JP2011097334A - Antenna device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an antenna device which uses a meta-material and is more compact than heretofore. <P>SOLUTION: The antenna device 1 is provided with: an antenna element 10 which emits or absorbs electromagnetic waves; and the meta-material 93 which has a negative dielectric constant arranged so as to face the antenna element 10. The meta-material 93 includes a plurality of coils 11 arranged by being separated from the antenna element 10. Each coil 11 is formed of a conductive wire with a length of a substantially half-wavelength or integer multiples of it, of the electromagnetic waves to be generated around each. The direction of a center axis of each coil substantially matches to the direction of a line of electric force to be generated from the antenna element 10. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an antenna device using a metamaterial having a negative dielectric constant.

  In recent years, devices called metamaterials have attracted attention. This metamaterial is an artificial material having electromagnetic or optical characteristics that a substance existing in nature does not have. Typical properties of such metamaterials include negative permeability (μ <0), negative dielectric constant (ε <0), or negative refractive index (when both permeability and dielectric constant are negative) Is mentioned.

  As a means for realizing a negative dielectric constant, a method using a metal rod is representative. A negative dielectric constant can be realized by lowering the plasma frequency with a metal rod having an infinite length (that is, sufficiently large with respect to the wavelength of the electromagnetic wave). It is also known that a negative dielectric constant is generated by a finite length metal rod. Specifically, a negative dielectric constant is generated when a metal rod having a length that is half the wavelength of an electromagnetic wave is resonated with the electromagnetic wave.

  An antenna device using such a metamaterial having a negative dielectric constant has been reported by RW Ziolkowski ("Metamaterial-Based Efficient Electrically Small Antennas", IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, July 2006, VOL. 54, NO.7, p.2113-2130 (Non-Patent Document 1)). In the antenna device of this document, a spherical shell-shaped metamaterial having a negative dielectric constant is arranged so as to surround a small antenna. The inductive characteristic of the metamaterial having a negative dielectric constant cancels out the capacity characteristic of the small antenna and acts as an LC resonator as a whole, so that the radiation efficiency can be increased as compared with the small antenna alone.

  As another method for downsizing an antenna device, a helical planar antenna described in Japanese Patent Publication No. 8-2005 (Patent Document 1) is known. This helical planar antenna has a parallel metal plate with a narrower interval than the wavelength of radio waves, a waveguide composed of a metal ring that short-circuits these parallel metal plates at the outer periphery, and a large number of inserted metal plates. A helical circular polarization element. Received radio waves are received by a number of helical circular polarization elements, synthesized in the same phase in the waveguide, and output from the probe.

Japanese Patent Publication No. 8-2005

R. W. Ziolkowski, "Metamaterial-Based Efficient Electrically Small Antennas", IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, July 2006, VOL.54, NO.7, p.2113-2130

  However, a metamaterial that realizes a negative dielectric constant with a metal rod sufficiently longer than the wavelength is too large for application to an antenna device. Further, it is difficult to reduce the size of the metamaterial even by a method using a half-wave metal rod. For example, in order to create a metamaterial that develops a negative dielectric constant at 3 GHz, a 50 mm metal rod is required. Therefore, the size of the entire antenna device combining these metamaterials and small antenna elements is not reduced compared to the conventional size.

  Since the outer peripheral length of each coil of the helical planar antenna described in the above-mentioned patent document is about the same as the wavelength of the electromagnetic wave, the size of the antenna device becomes larger than when the metamaterial is used.

  An object of the present invention is to provide an antenna device that is smaller than a conventional antenna device using a metamaterial.

  The present invention is an antenna device according to one aspect, and includes an antenna element that radiates or absorbs electromagnetic waves, and a metamaterial having a negative dielectric constant that is disposed so as to face the antenna element. The metamaterial includes a plurality of coils that are spaced apart from the antenna element. Each of the plurality of coils is formed by a conductive wire having a length of approximately half a wavelength of an electromagnetic wave generated around each coil or an integral multiple of the half wavelength.

  Preferably, each of the plurality of coils is formed in a helical shape. In this case, the winding directions of all the coils included in the metamaterial are the same. The direction of the central axis of each of the plurality of coils substantially coincides with the direction of the electric lines of force generated from the antenna element.

  More preferably, each end portion of the plurality of coils on the side close to the antenna element is arranged along an equipotential surface orthogonal to the electric field lines.

  In a preferred embodiment, the distance between the electric lines of force increases as the distance from the antenna element increases. In this case, the coil radius of each of the plurality of coils increases as the distance from the antenna element increases.

  Preferably, each end of the plurality of coils on the side close to the antenna element is arranged along a virtual spherical surface covering the antenna element.

  In another preferred embodiment, the antenna element is a planar antenna having a planar radiation surface. In this case, the central axis of each of the plurality of coils is orthogonal to the radiation surface.

  Preferably, the ends of the plurality of coils on the side close to the radiation surface are equidistant from the radiation surface.

  More preferably, the metamaterial further includes a plurality of insulating layers stacked on the radiation surface. In this case, each of the plurality of coils has a plurality of stripline electrodes each having a number of turns of less than one turn formed on the plurality of insulating layers. Strip line electrodes adjacent to each other in the stacking direction of the plurality of insulating layers are connected to each other by a conductor penetrating the insulating layer.

  Preferably, in the above-described embodiment and other embodiments, the metamaterial further includes a plurality of conductive plates each intersecting with the lines of electric force. In this case, any one of the plurality of conductive plates is connected to at least one end of each of the plurality of coils.

  In still another preferred embodiment, each of the plurality of coils includes a meandering conductive line. In this case, the metamaterial includes a plurality of pairs of conductive plates respectively corresponding to the plurality of coils. Each of the plurality of pairs of conductive plates is connected to both ends of the corresponding coil, and is disposed so as to intersect the lines of electric force.

  Preferably, each of the pair of conductive plates and the meandering conductive line included in the corresponding coil are provided in parallel to each other in such an arrangement that the meandering conductive line is sandwiched between the pair of conductive plates.

  In still another preferred embodiment, the metamaterial is constituted by a plurality of partial layers stacked on each other. In this case, each of the plurality of partial layers includes at least one of the plurality of coils. The partial layer relatively spaced from the antenna element includes more coils than the partial layer relatively close to the antenna element.

  Preferably, each of the plurality of coils is formed in a helical shape. In this case, the direction of the central axis of each of the plurality of coils substantially coincides with the stacking direction of the plurality of partial layers.

  Another aspect of the present invention is an antenna device, which is formed in a film shape on an insulating substrate and radiates or absorbs electromagnetic waves, and is formed in a meander shape on the substrate, each spaced apart from the antenna element A plurality of coils. The direction of the center line of each of the plurality of coils substantially coincides with the direction of the lines of electric force generated from the antenna element. Each of the plurality of coils is formed by a conductive wire having a length of approximately half a wavelength of an electromagnetic wave generated around each coil or an integral multiple of the half wavelength.

  Preferably, each end portion of the plurality of coils on the side close to the antenna element is disposed along an intersection line between the equipotential surface orthogonal to the electric field lines and the surface of the substrate.

  More preferably, the distance between the lines of electric force along the surface of the substrate increases as the distance from the antenna element increases. In this case, in each of the plurality of coils, the width in the direction perpendicular to the center line is longer as being separated from the antenna element.

  In the one aspect and the other aspect described above, the plurality of coils are divided into a plurality of groups. In this case, the coils belonging to the same group are formed by conductive wires having the same length. Coils belonging to different groups are formed by conductive wires having different lengths.

  According to the present invention, the metamaterial includes a plurality of coils formed in a helical shape or a meander shape. Each coil is formed by a conductive wire having a substantially half wavelength of electromagnetic waves or an integral multiple of the electromagnetic wave. For this reason, an antenna device smaller than the conventional one can be realized.

It is a perspective view which shows the structure of the antenna device 1 by Embodiment 1 of this invention. It is a figure which shows typically the cross-section of the antenna apparatus 1 of FIG. It is a figure for demonstrating the characteristic of the metamaterial 93 of FIG. It is a figure which shows the dielectric constant of the coil 100 shown in FIG. It is a figure which shows the relative magnetic permeability of the coil 100 shown in FIG. (A) is a figure for demonstrating the direction of the electric field in case the coil 100 shows a positive dielectric constant, (B) is for demonstrating the direction of the electric field in case the coil 100 shows a negative dielectric constant. FIG. It is a figure which shows the electric field distribution around the coil 100 in the case of FIG. 6 (B) in detail. It is a figure which shows typically the cross-section of 1 A of antenna apparatuses which are the modifications of the antenna apparatus 1 of FIG. It is a figure which shows the structure of the antenna apparatus made into the object of simulation (in the case of one coil). It is a figure which shows the structure of the antenna apparatus made into the object of simulation (when there are two or more coils). It is a perspective view which shows the structure of the antenna apparatus 2 by Embodiment 2 of this invention. It is a figure which shows typically the cross-section of the antenna apparatus 2 of FIG. It is a figure which shows the structure of the antenna device 3 by Embodiment 3 of this invention. 6 is a diagram showing a configuration of an antenna device 3A according to a first modification of the third embodiment. FIG. It is a figure which shows the structure of the antenna device 3B by the modification 2 of Embodiment 3. FIG. It is a perspective view which shows the structure of the antenna apparatus 4 by Embodiment 4 of this invention. It is a figure which shows typically the cross-section of the antenna apparatus 4 of FIG. FIG. 5 is a diagram for explaining a method for manufacturing the antenna device 4. It is a top view of insulating layers 54A-54D shown in FIG. FIG. 10 is a perspective view showing a configuration of an antenna device 4A according to a modification of the fourth embodiment. It is a perspective view which shows the structure of the antenna device 5 by Embodiment 5 of this invention. It is a figure which shows the structure of each coil unit 69 of FIG. It is a top view of the insulation sheets 64B-64F of FIG. It is a perspective view which shows the structure of the antenna device 6 by Embodiment 6 of this invention. It is a side view of the antenna apparatus 6 of FIG. It is a perspective view which shows the structure of 6 A of antenna apparatuses by the modification of Embodiment 6. FIG. It is a side view of the antenna device 6A of FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated.

<Embodiment 1>
[Configuration of Antenna Device 1]
FIG. 1 is a perspective view showing the configuration of an antenna device 1 according to Embodiment 1 of the present invention.

  FIG. 2 is a diagram schematically showing a cross-sectional structure of the antenna device 1 of FIG. 1 and 2, an antenna device 1 includes an antenna element 10, a plurality of helical coils 11 as a metamaterial 93, a ground plane 12 formed on an insulating substrate 15, and a power supply. An electric wire 13 and an insulating support member 14 for fixing the plurality of coils 11 are included. It is desirable that the substrate 15 and the support member 14 have dielectric properties. For ease of illustration, the support member 14 is shown only in outline.

  The antenna element 10 is a monopole antenna, and is a small antenna having an overall length that is 1/10 or less of the wavelength of electromagnetic waves. An electromagnetic wave is radiated from the antenna element 10 during transmission, and the electromagnetic wave is absorbed by the antenna element 10 during reception. One end of the antenna element 10 is connected to a feed line 13 provided through the substrate 15 and the ground plane 12. 1 and 2, the ground plane 12 is provided along the XY plane, and the central axis of the monopole antenna as the antenna element 10 is provided along the Z axis.

  The plurality of helical coils 11 are arranged so as to face the antenna element 10 (arrangement facing the antenna element or arrangement covering the antenna element) and are separated from the antenna element 10. Each coil 11 is formed by a conductive wire having a length approximately half the wavelength of the electromagnetic wave radiated from the antenna element 10. As a result, each coil 11 resonates at the frequency of the electromagnetic wave. It is preferable that the winding directions of all the coils 11 are the same so that the coils 11 do not cancel each other's electromagnetic characteristics.

  As shown in FIG. 2, the direction of the central axis of each coil 11 substantially coincides with the direction of the lines of electric force 90 generated from the antenna element 10. The end 11A of each coil 11 on the side close to the antenna element 10 is provided along a virtual hemisphere surrounding the antenna element 10 (in the case of FIG. 2, the inner surface 14A of the support member 14).

  The support member 14 fixes the coils 11 so that the coils 11 are in the above-described arrangement. Silicon resin, Teflon (registered trademark) resin, or the like can be used as the support member 14. The shape of the support member 14 is not limited to the shape shown in FIG. 2 as long as each coil 11 can be fixed. For example, the hollow portion 16 may be filled with silicon resin or the like without providing the hollow portion 16 as shown in FIG.

  The wavelength of the electromagnetic wave changes depending on the dielectric constant of the support member 14 that is a dielectric material. Therefore, the length of the conductive wire constituting each coil 11 needs to be determined in consideration of the dielectric constant of the support member 14.

  The metamaterial 93 having a negative dielectric constant can be realized by the plurality of coils 11 arranged as described above. Hereinafter, the reason why the metamaterial 93 exhibits a negative dielectric constant will be described.

[Characteristics of Metamaterial 93]
FIG. 3 is a diagram for explaining the characteristics of the metamaterial 93 of FIG. FIG. 3 shows one helical coil 100. The coil 100 is disposed between the signal line 200 and the ground plane 220 and is fixed by the support member 120 so as not to contact the signal line 200 and the ground plane 220. An alternating current I having a predetermined frequency flows through the signal line 200. As a result, an alternating electric field E is generated between the signal line 200 and the ground plane 220.

  The first feature of the coil 100 in FIG. 3 is that the coil 100 is formed by a conductive wire having a length approximately half the wavelength of the alternating current I flowing through the signal line 200. The second feature is that the direction of the central axis 110 of the coil 100 coincides with the direction of the alternating electric field E generated between the signal line 200 and the ground plane 220 (that is, the direction of the lines of electric force). Due to these characteristics, the coil 100 resonates at the frequency of the AC electric field E by being electrostatically coupled to the signal line 200 and the ground plane 220 by the AC electric field E.

FIG. 4 is a diagram showing the relative dielectric constant of the coil 100 shown in FIG.
FIG. 5 is a diagram showing the relative permeability of the coil 100 shown in FIG. In the calculation of the relative permittivity and the relative magnetic permeability shown in FIGS. 4 and 5, the length of the conductive wire forming the coil 100 (hereinafter referred to as “coil wire length”) was set to 13 mm.

  As shown in FIG. 4, when the frequency of the alternating current I flowing through the signal line 200 in FIG. 3 is gradually increased, the relative dielectric constant shows a maximum value near the frequency of 6.5 GHz (reference numeral 91 in FIG. 4). The minimum value is shown near the frequency of 6.6 GHz (reference numeral 92 in FIG. 4). When the relative dielectric constant shows a minimum value, the value is negative. On the other hand, the relative permeability shows a minimum value near a frequency of 6.5 GHz and a maximum value around a frequency of 6.6 GHz. However, the amount of change with respect to the frequency is small, and the value is almost 1 and is not negative.

  6A is a diagram for explaining the direction of the electric field when the coil 100 exhibits a positive dielectric constant, and FIG. 6B shows the direction of the electric field when the coil 100 exhibits a negative dielectric constant. It is a figure for demonstrating. 6A and 6B, it is assumed that an external electric field from the ground plane 220 toward the signal line 200 is applied to the coil 100 by the alternating current I flowing through the signal line 200.

  In the case of FIG. 6A, a negative charge is induced in the lower end portion 100B of the coil 100 by an external electric field directed from the lower side (the ground plane 220 side) to the upper side (the signal line 200 side), and the upper end portion 100A of the coil 100 is induced. A positive charge is induced in On the other hand, in the case of FIG. 6B in which the coil 100 is in a resonance state, the polarity of the induced charge is reversed, a positive charge is induced in the lower end portion 100B of the coil 100, and a negative charge is applied to the upper end portion 100A of the coil 100. A charge is induced. At this time, the charge at the upper end 100A of the coil 100 and the charge at the lower end 100B of the coil 100 are larger than the charges of the upper signal line 200 and the lower ground plane 220 due to resonance. For this reason, the direction of the electric field E generated above and below the coil 100 is reversed as compared with the case of FIG. That is, the coil 100 exhibits a negative dielectric constant characteristic. In discussing the sign of the dielectric constant, the direction of the electric field above and below the coil 100 is important. Although the direction of the electric field E ′ generated in the coil 100 is also reversed, since the coil 100 is a conductor, the magnitude of the electric field E ′ is smaller than the electric field E generated above and below the coil 100.

  FIG. 7 is a diagram showing in detail the electric field distribution around the coil 100 in the case of FIG. As shown in FIG. 7, a downward electric field from the signal line 200 toward the upper end of the coil 100 and a downward electric field from the lower end of the coil 100 toward the ground plane 220 are generated, and the coil 100 has a negative dielectric constant. It can be seen that

  As shown in FIGS. 6A and 6B, since positive or negative charges are accumulated in the upper end portion 100A and the lower end portion 100B of the coil 100, the substantial coil wire length related to resonance is It becomes shorter than the coil wire length on the outer shape. As a result, the actual resonance frequency becomes higher than the resonance frequency predicted from the coil wire length on the outer shape. For this reason, it is necessary to design the coil wire length on the outer shape slightly longer than half the wavelength of the electromagnetic wave in consideration of the above properties. In practice, the length of the coil wire is determined so as to have an appropriate resonance frequency by performing simulation or experiment.

[Operational effect of antenna device 1]
Referring to FIGS. 1 and 2 again, in the antenna device 1 of the first embodiment, as the metamaterial 93, a large number of coils 11 having a coil wire length of approximately a half wavelength are arranged. As already described, each coil 11 is provided apart from the antenna element, and the direction of the central axis of each coil 11 substantially coincides with the direction of the electric lines of force 90 generated from the antenna element 10. The element 10 is electrostatically coupled. As a result, when each coil 11 is in a resonance state, the metamaterial 93 exhibits a negative dielectric constant.

  In general, the smaller the antenna element 10 is, the smaller the resistance component and the capacitance component of the input impedance of the antenna element 10 are, so that matching between the antenna element 10 and the signal source becomes more difficult. As a result, there is a problem that the radiation efficiency of the antenna is lowered. Therefore, by disposing the metamaterial 93 having a negative dielectric constant so as to face the antenna element 10 (to face the antenna element or to cover the antenna element), the antenna has an inductive characteristic that the metamaterial 93 has. This cancels the capacitance characteristics of the element. This facilitates matching between the antenna element 10 and the signal source, so that the radiation efficiency can be increased as compared with the case of the antenna element 10 alone. In particular, in the case of the first embodiment, the size of each coil 11 can be made sufficiently smaller than the wavelength of electromagnetic waves, so that the entire antenna device 1 can be downsized.

  In order to increase the radiation efficiency of the antenna device 1, the end portions 11 </ b> A of the coils 11 on the side close to the antenna element 10 are periodically arranged along an equipotential surface perpendicular to the electric force lines 90. It is desirable. More preferably, when the interval between the lines of electric force 90 increases as the distance from the antenna element 10 increases as shown in FIG. 2, the coil radius of each coil 11 increases as the distance from the antenna element increases. Thereby, the area | region which the coil 11 occupies can be increased within the hemispherical area | region in which the metamaterial 93 was provided. As shown in FIG. 3, the coil radius refers to a distance CR from a point on the coil 100 to the central axis 110.

[Modification]
In the above description, the coil wire length of each coil 11 is approximately half of the wavelength of the electromagnetic wave. Therefore, a metamaterial exhibiting a negative dielectric constant can be realized. However, from the viewpoint of miniaturization of the antenna device 1, it is desirable that the coil wire length is approximately half wavelength.

  The plurality of coils 11 constituting the metamaterial 93 may be grouped so that the coil wire lengths of the coils 11 belonging to different groups are different. Accordingly, since the metamaterial 93 has a plurality of resonance frequencies, the band of the antenna device 1 can be expanded. In addition, when changing the coil wire length in this way, by changing the diameter of the conductive wire forming each coil 11, the coil radius, the number of turns of the coil, the dielectric constant of the support member 14, and the like for each group, It is desirable that the appearance size of the coil does not vary greatly.

  The shape of each coil 11 is not limited to that in which a metal wire is wound along the conical surface. For example, a shape in which a metal wire is wound along a quadrangular pyramid may be used.

  In the above description, the antenna element 10 is a monopole antenna, but is not limited thereto. For example, when the antenna element is a dipole antenna, the ground plane 12 is not provided, and a plurality of coils 11 as metamaterials are arranged in a spherical shape so as to surround the dipole antenna.

  In order to increase the efficiency of electrostatic coupling between the antenna element 10 and each coil 11, the shape of the tip of the monopole antenna as the antenna element 10 may be hemispherical as shown in FIG.

  FIG. 8 is a diagram schematically showing a cross-sectional structure of an antenna device 1A that is a modification of the antenna device 1 of FIG. As shown in FIG. 8, since the shape of the tip portion 10A is hemispherical, the distance from the tip portion 10A to the end portion 11A of each coil 11 can be made uniform.

[simulation result]
Hereinafter, the simulation result of the antenna device 1A of FIG.

  9 and 10 are diagrams showing the structure of the antenna device to be simulated. FIG. 9A shows a case where there is one coil 11 and the coil 11 and the tip 10A of the antenna element 10 are not connected (electrostatic coupling). FIG. 9B shows a case where there is one coil 11 and the coil 11 and the tip 10A of the antenna element 10 are connected. FIG. 10A shows a case where there are seven coils 11 and each coil 11 and the tip 10A of the antenna element 10 are not connected (electrostatic coupling). FIG. 10B shows a case where there are seven coils 11 and each coil 11 and the tip 10A of the antenna element 10 are connected. FIG. 10C shows a case where there are 13 coils 11 and each coil 11 and the tip 10A of the antenna element 10 are not connected (electrostatic coupling). FIGS. 10A and 10C show the case of this embodiment, and FIGS. 9A, 9B, and 10B show comparative examples. 9 and 10, each coil 11 is formed of a metal wire having a diameter of 1 mm and a length of 20 mm, and is embedded in silicon resin. The following table shows the results of obtaining the resonance frequency, reflected power, and radiation efficiency for each antenna device.

  First, when the number of coils 11 is one, a conventional antenna (FIG. 9B) that feeds power directly to a helical coil and one approximately half-wavelength coil are electrostatically coupled in the vicinity of the monopole antenna. Compared with the antenna (FIG. 9A), the radiation efficiency of the conventional antenna (FIG. 9B) that is directly fed is higher. That is, when the number of coils is one, there is no merit of separating the coil 11 and the tip 10A of the antenna element.

  As shown in FIGS. 10A and 10C, when the number of coils 11 whose coil wire length is approximately half wavelength is increased and the monopole antenna is covered with many coils 11, the number of coils 11 is increased. It can be seen that as the value increases, matching is achieved and radiation efficiency is improved. In this case, it can be seen that the efficiency is improved when the coil 11 and the antenna element are connected (FIG. 10 (B)) and when they are separated (FIG. 10 (A) and FIG. 10 (C)). .

  In the case of a single monopole antenna, radiation is mainly radiated from the portion where the electric field at the tip is concentrated. However, in the antenna device 1A of the first embodiment, an assembly of the coils 11 having a coil wire length of approximately half wavelength is the antenna element. The reason why the radiation efficiency is improved is that the tip 10A is electrostatically coupled to resonate and radiate from the entire hemisphere. As a result, since it is easy to achieve matching even if the entire antenna device is downsized, a small antenna device with high radiation efficiency can be realized.

<Embodiment 2>
FIG. 11 is a perspective view showing the configuration of the antenna device 2 according to the second embodiment of the present invention.

  FIG. 12 is a diagram schematically showing a cross-sectional structure of the antenna device 2 of FIG. 11 and 12, the metamaterial 94 constituting the antenna device 2 is implemented in that it further includes disk-shaped plate electrodes 21A and 21B (conductive plates) connected to both ends of each coil 11. It differs from the metamaterial 93 of the form 1. The plate electrodes 21A and 21B need to intersect the electric lines of force 90 so as to be electrostatically coupled to the antenna element 10 by an electric field. When the plate electrodes 21A and 21B and the lines of electric force 90 are orthogonal to each other, electrostatic coupling can be most efficiently performed. In other respects, the antenna device 2 is the same as the antenna device 1A. Therefore, the same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated.

  In the metamaterial 94 according to the second embodiment, the capacitance is added between the tip portion 10A of the antenna element 10 and the flat plate electrode 21B on the side close to the antenna element 10, so that the resonance frequency is lowered. That is, since the wavelength is shortened by generating the capacitance, the coil wire length of the coil 11 necessary for obtaining a certain resonance frequency can be shortened. Therefore, the size can be further reduced as compared with the metamaterial 93 of the first embodiment that does not have the flat plate electrode 21B. As a result, the entire antenna device 2 can also be reduced in size. Furthermore, since the radiation surface becomes wider by making the diameter of the plate electrode 21A provided on the side away from the antenna element larger than the coil diameter (coil diameter), the radiation efficiency of the antenna is increased. Only one of the plate electrodes 21A and 21B may be provided.

<Embodiment 3>
FIG. 13 is a diagram showing the configuration of the antenna device 3 according to the third embodiment of the present invention. FIG. 13A is a plan view, and FIG. 13B is a side view. The antenna device 3 of the third embodiment corresponds to a two-dimensional antenna device 1, 1A of the first embodiment. A meandering coil 31 corresponds to the helical coil 11 of the first embodiment. As in the case of the first embodiment, the coil wire length of the meandering coil 31 is approximately half the wavelength of the electromagnetic wave.

  The antenna device 3 includes an antenna element 30 and a plurality of meandering coils 31 formed in a film shape on a main surface 35A of an insulating substrate 35, and a ground plane 32 formed in a film shape on a back surface 35B. Including. The substrate 35 is preferably dielectric. The ground plane 32 is not provided on the back side of the meandering coil 31 so as not to disturb the radiation of electromagnetic waves. The antenna element 30, the plurality of coils 31, and the ground plane 32 can be easily manufactured using a printing method or the like.

  The antenna element 30 is formed in a line shape on the substrate 35, and one end 30B of the antenna element 30 is connected to the feeder line. The other end 30A of the antenna element 30 is formed in a semicircular shape. The other end 30A of the antenna element 30 is arranged so that one end 31A of each coil 31 formed in a meander shape is close to the other end 30A. The direction of the center line 39 of each coil 31 substantially coincides with the direction of the lines of electric force generated from the antenna element 30. In the case of FIG. 13, the center line 39 of the plurality of coils 31 extends from the other end 30 </ b> A of the antenna element 30. In such a case, it is desirable that the width of each coil 31 in the direction perpendicular to the center line 39 becomes longer as the distance from the antenna element 30 increases. Ends 31 </ b> A of the coils 31 on the side close to the antenna element 30 are provided at equidistant positions from the other end 30 </ b> A of the antenna element 30. From another point of view, the end 31A of each coil 31 is disposed along the line of intersection between the equipotential surface orthogonal to the lines of electric force and the main surface 35A of the substrate 35.

  By configuring the antenna device 3 as described above, it is possible to realize a small antenna device with good radiation efficiency, as in the case of the first embodiment. Furthermore, since the antenna device 3 is formed in a planar shape, the antenna device 3 can be easily manufactured as compared with the case of the first embodiment.

<Modification 1 of Embodiment 3>
FIG. 14 is a diagram illustrating a configuration of an antenna device 3A according to the first modification of the third embodiment. In the antenna device 3 </ b> A of FIG. 14, the ground plane 38 is not provided on the back surface 35 </ b> B of the substrate 35, but is provided on the surface of another insulating substrate 37. The substrate 35 on which the antenna element 30 and the plurality of coils 31 are formed is disposed so as to be perpendicular to the substrate 37 on which the ground plane 38 is formed. In this case, the axial direction of the monopole antenna as the antenna element 30 is orthogonal to the ground plane 38 provided on the substrate 37. A through hole is formed in the substrate 37 and the ground plane 38, and the feed line 33 is connected to the base end portion of the antenna element 30 through the through hole.

<Modification 2 of Embodiment 3>
FIG. 15 is a diagram illustrating a configuration of an antenna device 3B according to the second modification of the third embodiment. FIG. 15A is a plan view, and FIG. 15B is a side view. As in the case of the antenna device 3 of FIG. 13, the antenna device 3B includes an antenna element 40 and a plurality of meandering coils 41 formed on the main surface 35A of the insulating substrate 35 and a back surface 35B. And a ground plane 42 formed in a film shape.

  The antenna device 3B in FIG. 15 is different from the antenna device 3 in FIG. 13 in that the shape of the antenna element 40 is rectangular. One end 41 </ b> A of each coil 41 is disposed at a position equidistant from one side of the rectangular antenna element 40. The direction of the center line 49 of each coil 41 substantially coincides with the direction of the lines of electric force generated from the antenna element 40. In the case of FIG. 15, the direction of the center line 49 of each coil 41 is perpendicular to one side of the rectangular antenna element 40. In this case, the width of each coil 41 in the direction perpendicular to the center line 49 is constant.

  The antenna device 3B in FIG. 15 is small in size, has good radiation efficiency, and is easy to manufacture, similarly to the antenna device 3 in FIG.

<Embodiment 4>
FIG. 16 is a perspective view showing the configuration of the antenna device 4 according to the fourth embodiment of the present invention.

  FIG. 17 is a diagram schematically showing a cross-sectional structure of the antenna device 4 of FIG. Referring to FIGS. 16 and 17, antenna device 4 includes a planar antenna element 50 and ground plane 52 provided on main surface 55 </ b> A of insulating substrate 55, and a plurality of helical shapes as metamaterial 95. Coil 51, power supply line 53, and insulating support member 54 for fixing the plurality of coils 51. For ease of illustration, the support member 54 is shown only in outline. It is desirable that the substrate 55 and the support member 54 have dielectric properties. The ground plane 52 is disposed so as to surround the antenna element 50. The antenna element 50 is connected to a feed line 53 provided through the substrate 55.

  As in the case of the first embodiment, the coil wire length of each coil 51 is approximately half the wavelength of the electromagnetic wave radiated from the antenna element 50. Thereby, each coil 51 resonates at the frequency of the electromagnetic wave. Moreover, the winding direction of all the coils 51 is the same. The coil radius of each coil 51 is constant.

  The antenna device 4 of FIGS. 16 and 17 is characterized in that the antenna element 50 is a planar antenna having a planar radiation surface 50A. In this case, the direction of the electric force lines 90 generated from the antenna element 50 is a direction (Z-axis direction) perpendicular to the radiation surface 50A of the antenna element 50. Therefore, if the direction of the central axis of each coil 51 is aligned with the Z-axis direction, the direction of the central axis of each coil 51 can coincide with the direction of the electric force lines 90. Furthermore, if one end 51A of each helical coil 51 is formed at an equal distance from the radiation surface 50A of the antenna element 50, the one end 51A of each coil 51 is equipotential surface perpendicular to the lines of electric force 90. Can be arranged along.

  Thus, since the antenna element 50 is planar and the direction of the central axis of each coil 51 is aligned in the Z-axis direction, the antenna element 50 and each coil 51 can be easily manufactured using a printing method or the like. Can do.

  FIG. 18 is a diagram for explaining a method of manufacturing the antenna device 4. Referring to FIG. 18, the support member 54 configuring the antenna device 4 is configured by a plurality of insulating layers 54 </ b> A to 54 </ b> D stacked on a planar antenna element 50. In the case of FIG. 18, a case of a four-layer structure is shown as an example, but the number of layers is appropriately set according to the number of turns of the coil 51. Strip line electrodes having a number of turns of less than one turn are formed on each surface of the insulating layers 54A to 54D, and the coils 51 are formed by electrically connecting these strip line electrodes in the stacking direction.

  FIG. 19 is a plan view of the insulating layers 54A to 54D shown in FIG. Referring to FIG. 19, stripline electrodes 56A-56D having a number of turns of less than one turn are formed on the surfaces of insulating layers 54A-54D, respectively, by a printing method or the like. In FIG. 19, for the sake of simplicity, two stripline electrodes are shown on the surface of each insulating layer, but in actuality, the number of coils 51 to be manufactured is provided.

  Strip line electrodes adjacent to each other in the stacking direction (Z direction) of the insulating layers are connected to each other by conductive members formed in via holes that penetrate the insulating layer. Specifically, a via hole 57A for connecting to one end of the stripline electrode 56B adjacent in the Z direction is formed at one end of the stripline electrode 56A. Similarly, a via hole 57B for connecting to one end of the stripline electrode 56C adjacent in the Z direction is formed at the other end of the stripline electrode 56B. Furthermore, a via hole 57C is formed at the other end of the stripline electrode 56C to connect to one end of the stripline electrode 56D adjacent in the Z direction. In this way, the coil 51 whose central axis extends in the Z direction is formed.

<Modification of Embodiment 4>
FIG. 20 is a perspective view showing a configuration of an antenna device 4A according to a modification of the fourth embodiment. The antenna device 4A in FIG. 20 is different from the antenna device 4 in FIG. 16 in that a ground plane 59 is formed on the back surface 55B of the substrate 55. Furthermore, the antenna device 4A is different from the antenna device 4 of FIG. 16 in that it includes a strip line 58 formed on the main surface 55A of the substrate 55 as a feed line connected to the antenna element 50. In other respects, the configuration of antenna device 4A in FIG. 20 is the same as the configuration of antenna device 4 in FIG. 16, and therefore the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

<Embodiment 5>
FIG. 21 is a perspective view showing the configuration of the antenna device 5 according to the fifth embodiment of the present invention. Referring to FIG. 21, antenna device 5 includes a monopole antenna as antenna element 60, a ground plane 62, and a plurality of coil units 69 as metamaterial 96. Each coil unit 69 includes a meandering conductive line 61 and a pair of conductive plates 66A and 66B electrically connected to both ends of the meandering conductive line 61. The conductive plates 66 </ b> A and 66 </ b> B are arranged so as to intersect the electric lines of force generated from the antenna element 60.

  FIG. 22 is a diagram showing the configuration of each coil unit 69 of FIG. FIG. 22A is a perspective view, and FIG. 22B is a side view. Referring to FIG. 22, each coil unit 69 includes a pair of conductive plates 66 </ b> A and 66 </ b> B, a meandering conductive line 61 provided so as to be sandwiched between the pair of conductive plates 66 </ b> A and 66 </ b> B, and one end of the conductive line 61. A conductive portion 67A that connects the conductive plate 66A, a conductive portion 67B that connects the other end of the conductive line 61 and the conductive plate 66B, and an insulating support member 64 that supports and fixes them. The pair of conductive plates 66A and 66B and the conductive line 61 are provided in parallel to each other along the XY plane. The support member 64 is preferably dielectric.

  The conductive line 61 and the conductive portions 67A and 67B correspond to the coil 11 of the first embodiment and are formed so that the total length is approximately half the wavelength of the electromagnetic wave radiated from the antenna element 60 of FIG. . As a result, the entire conductive line 61 and the conductive portions 67A and 67B resonate at the frequency of the electromagnetic wave. Further, as described above, the pair of conductive plates 66A and 66B are arranged so as to intersect the electric lines of force generated from the antenna element 60, so that the coil unit 69 is electrostatically coupled to the antenna element 60. As a result, the metamaterial 96 composed of the plurality of coil units 69 exhibits a negative dielectric constant.

  As shown in FIG. 22B, the support member 64 is composed of six layers of insulating sheets 64A to 66F stacked in the Z direction. With such a configuration, the meandering conductive line 61 and the pair of conductive plates 66A and 66B can be easily manufactured by a printing method or the like.

  23A to 23E are plan views of the insulating sheets 64B to 64F in FIG. Referring to FIG. 23, conductive plate 66B is formed on the surface of insulating sheet 64B, meandering conductive line 61 is formed on the surface of insulating sheet 64D, and conductive plate 66A is formed on the surface of insulating sheet 64F. Further, a conductive portion 67B is formed so as to penetrate the insulating sheets 64B and 64C, and the conductive plate 66B and one end of the conductive line 61 are connected by the conductive portion 67B. Similarly, a conductive portion 67A is formed so as to penetrate the insulating sheets 64D and 64E, and the conductive plate 66A and the other end of the conductive line 61 are connected by the conductive portion 67A.

<Embodiment 6>
FIG. 24 is a perspective view showing the configuration of the antenna device 6 according to the sixth embodiment of the present invention.

  FIG. 25 is a side view of the antenna device 6 of FIG. 24 and 25, antenna device 6 includes a monopole antenna as antenna element 70, a ground plane 72, and metamaterials 97A and 97B stacked in the Z direction. That is, the antenna device 6 of FIGS. 24 and 25 is configured by partial layers 97A and 97B in which the entire metamaterial is laminated with each other.

  The metamaterial 97 </ b> A provided in the vicinity of the antenna element 70 includes one helical coil 81. The coil wire length of the coil 81 is approximately half the wavelength of the electromagnetic wave radiated from the antenna element 70. The coil 81 is fixed by an insulating support member 86. For ease of illustration, the support member 86 is shown only in outline.

  As shown in FIGS. 24 and 25, the direction of the central axis 110 of the coil 81 is the Z-axis direction, matches the axial direction of the monopole antenna 70, and is orthogonal to the ground plane 72. The coil 81 is provided immediately above the antenna element 70 so as to cover the antenna element 70 when viewed from above (Z-axis direction). With this arrangement, electrostatic coupling between the antenna element 70 and the coil 81 is strengthened.

  The metamaterial 97B includes four helical coils 82A to 82D. Each coil wire length of the coils 82 </ b> A to 82 </ b> D is approximately half the wavelength of the electromagnetic wave radiated from the antenna element 70. The coils 82 </ b> A to 82 </ b> D are fixed by an insulating support member 87. For ease of illustration, the support member 87 is shown only in outline.

  As shown in FIGS. 24 and 25, the direction of the central axis 110 of each of the coils 82 </ b> A to 82 </ b> D is the Z-axis direction, coincides with the axial direction of the monopole antenna 70, and is orthogonal to the ground plane 72. When viewed from above (Z-axis direction), the coils 82 </ b> A to 82 </ b> D are arranged so as to surround the coil 81. When viewed from the side (X direction or Y direction), the upper end of the coil 81 and the lower ends of the coils 82A to 82D are arranged so as to be substantially on the same plane. With this arrangement, electrostatic coupling between the coil 81 and the coils 82A to 82D is strengthened.

  According to the configuration of the antenna device 6 described above, the central axes of the coils 81, 82 </ b> A to 82 </ b> B are arranged so as to substantially follow the electric lines of force generated from the antenna element 70. Therefore, the coils 81 and 82A to 82D are efficiently electrostatically coupled to the antenna element 70. Furthermore, since the coil wire lengths of the coils 81 and 82A to 82D are substantially half the wavelength of the electromagnetic wave radiated from the antenna element 70, the coils 81 and 82A to 82D resonate at the frequency of the electromagnetic wave. As a result, the metamaterials 97A and 97B as a whole exhibit a negative dielectric constant, and a small and highly efficient antenna device 6 can be realized.

  Furthermore, in antenna device 6, since the directions of the central axes of coils 81, 82A to 82D are aligned in the Z-axis direction (the stacking direction of metamaterials 97A, 97B), the same as in antenna device 4 of the fourth embodiment. There is an advantage that the coils 81 and 82A to 82D can be easily manufactured by using the printing method.

<Modification of Embodiment 6>
FIG. 26 is a perspective view showing a configuration of an antenna device 6A according to a modification of the sixth embodiment.

  FIG. 27 is a side view of the antenna device 6A of FIG. Referring to FIGS. 26 and 27, antenna device 6A differs from antenna device 6 in FIGS. 24 and 25 in that antenna device 6A further includes metamaterial 97C laminated above metamaterial 97B (+ Z direction). Since the other points of the antenna device 6A are the same as those of the antenna device 6, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

  The metamaterial 97C includes nine helical coils 83A to 83I. Each coil wire length of the coils 83 </ b> A to 83 </ b> I is approximately half the wavelength of the electromagnetic wave radiated from the antenna element 70. The coils 83A to 83I are fixed by an insulating support member 88. For ease of illustration, the support member 88 is shown only in outline.

  As shown in FIGS. 26 and 27, the direction of the central axis 110 of each of the coils 83A to 83I is the Z-axis direction, coincides with the axial direction of the monopole antenna 70, and is orthogonal to the ground plane 72. When viewed from above (Z-axis direction), four of the coils 83A to 83I are arranged so as to surround any one of the coils 82A to 82D. When viewed from the side (X direction or Y direction), the upper ends of the coils 82A to 82D and the lower ends of the coils 83A to 83I are arranged so as to be substantially on the same plane. With this arrangement, electrostatic coupling between the coils 82A to 82D and the coils 83A to 83I is strengthened.

  In the antenna device 6A, the radiation efficiency can be further increased by increasing the number of stacked metamaterials.

  The embodiment disclosed this time must be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  1, 1A, 2, 3, 3A, 3B, 4, 4A, 5, 6, 6A Antenna device 10, 30, 40, 50, 60, 70 Antenna elements 11, 31, 41, 51, 81, 82A- 82D, 83A to 83I coil, 14 support member, 15 substrate, 21A, 21B flat plate electrode, 50A radiation surface, 54 support member, 54A to 54D insulation layer, 56A to 56D stripline electrode, 61 meander-shaped conductive line, 64 support Member, 64A-64F insulating sheet, 66A, 66B conductive plate, 69 coil unit, 90 lines of electric force, 93-96, 97A, 97B, 97C metamaterial.

Claims (17)

An antenna element that radiates or absorbs electromagnetic waves;
A metamaterial having a negative dielectric constant disposed so as to face the antenna element,
The metamaterial includes a plurality of coils that are spaced apart from the antenna element, and each of the plurality of coils is a conductive wire having a substantially half wavelength of the electromagnetic wave generated around each of the coils or a length that is an integral multiple of the electromagnetic wave. Formed by the antenna device. Each of the plurality of coils is formed in a helical shape,
The winding direction of all the coils included in the metamaterial is the same,
The antenna device according to claim 1, wherein a direction of a central axis of each of the plurality of coils substantially coincides with a direction of a line of electric force generated from the antenna element.   3. The antenna device according to claim 2, wherein end portions of each of the plurality of coils on the side close to the antenna element are disposed along an equipotential surface orthogonal to the electric field lines. The distance between the lines of electric force increases as the distance from the antenna element increases.
4. The antenna device according to claim 2, wherein a coil radius of each of the plurality of coils is larger as being separated from the antenna element. 5.   5. The antenna device according to claim 4, wherein end portions of each of the plurality of coils on a side close to the antenna element are arranged along a virtual spherical surface covering the antenna element. The antenna element is a planar antenna having a planar radiation surface;
The antenna device according to claim 2 or 3, wherein a central axis of each of the plurality of coils is orthogonal to the radiation surface.   The antenna device according to claim 6, wherein end portions of the plurality of coils on the side close to the radiation surface are equidistant from the radiation surface. The metamaterial further includes a plurality of insulating layers stacked on the radiation surface,
Each of the plurality of coils has a plurality of stripline electrodes each having a number of turns of less than one turn formed on the plurality of insulating layers,
The antenna device according to claim 6 or 7, wherein the strip line electrodes adjacent to each other in the stacking direction of the plurality of insulating layers are connected to each other by a conductor penetrating the insulating layer.   The metamaterial further includes a plurality of conductive plates each intersecting the lines of electric force, and at least one end of each of the plurality of coils is connected to any one of the plurality of conductive plates. The antenna device according to any one of claims 2 to 8. Each of the plurality of coils includes a meandering conductive line,
The metamaterial includes a plurality of pairs of conductive plates respectively corresponding to the plurality of coils,
4. The antenna device according to claim 2, wherein each of the plurality of pairs of conductive plates is connected to both ends of a corresponding coil one by one and arranged so as to intersect with the lines of electric force.   The meander-shaped conductive lines included in each of the plurality of pairs of conductive plates and the corresponding coils are provided in parallel with each other in an arrangement such that the meander-shaped conductive lines are sandwiched between the pair of conductive plates. 10. The antenna device according to 10. The metamaterial is composed of a plurality of partial layers stacked on each other,
Each of the plurality of partial layers includes at least one of the plurality of coils,
The antenna device according to claim 1, wherein the partial layer relatively spaced from the antenna element includes more coils than the partial layer relatively close to the antenna element. Each of the plurality of coils is formed in a helical shape,
The antenna device according to claim 12, wherein a direction of a central axis of each of the plurality of coils substantially coincides with a stacking direction of the plurality of partial layers. An antenna element that is formed into a film on an insulating substrate and radiates or absorbs electromagnetic waves;
Each comprising a plurality of coils spaced apart from the antenna element and formed in a meander shape on the substrate;
The direction of the center line of each of the plurality of coils substantially coincides with the direction of the lines of electric force generated from the antenna element,
Each of the plurality of coils is an antenna device formed by a conductive wire having a length substantially equal to a half wavelength of the electromagnetic wave generated around each of the coils or an integral multiple thereof.   The end of each of the plurality of coils on the side close to the antenna element is disposed along a line of intersection between an equipotential surface orthogonal to the electric field lines and the surface of the substrate. Antenna device. The distance between the lines of electric force along the surface of the substrate increases as the distance from the antenna element increases.
16. The antenna device according to claim 14, wherein a width of each of the plurality of coils in a direction perpendicular to the center line is longer as being separated from the antenna element. The plurality of coils are divided into a plurality of groups,
Coils belonging to the same group are formed by conductive wires of the same length,
The antenna device according to any one of claims 1 to 16, wherein the coils belonging to different groups are formed by conductive wires having different lengths.

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