JP4853329B2 - Radio wave reflector and antenna - Google Patents

Description

  The present invention relates to a radio wave reflector and an antenna for efficiently radiating radio waves from an antenna and efficiently receiving radio waves to the antenna. In particular, the present invention relates to a radio wave reflector and an antenna having translucency with respect to visible light.

  There are many restrictions on the installation location of a vehicle-mounted antenna. An antenna of the type installed outside the vehicle can obtain stable performance, but is not preferable because it deteriorates the appearance of the vehicle.

  A typical antenna that does not impair the appearance of a vehicle is an antenna installed on a window. However, since it is affected by the window glass, the operating frequency is shifted compared to the case where the antenna is placed in free space, and the design is difficult. Moreover, since it has directivity not only outside the vehicle but also inside the vehicle, the radiation or reception efficiency is poor, and the radiation pattern is also degraded by the reflected wave from the inside of the vehicle. Regardless of which antenna is used, a surface current flows on the vehicle body, and the directivity characteristics of the antenna are not as designed as compared with a single antenna and deteriorate. Another limitation is that the body shape differs greatly from vehicle type to vehicle type, so that it is necessary to adjust the antenna shape and installation position in order to obtain desired directivity.

  As a method for solving the above problem, a reflector using EBG (Electromagnetic Band-Gap) is conceivable. Unlike ordinary conductor reflectors, EBG reflects incident waves in phase, so there is no need for a distance from the antenna when used as a reflector, and a low-profile antenna can be realized.

  Various types of such EBG have been proposed, and typical configurations include those described in Non-Patent Documents 1, 2, 3, and 4.

D. Sievenpiper, L. Zhang, F.A. J. Broas, N.M. G. Alexoplous, and E. Yablonovitch, “High-Impedance Electromagnetic Surfaces with a Forbidden Frequency Band,” IEEE Trans. Microwave Theory Tech. , Vol. 47, no. 11, pp. 2059-2074, Nov. 1999. G. Goussetis, A. P. Feresidis, and J. C. Vardaxoglou, “Tailoring the AMC and EBG Characteristics of Periodic Metallic Arrays Printed on Grounded Dielectric Substrate,” IEEE Trans. Antennas Propag. , Vol. 54, no. 1, pp. 82-89, Jan. 2006. K. -P. Ma, K. Hirose, F. -R. Yang, Y. Qian, and T. Itoh, “Realization of Magnetic Conducting Surface Using Novel Photonic Bandgap Structure,” Electronics Letters, vol. 34, no. 21, Oct. 1998. J. McVay, N.C. Engheta, and A. Hoorfar, "High Impedance Metamaterial Surfaces Using Hilbert-Curve Inclusions," IEEE Trans. Microwave and Components Letters, vol. 14, no. 3, March 2004.

However, in the above-mentioned document, there are a large number of divided conductor patches and vias connected to the ground conductor on the back surface of the dielectric substrate at the center of each conductor patch, or rectangular on the surface of the dielectric. The conductor patch is formed, and a uniform conductor is formed on the back surface. For this reason, these radio wave reflectors are inevitably opaque.
For this reason, for example, if this reflector is attached to the window glass of a vehicle, the view of the driver is impaired, so this reflector is not desirable for providing the transparent member.
Further, when the antenna is attached to a vehicle, for example, it is affected by reflection from the vehicle casing. For this reason, in a state where the antenna is attached to the vehicle, the directivity characteristic designed by the antenna alone cannot be obtained, and the directional characteristic is distorted. Therefore, it is necessary to design the antenna so that desired directivity characteristics can be obtained with the antenna actually attached.

The present invention has been made to solve the above-described problems, and is to realize a radio wave reflector that can be attached to a transparent body and does not block the field of view.
Another object is to realize an antenna that can obtain a desired designed initial directivity even when the antenna is actually attached to an object such as a vehicle.
Another object is to realize a radio wave reflector and an antenna that can be attached to a curved surface.
Another object is to realize an E-plane omnidirectional antenna.

In order to solve the above problems, the following means are effective.
According to a first invention, in a film-like antenna having translucency and flexibility, a dielectric substrate made of a polymer film having flexibility transparent to visible light, and a first of the dielectric substrate A conductor ground layer formed in a mesh on the surface and a second surface opposite to the first surface, the conductor patterns are periodically arranged, and each conductor pattern is formed in a mesh. (Frequency Selective Surface) layer, a radio wave reflector that reflects radio waves in the same phase at the frequency of the radio wave used, and a polymer with translucency and flexibility bonded on the FSS layer on the radio wave reflector An antenna comprising: a dielectric thin film made of a film; and an antenna element layer made of a conductive pattern formed in a mesh shape on the dielectric thin film so as to be insulated from the FSS layer.

Here, the dielectric substrate is transparent to visible light . By the induction conductor substrate and having a flexible material, it is possible to present an antenna attached to a curved surface such as a window of the vehicle. Furthermore, derivative collector substrate, in order to have a light transmitting property and flexibility, is constituted by a polymer film. The unit pattern of the periodic conductor pattern of the FSS layer is preferably formed by a rectangular patch, but is not limited thereto. The periodicity has periodicity in two orthogonal directions on the plane (for example, the x and y axes in the orthogonal coordinate system, the azimuth angle direction θ and the radial direction r in the polar coordinate system, etc.). As the periodic conductor pattern of the FSS layer, PBG, Hilbert curve, piano curve or the like can be used in addition to the rectangle. The unit pattern of the conductor ground layer and the FSS layer is formed of a mesh-like conductor. The mesh may be a multi-concentric shape similar to the outer peripheral shape of the unit pattern, in addition to a lattice-shaped mesh composed of line conductors extending in two directions perpendicular to each other. In this case, the line conductors do not intersect. For example, if the unit pattern is rectangular, the unit pattern is composed of multiple and concentric rectangular line conductors. Further, it may be a mesh formed by translating two orthogonal straight lines along a rectangular diagonal.

In the case of PBG, Hilbert curve, and piano curve, a mesh formed by translating this curve can be used. The intervals between the meshes may be constant or unequal, and the intervals between the conductor lines constituting the mesh may be made smaller toward the periphery of the dielectric substrate. Similarly, the mesh of the conductor ground layer can also adopt a lattice shape or the other mesh structure described above. Further, the intervals between the conductor lines of the mesh of the conductor ground layer may be unequal, or the line intervals may become smaller toward the periphery of the dielectric substrate. The FSS layer and the conductor ground layer may be formed into a mesh-like periodic conductor pattern by uniformly depositing copper on the dielectric substrate and then etching using photolithography. Since the FSS layer and the conductor ground layer are formed in a mesh shape and the dielectric substrate is transparent to visible light, even if this antenna is attached to a transparent member, for example, a window, it does not transmit light. There is no hindrance.

According to a second aspect of the present invention, in the first aspect, the antenna layer is formed outside, the both ends of the dielectric substrate are connected, and the periodicity of the conductor pattern of the FSS layer is maintained to form a cylinder. Features. That is, it becomes a cylindrical antenna with the antenna element layer on the outside.
It is characterized in that the FSS layer is arranged outside and both ends of the dielectric substrate are connected to form a cylindrical shape while maintaining the periodicity of the conductor pattern.
In this case, it is possible to configure a cylindrical antenna, the cylindrical objects, such as pillars of a vehicle, Ru can be used by winding this antenna. The directional characteristics of the installed antenna to actually be a characteristic as designed.

In the first and second inventions, ideal orientation characteristics as designed can be obtained when actually installed on an object. In order to form an antenna element layer consisting of a conductor pattern in an insulated state on the FSS layer, in addition to the method using a polymer film , an insulating film is applied on the FSS layer only in the area where the antenna conductor pattern is to be formed. Then, an antenna conductor pattern may be formed thereon.

In the present invention , the antenna element layer is formed on a light-transmitting and flexible dielectric thin film and adhered to the FSS layer . As a result, the FSS layer and the antenna element layer can be insulated and separated, and an original antenna with good directivity can be obtained.

In the present invention, the conductor pattern of the antenna element layer is formed in a mesh shape .
That is, when the antenna element layer is also meshed, the transparency of the antenna can be improved.

According to a third invention, in the second invention, the antenna element layer is arranged so that a polarization direction thereof is a direction perpendicular to a cylindrical axis.
Thereby, an omnidirectional antenna can be realized.

The fourth invention is characterized in that the conductor ground layer and the FSS layer have a mesh shape in which the line widths or intervals of the conductors are not uniform.
For example, as in the fifth invention, the mesh band of the FSS layer can expand the use band by making the interval narrower toward the periphery of the dielectric substrate.

According to the first invention, a transparent antenna can be configured. Therefore, even if this antenna is attached to a transparent member such as a vehicle window, the visibility is not lowered. Further, since the antenna is assumed that has flexibility, a curved surface such as a vehicle window and body, can be affixed to the antenna, usability is expanded.
In addition, since the antenna element layer is formed on the front surface of the radio wave reflector, the antenna directivity can be set to an ideal design directivity that is not affected by the object to be installed.

Also, since the conductor pattern of the antenna element layer is formed in a mesh shape, it is possible to realize a transparent antenna. Therefore, it is possible to provide an antenna that does not impair visibility even when pasted on a vehicle window.
Further, according to the second invention, since it can be a cylindrical antenna, for example, the antenna can be wound around a columnar object such as a pillar of a vehicle and the usability is improved.
According to the third invention, the E-plane radiation characteristic can be made omnidirectional. Therefore, according to this antenna, it is possible to receive radio waves coming from all directions and to radiate radio waves in all directions.
Further, according to the fourth invention, the frequency characteristics of the antenna can be improved.
Further, according to the fifth invention, the current distribution at the resonance frequency of the FSS layer can be made close to uniform, and the operating band of the antenna can be expanded.

  Hereinafter, the present invention will be described based on specific examples. The present invention is not limited to the following specific examples, but includes the full scope conceived by the specific examples.

  As shown in FIG. 1, the radio wave reflector 10 according to the present embodiment is designed to reflect an incident wave in phase with respect to an operating frequency of 2.4 GHz. The radio wave reflector 10 has a dielectric substrate 12 made of a rectangular polyethylene film having a relative dielectric constant of 3.0, a thickness of 0.25 mm, a length of 300 mm, and a width of 170 mm, and a second surface 12 a of the dielectric substrate 12. The FFS layer 14 made of the formed copper conductor and the conductor ground layer 16 formed on the first surface 12b of the dielectric substrate 12 are formed. The dielectric substrate 12 is formed by laminating the back surface of a 0.125 mm thick polyethylene film with the FFS layer 14 formed on the surface and the back surface of the 0.125 mm thick polyethylene film with the conductor ground layer 16 formed on the surface. It is formed. In this example, such a configuration is adopted for ease of manufacturing, but the FFS layer 14 is formed on one surface of one film and the conductor ground layer 16 is formed on the other surface. It may be. The FFS layer 14 is formed by depositing copper in a uniform thickness on the second surface 12a of the dielectric substrate 12, and the length L of one side is 41.5 mm, the period D is 45 mm, the interval is 3.5 mm, and many A rectangular mesh mesh 141 is formed. As shown in FIG. 2, the mesh shape of one patch 141 is formed in a lattice shape having a line width T of 10 μm and a period S of 200 μm. Further, the conductor ground layer 16 is also uniformly formed on the first surface 12b of the dielectric substrate 12, as shown in FIG. 2, in a lattice shape having a similar width, a line width T of 10 μm, and a period S of 200 μm. Is formed. The conductor mesh shape of the FFS layer 14 and the conductor ground layer 16 was formed by depositing copper in a thickness of 30 μm and then etching it into a lattice shape as shown in FIG.

  The frequency characteristics of the phase of the reflected wave of the radio wave reflector 10 are shown in FIG. The phase of the reflected wave indicates the amount of phase change with respect to the incident wave. It is understood that at 2.4 GHz, it is reflected with a phase of −15 degrees with respect to the incident wave and is reflected with the same phase with respect to the incident wave at 2.3395 GHz. Thus, it can be seen that in-phase reflection is realized with respect to the design frequency.

  In this embodiment, the operating frequency is designed to be 5.8 GHz. The thickness, size, and relative dielectric constant of the radio wave reflector 10 are the same as those in the first embodiment. A number of rectangular patches of the FFS layer 14 had a side length L of 15.5 mm, a period D of 18.0 mm, and an interval of 2.5 mm. FIG. 4 shows the frequency characteristics of the phase of the reflected wave with respect to the phase of the incident wave. At 5.8 GHz, in-phase reflection was obtained for the incident wave.

  This embodiment relates to an antenna. The operating frequency is designed to be 2.4 GHz. As shown in FIG. 5, a thin film antenna element on a dielectric thin film 22 made of a polyethylene film having a thickness of 0.25 mm, a length of 110 mm, a width of 41 mm, and a relative dielectric constant of 3.0, which is the same as that of the dielectric substrate Layer 24 was formed. The dielectric thin film 22 is a laminate of the back surfaces of two 0.125 mm polyethylene films. A ring-shaped first thin film conductor 241 is formed on the surface of one polyethylene film. In addition, a ring-shaped second thin film conductor 242 and a third thin film conductor 243 are formed on the surface of another polyethylene film so as to be electromagnetically coupled to the first thin film conductor 241. These three first thin film conductors 241, second thin film conductors 242 and third thin film conductors 243 constitute the antenna element layer 24. The first thin film conductor 241 has feeding points P1 and P2, and a voltage variable reactance element (for example, a reverse-biased varicap diode) # 1 is provided on a circle that forms 180 degrees with the feeding points. . Further, the second thin film conductor 242 and the third thin film conductor 243 have voltage variable reactance elements # 2 and # 2, respectively, in a positional relationship of 180 degrees on a straight line (y axis) passing through the center point of each thin film conductor. 3 and voltage variable reactance elements # 4 and # 5 are arranged.

Distance G _a between the center points of each ring-shaped thin film conductor 31.3Mm, width L _a is 1.5mm thin film conductor ring-shaped, (the width of the antenna element layer 24) diameter H _a is 39.8 mm, 3 The distance W _a (the length of the antenna element layer 24) from one end to the other end of the two rings is 102.3 mm. Each ring-shaped thin film copper conductor is formed in a concentric mesh shape with a line width of 10 μm and an interval of 20 μm.

  The antenna element layer 24 including the ring-shaped first, second, and third thin film copper conductors 241, 242, and 243 can change directivity depending on the voltage distribution applied to the voltage variable reactance element. This technique is described in Japanese Patent Application Laid-Open No. 2006-339769 filed by the present applicant.

  The dielectric thin film 22 on which the antenna element layer 24 having such a configuration was formed was bonded onto the radio wave reflecting plate 10 having the configuration shown in FIG. However, the patch 141 at this time is configured in 5 rows and 7 columns. Thereby, the variable directivity antenna was configured. The directivity characteristics of this antenna are shown in FIG. FIG. 6 shows directivity characteristics when the applied voltage is controlled so that the reactances x1 to x5 of the voltage variable reactance elements # 1 to # 5 have the values shown in FIG. It is understood that an antenna having directivity is realized only in front of the dielectric substrate 12. Further, it has a characteristic having directivity only in directions of desired design angles of −30 degrees, 0 degrees, and 30 degrees. For this reason, this antenna does not have directivity on the back surface side of the dielectric substrate 12 where the antenna element layer 24 is not affixed. Therefore, even when this antenna is attached to an automobile window, It is possible to prevent the reception of radio waves reflected by the conductive casing in the room and the emission of radio waves to the vehicle interior side. Further, as is apparent from the characteristics of FIG. 6, it can be seen that the directional characteristics before the antenna is attached to the vehicle are maintained, and the directional characteristics are not disturbed even if the antenna is attached to the vehicle.

An antenna having the same configuration as in Example 3 was created. In the antenna of this example, the operating frequency was set to 5.8 GHz. The radio wave reflector 10 and the antenna element layer 24 are excluded except for the arrangement relationship such as the dimensions and distances between the centers of the first, second, and third thin film copper conductors 241, 242, and 243 and the dimensions of the patch 141 of the radio wave reflector 10. The configuration is the same as that of the third embodiment. In Example 4, the distance G _a between the center points of each ring-shaped thin film conductor is 12.9 mm, the width L _a thin film conductor ring-shaped 0.8 mm, the diameter H _a (the width of the antenna element layer 24) The distance W _a (length of the antenna element layer 24) from one end of the three rings to the other end is 43.3 mm. In addition, the size of the patch 141 of the radio wave reflector 10 is the same as that of the second embodiment. That is, in the large number of rectangular patches of the FFS layer 14, the length L of one side shown in the figure is 15.5 mm, the period D is 18.0 mm, and the interval is 2.5 mm. The number of patches is 5 rows and 7 columns. This antenna also obtained directivity characteristics as shown in FIG.

Next, an antenna according to Example 5 will be described. This antenna uses a dipole antenna in place of the ring-shaped antenna of the third embodiment. In this embodiment, the operating frequency is designed to be 2.4 GHz. As shown in FIG. 8, the dielectric thin film 26 is formed of a 0.125 mm polyethylene film, and an antenna element layer 28 that is a dipole antenna shown in FIG. 8 is formed on the surface thereof. The antenna element layer 28 had a length L ₁ of 31.25 mm with a wavelength of / 4 and a width W ₁ of 15.5 mm. The mesh shape was a lattice shape with a line width of 10 μm and an interval of 200 μm. The back surface of the dielectric thin film 26 on which the antenna element layer 28 is formed, on which the antenna element layer 28 is not formed, is attached to the radio wave reflector 10 shown in FIG. In this embodiment, the patch 141 of the radio wave reflector 10 has a length L of 36.7 mm, a period D of 41.0 mm, an interval of 4.3 mm, and 7 rows and 4 columns. The dielectric substrate 12 has a thickness of 2.0 mm and a relative dielectric constant of 3. As shown in FIG. 9, this antenna is formed in a cylindrical shape with the row direction of the patch being the circumferential direction and the column direction being the axial direction, with the antenna element layer 28 being on the outside, and the patch 141 is circumferential. It was made to have periodicity in the direction.

  The E-plane directivity of this antenna is shown by curve B in FIG. A directivity characteristic of only the dipole antenna of FIG. 8A without using the radio wave reflector 10 is shown by a curve A of FIG. When the dipole antenna is simply made into a cylinder, it has an 8-shaped directivity characteristic in a plane perpendicular to the axis. However, when the dipole antenna is formed on the radio wave reflector 10 and formed into a cylinder as in the present embodiment, it has isotropic, that is, omnidirectional characteristics in a cross section perpendicular to the axis. I found out.

  In the present embodiment, as shown in FIG. 11, the mesh interval of the patch 141 of the FSS layer 14 is closer to the center point O of the dielectric substrate 12, and the mesh interval is coarser. It is configured to become finer. The patches 141a, b, c, and d at the four corners have the same mesh spacing pattern and are the finest. In addition, the mesh spacing is coarser as these patches are closer to the center O. Next, the meshes of the patches 141e to 141j located near the center O have a medium roughness, and even in these patches, the mesh interval gradually becomes closer to the center O. ing. The patches 141k and 141l closest to the center O are the roughest, and in these patches, the closer to the center O, the rougher. The spacing of the coarsest part of the mesh was 5 times the spacing of the finest part. With regard to this difference in spacing, the roughest spacing can be about 2 to 10 times the finest spacing. Then, a dielectric thin film having an antenna layer composed of three ring-shaped conductor patterns used in Example 3 was stuck on the FSS layer 14 to form a directional variable antenna. The operating frequency of this antenna could be operated in the range of 2.35 GHz to 2.45 GHz with 2.4 GHz as the center.

  In this embodiment, the conductor pattern of the FSS layer 14 is composed of a piano curve shown in FIG. 12A and a Hilbert curve shown in FIG. In the figure, a double mesh is shown, but in actuality, it is formed into a mesh in which n-fold (n is 2 or more) similar shapes are repeated. Even such a radio wave reflector can be reflected in phase with respect to the incident wave. Further, a dielectric thin film on which a ring-shaped directional variable antenna layer shown in FIG. 5 was formed was pasted on the FSS layer 14 of the dielectric substrate. A dielectric thin film on which an antenna layer composed of a dipole antenna having the configuration shown in FIG. 8 was formed was pasted on the FSS layer 14. Even with such a configuration, an antenna with good directivity can be formed.

  The present invention can be used for a radio wave reflector and an antenna that are transparent to visible light, and in particular, can be applied to a radio wave reflector and an antenna for a vehicle.

The perspective view which showed the structure of the electromagnetic wave reflector which concerns on the specific Example 1 of this invention. The top view which showed the mesh structure of one patch in the FSS layer of the Example. The frequency characteristics of the phase of the reflected wave at the operating frequency of 2.4 GHz in the radio wave reflector of the same embodiment. The frequency characteristic of the phase of the reflected wave in the operating frequency 5.8GHz in the electromagnetic wave reflector of Example 2. FIG. FIG. 6 is a configuration diagram showing an antenna element layer of an antenna of Example 3. Directional characteristics of the antenna of the same example. FIG. 7 is a table showing variable reactance values for obtaining the directivity characteristics of FIG. 6 of the antenna of the embodiment. FIG. 6 is a configuration diagram showing an antenna element layer of an antenna of Example 5. The perspective view which showed the structure of the antenna of the Example. Directional characteristics of the antenna of the same example. The top view which showed the mesh structure of the patch of the FSS layer of the antenna of Example 6. FIG. The top view which showed the mesh structure of the patch of the FSS layer of the antenna of Example 7. FIG.

DESCRIPTION OF SYMBOLS 10 ... Radio wave reflecting plate 12 ... Dielectric board 14 ... FSS layer 16 ... Conductor ground layer 22 ... Dielectric thin film 24 ... Antenna element layer 241 ... 1st thin film copper conductor 242 ... 2nd thin film copper conductor 243 ... 3rd thin film copper conductor

Claims (5)

In a film-like antenna having translucency and flexibility,
A dielectric substrate made of a polymer film having flexibility that is transparent to visible light ;
A conductor ground layer formed in a mesh on the first surface of the dielectric substrate;
An FSS (Frequency Selective Surface) layer formed on a second surface opposite to the first surface, in which conductor patterns are periodically arranged and each conductor pattern is formed in a mesh shape;
A radio wave reflector that reflects radio waves in the same phase at the frequency of radio waves used, and
A dielectric thin film composed of a polymer film having translucency and flexibility adhered on the FSS layer on the radio wave reflector;
On the dielectric thin film, an antenna element layer composed of a conductor pattern disposed in a mesh-like manner and insulated from the FSS layer;
An antenna comprising: The said antenna layer is made into the outer side, the both ends of the said dielectric substrate were connected, the periodicity of the said conductor pattern of the said FSS layer was hold | maintained, and it formed in the cylinder shape of Claim 1 characterized by the above-mentioned. antenna. The antenna according to claim 2 , wherein the antenna element layer is disposed so that a polarization direction thereof is a direction perpendicular to the cylindrical axis. 4. The antenna according to claim 1, wherein the conductor ground layer and the FSS layer have a mesh shape in which line widths or intervals of the conductors are not uniform. 5. The antenna according to any one of claims 1 to 3 , wherein the mesh shape of the FSS layer is narrowed toward the periphery of the dielectric substrate.

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