JP2008125115A - Composite antenna - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a composite antenna which operates not only at a high-frequency band used for a radio wave system, but also at a low-frequency band used in electromagnetic induction systems. <P>SOLUTION: The composite antenna comprises a first antenna which operates at a first frequency band, utilized for a radio wave system of a UHF band or a 2.45 GHz band and is a patch antenna in which a radiation conductor and a grounding conductor are provided on one surface and on the other surface, respectively, a second antenna which operates at a second frequency band utilized for an electromagnetic induction system which uses a frequency band lower than a first frequency band and has a coil-shaped conductor, and a holding member consisting of a dielectric that integrally holds the first antenna and the second antenna, wherein the thicknesses of the radiation conductor layer and the grounding conductor layer which are the conductor layers forming the first antenna are made smaller than the skin depth, through which the current of the second frequency band flows, and the thickness of the conductor layer that forms the second antenna is made larger than the skin depth, through which the current of the second frequency band flows. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a composite antenna that operates in a plurality of different frequency bands.

Conventionally, as a composite antenna that operates in a plurality of different frequency bands, a circularly polarized loop antenna for 1.5 GHz band is formed on a dielectric substrate, and a rectangular patch antenna for 5.8 GHz band on substantially the same axis. (For example, refer to Patent Document 1).
JP 2003-152445 A

  Incidentally, in recent years, an RFID (Radio Frequency Identification) system is known as an automatic recognition technique using radio. The RFID system performs wireless communication between an interrogator called a reader / writer or the like and a responder called an RFID tag or the like. As a transmission method at that time, in addition to an electromagnetic coupling method using mutual induction of coils by an alternating magnetic field, an electromagnetic induction method using a frequency of 135 kHz or lower or 13.56 MHz as a frequency, a UHF band of 860 to 960 MHz, or 2 The radio system using the .45 GHz band is adopted.

  In particular, the electromagnetic induction method using the 13.56 MHz band is used in a non-contact IC card system which is an aspect of the RFID system, and is adopted in most countries. On the other hand, although the radio system using the UHF band of 860 to 960 MHz can be used in Europe and the United States, it was assigned to a mobile phone etc. in Japan and was not allowed to be used in the RFID system. Recently, an action has been started so that the 950 to 956 MHz band can be used in the RFID system. Therefore, development of a composite antenna that operates not only in the 13.56 MHz band but also in the 950 to 956 MHz band has been desired. By developing this type of composite antenna, it is possible to obtain a reader / writer antenna that can be used not only for an RFID system using the 13.56 MHz band but also for an RFID system using the 950 to 956 MHz band.

  However, the conventional composite antenna corresponds to two frequency bands used in the radio wave system such as 1.5 GHz band and 5.8 GHz band, for example, 950 MHz band and 13.56 MHz band. However, there was no one corresponding to the two frequency bands respectively used in the radio wave system and the electromagnetic induction system.

  The present invention has been made based on such circumstances, and its purpose is not only to operate in the high frequency band used in the radio wave system, but also to operate in the low frequency band used in the electromagnetic induction system. It is intended to provide a composite antenna.

  The composite antenna of the present invention is a patch antenna in which a radiation conductor is provided on one surface and a ground conductor is provided on the other surface, and in the first frequency band used in the radio system of the UHF band or 2.45 GHz band. A first antenna that operates, a second antenna having a coiled conductor that operates in a second frequency band utilized in an electromagnetic induction system lower than the first frequency band, and the first antenna and the second antenna And holding portions made of a dielectric that integrally hold the first and second antennas, and the thicknesses of the radiation conductor layer and the ground conductor layer, which are conductor layers forming the first antenna, are both in the second frequency band. It is thinner than the skin depth through which the current flows, and the thickness of the conductor layer forming the second antenna is greater than or equal to the skin depth through which the current in the second frequency band flows.

  According to the present invention in which such measures are taken, it is possible to provide a composite antenna that operates not only in the high frequency band used in the radio wave system but also in the low frequency band used in the electromagnetic induction system.

The best mode for carrying out the present invention will be described below with reference to the drawings.
[First Embodiment]
First, the composite antenna 10 which is the 1st Embodiment of this invention is demonstrated using FIGS. 1-4. FIG. 1 is an external perspective view of the composite antenna 10, FIG. 2 is an exploded perspective view of the composite antenna 10, and FIG. 3 is an enlarged view taken along the line AA in FIG. 1.

  The composite antenna 10 is used in the electromagnetic induction system as a first antenna 11 that operates in a 950 MHz band, for example, which is used in a radio wave system as a first frequency band, and in a second frequency band lower than the first frequency band. For example, the second antenna 12 operating in the 13.56 MHz band is provided. The first antenna 11 and the second antenna 12 are integrated by laminating a holding substrate 13 made of a dielectric.

  The first antenna 11 includes a first dielectric substrate 111, a radiation conductor (patch electrode) 112 disposed on one surface side of the first dielectric substrate 111, and the first dielectric substrate 111. And a grounding conductor (ground) 113 disposed on the other surface side of the. The second antenna 12 includes a second dielectric substrate 121, a coiled conductor pattern 122 disposed on one surface side of the second dielectric substrate 121, and the other of the second dielectric substrate 121. It is comprised from the rod-shaped conductor pattern 123 arrange | positioned at the surface side. The first dielectric substrate 111, the second dielectric substrate 121, and the holding substrate 13 are all rectangular and of the same size.

  In the first antenna 11, the ground conductor 113 is a rectangular conductor pattern having substantially the same area as the first dielectric substrate 111, and is provided on the holding substrate 13. The radiating conductor 112 is a substantially rectangular conductor pattern having an area smaller than that of the first dielectric substrate 111, and is provided at substantially the center on the first dielectric substrate 111. The radiation conductor 112 is notched in a concave shape on one side, and the conductor pattern 114 is extended from the bottom of the notch to one side of the dielectric substrate 111.

  The conductor pattern 114 functions as a feed line to the radiation conductor 112. That is, although not shown, the core wire on one end side of the coaxial cable is connected to the conductor pattern 114, the outer line on one end side is connected to a part of the ground conductor 113, and the other end side of the coaxial cable is connected to the radio wave system. Connect to a wireless device that performs wireless communication. By doing so, the first antenna 11 performs a transmission / reception operation in the first frequency band used in the radio wave system.

  FIG. 4A shows the strength of directivity of the first antenna 11. As shown in the figure, the first antenna 11 has strong directivity on the side where the radiation conductor 112 is provided. That is, it has a characteristic of strongly radiating radio waves on the side where the radiation conductor 112 is provided. Here, the first antenna 11 functions as a planar patch antenna that operates effectively with respect to the electric field of radio waves.

  In the second antenna 12, the coiled conductor pattern 122 is spirally wound so that one end is located at one side of the second dielectric substrate 121 and the other end is located at a substantially central portion of the second dielectric substrate 121. And the other end is located in the vicinity of the other end of the spiral portion 124 and the other end is located near the other end of the spiral portion 124. It comprises a straight line portion 125 provided so as to be located at a portion not overlapping with the portion 124. One end of the rod-shaped conductor pattern 123 overlaps the other end of the spiral portion 124 with respect to the thickness direction of the second dielectric substrate 121 on the back surface side of the second dielectric substrate 121, and the other end is the straight line. It is provided at a position overlapping the other end of the portion 125. A first through hole 126 penetrating from the front surface to the back surface is formed at a position where the other end of the spiral portion 124 of the second dielectric substrate 121 and one end of the rod-shaped conductor pattern 123 are located. Further, a second through hole 127 penetrating from the front surface to the back surface is formed at a position where the other end of the linear portion 125 of the second dielectric substrate 121 and the other end of the rod-shaped conductor pattern 123 are located. .

  One end of the spiral portion 124 and the straight portion 125 located on one side of the second dielectric substrate 121 function as a power feeding portion to the coiled conductor pattern 122. That is, although not shown, the core wire on one end side of the coaxial cable is connected to one end of the spiral portion 124, the outer line on the one end side is connected to one end of the straight portion 125, and the other end side of the coaxial cable is connected to the electromagnetic induction system. Connect to a wireless device for wireless communication. By doing so, the current input from the coaxial cable to one end of the spiral portion 124 flows through the spiral portion 124 and is input from the other end to the one end of the rod-shaped conductor pattern 123 through the first through hole 126. The current input to one end of the rod-shaped conductor pattern 123 flows through the rod-shaped conductor pattern 123 and is input from the other end to the other end of the linear portion 125 through the second through hole 127. The current input to the other end of the straight portion 125 is output from one end of the straight portion 125 to the coaxial cable. Further, the current input from the coaxial cable to one end of the straight portion 125 flows in the opposite direction to the above, and is output from one end of the spiral portion 124 to the coaxial cable. As a result, the second antenna 12 performs a transmission / reception operation in the second frequency band used in the electromagnetic induction method.

  The magnetic field distribution of the second antenna 12 is shown in FIG. In the figure, broken lines indicate magnetic flux, and the portion where the magnetic flux is concentrated is where the magnetic flux density is high. As shown in the drawing, there is a portion having a high magnetic flux density in the vertical direction from the center of the coiled conductor pattern 122 constituting the second antenna 12. If communication is performed at a location where the magnetic flux density is high, good communication characteristics can be obtained. Here, the second antenna 12 functions as a coiled antenna that operates effectively against a magnetic field of radio waves.

  In the present embodiment, the thickness d1 of the conductor layer that forms the first antenna 11, that is, the radiation conductor 112 and the ground conductor 113, is the conductor layer that forms the second antenna 12, that is, the coil shape. The conductor pattern 122 is thinner than the thickness d2.

As the frequency increases, the current flowing through the conductor flows only in a portion where the depth from the conductor surface is shallow. This phenomenon is called the skin effect, and the skin depth δ through which current flows is expressed by the following equation (1). In equation (1), ω is 2πf, f is the frequency, μ is the magnetic permeability, and σ is the conductivity.

For example, when the conductor is made of copper, the conductivity σ is 58 × 10 ⁶ (S / m). Since the permeability μ is 4π × 10 ⁻⁷ , the skin depth δ is 18 μm when the frequency is 13.56 MHz used in the electromagnetic induction method. When the frequency is 950 MHz used in the radio wave system, the skin depth δ is 2 μm.

  Therefore, if the thickness of the copper foil pattern of the antenna operating in the 950 MHz band is 2 μm, power loss in the copper foil pattern can be reduced. On the other hand, if the thickness of the copper foil pattern of the antenna operating in the 13.56 MHz band is 18 μm or more, power loss in the copper foil pattern can be reduced. In addition, when there is a copper foil having a thickness of 18 μm or more, 13.56 MHz band electromagnetic waves hardly pass. In other words, when the thickness of the copper foil is 18 μm or less, the 13.56 MHz band electromagnetic wave passes, and the amount of passage increases as the thickness of the copper foil decreases.

  Therefore, in the present embodiment, the first frequency band used in the radio wave system is 950 MHz, and the conductor thickness d1 of the first antenna 11 operating in the 950 MHz band is 2 μm to 18 μm. In addition, the second frequency band used in the electromagnetic induction method is 13.56 MHz, and the conductor thickness d2 of the second antenna 12 operating in the 13.56 MHz band is 18 μm or more.

  In the composite antenna having such a configuration, since the second antenna 12 is provided outside the side on which the radiation conductor 112 is provided, the radiation conductor 112 is included in the radio wave radiated from the first antenna 11. The radio wave strongly radiated to the provided side is not affected by the second antenna 12. On the other hand, since the thickness of the conductor layer forming the first antenna 11 is 18 μm or less, the amount of electromagnetic waves radiated from the second antenna 12 is attenuated by the conductor layer of the first antenna 11 is small.

  Therefore, according to the present embodiment, the first antenna 11 is used in the first frequency band used in the radio wave system, and the second antenna 12 is used in the second frequency band used in the electromagnetic induction system. A small composite antenna 10 that can be used for stable wireless communication and that can handle two frequency bands respectively used in the radio wave system and the electromagnetic induction system, such as the 950 MHz band and the 13.56 MHz band, for example. Can be provided.

[Second Embodiment]
Next, the composite antenna 20 which is the 2nd Embodiment of this invention is demonstrated using FIGS. 5 is a plan view of the composite antenna 20 as viewed from above, FIG. 6 is a cross-sectional view taken along the line BB in FIG. 5, and FIG. 7 is a plan view of the composite antenna 20 as viewed from below.

  This composite antenna 20 is also used in the electromagnetic induction method as the first antenna 21 operating in the 950 MHz band, for example, which is used in the radio wave system as the first frequency band, and in the second frequency band lower than the first frequency band. For example, a second antenna 22 operating in a 13.56 MHz band. Then, the first antenna 11 and the second antenna 12 are integrated by providing the second antenna 22 on the outer periphery where the radiation gain of the first antenna 21 is small.

  The first antenna 21 is disposed on a dielectric substrate 211, a radiation conductor (patch electrode) 212 disposed on one surface side of the dielectric substrate 211, and the other surface side of the dielectric substrate 211. It comprises a ground conductor (ground) 213. The second antenna 22 includes a holding frame 221 made of a dielectric having a mouth-shaped opening, and a conductor coil 222 made of, for example, copper wire or the like wound around the holding frame 221.

  In the first antenna 21, the ground conductor 213 is a substantially rectangular conductor pattern having substantially the same area as the dielectric substrate 211, and is provided on the lower surface of the dielectric substrate 211. The radiation conductor 212 is a rectangular conductor pattern having an area smaller than that of the dielectric substrate 211, and is provided substantially at the center on the dielectric substrate 211. Further, a through hole 214 penetrating in the thickness direction is formed at a position approximately １ ／ from the right end on the BB arrow line of the radiation conductor 214 of the dielectric substrate 211. The position of the through hole 214 is determined by the impedance of the wireless device to which the antenna 21 is connected. A connector 215 is inserted into the through hole 214 from the ground conductor 213 side. Thereby, the inner conductor of the connector is connected to the radiation conductor 212 and the outer conductor is connected to the ground conductor 213. Therefore, the first antenna 21 performs a transmission / reception operation in the first frequency band used in the radio wave system by connecting a radio device that performs radio communication using the radio wave system to the connector 215. At this time, the directivity of the first antenna 21 has a strong directivity on the side where the radiation conductor 212 is provided, similarly to the directivity shown in FIG. That is, the radiation gain on the side where the radiation conductor 212 of the dielectric substrate 211 is provided is high, and the radiation gain in the outer peripheral direction parallel to the surface of the ground conductor 213 is small. Here, the first antenna 21 functions as a planar patch antenna that operates effectively with respect to the electric field of radio waves.

  In the second antenna 12, the holding frame 221 has its mouth-shaped opening fitted to the outer periphery parallel to the surface of the ground conductor 213 of the dielectric substrate 211 in the first antenna. A conductor coil 222 is wound around the outer periphery of the holding frame 221. One end of the conductor coil 222 is connected to one terminal 224 of the two-terminal connector 223, and the other end of the conductor coil 222 is connected to the other terminal 225 of the two-terminal connector 223. The two-terminal connector 223 is provided at a portion of the dielectric substrate 211 where the ground conductor 213 on the back surface side is notched. Therefore, by connecting a wireless device that performs wireless communication using the electromagnetic induction method to the two-terminal connector 223, a current input from one terminal 224 of the two-terminal connector 223 flows through the conductor coil 222 and the two-terminal connector. The current input from the other terminal 225 of the H.223 and input from the other terminal 225 flows in the reverse direction through the conductor coil 222 and is input to the first terminal 224. Thereby, the second antenna 22 performs transmission / reception operation in the second frequency band used in the electromagnetic induction method. Similarly to the magnetic field distribution shown in FIG. 4B, the magnetic field distribution of the second antenna 12 includes a portion having a high magnetic flux density in the vertical direction from the center of the conductor coil 222. If communication is performed at a location where the magnetic flux density is high, good communication characteristics can be obtained. Here, the second antenna 22 functions as a coiled antenna that operates effectively against a magnetic field of radio waves.

  Also in the composite antenna 20 of the second embodiment configured as described above, similarly to the first embodiment, the conductor layers forming the first antenna 21, that is, the radiation conductor 212 and the ground conductor 213. The thickness d3 is made thinner than the conductor layer that forms the second antenna 22, that is, the thickness d4 of the conductor coil 222. Specifically, the thickness d3 of the radiation conductor 212 and the ground conductor 213 is set to be thicker than the skin depth δ through which the current in the first frequency band in which the first antenna 21 operates and the second antenna 22 is It is thinner than the skin depth δ through which the current in the second frequency band that operates is flowing. Further, the thickness d4 of the conductor coil 222 is set to be thicker than the skin depth δ through which the current in the second frequency band in which the second antenna 22 operates is flowing.

  In the composite antenna having such a configuration, the second antenna 22 is provided outside the side on which the radiation conductor 212 is provided as in the first embodiment, so that the radiation is radiated from the first antenna 21. The electromagnetic wave strongly radiated to the side where the radiation conductor 212 is provided is not affected by the second antenna 22. On the other hand, since the thickness of the conductor layer forming the first antenna 21 is 18 μm or less, the amount of electromagnetic waves radiated from the second antenna 22 is attenuated by the conductor layer of the first antenna 21 is small. Thus, the first antenna 21 is used in the first frequency band used in the radio wave system, and the second antenna 22 is used in the second frequency band used in the electromagnetic induction system for stable wireless communication. A small composite antenna 20 that can be provided can be provided.

The present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage.
For example, the shape of the composite antennas 10 and 20 is not limited to a rectangular shape, and may be a circular shape or a polygonal shape such as a triangle, pentagon, or hexagon.

  The thicknesses d1 and d3 of the conductors constituting the first antennas 11 and 21 may be any thickness that can suppress the influence of the second antennas 12 and 22, and the second antennas 12 and 22 The thicknesses d2 and d4 of the constituent conductors may be any thickness that can use the second frequency band. The material of the conductor is not limited to copper.

  In addition, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, the constituent elements over different embodiments may be combined.

1 is an external perspective view of a composite antenna according to a first embodiment of the present invention. The disassembled perspective view of the composite antenna in the said 1st Embodiment. The enlarged view of the AA arrow cross section in FIG. The schematic diagram which shows the directivity of a 1st antenna, and the magnetic field distribution of a 2nd antenna. The top view which looked at the compound antenna in the 2nd Embodiment of this invention from upper direction. BB arrow sectional drawing in FIG. The top view which looked at the compound antenna in the 2nd embodiment from the lower part.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10,20 ... Composite antenna, 11, 21 ... First antenna, 12, 22 ... Second antenna, 13 ... Holding substrate, 111 ... First dielectric substrate, 112, 212 ... Radiation conductor, 113, 213 ... Ground conductor, 121 ... second dielectric substrate, 122 ... coiled conductor pattern, 123 ... bar-shaped conductor pattern, 211 ... dielectric substrate, 221 ... holding frame, 222 ... conductor coil.

Claims (3)

A patch antenna having a radiating conductor on one surface and a ground conductor on the other surface, the first antenna operating in a first frequency band used in a radio system of UHF band or 2.45 GHz band; ,
A second antenna having a coiled conductor operating in a second frequency band utilized in an electromagnetic induction scheme lower than the first frequency band;
A holding portion made of a dielectric that integrally holds the first antenna and the second antenna;
The thicknesses of the radiation conductor layer and the ground conductor layer, which are conductor layers forming the first antenna, are both thinner than the skin depth through which the current in the second frequency band flows,
A composite antenna, wherein a thickness of a conductor layer forming the second antenna is equal to or greater than a skin depth through which a current in the second frequency band flows. The second antenna is provided with the coiled conductor on one side,
The holding portion made of the dielectric holds the ground conductor of the first antenna, which is the patch antenna, on one surface and holds the pattern of the coiled conductor of the second antenna on the other surface. The composite antenna according to claim 1. The holding portion is made of a dielectric provided on the outer periphery of the first antenna that is the patch antenna,
The composite antenna according to claim 1, wherein the second antenna is formed by winding the coiled conductor around an outer periphery of the holding portion.

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