding to the two capacitance upper electrodes 21. The electrode 32, the center electrode 33 disposed at the center of the first square, and two inductance portions 34 extending in the y direction and connecting the center electrode 33 and the ground electrode 31 are provided. Here, the capacitive lower electrode 32 has a third rectangular shape that is slightly smaller than the second rectangular shape, and is connected to the central electrode 33 in the x direction. The third square in the present embodiment is a rectangle having a side 32b in the x direction and a side 32a that is approximately twice as long as the side 32b. The center electrode 33 has a fourth rectangular shape that is smaller than the third square, and is disposed on the center point of the first square.

  Each of the two capacitor lower electrodes 32 is formed with a slit 35 for increasing the inductance component. The slit 35 in the present embodiment is formed to extend in a direction parallel to the long side 32a of the third square. The slit 35 of one capacitor lower electrode has a length that does not exceed the long side 32a, and is formed to extend from the short side 32b of the third square toward the surface. The other capacitor lower electrode is formed so that one capacitor lower electrode is rotated 180 degrees around the center electrode.

  In this embodiment, the slits formed in the two capacitor lower electrodes may be formed in a direction parallel to the short side 32b of the third square as shown in FIG. Further, as shown in FIG. 4, the direction in which the slit extends may be different between the two capacitor lower electrodes. Further, as shown in FIG. 5, one or more slits may be formed in one capacitor lower electrode.

  In particular, in the example shown in FIG. 5, a meander shape is formed by inserting one slit from each of the different short sides 32b for one capacitor lower electrode. This shape makes the loop through which the current flows longer, so that more inductance components can be obtained. The shape of the slit formed in the capacitor lower electrode is not limited to a linear shape. The shape of the slit may be, for example, a curved shape or a zigzag shape.

  Hereinafter, an increase in inductance component and its effect will be described.

  FIG. 6 represents the unit structure described above with an equivalent circuit. The unit structure described above may be expressed by an equivalent circuit as shown in FIG.

  When viewed from a plane wave incident on the unit structure from the upper surface of the first conductor layer 20, the equivalent circuits shown in FIGS. 6 and 7 can be simply approximated to an LC parallel resonant circuit in an appropriate frequency range. This can be expected from the fact that the gap between adjacent central electrodes 33 has a parallel connection structure of a gap and a continuous conductor.

Here, the surface admittance Ys (reciprocal of the surface impedance Zs) of the surface approximated by the LC parallel resonance circuit having the inductance L and the capacitance C can be expressed by the following formula (1). ω is an angular frequency, and j is an imaginary unit.

When the equation (1) is differentiated by ω, the following equation (2) is obtained.

Here, when the resonance angular frequency of the LC parallel circuit is ω ₀ and Equation (2) is modified using Equation (3) below, Equation (4) is obtained.

From equation (4), the amount of change of the surface admittance Ys in the vicinity of ω _{0 with} respect to the change in ω is obtained as in equation (5).

  As apparent from the equation (5), in the LC parallel resonance circuit, the amount of change with respect to the frequency change of the surface admittance at the resonance frequency is smaller as C is smaller (L is larger) and becomes j2C. That is, the surface impedance Zs, which is the reciprocal of the surface admittance Ys, is also less changed with respect to frequency as C is smaller (L is larger) (see FIG. 8).

FIG. 8 shows frequency characteristics of the surface impedance Zs that is the reciprocal of the surface admittance shown in the equation (1).

As shown in FIG. 8, in the frequency range where the absolute value of the surface impedance Zs is large, if the product of LC is constant, that is, if the resonance frequency ω ₀ is constant (L × C is constant), the larger L is and the smaller C is. It turns out that it becomes wide.

  Therefore, if the LC parallel resonant circuit is formed by combining a small capacitance and a large inductance as shown in FIG. 9, a broadband common-mode reflection effect can be obtained.

  According to the present embodiment, since the slit for increasing the inductance component is provided in the lower capacitance electrode, a frequency region exhibiting a high surface impedance can be made relatively wide. In addition, when a magnetic layer is applied to at least one of the first conductor layer 20 and the second conductor layer 30, a wider-band in-phase reflection effect can be obtained.

  Referring to FIGS. 10 to 13, an example in which the above-described sheet-like structure is applied to an RFID tag is shown. 10, 12, and 13, reference numerals 10 ′, 20 ′, and 30 ′ denote the dielectric layer 10, the first conductor layer 20, and the second conductor layer 30 having the unit structure described above, respectively. It is formed by periodically connecting in the direction. In addition, as the actual dielectric material, a relatively transparent material (which can be seen through at least inside) may be used. However, in FIGS. It is drawn.

  The illustrated RFID tag is an example of a 2.4 GHz metal-compatible tag, and includes a sheet-like structure formed by connecting five unit structures each having a planar shape of 12 × 12 mm in a row (in particular, FIG. 12 and FIG. 12). (See FIG. 13). As shown in FIGS. 10 and 11, an antenna support layer 40 made of a dielectric is formed on the first conductor layer 20 ′, and the antenna support layer 40 has a predetermined antenna pattern on the upper surface. An antenna layer 50 and an IC 60 connected to the antenna pattern are arranged. On the other hand, a shield support layer 70 is provided on the lower surface side of the second conductor layer 30 ′, and a shield layer 80 made of a solid pattern conductor is formed on the lower surface of the shield support layer 70. . Since the second conductor layer 30 ′ is not a solid electrode, when the tag is stuck on the metal surface, the performance may change due to the influence of the metal. Therefore, in the tag of this example, a shield layer 80 made of a conductor is provided in advance so as to be separated from the second conductor layer 30 ′ by a certain distance.

In this example, the dielectric layer 10 ', the antenna support layer 40, and the shield support layer 70 are made of PET (Polyethylene
Terephthalate) resin. On the other hand, the first conductor layer 20 ′, the second conductor layer 30 ′, the antenna layer 50, and the shield layer 80 are made of metal foil, more specifically, aluminum foil or copper foil. The distance between the first conductor layer 20 ′ and the second conductor layer 30 ′, that is, the thickness of the dielectric layer 10 ′ is 0.2 mm, and the first conductor layer 20 ′ and the antenna layer 50 , The thickness of the antenna support layer 40 is also 0.2 mm. The distance between the second conductor layer 30 'and the shield layer 80, that is, the thickness of the shield support layer 70 is 0.5 mm.

  As can be understood from FIG. 11, the antenna in this example is a dipole antenna including an antenna pattern 50 a having the x direction as the longitudinal direction and extending symmetrically in the longitudinal direction of the sheet-like structure 1 around the IC 60. The antenna element 50 according to the present embodiment is further provided with a beam portion conductor 50b for connecting the antenna conductor pattern 50a extending symmetrically for impedance matching. As understood from FIGS. 11 and 13, the longitudinal direction (x direction) of the dipole antenna and the longitudinal direction (y direction) of the inductance portion 34 are orthogonal to each other. Therefore, no induced current is generated in the inductance portion 34 by the antenna. Therefore, the conductor loss in the inductance part 34 is the minimum.

  In order to reduce the correlation between the sheet-like structure and the antenna layer 50 and the correlation between the sheet-like structure and the shield layer 80, the thickness of the antenna support layer 40 or the shield support layer 70 is increased, or a low dielectric constant. It is necessary to configure the antenna support layer 40 and the shield support layer 70 with a material having a ratio.

  Specifically, as a material of the antenna support layer 40 and the shield support layer 70, a general resin such as PET (Polyethylene Terephthalate) or PET-G (Polyethylene Terephthalate Glycol) or a dielectric such as plastic can be used. A resin having a low dielectric constant, a foam material containing air, sponge, urethane, fiber, polyethylene foam, acrylic foam and the like are preferable. In particular, the air layer and the holes concentrate the electric field in the air and lower the electric field in the material, which is effective in reducing the loss.

(Second Embodiment)
The sheet-like structure having a high surface impedance according to the second embodiment of the present invention has a surface impedance for a specific frequency band due to a periodic structure in which unit structures as shown in FIG. 14 are repeatedly arranged in at least one direction. In this way, incident waves having frequencies belonging to the specific frequency band are reflected in phase.

  As shown in FIG. 14, the unit structure according to the present embodiment is formed on the dielectric layer 110, the first conductor layer 120 formed on the upper surface of the dielectric layer 110, and the lower surface of the dielectric layer 110. And a second conductor layer 130. Here, as understood from FIGS. 15A and 15B, the upper surface and the lower surface of the unit structure in the present embodiment are both square. Hereinafter, this square is referred to as a first square.

  As shown in FIG. 15A, the first conductor layer 120 is composed of four capacitor upper electrodes 121 arranged so as to be separated from each other. Each capacitor upper electrode 121 is arranged in contact with each side of the first square, that is, the edge of the unit structure. Thereby, when unit structures are juxtaposed, the capacitor upper electrodes 121 of adjacent unit structures are connected to each other.

  More specifically, the capacitor upper electrode 121 in the present embodiment has a right-angled isosceles triangle shape having a base shorter than one side of the first square. Hereinafter, this isosceles right triangle is referred to as a first triangle. The bottom side of the first triangular capacitor upper electrode 121 is arranged on each side of the first square, and the vertex of the electrode 121 is arranged to face the center point of the first square.

  As shown in FIG. 15B, the second conductor layer 130 includes a frame-shaped ground electrode 131 having the same outer shape as the first square, and a center electrode 132 disposed at the center of the first square. The four capacitive lower electrodes 133 respectively connected to the central electrode 132 and the four inductance portions 134 for connecting the central electrode 132 and the ground electrode 131 between the four capacitive lower electrodes 133 are provided.

  Specifically, the ground electrode 131 is a rectangular frame designed so that its outer shape matches the first square and has a predetermined width. The center electrode 132 has a square shape having four sides shorter than the length of the bottom side of the capacitor upper electrode 121. Hereinafter, the square of the center electrode 132 is referred to as a second square. The center electrode 132 is formed by rotating the center electrode 132 around the center point of the first square by 45 degrees on the center point of the first square. That is, the diagonal of the first square and the diagonal of the second square are shifted by 45 degrees. The capacitor lower electrode 133 is provided to face the capacitor upper electrode 121, and in this embodiment, has a right isosceles triangle shape that is slightly smaller than the first triangle. Hereinafter, the right isosceles triangle of the capacitor lower electrode 133 is referred to as a second triangle. The second triangle in the present embodiment is an isosceles triangle having a long side 133a constituting the base and two short sides 133b having the same length. The long side 133a of the capacitor lower electrode 133 is located at a predetermined distance from the four inner sides of the square frame constituting the ground electrode 131, while the vertex of the second triangle is one-to-one with the vertex of the second square. It is connected to the.

  Each of the four capacitor lower electrodes 133 is formed with a slit 135 for increasing the inductance component. In the present embodiment, the slit 135 is formed to extend from the short side 133b of the second triangle toward the inner surface in a direction parallel to the long side 133a of the second triangle.

  In the present embodiment, one slit is formed in each of the four capacitor lower electrodes. However, as shown in FIG. 16, one or more slits may be formed in one capacitor lower electrode.

  In particular, in the example shown in FIG. 16, a meander shape is formed by inserting slits from different short sides 133b in one capacitor lower electrode. This shape makes the loop through which the current flows longer, so that more inductance components can be obtained. Note that the shape of the slit formed in the capacitor lower electrode is not limited to a linear shape, and may be, for example, a curved shape or a zigzag shape.

  Since the slit is formed in the capacitor lower electrode in the present embodiment and the inductance is increased, a frequency region exhibiting a high surface impedance can be made relatively wide. In addition, when a magnetic layer is applied to at least one of the first conductor layer 120 and the second conductor layer 130, L can be increased and C can be decreased in the surface impedance of the sheet-like structure. It is possible to further broaden the frequency band exhibiting the surface impedance.

  Note that the sheet-like structure according to the present embodiment described above can also be applied to the antenna device and the RFID tag as in the first embodiment.

DESCRIPTION OF SYMBOLS 10 Dielectric layer 20, 20 '1st conductor layer 21 Capacity | capacitance upper electrode 30, 30' 2nd conductor layer 31 Ground electrode 32 Capacity | capacitance upper electrode 32a Capacity | capacitance upper electrode long side 32b Capacity | capacitance upper electrode short side 33 Central electrode 34 Inductance Part 35 Slit 40 Antenna support layer 50 Antenna layer 60 IC
70 Shield Support Layer 80 Shield Layer 110 Dielectric Layer 120 First Conductor Layer 121 Capacitor Upper Electrode 130 Second Conductor Layer 131 Ground Electrode 131 Center Electrode 133 Capacitor Lower Electrode 133a Capacitor Lower Electrode Long Side 133b Capacitor Lower Electrode Short Side 134 Inductance part 135 Slit

Claims (8)

A sheet-like structure that enhances the surface impedance for a specific frequency band by a periodic structure in which unit structures are repeatedly arranged in a predetermined direction, thereby reflecting the incident wave having a frequency belonging to the specific frequency band in-phase. A sheet-like structure that can be supported;
The unit structure includes a dielectric layer having first and second main surfaces, a first conductor layer formed on the first main surface, and a first layer formed on the second main surface. 2 conductor layers,
The first conductor layer includes a first predetermined number of capacitive upper electrodes,
The second conductor layer is connected to the frame-shaped ground electrode having the same outer shape as the second main surface, a central electrode disposed at a central portion of the second main surface, and the central electrode. And a second predetermined number of capacitor lower electrodes arranged corresponding to the capacitor upper electrode, and a plurality of inductance portions connecting the center electrode and the ground electrode,
The capacitor upper electrode and the capacitor lower electrode are not in contact with each other,
A slit for increasing the inductance component is provided in the capacitor lower electrode ,
The first predetermined number and the second predetermined number are both 4, and each of the plurality of inductance portions has a linear shape .   2. The sheet-like structure according to claim 1, wherein the capacitor upper electrodes are disposed so as to be spaced apart from each other, and are disposed so as to be in contact with an edge of the first main surface. Each of the first and second main surfaces has a first square shape with one side having a first predetermined length;
Each of the capacitor upper electrodes has a first right isosceles triangle shape having a base of a second predetermined length shorter than the first predetermined length,
The four first right-angled isosceles triangles are arranged such that the base is arranged on each side of the first square while the vertex is directed to the center point of the first square,
The ground electrode is a quadrangular frame having an outer shape that matches the first square and has a predetermined width,
The center electrode has a second square shape smaller than the first square, and is arranged on the center point of the first square in a state rotated by 45 degrees around the center point. Yes,
Each of the capacitor lower electrodes has a second right-angled isosceles triangle shape arranged so as to be separated from any one of the four inner sides of the square frame by a predetermined distance, with the vertex at the center portion. The sheet-like structure according to claim 2 , which has a second right-angled isosceles triangle shape connected to any one of the four vertices. Sheet-like structure according to claim 1 to 3, wherein slits are formed so as to extend toward the inner surface from one side of the capacitor lower electrode. The slits are each, straight, curved or sheet-like structure according to claim 1 to 3, wherein a shape of a combination thereof. An antenna support comprising the sheet-like structure according to any one of claims 1 to 5 , an antenna layer having an antenna pattern, and a dielectric formed on the first conductor layer of the sheet-like structure. An antenna device comprising a layer. The antenna device according to claim 6 , further comprising: a shield layer made of a conductor having a solid pattern; and a shield support layer made of a dielectric formed on the second conductor layer of the sheet-like structure. An RFID (Radio) comprising the antenna device according to claim 6 and an IC connected to the antenna pattern on the antenna support layer, wherein the sheet-like structure is a part of a tag base. Frequency Identification) tag.

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