Antenna for RF tag

Abstract

Provided are an antenna for RF tags that operates in a wide frequency band, and an RF tag.　An antenna 1 for RF tags according to the present invention comprises an insulating substrate 10, a main waveguide element 20, a base plate 30 that is electrically connected to the main waveguide element, an auxiliary waveguide element 40 that is connected to the main waveguide element via an IC chip 60, and a capacitor 203 for frequency adjustment. At least part of the auxiliary waveguide element overlaps the base plate with a coating layer 70 composed of an insulating material interposed therebetween, whereby a capacitor is formed by the auxiliary waveguide element, the coating layer, and the base plate. The insulating substrate is enclosed in ring form by the main waveguide element, the base plate, and the auxiliary waveguide element. The capacitor for frequency adjustment is provided between the main waveguide element and the auxiliary waveguide element. Due to the insulating substrate being enclosed in ring form, inductance increases, a resistance value increases, and the Q value of a series resonance circuit decreases. As a result, a bandwidth increases, making it possible to obtain an antenna for RF tags that operates in a wide frequency band and an RF tag.

Description

RF tag antenna and RF tag

[0001] The present invention relates to an antenna for an RF tag that operates over a wide frequency band, and to an RF tag.

[0002] The RF tags used in RFID (Radio Frequency Identification) systems contain an antenna and an RF chip (IC chip), which receives the carrier wave transmitted from the antenna of the reader / writer and transmits the identification data recorded on the RF chip on a reflected wave back to the reader / writer, thereby achieving contactless communication.

[0003] RF tags are sometimes required to operate over a wide frequency band. For example, the dual RF tag disclosed in Patent Document 1 includes a low-band radiating element, a high-band radiating element, an inductor pattern, a balance coil, and an IC chip on its front surface, a ground element on its back surface, and an insulating substrate between the front and back surfaces, electrically connecting the ground element and balance coil. The low-band radiating element is connected to one end of the primary coil of the balance coil, the high-band radiating element is connected to the other end, and a ground element is connected to the midpoint of the primary coil. Since the ground element is connected to the midpoint of the primary coil, the tag has a two-coil configuration: the first coil extends from one end to the midpoint of the primary coil, and the second coil extends from the other end to the midpoint of the primary coil. The low-band radiating element functions as a low-frequency antenna, while the high-band radiating element functions as a high-frequency antenna, allowing the tag to operate over two frequency bands without switching between the low and high bands using a switch mechanism.

[0004] Furthermore, the dual RF tag of Patent Document 2 comprises an insulating substrate, a main waveguide element, a secondary waveguide element, a ground plane, a power feed section, and a short-circuit section to form a planar inverted-F antenna. By changing the position of the secondary waveguide element and changing the area of ​​the portion where the secondary waveguide element and the main waveguide element face each other, the wavelength λ of the radio wave can be switched between low and high frequencies.

[0005] International Publication No. 2019 / 039447 International Publication No. 2022 / 118595

[0006] The technology of Patent Document 1 uses two coils, a first coil and a second coil, as the primary coil. However, compared to a case where the primary coil is configured as a single coil extending from one end to the other, the configuration of Patent Document 1 reduces the transmission and reception power between the balance coil and the secondary coil by half. Thus, when operating in two frequency bands without a switch mechanism for switching between the low band and the high band, the transmission and reception power is reduced by half, resulting in a shorter communication distance. The technology of Patent Document 2 requires changing the position of the auxiliary waveguide element to switch between the low frequency side and the high frequency side, which results in the problems of time-consuming changeover work and high manufacturing costs.

[0007] In consideration of such problems, the present invention aims to provide an antenna for an RF tag and an RF tag that operate over a wide frequency band.

[0008] The RF tag antenna of the present invention comprises an insulating substrate, a main waveguide element, a ground plate electrically connected to the main waveguide element, a secondary waveguide element connected to the main waveguide element via an IC chip, and a frequency adjustment capacitor, wherein the main waveguide element is provided on the front surface of the insulating substrate and the ground plate is provided on the back surface of the insulating substrate, at least a portion of the secondary waveguide element overlaps with the ground plate via a coating layer made of an insulating material, thereby forming a capacitor with the secondary waveguide element, the coating layer, and the ground plate, and the main waveguide element, the ground plate, and the secondary waveguide element surround the insulating substrate in a ring shape, and the frequency adjustment capacitor is provided between the main waveguide element and the secondary waveguide element. Also, the frequency adjustment capacitor is characterized in that the frequency adjustment capacitor is a frequency adjustment element consisting of an insulator layer and a conductor layer, the insulator layer spans between the main waveguide element and the secondary waveguide element, and the conductor layer is disposed on the insulator layer.

[0009] The frequency adjustment capacitor is also characterized in that it comprises a first extension piece extending from the end of the main waveguide element toward the secondary waveguide element, a second extension piece facing the first extension piece and extending from the end of the secondary waveguide element toward the main waveguide element, and a gap formed between the tip of the first extension piece and the tip of the second extension piece.The frequency adjustment capacitor is also characterized in that it comprises an island-shaped piece arranged in an island shape between the main waveguide element and the secondary waveguide element, and gaps formed between the island-shaped piece and the main waveguide element and the secondary waveguide element.

[0010] The frequency adjusting capacitor may be provided between the ground plane and the secondary waveguide element. ... The frequency adjusting capacitor may be provided between the ground plane and the secondary waveguide element. The frequency adjusting capacitor may be provided between the ground plane and the secondary waveguide element. The frequency adjusting capacitor may be provided between the ground plane and the secondary waveguide element. The frequency adjusting capacitor may be provided between the ground plane and the secondary waveguide element. The frequency adjusting capacitor may be provided between the ground plane and the secondary waveguide element. The frequency adjusting capacitor may be provided between the ground plane and the secondary waveguide element. The frequency adjusting capacitor may be provided between the ground plane and the secondary waveguide element. The frequency adjusting capacitor may be provided between the ground plane and the secondary waveguide element. The frequency adjusting capacitor may be provided between the ground plane and the secondary waveguide element. The frequency adjusting capacitor may be provided between the ground plane and the secondary waveguide element. The frequency adjusting capacitor may be provided between the ground plane and the secondary waveguide element. The frequency adjusting capacitor may be provided between the ground plane and the secondary waveguide element. The frequency adjusting capacitor may be provided between the ground plane and the secondary waveguide element. The frequency adjusting capacitor may be provided between the ground plane and the secondary waveguide element. The frequency adjusting capacitor

[0011] The frequency adjustment capacitor is characterized by comprising a first extension piece extending from the end of the base plate toward the secondary waveguide element, a second extension piece opposing the first extension piece and extending from the end of the secondary waveguide element toward the primary waveguide element, and a gap formed between the tip of the first extension piece and the tip of the second extension piece.The frequency adjustment capacitor is characterized by comprising an island-shaped piece arranged in an island shape between the base plate and the secondary waveguide element, and a gap formed between the island-shaped piece and the base plate and / or the secondary waveguide element.The frequency adjustment capacitor is characterized by comprising an adhesive layer made of an insulating material.The frequency adjustment capacitor is characterized by comprising a notch on the side of the primary waveguide element.

[0012] The RF tag of the present invention comprises the RF tag antenna, the IC chip, and a resonant circuit that resonates in the frequency band of the radio waves, and the resonant circuit is characterized in that it is composed of an inductor pattern formed by the main wave element and the ground plane, the capacitor, and the IC chip.

[0013] In this invention, the insulating substrate is surrounded by a main waveguide element, a ground plane, and a secondary waveguide element in an annular shape to increase inductance La. Because the resistance value increases in the equation for inductive reactance XL = 2πfLa, the Q value of the series resonant circuit decreases based on the resistance value, resulting in a wider bandwidth and an RF tag antenna and RF tag that can operate over a wide frequency band. Furthermore, by locating a frequency adjustment capacitor parallel to the IC chip, f0 can be adjusted to a low value.

[0014] In addition, the capacitance of the capacitor can be adjusted by changing the area where the secondary waveguide element overlaps with the ground plane via the coating layer, thereby adjusting the resonant frequency. The RF tag can be attached to the conductor using an adhesive layer made of insulating material. In this case, a coupling capacitance capacitor is formed consisting of the ground plane, secondary waveguide element, adhesive layer, and conductor, allowing the conductor to be used as a director due to the capacitive coupling effect. By providing a notch on the side edge of the primary waveguide element, the wavelength of the radio waves transmitted from the reader and received by the primary waveguide element can be adjusted.

[0015] (a) to (c) are perspective views showing the structure of an RF tag antenna and an RF tag, and an enlarged front view of the circled area in FIG. 1(c). (d) is an equivalent circuit diagram of an RF tag. (a) and (b) are equivalent circuit diagrams of an RF tag without a frequency adjustment capacitor. (a) and (b) are graphs showing the radio wave frequency and reading distance of an RF tag antenna. (a) is a perspective view and a front view showing the state where an RF tag is installed on a conductor. (b) is an equivalent circuit diagram of an RF tag installed on a conductor. (a) is a plan view showing the structure of an RF tag antenna according to a second embodiment, (b) is a front view showing the structure of an RF tag, and (c) is an enlarged front view of the circled area in FIG. 6(b). 10(a) and 10(b) are equivalent circuit diagrams of an RF tag according to a second embodiment; a plan view showing the structure of an RF tag antenna according to a third embodiment (a) and an enlarged plan view of the circled portion in FIG. 9(a) (b); a plan view showing the structure of an RF tag antenna according to a fourth embodiment (a) and an enlarged plan view of the circled portion in FIG. 10(a) (b); an equivalent circuit diagram of an RF tag according to the fourth embodiment; plan views of an RF tag antenna according to a fifth embodiment (a) and (b); plan views of modified examples of an RF tag antenna according to the fifth embodiment (a) and (b); and diagrams (a) to (f) showing modified examples of an RF tag antenna and an RF tag.

[0016] [First embodiment] A first embodiment of an RF tag antenna and RF tag of the present invention will be described with reference to the drawings. As shown in Figures 1 and 2, the RF tag antenna 1 comprises an insulating substrate 10, a main waveguide element 20, a ground plate 30, a secondary waveguide element 40, a coating layer 70 made of an insulating material, and a frequency adjustment capacitor 203. The main waveguide element 20, the ground plate 30, and the secondary waveguide element 40 are formed on the surface of the coating layer 70. The RF tag 2 is constructed by attaching an IC chip 60 to the RF tag antenna 1.

[0017] The insulating substrate 10 has a front surface 11, a back surface 12, and side surfaces 13. The shape of the insulating substrate 10 is, for example, a substantially rectangular parallelepiped, but is not limited to this and may be, for example, a disk-like or arc-shaped curved shape. The insulating substrate 10 preferably has a shape that corresponds to the surface shape of the object to which the RF tag 2 is to be attached. For example, if the object to be attached is cylindrical and the RF tag 2 is to be attached to its curved surface, it is preferable that the shape of the RF tag 2 matches the curvature of the curved surface. The insulating substrate 10 may be made of polystyrene foam, polyethylene, polyimide, or the like. Alternatively, the insulating substrate 10 may be made of a dielectric material such as ceramic, paper, or resin.

[0018] The main waveguide element 20 is provided on the surface 11 of the insulating substrate 10. The main waveguide element 20 of this embodiment has a rectangular shape and is formed by well-known methods such as etching a thin metal film such as aluminum or pattern printing. The ground plane 30 is electrically connected to the main waveguide element 20 and is provided on the back surface 12 of the insulating substrate 10. The ground plane 30 of this embodiment has a rectangular shape and is formed on the surface of the coating layer 70 by well-known methods such as etching a thin metal film such as aluminum or pattern printing, similar to the main waveguide element 20.

[0019] As shown in Figures 1(a) and 1(d), the secondary waveguide element 40 is not directly (physically) connected to the primary waveguide element 20; that is, the edges are disconnected. A protrusion 41 is provided on a portion of the side edge of the secondary waveguide element 40, and a protrusion 23 is provided on a portion of the side edge of the primary waveguide element 20. The secondary waveguide element 40 and the primary waveguide element 20 are connected via the IC chip 60 by connecting one terminal of the IC chip 60 to the protrusion 41 and the other terminal to the protrusion 23 of the primary waveguide element 20. Note that both terminals of the IC chip 60 may be directly connected to the secondary waveguide element 40 and the primary waveguide element 20 without providing the protrusions 23 and 41. As shown in Figure 1(b), the coating layer 70 is folded at the edge of the insulating substrate 10 (see arrows) and attached to the insulating substrate 10 via an adhesive layer (not shown). As a result, as shown in Figures 1(c) and (d), at least a portion of the secondary waveguide element 40 overlaps with the ground plane 30 via the coating layer 70, and the secondary waveguide element 40, the coating layer 70, and the ground plane 30 form a capacitor 80 (see Figure 2).

[0020] In this embodiment, the main waveguide element 20, the ground plane 30, and the secondary waveguide element 40 are formed on the surface of the coating layer 70, but the coating layer 70 need only be present in the area where the secondary waveguide element 40 and the ground plane 30 overlap. As will be described in detail later, the resonant frequency can be adjusted by changing the area of ​​the portion where the secondary waveguide element 40 overlaps with the ground plane 30 via the coating layer 70. The material of the coating layer 70 is not particularly limited as long as it is flexible and insulating, and examples of such materials include PET, polyimide, and vinyl. The thickness of the coating layer 70 is not particularly limited, but is generally approximately several tens of micrometers. The main waveguide element 20, the ground plane 30, and the secondary waveguide element 40 surround the insulating substrate 10 in a ring shape.

[0021] The main wave element 20 is preferably designed so that the total length L of its side edges 21a to 21i is any one of λ / 4, λ / 2, 3λ / 4, and 5λ / 8, where λ is the wavelength of the radio wave transmitted from the reading device. In this embodiment, the length of the side edges of the main wave element 20 is adjusted to be large by providing a notch 22 in the side edge. The main wave element 20 may also be configured without the notch 22.

[0022] The frequency adjusting capacitor 203 is provided between the main waveguide element 20 and the secondary waveguide element 40. The frequency adjusting capacitor 203 of this embodiment is composed of a frequency adjusting element 200 including an insulator layer 201 and a conductor layer 202. The insulator layer 201 is made of an insulator and is disposed between the main waveguide element 20 and the secondary waveguide element 40. The conductor layer 202 is disposed on the insulator layer 201. The conductor layer 202 needs to be long enough to overlap with the main waveguide element 20 and the secondary waveguide element 40. In this way, the upper part of the insulator layer 201 is covered with the conductor layer 202, and part of the lower part of the insulator layer 201 is covered with the main waveguide element 20 and the secondary waveguide element 40, thereby forming the frequency adjusting capacitor 203.

[0023] The IC chip 60 operates based on the radio waves received by the RF tag antenna 1. Specifically, the IC chip 60 rectifies a portion of the carrier waves transmitted from the reader and generates the power supply voltage required for operation. The generated power supply voltage is then used by the IC chip 60 to operate the control logic circuit within the IC chip 60 and the non-volatile memory that stores product-specific information, etc., and to operate the communication circuit for transmitting and receiving data to and from the reader.

[0024] Next, we will explain the configuration of an RF tag antenna that does not include the frequency adjustment capacitor 203, that is, the configuration of an RF tag antenna in which the frequency adjustment capacitor 203 is deleted from the configuration shown in Figure 1. In an RF tag antenna that does not include the frequency adjustment capacitor 203, a resonant circuit is configured to resonate in the frequency band of the radio waves to be received. This resonant circuit is configured by an inductor pattern, a capacitor 80, and an IC chip 60, as shown in the equivalent circuit diagram of Figure 3. The inductor pattern is configured by the primary waveguide element 20 and the ground plane 30. The primary waveguide element 20 and the secondary waveguide element 40 are connected by the equivalent capacitance of the IC chip 60. As described above, the capacitor 80 is configured by the secondary waveguide element 40, the coating layer 70, and the ground plane 30.

[0025] Some IC chips 60 include an internal capacitor and have stray capacitance. Therefore, when setting the resonant frequency of the resonant circuit, it is preferable to take into account the equivalent capacitance within the IC chip 60. In other words, it is preferable that the resonant circuit has a resonant frequency set taking into account the inductance of the inductor pattern L, the capacitance of the capacitor 80, and the equivalent capacitance within the IC chip 60. The resonant frequency f0 [Hz] of this series resonant circuit is given by equation (1). It is preferable to set the value of the resonant frequency f0 to be approximately the center value of the frequency bandwidth of the multiple radio waves transmitted from the reader. Here, La is the inductance of the inductor pattern, Ca is the capacitance of the capacitor 80, and Cb is the equivalent capacitance inside the IC chip 60. Note that, for example, a capacitance value published as one of the specifications of the IC chip 60 to be used can be used as Cb.

[0026] By taking the equivalent capacitance inside the IC chip 60 into consideration in this way, the resonant frequency f0 of the resonant circuit can be set accurately to the frequency band of the radio waves. As a result, the reading performance of the RF tag 2 can be improved. Furthermore, the power supply voltage generated by the IC chip 60 can be increased. Compared to FIG. 3(a), FIG. 3(b) shows a case where the area of ​​the portion where the auxiliary waveguide element 40 overlaps with the ground plate 30 via the coating layer 70 is relatively large (see the circled area in FIG. 3(b)). In this way, by changing the area of ​​the portion where the auxiliary waveguide element 40 overlaps with the ground plate 30 via the coating layer 70, Ca can be adjusted, and therefore the resonant frequency f0 can be adjusted.

[0027] In addition, in an RF tag antenna that does not include the frequency adjustment capacitor 203, the inductance La can be increased by annularly surrounding the insulating substrate 10 with the primary waveguide element 20, the ground plane 30, and the secondary waveguide element 40. L In the equation (πfLa), the resistance value increases, and the Q value of the series resonant circuit decreases based on the resistance value, resulting in a wider bandwidth and an RF tag antenna and RF tag that can operate over a wide frequency band. Increasing the inductance La also increases the impedance and lowers the resonant frequency. As a result, tuning to the target resonant frequency f0 becomes difficult. However, by setting the capacitance C, which combines the electrostatic capacitance Ca of the capacitor 80 and the equivalent capacitance Cb within the IC chip 60, C = 1 / Ca + 1 / Cb, so the capacitance becomes smaller and it becomes possible to tune to the target resonant frequency f0.

[0028] 1 and 2, the RF tag antenna 1 of the present invention is characterized by including a frequency adjustment capacitor 203 (frequency adjustment element 200). When the dimensions of the insulating substrate 10 are reduced to miniaturize the RF tag, the main wave element 20 and ground plane 30 that make up the inductor pattern L also become smaller. As a result, the frequency f0 in the above formula (1) becomes high, which may cause it to fall outside the desired frequency band. Therefore, by providing the frequency adjustment capacitor 203 parallel to the IC chip 60, the resonant frequency f0 [Hz] is given by formula (2), and f0 can be adjusted to a low value. Here, La is the inductance of the inductor pattern L, Ca is the capacitance of the capacitor 80, Cb is the equivalent capacitance inside the IC chip 60, and Cc is the capacitance of the frequency adjusting capacitor 203.

[0029] In addition, in Japanese Patent No. 6705116 of the present applicant, both ends of the short-circuited part are electrically connected to the first and second waveguide elements to form a planar inverted-F antenna (see FIG. 4C of Japanese Patent No. 6705116). On the other hand, in the RF tag antenna 5 of this embodiment, an insulator layer 201 is placed across the primary waveguide element 20 and the secondary waveguide element 40, and a conductor layer 202 is placed on top of that. In other words, it should be noted that the conductor layer 202 is not electrically connected to the primary waveguide element 20 and the secondary waveguide element 40, and the RF tag antenna 5 does not form a planar inverted-F antenna.

[0030] Figure 4 is a graph showing the radio wave frequency (horizontal axis) and reading distance (vertical axis) of RF tag antenna 1. As a result of lowering the Q value and widening the bandwidth, it can be seen that a single RF tag 2 can handle two frequency bands: the low frequency side (around 860 MHz) used mainly in Europe, and the high frequency side (around 920 MHz) used mainly in Japan.

[0031] 5 and 6, an RF tag 2 attached to a conductor 100 will be described. The RF tag 2 of the present invention can be used as is, or can be brought into contact with the conductor 100. Specifically, the back side of the RF tag 2 can be attached to the conductor 100 using an adhesive layer 101 made of an insulating material. In this application, the term "conductor" is the same as its general dictionary meaning: "a general term for a substance with a relatively high electrical conductivity," with metal being a typical example. However, the term "conductor" is not limited to metal, and may be, for example, the human body, grass, trees, water, the ground, etc.

[0032] By attaching the RF tag 2 to the conductor 100 using the adhesive layer 101, a capacitor 81 with a coupling capacitance C is formed, which is made up of the ground plane 30, the sub-wavedirection element 40, the adhesive layer 101, and the conductor 100, and the conductor 100 can be used as a director due to the capacitive coupling effect. In this case, as shown in Fig. 5, the RF tag 2 can receive not only radio waves that reach the front side of the conductor 100, but also radio waves that reach the back side of the conductor 100. The "front side of the conductor" line in Fig. 4 shows the case where radio waves that reach the front side of the conductor 100 are read, and the "back side of the conductor" line shows the case where radio waves that reach the back side of the conductor 100 are read.

[0033] [Second Embodiment] A second embodiment of the RF tag antenna and RF tag of the present invention will be described with reference to the drawings. Components identical to those in the first embodiment are designated by the same reference numerals and will not be described again. As shown in FIGS. 7 and 8 , the RF tag antenna 3 of this embodiment connects the secondary waveguide element 40 and the ground plane 30 via an IC chip 60. This embodiment is characterized in that at least a portion of the secondary waveguide element 40 overlaps the primary waveguide element 20 via a coating layer 70, thereby forming a capacitor 82 with the secondary waveguide element 40, the coating layer 70, and the primary waveguide element 20. The insulating substrate 10 is surrounded by the primary waveguide element 20, the ground plane 30, and the secondary waveguide element 40 in a ring shape. A frequency adjustment capacitor 203 is provided between the ground plane 30 and the secondary waveguide element 40. The resonant frequency can be adjusted by changing the area of ​​the portion where the secondary waveguide element 40 overlaps the primary waveguide element 20 via the coating layer 70.

[0034] In the RF tag antenna 3, a resonant circuit is configured to resonate in the frequency band of the radio waves to be received. This resonant circuit is configured from an inductor pattern, a capacitor 82, a frequency adjustment capacitor 203, and an IC chip 60, as shown in the equivalent circuit diagram of Fig. 8. The inductor pattern is configured from the main waveguide element 20 and the ground plane 30. The secondary waveguide element 40 and the ground plane 30 are connected by the equivalent capacitance of the IC chip 60. As described above, the capacitor 82 is configured from the secondary waveguide element 40, the coating layer 70, and the main waveguide element 20.

[0035] In the present invention, the inductance La is increased by surrounding the insulating substrate 10 in an annular shape with the main waveguide element 20, the ground plane 30, and the sub-directive element 40. L = 2πfLa, the resistance value increases, and the Q value of the series resonant circuit decreases based on the resistance value, resulting in a wider bandwidth and an RF tag antenna 3 and an RF tag 4 that operate over a wide frequency band. Compared to Fig. 8(a), Fig. 8(b) shows a case where the area of ​​the portion where the secondary waveguide element 40 overlaps with the primary waveguide element 20 via the coating layer 70 is relatively large (see the circled area in Fig. 8(b)). In this way, by changing the area of ​​the portion where the secondary waveguide element 40 overlaps with the primary waveguide element 20 via the coating layer 70, Ca in the above formula (2) can be adjusted, thereby adjusting the resonant frequency f0.

[0036] [Third embodiment] A third embodiment of the RF tag antenna and RF tag of the present invention will be described with reference to the drawings, but parts having the same configuration as those of the above-mentioned embodiments will be assigned the same reference numerals and their description will be omitted. As shown in Fig. 9, this embodiment is characterized in that the frequency adjustment capacitor 203 is composed of a first extension piece 204 extending from the end of the main waveguide element 20 toward the secondary waveguide element 40, a second extension piece 205 opposing the first extension piece 204 and extending from the end of the secondary waveguide element 40 toward the main waveguide element 20, and a gap 206 formed between the tip of the first extension piece and the tip of the second extension piece.

[0037] Specifically, the first extension piece 204 is T-shaped and is composed of a base portion 204a extending from the end of the secondary waveguide element 20 toward the secondary waveguide element 40, and a tip portion 204b extending from the tip of the base portion 204a in a direction perpendicular to the base portion 204a. The second extension piece 205 is also T-shaped and is composed of a base portion 205a extending from the end of the secondary waveguide element 40 toward the primary waveguide element 20, and a tip portion 205b extending from the tip of the base portion 205a in a direction perpendicular to the base portion 205a. The two tip portions 204b, 205b are arranged in parallel with a gap 206 between them. The first extension piece and the second extension piece are formed by well-known techniques such as etching or pattern printing of a metal thin film such as aluminum. The two tip portions 204b, 205b and the gap 206 form a capacitor. By providing a frequency adjustment capacitor in a position parallel to the IC chip 60, the resonance frequency f0 [Hz] is given by the above formula (2), and f0 can be adjusted to a low value. Also, by changing the length of the tip portions 204b and 205b and the width of the gap 206, the capacitance C C can be changed to adjust f0.

[0038] [Fourth embodiment] A fourth embodiment of the RF tag antenna and RF tag of the present invention will be described with reference to the drawings. Components having the same configuration as those of the above embodiments will be assigned the same reference numerals and their description will be omitted. As shown in Figure 10, this embodiment is characterized in that the frequency adjustment capacitor is composed of an island-shaped piece 207 arranged in an island shape between the main waveguide element 20 and the secondary waveguide element 40, and gaps 208a to 208d formed between the island-shaped piece 207 and the main waveguide element 20 and the secondary waveguide element 40. The island-shaped piece 207 is formed by a well-known method such as etching a thin metal film such as aluminum or pattern printing.

[0039] In this embodiment, two island pieces 207 are arranged with the IC chip 60 sandwiched between them, forming four gaps 208a to 208d, which form four capacitors 209a to 209d as frequency adjustment capacitors as shown in FIG. 11. In this case, the capacitance C ｄis given by equation (3). By providing a frequency adjustment capacitor in a position parallel to the IC chip 60, the resonant frequency f0 [Hz] is given by equation (4), and f0 can be adjusted to a low value. In addition, by changing the length and width of the island-shaped piece 207 and the width of the gaps 208a to 208d, the capacitance C ｄ It is possible to adjust f0 by changing the value of the island-shaped piece 207. It is also possible to arrange only one island-shaped piece 207, or three or more island-shaped pieces 207. Here, Cd is the capacitance of the frequency adjustment capacitor, C1 is the capacitance of capacitor 209a, C2 is the capacitance of capacitor 209b, C3 is the capacitance of capacitor 209c, and C4 is the capacitance of capacitor 209d. Here, La is the inductance of the inductor pattern L, Ca is the capacitance of the capacitor 80, Cb is the equivalent capacitance inside the IC chip 60, and Cd is the capacitance of the frequency adjustment capacitor.

[0040] [Fifth Embodiment] A fourth embodiment of the RF tag antenna and RF tag of the present invention will be described with reference to the drawings. The same components as those in the above embodiments will be designated by the same reference numerals and will not be described again. As shown in Fig. 12(a), in this embodiment, an L-shaped slit 42 is provided in a portion of the secondary waveguide element 40 to form a tongue-shaped piece 210. The base of the tongue-shaped piece 210 is bent along the dotted line and joined to the back surface of the primary waveguide element 20 via an insulator to insulate the primary waveguide element 20 from the tongue-shaped piece 210, as shown in Fig. 12(b), to form a frequency adjustment capacitor. The frequency adjustment capacitor is composed of the primary waveguide element 20, the secondary waveguide element 40, a coating layer 70 made of insulating material, and the tongue-shaped piece 210.

[0041] Although not shown, a frequency adjustment capacitor may be formed by forming a tongue-shaped piece by providing a slit in a portion of the primary waveguide element 20, bending the base of the tongue-shaped piece, and joining it to the rear surface of the secondary waveguide element 40 via an insulator to insulate the secondary waveguide element 40 from the tongue-shaped piece. Alternatively, as shown in FIG. 13(a), a frequency adjustment capacitor may be formed by providing an L-shaped slit 42 in a portion of the secondary waveguide element 40 to form a tongue-shaped piece 210, bending the base of the tongue-shaped piece 210 at the dotted line, and joining it to the rear surface of the base plate 30 via an insulator to insulate the base plate 30 from the tongue-shaped piece 210, as shown in FIG. 13(b). The frequency adjustment capacitor is composed of the base plate 30, the secondary waveguide element 40, a coating layer 70 made of an insulating material, and the tongue-shaped piece 210. Alternatively, a frequency adjustment capacitor may be formed by providing a slit in a portion of the base plate 30 to form a tongue-shaped piece, bending the base of the tongue-shaped piece, and joining it to the rear surface of the secondary waveguide element 40.

[0042] [Fourth embodiment] Fig. 14 comprehensively shows modified examples of the RF tag antenna and RF tag of the present invention. Fig. 14(a) shows a configuration in which the secondary waveguide element 40, the primary waveguide element 20, and the ground plane 30 are wound around the insulating substrate 10 with the coating layer 70 in contact with the insulating substrate 10, and the surface of the secondary waveguide element 40 is partially covered by the ground plane 30. Fig. 14(b) shows a configuration in which the secondary waveguide element 40, the ground plane 30, and the primary waveguide element 20 are wound around the insulating substrate 10 with the coating layer 70 in contact with the insulating substrate 10, and the surface of the secondary waveguide element 40 is partially covered by the primary waveguide element 20. Fig. 14(c) shows a configuration in which the primary waveguide element 20 and the ground plane 30 are wound around the insulating substrate 10 with the coating layer 70 exposed to the outside, i.e., turned upside down from the state shown in Fig. 1(a), and the secondary waveguide element 40 partially covers the surface of the ground plane 30. In this configuration, the IC chip 60 is not exposed to the outside, reducing the risk of damage. Figure 14(d) shows a configuration in which the main waveguide element 20 and the ground plane 30 are wrapped around the insulating substrate 10 with the coating layer 70 exposed to the outside, and a portion of the surface of the main waveguide element 20 is covered with the secondary waveguide element 40. Figure 14(e) shows a configuration in which the secondary waveguide element 40, the main waveguide element 20, and the ground plane 30 are wrapped around the insulating substrate 10 with the coating layer 70 exposed to the outside, and a portion of the ground plane 30 covers the surface of the secondary waveguide element 40. Figure 14(f) shows a configuration in which the secondary waveguide element 40, the ground plane 30, and the main waveguide element 20 are wrapped around the insulating substrate 10 with the coating layer 70 exposed to the outside, and a portion of the surface of the secondary waveguide element 40 is covered with the primary waveguide element 20. All of the configurations shown in Figures 14(a) to 14(f) provide RF tag antennas and RF tags that operate over a wide frequency band. Note that a frequency adjustment capacitor is provided in each of the configurations shown in FIGS. 14(a) to 14(f).

[0043] INDUSTRIAL APPLICABILITY The present invention provides an RF tag antenna and an RF tag that operate over a wide frequency band, and has industrial applicability.

[0044] DESCRIPTION OF SYMBOLS 1 RF tag antenna 2 RF tag 3 RF tag antenna 4 RF tag 5 RF tag antenna 6 RF tag 10 Insulating substrate 11 Surface 12 Back surface 13 Side surface 20 Primary waveguide element 21a to 21i Side edge 22 Notch 23 Convex portion 30 Ground plate 40 Secondary waveguide element 41 Convex portion 42 Slit 60 IC chip 70 Coating layer 80 Capacitor 81 Capacitor 82 Capacitor 100 Conductor 101 Adhesive layer 200 Frequency adjustment element 201 Insulating layer 202 Conductive layer 203 Frequency adjustment capacitor 204 First extension piece 204a Base 204b Tip 205 Second extension piece 205a Base 205b Tip 206 Gap 207 Island-shaped piece 208a to 208d Gap 209a to 209d Condenser 210 Tongue

Claims

1. It includes an insulating substrate, a main waveguide element, a ground plane electrically connected to the main waveguide element, a sub-waveguide element connected to the main waveguide element via an IC chip, and a frequency adjustment capacitor. The main waveguide element is provided on the surface of the insulating substrate, and the ground plane is provided on the back surface of the insulating substrate. At least a part of the sub-waveguide element overlaps with the ground plane through a coating layer made of an insulating material, so that a capacitor is formed by the sub-waveguide element, the coating layer, and the ground plane, and the insulating substrate is surrounded in a ring shape by the main waveguide element, the ground plane, and the sub-waveguide element. The frequency adjustment capacitor is provided between the main waveguide element and the sub-waveguide element. The frequency adjustment capacitor is composed of a first extension piece extending from an end of the main waveguide element toward the sub-waveguide element side, a second extension piece extending from an end of the sub-waveguide element toward the main waveguide element side facing the first extension piece, and a gap formed between the tip of the first extension piece and the tip of the second extension piece. An antenna for an RF tag characterized by this.

2. It includes an insulating substrate, a main waveguide element, a ground plane electrically connected to the main waveguide element, a sub-waveguide element connected to the main waveguide element via an IC chip, and a frequency adjustment capacitor. The main waveguide element is provided on the surface of the insulating substrate, and the ground plane is provided on the back surface of the insulating substrate. At least a part of the sub-waveguide element overlaps with the ground plane through a coating layer made of an insulating material, so that a capacitor is formed by the sub-waveguide element, the coating layer, and the ground plane, and the insulating substrate is surrounded in a ring shape by the main waveguide element, the ground plane, and the sub-waveguide element. The frequency adjustment capacitor is provided between the main waveguide element and the sub-waveguide element. The frequency adjustment capacitor is composed of an island-shaped piece arranged in an island shape between the main waveguide element and the sub-waveguide element, and a gap formed between the island-shaped piece and the main waveguide element and the sub-waveguide element. The antenna for RF tag is characterized by this.

3. An insulating substrate, a main waveguide element, a ground plane electrically connected to the main waveguide element, a sub-waveguide element connected to the ground plane via an IC chip, and a frequency adjustment capacitor are provided. The main waveguide element is provided on the surface of the insulating substrate, and the ground plane is provided on the back surface of the insulating substrate. At least a part of the sub-waveguide element overlaps with the main waveguide element via a coating layer made of an insulating material, so that a capacitor is formed by the sub-waveguide element, the coating layer, and the main waveguide element, and the insulating substrate is surrounded in a ring shape by the main waveguide element, the ground plane, and the sub-waveguide element. The frequency adjustment capacitor is provided between the ground plane and the sub-waveguide element. The antenna for RF tag is characterized by this.

4. The frequency adjustment capacitor is composed of a frequency adjustment element composed of an insulator layer and a conductor layer. The insulator layer is stretched between the ground plane and the sub-waveguide element. The conductor layer is arranged on the insulator layer. The antenna for RF tag according to claim 3 is characterized by this.

5. The frequency adjustment capacitor is composed of a first extension piece extending from the end of the ground plane toward the sub-waveguide element side, a second extension piece extending from the end of the sub-waveguide element toward the main waveguide element side facing the first extension piece, and a gap formed between the tip of the first extension piece and the tip of the second extension piece. The antenna for RF tag according to claim 3 is characterized by this.

6. The frequency adjustment capacitor is composed of an island-shaped piece arranged in an island shape between the ground plane and the sub-waveguide element, and a gap formed between the island-shaped piece and the ground plane and / or the sub-waveguide element. The antenna for RF tag according to claim 3 is characterized by this.