WO2008047953A1 - Transparent antenna - Google Patents

Transparent antenna Download PDF

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Publication number
WO2008047953A1
WO2008047953A1 PCT/JP2007/070965 JP2007070965W WO2008047953A1 WO 2008047953 A1 WO2008047953 A1 WO 2008047953A1 JP 2007070965 W JP2007070965 W JP 2007070965W WO 2008047953 A1 WO2008047953 A1 WO 2008047953A1
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WO
WIPO (PCT)
Prior art keywords
transparent
conductive film
transparent conductive
antenna
ghz
Prior art date
Application number
PCT/JP2007/070965
Other languages
French (fr)
Inventor
Ning Guan
Hirotaka Furuya
Kenji Goto
Koichi Ito
Original Assignee
Fujikura Ltd.
Chiba University
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Fujikura Ltd., Chiba University filed Critical Fujikura Ltd.
Priority to JP2008548894A priority Critical patent/JP2009533888A/en
Publication of WO2008047953A1 publication Critical patent/WO2008047953A1/en

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q1/00—Details of, or arrangements associated with, antennas
    • H01Q1/40—Radiating elements coated with or embedded in protective material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q1/00—Details of, or arrangements associated with, antennas
    • H01Q1/12—Supports; Mounting means
    • H01Q1/1271—Supports; Mounting means for mounting on windscreens
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q1/00—Details of, or arrangements associated with, antennas
    • H01Q1/12—Supports; Mounting means
    • H01Q1/22—Supports; Mounting means by structural association with other equipment or articles
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q9/00—Electrically-short antennas having dimensions not more than twice the operating wavelength and consisting of conductive active radiating elements
    • H01Q9/04—Resonant antennas
    • H01Q9/30—Resonant antennas with feed to end of elongated active element, e.g. unipole
    • H01Q9/40—Element having extended radiating surface

Definitions

  • the present invention relates to an optically transparent antenna.
  • Priority is claimed on Japanese Patent Application No. 2006-286244, filed October 20, 2006, the content of which is incorporated herein by reference.
  • Apparatuses consistent with the present invention relate to a transparent antenna, and more particularly, to an optically transparent antenna which can be located on a surface of a wireless device or of a wireless terminal, or on a display window without damaging the appearance thereof.
  • transparent antennas have been proposed in various designs, for example, a transparent antenna using lattice-shaped metal, a transparent antenna using very thin metal and transparent antennas using a transparent electrode.
  • the transparent electrodes of some transparent antennas are formed with a tin-doped indium oxide (ITO) thin film.
  • ITO indium oxide
  • An antenna using the lattice-shaped metal should have a portion for shielding visible light.
  • transmittance of visible light is significantly reduced even when the metal film is thinned. Accordingly, it is difficult to install any antenna on the surface of a small-sized wireless device with respect to the appearance thereof.
  • an ITO film is transparent to transmit visible light, but has a high resistance value due to high resistivity.
  • the antenna has a low gain and is not practical, since the resistance of a radiating element is high.
  • Exemplary embodiments of the present invention overcome the above disadvantages and other disadvantages not described above. Also, the present invention is not required to overcome the disadvantages described above, and an exemplary embodiment of the present invention may not overcome any of the problems described above.
  • a transparent antenna having sufficient transparency and sufficient radiation characteristics is provided.
  • a transparent antenna including: a radiating element for transmitting light in a visible light wavelength range about of 350 nm to 780 nm and radiating an electromagnetic wave in a frequency band of about 100 MHz to 20 GHz, the radiating element being a transparent conductive film including at least one of a tin-doped indium oxide (ITO) thin film and a fluorine-doped tin oxide (FTO) thin film, the transparent conductive film having a film thickness of about 100 nm or more, a transmittance of about 40% or more in the visible light wavelength range, and a sheet resistivity of about 20 ohms/square or less.
  • ITO tin-doped indium oxide
  • FTO fluorine-doped tin oxide
  • the transparent conductive film may be formed on a transparent dielectric substrate.
  • the transparent conductive film may have a film thickness of about 100 nm or more, a transmittance of about 60% or more in the visible light wavelength range, and a sheet resistivity of about 20 ohms/square or less.
  • the transparent conductive film may have a thickness in a range of 100 nm or more and 1 ⁇ m or less.
  • the transparent conductive film may include the FTO thin film.
  • the transmittance may be about 30% or more in the visible light wavelength range of about 350 nm to 780 nm in a state in which the transparent conductive film is formed on the transparent dielectric substrate.
  • the transmittance may be about 50% or more in the visible light wavelength range of about 350 nm to 780 nm in a state in which the transparent conductive film is formed on the transparent dielectric substrate.
  • the transparent conductive film may be formed on a non-transparent dielectric substrate.
  • a reduction of a maximum gain may be about 6 dB or less and a radiation efficiency be about 20% or more, in comparison with an antenna manufactured using an isometric metal thin film at about 1 GHz to 12 GHz.
  • a reduction rate of a maximum gain be about 0.5 dB/(ohrns/square) or less, and a reduction rate of a radiation efficiency be about 5 %/(ohms/square) or less, owing to the sheet resistivity of the transparent conductive film at about 1 GHz to 12 GHz.
  • the transparent antenna may be a monopole antenna in which the transparent conductive film is a four-sided polygon and the lower side thereof is electrically connected to an electrical circuit and that a relationship such that a lower side W 1 , an upper side W 2 , and a height L is 0.1 mm ⁇ Wj ⁇ 15 mm, 0.1 mm ⁇ W 2 ⁇ 15 mm, and 2 mm ⁇ L ⁇ 50 mm may be satisfied in the monopole antenna.
  • the transparent antenna may be a dipole antenna in which a transparent dielectric film includes two parallel stripe-shaped bases and two main bodies of externally extended four-sided polygons bent from ends of the bases, other ends of the bases being connected to an electrical circuit and that a relationship such that a length W 1 of a side of a base of the main body, a length W 2 of a side facing W 1 , a length W 3 of the base, a length L of the main body, and a interval of the bases G are 0.1 mm ⁇ W 1 ⁇ 15 mm, 0.1 mm ⁇ W 2 ⁇ 15 mm, 0 mm ⁇ W 3 ⁇ 10 mm, 2 mm ⁇ L ⁇ 50 mm, and 0.05 mm ⁇ G ⁇ 5 mm may be satisfied in the dipole antenna.
  • the transparent conductive film may be formed on a surface of a wireless device having a dielectric case or on at least one of inner and outer surfaces of a display.
  • the transparent conductive film may be formed on a surface of a wireless device having a dielectric case or on at least one of inner and outer surfaces of a display and have a structure in which a dielectric substrate is layered to insert the transparent conductive film.
  • the transparent antenna of the invention may have transparency in the visible light range, thereby radiating an electromagnetic wave of a frequency band of about 100 MHz to 20 GHz.
  • the antenna can be provided which has sufficient transparency and sufficient radiation characteristics by employing the ITO film in which the sheet resistivity is low and the transparency is high and by designing the shape of the antenna optimally.
  • the transparent antenna of the invention is transparent and inconspicuous, the antenna can be installed on a window glass and can be used as an indoor antenna or an in-vehicle antenna. Since the antenna can be mounted on a surface of a wireless terminal or a display being miniaturized year after year, not only can an installation location of the antenna be secured, but the antenna can also be easily designed. According to the aspect of the invention, it is possible to provide an antenna in which the reduction of the maximum gain of the antenna is about 1 dB or less and the radiation efficiency is about 80% or more while maintaining the transmittance of about 70% or more.
  • FIG. 1 is a graph showing a relationship between transmittance and sheet resistivity at a wavelength of 550 nm of an ITO thin film and an FTO thin film used in an exemplary embodiment of a transparent antenna of the present invention.
  • FIG. 2 is a graph showing wavelength dependency of transmittances of the ITO thin film and the FTO thin film used in the exemplary embodiment of the transparent antenna of the present invention.
  • FIG. 3 is a schematic diagram showing a shape of a transparent conductive film of a monopole antenna as an exemplary embodiment of the transparent antenna of the present invention.
  • FIG. 4 is a graph showing a frequency characteristic of a VSWR when the sheet resistivity is varied in the antenna of FIG. 3.
  • FIG. 5 is a graph showing a frequency characteristic of a maximum gain when the sheet resistivity is varied in the antenna of FIG. 3.
  • FIG. 6 is a graph showing a frequency characteristic of radiation efficiency when the sheet resistivity is varied in the antenna of FIG. 3.
  • FIG. 7 is a graph showing a radiation pattern of E ⁇ of the XY plane at 5.6 GHz in the antenna of FIG. 3.
  • FIG. 8 is a graph showing a radiation pattern of E 0 of the XZ plane at the same 5.6 GHz.
  • FIG. 9 is a graph showing a radiation pattern of E ⁇ of the YZ plane at the same 5.6 GHz.
  • FIG. 10 is a plan view showing a configuration of an antenna of exemplary
  • FIG. 11 is a graph showing a relationship between transmittance in a state in which a transparent conductive film is formed on a glass substrate of the transparent antenna of exemplary Embodiment 1 and sheet resistivity at a wavelength of 550 run.
  • FIG. 12 is a graph showing a frequency characteristic of a VSWR when a sheet resistivity is varied in the transparent antenna of exemplary Embodiment 1.
  • FIG. 13 is a graph showing a radiation pattern of E ⁇ of the XY plane at 2.4 GHz in the antenna of exemplary Embodiment 1.
  • FIG. 14 is a graph showing a radiation pattern of E 0 of the XZ plane at the same 2.4 GHz.
  • FIG. 15 is a graph showing a radiation pattern of E ⁇ of the YZ plane at the same 2.4 GHz.
  • FIG. 16 is a graph showing a relationship between maximum gain and sheet resistivity at 2.4 GHz and 5.0 GHz of the antenna of exemplary Embodiment 1.
  • FIG. 17 is a graph showing a relationship between radiation efficiency and sheet resistivity at 2.4 GHz and 5.0 GHz of the antenna of exemplary Embodiment 1.
  • FIG. 18 is a graph showing a relationship between transmittance in a state in which a transparent conductive film is formed on a glass substrate of an antenna of exemplary Embodiment 2 and sheet resistivity at a wavelength of 550 nm.
  • FIG. 19 is a graph showing a radiation pattern of E ⁇ of the XY plane at 2.4 GHz in the antenna of exemplary Embodiment 2.
  • FIG. 20 is a graph showing a radiation pattern of E ⁇ of the XZ plane at the same 2.4 GHz.
  • FIG. 21 is a graph showing a radiation pattern of E 0 of the YZ plane at the same 2.4 GHz.
  • FIG. 22 is a graph showing a relationship between maximum gain and sheet resistivity at 2.4 GHz and 5.0 GHz of the antenna of exemplary Embodiment 2.
  • FIG. 23 is a graph showing a relationship between radiation efficiency and sheet resistivity at 2.4 GHz and 5.0 GHz of the antenna of exemplary Embodiment 2.
  • FIG. 24 is a plan view showing a shape of a transparent conductive film of a dipole antenna of exemplary Embodiment 3.
  • FIG. 25 is a perspective view showing main portions of a wireless device attached to a dipole antenna of exemplary Embodiment 4.
  • FIG. 26 is a perspective view showing main portions of a wireless device attached to a dipole antenna of exemplary Embodiment 5.
  • FIG. 27 is a view illustrating a positional relationship of coordinate axes used in an exemplary embodiment of the present invention.
  • Exemplary embodiments of the present invention provide a transparent antenna including a radiating element for transmitting light in a visible light wavelength range of about 350 nm to 780 nm and radiating an electromagnetic wave in a frequency band of about 100 MHz to 20 GHz.
  • the radiating element is a transparent conductive film including either a tin-doped indium oxide (ITO) thin film or a fluorine-doped tin oxide (FTO) thin film, or both thereof.
  • the transparent conductive film has a film thickness of about 100 nm or more, a transmittance of about 40% or more in the visible light wavelength range, and a sheet resistivity of about 20 ohms/square or less.
  • the transparent conductive film may use an ITO thin film in which the sheet resistivity is in a range of about 1 ohm/square to 20 ohms/square and the transmittance is about 70% or more in a wavelength of about 550 nm.
  • an FTO thin film may be used in which the sheet resistivity is in a range of about 1 ohm/square to 5 ohms/square and the transmittance is about 50% or more in the wavelength of about 550 nm or an FTO thin film in which the sheet resistivity is in a range of about 5 ohms/square to 20 ohms/square and the transmittance is about 80% or more in the wavelength of about 550 nm.
  • the sheet resistivity is from about 0.6 ohms/square and the transmittance is about 70% or more if the sheet resistivity is 0.6 ohms/square or more.
  • the sheet resistivity is from about 1 ohm/square and the transmittance is about 50% or more if the sheet resistivity is 1 ohm/square or more.
  • FIG. 2 is a graph showing the wavelength dependency of the transmittances of an ITO thin film whose sheet resistivity is 1.6 ohms/square and an FTO thin film whose sheet resistivity is 15.5 ohms/square. A sudden variation of the transmittance is caused by the film-thickness interference.
  • a monopole antenna as shown in FIG.
  • a monopole antenna 1 has a transparent conductive film 2 having an inverse trapezoidal shape.
  • Reference numeral 3 refers to electrical ground.
  • a lower side W 1 , an upper side W 2 , and a height L of the transparent conductive film 2 satisfy the following relationships: 0.1 mm ⁇ W 1 ⁇ 15 mm, 0.1 mm ⁇ W 2 ⁇ 15 mm, and 2 mm ⁇ L ⁇ 50 mm.
  • the characteristic impedance of the transmission line is 50 ⁇ .
  • the VSWR characteristic of the antenna 1 is close to that of an isometric antenna manufactured in a conventional metal thin film (for example, copper foil) and is not especially different from that of the isometric antenna.
  • the characteristic impedance of the transmission line is 50 ⁇ .
  • the VSWR characteristic of the antenna 1 is close to that of an isometric antenna manufactured in a conventional metal thin film (for example, copper foil) and is not especially different from
  • FIG. 5 is a graph showing a frequency characteristic of a maximum gain (or a gain in a maximum radiation direction of an antenna using the transparent conductive film) when the sheet resistivity is varied.
  • the maximum gain is a relative value based on a gain in a maximum radiation direction of an antenna using a metal film.
  • the reduction of the maximum gain has a unique frequency characteristic according to each sheet resistivity. For example, if the transparent conductive film whose sheet resistivity is 10 ohms/square is used, the reduction of the maximum gain is 4.5 dB at 2 GHz, but the reduction of the maximum gain is reduced to 1.4 dB at 5 GHz.
  • the ITO thin film is used as the transparent conductive film, as shown in FIG.
  • the transmittance is 95 % when the sheet resistivity is 10 ohms/square.
  • the transmittance is 89 % when the sheet resistivity is 10 ohms/square.
  • the transparent conductive film whose sheet resistivity is 1 ohm/square is used, the reduction of the maximum gain is only 0.9 dB at 2 GHz, and the reduction of the maximum gain is further reduced to 0.2 dB at 5 GHz.
  • the transmittance is 74 % when the sheet resistivity is 1 ohm/square in the case of using the ITO thin film, and the transmittance is 50% when the sheet resistivity is 1 ohm/square in the case of using the FTO thin film.
  • FIG. 6 is a graph showing the frequency characteristic of the radiation efficiency when the sheet resistivity is varied. Like the gain, the radiation efficiency has a unique frequency characteristic according to each sheet resistivity. High radiation efficiency is obtained in the vicinity of 5 GHz. For example, when the transparent conductive film whose sheet resistivity is 10 ohms/square is used, the radiation efficiency is 34 % at 2 GHz, but the radiation efficiency increases to 72 %. When the transparent conductive film whose sheet resistivity is 1 ohm/square is used, the radiation efficiency is 80% at 2 GHz and the radiation efficiency further increases to 95 % at 5 GHz.
  • FIGS. 7 to 9 Radiation patterns at 5.6 GHz are shown in FIGS. 7 to 9.
  • the z-axis is set in a length direction of the transparent conductive film 2
  • the y-axis is orthogonal to the z-axis and in a direction parallel to the surface of the transparent conductive film 2
  • the x-axis is set in a direction orthogonal to the y- and z-axes.
  • an angle formed by the z-axis and a line segment OP connected between the origin point O and a measurement point P is set to ⁇ .
  • An angle formed by the x-axis and a line segment OP' connected between the origin point O and a point P' to which the measurement point P is projected on the XY plane is set to ⁇ .
  • FIG. 7 is a graph showing a radiation pattern of E ⁇ of the XY plane at 5.6 GHz.
  • FIG. 8 is a graph showing a radiation pattern of E 0 of the XZ plane at 5.6 GHz.
  • FIG. 9 is a graph showing a radiation pattern of Ee of the YZ plane at 5.6 GHz.
  • the exemplary embodiments of the present invention clearly define a relationship between the sheet resistivity of the transparent conductive film and the characteristics of the antenna. Using this relationship, the antenna having high gain and radiation efficiency can be optimally designed while maintaining high transparency.
  • Exemplary Embodiment 1
  • An antenna 4 as shown in FIG. 10 was manufactured and characteristics of the antenna 4 were measured.
  • a transparent conductive film 6 was formed on a transparent glass substrate 5.
  • an ITO thin film was used for the transparent conductive film 6.
  • a thickness of the glass substrate 5 was 1.1 mm and a relative permittivity was 4.8.
  • a ground plate 7 used for measurement was made of copper and had a size of 300 mm x 300 mm.
  • the conductive thin film 6 had the same size as the transparent conductive film 2 (see Fig. 3) for the basic inspection.
  • FIG. 11 is a graph showing a relationship between the transmittance of the antenna 4 in a state in which the transparent conductive film 6 (or the ITO film) is formed on the glass substrate 5 and the sheet resistivity of the ITO thin film at a wavelength of 550 nm.
  • FIG. 12 is a graph showing a VSWR characteristic of the antenna 4 of exemplary Embodiment 1 when the sheet resistivity was varied. As shown in FIG. 12, if the sheet resistivity was 10 ohms/square, the VSWR characteristic of the antenna 4 was not especially different from that of an antenna made of copper.
  • FIGS. 13 to 15 Radiation patterns of the antenna 4 of exemplary Embodiment 1 at 2.4 GHz are shown in FIGS. 13 to 15.
  • FIG. 13 is a graph showing the radiation pattern of E 0 of the XY plane at 2.4 GHz.
  • FIG. 14 is a graph showing the radiation pattern of E 0 of the XZ plane at 2.4 GHz.
  • FIG. 15 is a graph showing the radiation pattern of E 0 of the YZ plane at 2.4 GHz.
  • Maximum gains were measured at 2.4 GHz and 5.0 GHz of the antenna 4 of exemplary Embodiment 1. Along with the theoretically expected maximum gains, the measured maximum gains are shown in FIG. 16.
  • the maximum gain was a relative value based on a gain in a maximum radiation direction of an antenna using a metal film.
  • a reduction rate of the maximum gain by the sheet resistivity was about 0.2 dB/(ohms/square) at 2.4 GHz and was about 0.12 dB/(ohms/square) at 5.6 GHz.
  • the FTO film was used for the transparent conductive film 6, the antenna 4 was manufactured in the same dimensions as those of exemplary Embodiment 1 , and an antenna characteristic was measured.
  • a relationship between the transmittance of the antenna 4 in a state in which the transparent conductive film 6 (or the FTO film) was formed on the glass substrate 5 and the sheet resistivity of the FTO thin film is shown in FIG. 18.
  • FIGS . 19 to 21 Radiation patterns at 2.4 GHz of the antenna 4 of Embodiment 2 are shown in FIGS . 19 to 21.
  • FIG. 19 is a graph showing the radiation pattern of E 0 of the XY plane at 2.4 GHz.
  • FIG. 20 is a graph showing the radiation pattern of Ee of the XZ plane at 2.4 GHz.
  • FIG. 21 is a graph showing the radiation pattern of E 0 of the YZ plane at 2.4 GHz.
  • Maximum gains were measured at 2.4 GHz and 5.0 GHz of the antenna 4 of exemplary Embodiment 2. Along with the theoretically expected maximum gains, the measured maximum gains are shown in FIG. 22. The maximum gain was a relative value based on a gain in a maximum radiation direction of an antenna using a metal film. Radiation efficiencies of the antenna 4 of exemplary Embodiment 2 were measured at 2.4 GHz and 5.0 GHz. Along with the theoretically expected radiation efficiencies, the measured radiation efficiencies are shown in FIG. 23. Exemplary Embodiment 3
  • a dipole antenna 8 as shown in FIG. 24 was manufactured using an ITO thin film and an FTO thin film as transparent conductive films and characteristics of the dipole antenna 8 were measured.
  • the dipole antenna 8 included transparent conductive films 9A and 9B having two parallel stripe-shaped bases and two main bodies of externally extended four-sided polygons bent from ends of the bases. Other ends of the bases were connected to an electrical circuit.
  • a length W 1 of a side of a base of the main body, a length W 2 of a side facing W 1 , a length W 3 of the base, a length L of the main body, and an interval of the bases G satisfy the following relationships: 0.1 mm ⁇ W 1 ⁇ 15 mm, 0.1 mm ⁇ W 2 ⁇ 15 mm, 0 mm ⁇ W 3 ⁇ 10 mm, 2 mm ⁇ L ⁇ 50 mm, and 0.05 mm ⁇ G ⁇ 5 mm
  • the lengths W 1 and W 2 of the sides of the base of the main body, the length W 3 of the base, the length L of the main body, and the interval of the bases G satisfy the following relationships: 0.1 mm ⁇ W 1 ⁇ 15 mm, 0.1 mm ⁇ W 2 ⁇ 15 mm, 0 mm ⁇ W 3 ⁇ 10 mm, 2 mm ⁇ L ⁇ 50 mm, and 0.05 mm ⁇ G ⁇ 5 mm.
  • the antenna 8 of exemplary Embodiment 3 was film-formed on a surface of a wireless device having a dielectric case 10 as shown in FIG. 25.
  • An upper surface of the wireless device was made of an insulating material.
  • a radiation characteristic of the antenna 8 is affected by the permittivity of the dielectric case 10 formed on the upper surface of the wireless device.
  • a VSWR characteristic was only slightly varied. Accordingly, this antenna can be installed on a display portion of the wireless device, and can also be installed on a display glass or the backside of a transparent plastic.
  • Exemplary Embodiment 5 Exemplary Embodiment 5
  • the antenna 8 of exemplary Embodiment 3 was film-formed on a surface of a dielectric case 10 of a wireless device as shown in FIG. 26.
  • An upper surface of the wireless device was made of an insulating material, the antenna 8 was formed on a transparent dielectric substrate, for example, but not limited to, glass or plastic, and a dielectric substrate 11 was layered to insert transparent conductive films 9 A and 9B.
  • a radiation characteristic of the antenna 8 was affected by the permittivity of the dielectric case 10 formed on the upper surface of the wireless device.
  • a VSWR characteristic was only slightly varied.
  • the dielectric substrate 11 covered from the upper surface also played a role of protecting the antenna.
  • the transparent antenna of the invention may have transparency in the visible light range, thereby radiating an electromagnetic wave of a frequency band of about 100 MHz to 20 GHz.
  • the antenna can be provided which has sufficient transparency and sufficient radiation characteristics by employing the ITO film in which the sheet resistivity is low and the transparency is high and by designing the shape of the antenna optimally.

Abstract

A transparent antenna includes a radiating element for radiating an electromagnetic wave in a frequency band of 100 MHz to 20 GHz. A transparent conductive film including either an ITO thin film or an FTO thin film, or both, transmits light in a visible light wavelength range of 350 nm to 780 nm. The transparent conductive film has a film thickness of 100 nm or more, a transmittance of 40% or more in the visible light wavelength range, and a sheet resistivity of 20 ohms/square or less.

Description

DESCRIPTION
TRANSPARENTANTENNA ,
TECHNICAL FIELD
The present invention relates to an optically transparent antenna. Priority is claimed on Japanese Patent Application No. 2006-286244, filed October 20, 2006, the content of which is incorporated herein by reference.
BACKGROUND ART
Apparatuses consistent with the present invention relate to a transparent antenna, and more particularly, to an optically transparent antenna which can be located on a surface of a wireless device or of a wireless terminal, or on a display window without damaging the appearance thereof. Conventionally, transparent antennas have been proposed in various designs, for example, a transparent antenna using lattice-shaped metal, a transparent antenna using very thin metal and transparent antennas using a transparent electrode.
The transparent electrodes of some transparent antennas are formed with a tin-doped indium oxide (ITO) thin film. However, there are the following problems in the prior art.
An antenna using the lattice-shaped metal should have a portion for shielding visible light. In the case of an antenna using a metal film, transmittance of visible light is significantly reduced even when the metal film is thinned. Accordingly, it is difficult to install any antenna on the surface of a small-sized wireless device with respect to the appearance thereof. On the other hand, an ITO film is transparent to transmit visible light, but has a high resistance value due to high resistivity. However, the antenna has a low gain and is not practical, since the resistance of a radiating element is high.
DISCLOSURE OF INVENTION
Exemplary embodiments of the present invention overcome the above disadvantages and other disadvantages not described above. Also, the present invention is not required to overcome the disadvantages described above, and an exemplary embodiment of the present invention may not overcome any of the problems described above.
A transparent antenna having sufficient transparency and sufficient radiation characteristics is provided.
According to an aspect of the invention, there is provided a transparent antenna including: a radiating element for transmitting light in a visible light wavelength range about of 350 nm to 780 nm and radiating an electromagnetic wave in a frequency band of about 100 MHz to 20 GHz, the radiating element being a transparent conductive film including at least one of a tin-doped indium oxide (ITO) thin film and a fluorine-doped tin oxide (FTO) thin film, the transparent conductive film having a film thickness of about 100 nm or more, a transmittance of about 40% or more in the visible light wavelength range, and a sheet resistivity of about 20 ohms/square or less.
The transparent conductive film may be formed on a transparent dielectric substrate.
The transparent conductive film may have a film thickness of about 100 nm or more, a transmittance of about 60% or more in the visible light wavelength range, and a sheet resistivity of about 20 ohms/square or less. The transparent conductive film may have a thickness in a range of 100 nm or more and 1 μm or less.
The transparent conductive film may include the FTO thin film. The transmittance may be about 30% or more in the visible light wavelength range of about 350 nm to 780 nm in a state in which the transparent conductive film is formed on the transparent dielectric substrate.
The transmittance may be about 50% or more in the visible light wavelength range of about 350 nm to 780 nm in a state in which the transparent conductive film is formed on the transparent dielectric substrate. The transparent conductive film may be formed on a non-transparent dielectric substrate.
A reduction of a maximum gain may be about 6 dB or less and a radiation efficiency be about 20% or more, in comparison with an antenna manufactured using an isometric metal thin film at about 1 GHz to 12 GHz. A reduction rate of a maximum gain be about 0.5 dB/(ohrns/square) or less, and a reduction rate of a radiation efficiency be about 5 %/(ohms/square) or less, owing to the sheet resistivity of the transparent conductive film at about 1 GHz to 12 GHz.
The transparent antenna may be a monopole antenna in which the transparent conductive film is a four-sided polygon and the lower side thereof is electrically connected to an electrical circuit and that a relationship such that a lower side W1, an upper side W2, and a height L is 0.1 mm < Wj < 15 mm, 0.1 mm < W2 < 15 mm, and 2 mm < L < 50 mm may be satisfied in the monopole antenna.
The transparent antenna may be a dipole antenna in which a transparent dielectric film includes two parallel stripe-shaped bases and two main bodies of externally extended four-sided polygons bent from ends of the bases, other ends of the bases being connected to an electrical circuit and that a relationship such that a length W1 of a side of a base of the main body, a length W2 of a side facing W1, a length W3 of the base, a length L of the main body, and a interval of the bases G are 0.1 mm < W1 < 15 mm, 0.1 mm < W2 < 15 mm, 0 mm < W3 < 10 mm, 2 mm < L< 50 mm, and 0.05 mm < G < 5 mm may be satisfied in the dipole antenna.
The transparent conductive film may be formed on a surface of a wireless device having a dielectric case or on at least one of inner and outer surfaces of a display.
The transparent conductive film may be formed on a surface of a wireless device having a dielectric case or on at least one of inner and outer surfaces of a display and have a structure in which a dielectric substrate is layered to insert the transparent conductive film.
The transparent antenna of the invention may have transparency in the visible light range, thereby radiating an electromagnetic wave of a frequency band of about 100 MHz to 20 GHz. The antenna can be provided which has sufficient transparency and sufficient radiation characteristics by employing the ITO film in which the sheet resistivity is low and the transparency is high and by designing the shape of the antenna optimally.
When the FTO film is used, the use of indium as a rare metal can be avoided and hence the cost is lowered. Since the transparent antenna of the invention is transparent and inconspicuous, the antenna can be installed on a window glass and can be used as an indoor antenna or an in-vehicle antenna. Since the antenna can be mounted on a surface of a wireless terminal or a display being miniaturized year after year, not only can an installation location of the antenna be secured, but the antenna can also be easily designed. According to the aspect of the invention, it is possible to provide an antenna in which the reduction of the maximum gain of the antenna is about 1 dB or less and the radiation efficiency is about 80% or more while maintaining the transmittance of about 70% or more.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings.
FIG. 1 is a graph showing a relationship between transmittance and sheet resistivity at a wavelength of 550 nm of an ITO thin film and an FTO thin film used in an exemplary embodiment of a transparent antenna of the present invention.
FIG. 2 is a graph showing wavelength dependency of transmittances of the ITO thin film and the FTO thin film used in the exemplary embodiment of the transparent antenna of the present invention. FIG. 3 is a schematic diagram showing a shape of a transparent conductive film of a monopole antenna as an exemplary embodiment of the transparent antenna of the present invention.
FIG. 4 is a graph showing a frequency characteristic of a VSWR when the sheet resistivity is varied in the antenna of FIG. 3. FIG. 5 is a graph showing a frequency characteristic of a maximum gain when the sheet resistivity is varied in the antenna of FIG. 3.
FIG. 6 is a graph showing a frequency characteristic of radiation efficiency when the sheet resistivity is varied in the antenna of FIG. 3.
FIG. 7 is a graph showing a radiation pattern of Eθ of the XY plane at 5.6 GHz in the antenna of FIG. 3. FIG. 8 is a graph showing a radiation pattern of E0 of the XZ plane at the same 5.6 GHz.
FIG. 9 is a graph showing a radiation pattern of Eθ of the YZ plane at the same 5.6 GHz. FIG. 10 is a plan view showing a configuration of an antenna of exemplary
Embodiment 1.
FIG. 11 is a graph showing a relationship between transmittance in a state in which a transparent conductive film is formed on a glass substrate of the transparent antenna of exemplary Embodiment 1 and sheet resistivity at a wavelength of 550 run. FIG. 12 is a graph showing a frequency characteristic of a VSWR when a sheet resistivity is varied in the transparent antenna of exemplary Embodiment 1.
FIG. 13 is a graph showing a radiation pattern of Eθ of the XY plane at 2.4 GHz in the antenna of exemplary Embodiment 1.
FIG. 14 is a graph showing a radiation pattern of E0 of the XZ plane at the same 2.4 GHz.
FIG. 15 is a graph showing a radiation pattern of Eθ of the YZ plane at the same 2.4 GHz.
FIG. 16 is a graph showing a relationship between maximum gain and sheet resistivity at 2.4 GHz and 5.0 GHz of the antenna of exemplary Embodiment 1. FIG. 17 is a graph showing a relationship between radiation efficiency and sheet resistivity at 2.4 GHz and 5.0 GHz of the antenna of exemplary Embodiment 1.
FIG. 18 is a graph showing a relationship between transmittance in a state in which a transparent conductive film is formed on a glass substrate of an antenna of exemplary Embodiment 2 and sheet resistivity at a wavelength of 550 nm. FIG. 19 is a graph showing a radiation pattern of Eθ of the XY plane at 2.4 GHz in the antenna of exemplary Embodiment 2.
FIG. 20 is a graph showing a radiation pattern of Eθ of the XZ plane at the same 2.4 GHz.
FIG. 21 is a graph showing a radiation pattern of E0 of the YZ plane at the same 2.4 GHz.
FIG. 22 is a graph showing a relationship between maximum gain and sheet resistivity at 2.4 GHz and 5.0 GHz of the antenna of exemplary Embodiment 2.
FIG. 23 is a graph showing a relationship between radiation efficiency and sheet resistivity at 2.4 GHz and 5.0 GHz of the antenna of exemplary Embodiment 2. FIG. 24 is a plan view showing a shape of a transparent conductive film of a dipole antenna of exemplary Embodiment 3.
FIG. 25 is a perspective view showing main portions of a wireless device attached to a dipole antenna of exemplary Embodiment 4.
FIG. 26 is a perspective view showing main portions of a wireless device attached to a dipole antenna of exemplary Embodiment 5.
FIG. 27 is a view illustrating a positional relationship of coordinate axes used in an exemplary embodiment of the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the attached drawings.
Exemplary embodiments of the present invention provide a transparent antenna including a radiating element for transmitting light in a visible light wavelength range of about 350 nm to 780 nm and radiating an electromagnetic wave in a frequency band of about 100 MHz to 20 GHz. The radiating element is a transparent conductive film including either a tin-doped indium oxide (ITO) thin film or a fluorine-doped tin oxide (FTO) thin film, or both thereof. The transparent conductive film has a film thickness of about 100 nm or more, a transmittance of about 40% or more in the visible light wavelength range, and a sheet resistivity of about 20 ohms/square or less. Since a sufficient radiation characteristic is not obtained when a film thickness of the transparent conductive film is less than 100 nm, it is difficult for the transparent conductive film to be practically used for the antenna. When the transmittance in the visible light wavelength range is less than 40%, it is difficult to install the antenna on the surface of a small-sized wireless device with respect to the appearance thereof. Since the gain is lowered when the sheet resistivity exceeds 20 ohms/square, the sheet resistivity is may not be practical for the antenna. The film thickness of the transparent conductive film is about 1 μm or less. When the film is thick, the sheet resistivity is lowered and the transmittance is lowered. The sheet resistivity is nearly in inverse proportion to the film thickness. The transparent conductive film may use an ITO thin film in which the sheet resistivity is in a range of about 1 ohm/square to 20 ohms/square and the transmittance is about 70% or more in a wavelength of about 550 nm.
Moreover, a cost-effective FTO thin film can be used. In this case, an FTO thin film may be used in which the sheet resistivity is in a range of about 1 ohm/square to 5 ohms/square and the transmittance is about 50% or more in the wavelength of about 550 nm or an FTO thin film in which the sheet resistivity is in a range of about 5 ohms/square to 20 ohms/square and the transmittance is about 80% or more in the wavelength of about 550 nm.
In the ITO thin film or the FTO thin film used for the transparent conductive film serving as the radiating element, a relationship between the sheet resistivity and the transmittance in the wavelength of 550 nm is shown in FIG. 1.
In the ITO thin film, the sheet resistivity is from about 0.6 ohms/square and the transmittance is about 70% or more if the sheet resistivity is 0.6 ohms/square or more. In the FTO thin film, the sheet resistivity is from about 1 ohm/square and the transmittance is about 50% or more if the sheet resistivity is 1 ohm/square or more.
FIG. 2 is a graph showing the wavelength dependency of the transmittances of an ITO thin film whose sheet resistivity is 1.6 ohms/square and an FTO thin film whose sheet resistivity is 15.5 ohms/square. A sudden variation of the transmittance is caused by the film-thickness interference. Using these transparent conductive films, a monopole antenna as shown in FIG.
3 was manufactured for a basic inspection. The analysis was carried out while considering the resistivity of an antenna radiation element and employing a moment method (see R. F. Harrington, Field Computation by Moments Methods, IEEE PRESS, 1993). When the sheet resistivity is constant, the values of a voltage standing wave ratio (VSWR) characteristic, maximum gain, radiation efficiency, and radiation pattern are constant, independent of a thin film type.
As shown in FIG. 3, a monopole antenna 1 has a transparent conductive film 2 having an inverse trapezoidal shape. Reference numeral 3 refers to electrical ground. In the monopole antenna 1, a lower side W1, an upper side W2, and a height L of the transparent conductive film 2 satisfy the following relationships: 0.1 mm < W1 < 15 mm, 0.1 mm < W2 < 15 mm, and 2 mm < L < 50 mm.
FIG. 4 is a graph showing a frequency characteristic of the VSWR when the sheet resistivity of the transparent conductive film 2 is varied in the antenna 1 using the transparent conductive film 2 having W1 = 3 mm, W2 = 9 mm, and L = 21 mm. The characteristic impedance of the transmission line is 50 Ω. As shown in FIG. 4, when the sheet resistivity is 10 ohms/square or less, the VSWR characteristic of the antenna 1 is close to that of an isometric antenna manufactured in a conventional metal thin film (for example, copper foil) and is not especially different from that of the isometric antenna. FIG. 5 is a graph showing a frequency characteristic of a maximum gain (or a gain in a maximum radiation direction of an antenna using the transparent conductive film) when the sheet resistivity is varied. The maximum gain is a relative value based on a gain in a maximum radiation direction of an antenna using a metal film. As shown, it can be seen that the reduction of the maximum gain has a unique frequency characteristic according to each sheet resistivity. For example, if the transparent conductive film whose sheet resistivity is 10 ohms/square is used, the reduction of the maximum gain is 4.5 dB at 2 GHz, but the reduction of the maximum gain is reduced to 1.4 dB at 5 GHz. When the ITO thin film is used as the transparent conductive film, as shown in FIG. 1, the transmittance is 95 % when the sheet resistivity is 10 ohms/square. When the FTO thin film is used, the transmittance is 89 % when the sheet resistivity is 10 ohms/square. When the transparent conductive film whose sheet resistivity is 1 ohm/square is used, the reduction of the maximum gain is only 0.9 dB at 2 GHz, and the reduction of the maximum gain is further reduced to 0.2 dB at 5 GHz. As shown in FIG. I5 the transmittance is 74 % when the sheet resistivity is 1 ohm/square in the case of using the ITO thin film, and the transmittance is 50% when the sheet resistivity is 1 ohm/square in the case of using the FTO thin film.
FIG. 6 is a graph showing the frequency characteristic of the radiation efficiency when the sheet resistivity is varied. Like the gain, the radiation efficiency has a unique frequency characteristic according to each sheet resistivity. High radiation efficiency is obtained in the vicinity of 5 GHz. For example, when the transparent conductive film whose sheet resistivity is 10 ohms/square is used, the radiation efficiency is 34 % at 2 GHz, but the radiation efficiency increases to 72 %. When the transparent conductive film whose sheet resistivity is 1 ohm/square is used, the radiation efficiency is 80% at 2 GHz and the radiation efficiency further increases to 95 % at 5 GHz.
Radiation patterns at 5.6 GHz are shown in FIGS. 7 to 9. Herein, the z-axis is set in a length direction of the transparent conductive film 2, the y-axis is orthogonal to the z-axis and in a direction parallel to the surface of the transparent conductive film 2, and the x-axis is set in a direction orthogonal to the y- and z-axes. As shown in FIG. 27, an angle formed by the z-axis and a line segment OP connected between the origin point O and a measurement point P is set to θ. An angle formed by the x-axis and a line segment OP' connected between the origin point O and a point P' to which the measurement point P is projected on the XY plane is set to φ. These angles are similar to those of FIGS. 13 to 15 and FIGS. 19 to 21. FIG. 7 is a graph showing a radiation pattern of Eø of the XY plane at 5.6 GHz. FIG. 8 is a graph showing a radiation pattern of E0 of the XZ plane at 5.6 GHz. FIG. 9 is a graph showing a radiation pattern of Ee of the YZ plane at 5.6 GHz.
The exemplary embodiments of the present invention clearly define a relationship between the sheet resistivity of the transparent conductive film and the characteristics of the antenna. Using this relationship, the antenna having high gain and radiation efficiency can be optimally designed while maintaining high transparency. Exemplary Embodiment 1
An antenna 4 as shown in FIG. 10 was manufactured and characteristics of the antenna 4 were measured. In the antenna 4, a transparent conductive film 6 was formed on a transparent glass substrate 5. In exemplary Embodiment 1, an ITO thin film was used for the transparent conductive film 6. A thickness of the glass substrate 5 was 1.1 mm and a relative permittivity was 4.8. A ground plate 7 used for measurement was made of copper and had a size of 300 mm x 300 mm. The conductive thin film 6 had the same size as the transparent conductive film 2 (see Fig. 3) for the basic inspection.
FIG. 11 is a graph showing a relationship between the transmittance of the antenna 4 in a state in which the transparent conductive film 6 (or the ITO film) is formed on the glass substrate 5 and the sheet resistivity of the ITO thin film at a wavelength of 550 nm.
FIG. 12 is a graph showing a VSWR characteristic of the antenna 4 of exemplary Embodiment 1 when the sheet resistivity was varied. As shown in FIG. 12, if the sheet resistivity was 10 ohms/square, the VSWR characteristic of the antenna 4 was not especially different from that of an antenna made of copper.
Radiation patterns of the antenna 4 of exemplary Embodiment 1 at 2.4 GHz are shown in FIGS. 13 to 15. FIG. 13 is a graph showing the radiation pattern of E0 of the XY plane at 2.4 GHz. FIG. 14 is a graph showing the radiation pattern of E0 of the XZ plane at 2.4 GHz. FIG. 15 is a graph showing the radiation pattern of E0 of the YZ plane at 2.4 GHz.
Maximum gains were measured at 2.4 GHz and 5.0 GHz of the antenna 4 of exemplary Embodiment 1. Along with the theoretically expected maximum gains, the measured maximum gains are shown in FIG. 16. The maximum gain was a relative value based on a gain in a maximum radiation direction of an antenna using a metal film. A reduction rate of the maximum gain by the sheet resistivity was about 0.2 dB/(ohms/square) at 2.4 GHz and was about 0.12 dB/(ohms/square) at 5.6 GHz.
Similarly, radiation efficiencies of the antenna 4 were measured at 2.4 GHz and 5.0 GHz. Along with the theoretically expected radiation efficiencies, the measured radiation efficiencies are shown in FIG. 17. A reduction rate of the radiation efficiency by the sheet resistivity was about 2.7 %/(ohms/square) at 2.4 GHz and was about 1.7 %/(ohms/square) at 5.6 GHz.
Exemplary Embodiment 2
In exemplary Embodiment 2, the FTO film was used for the transparent conductive film 6, the antenna 4 was manufactured in the same dimensions as those of exemplary Embodiment 1 , and an antenna characteristic was measured. A relationship between the transmittance of the antenna 4 in a state in which the transparent conductive film 6 (or the FTO film) was formed on the glass substrate 5 and the sheet resistivity of the FTO thin film is shown in FIG. 18.
Radiation patterns at 2.4 GHz of the antenna 4 of Embodiment 2 are shown in FIGS . 19 to 21. FIG. 19 is a graph showing the radiation pattern of E0 of the XY plane at 2.4 GHz. FIG. 20 is a graph showing the radiation pattern of Ee of the XZ plane at 2.4 GHz. FIG. 21 is a graph showing the radiation pattern of E0 of the YZ plane at 2.4 GHz.
Maximum gains were measured at 2.4 GHz and 5.0 GHz of the antenna 4 of exemplary Embodiment 2. Along with the theoretically expected maximum gains, the measured maximum gains are shown in FIG. 22. The maximum gain was a relative value based on a gain in a maximum radiation direction of an antenna using a metal film. Radiation efficiencies of the antenna 4 of exemplary Embodiment 2 were measured at 2.4 GHz and 5.0 GHz. Along with the theoretically expected radiation efficiencies, the measured radiation efficiencies are shown in FIG. 23. Exemplary Embodiment 3
A dipole antenna 8 as shown in FIG. 24 was manufactured using an ITO thin film and an FTO thin film as transparent conductive films and characteristics of the dipole antenna 8 were measured. The dipole antenna 8 included transparent conductive films 9A and 9B having two parallel stripe-shaped bases and two main bodies of externally extended four-sided polygons bent from ends of the bases. Other ends of the bases were connected to an electrical circuit. A length W1 of a side of a base of the main body, a length W2 of a side facing W1, a length W3 of the base, a length L of the main body, and an interval of the bases G satisfy the following relationships: 0.1 mm < W1 < 15 mm, 0.1 mm < W2 < 15 mm, 0 mm < W3 < 10 mm, 2 mm < L < 50 mm, and 0.05 mm < G < 5 mm
In the dipole antenna 8, L = 21 mm, W1 = 3 mm, W2 = 9 mm, W3 = 6 mm, and G = I mm. A pattern was formed on the glass substrate as in exemplary Embodiment 1. Upon measuring the transmittance or radiation characteristic of the antenna 8 as in exemplary Embodiment 1 and exemplary Embodiment 2, results almost equal to those of exemplary Embodiment 1 and exemplary Embodiment 2 were obtained.
Dimensions of the antenna 8 were varied such that the lengths W1 and W2 of the sides of the base of the main body, the length W3 of the base, the length L of the main body, and the interval of the bases G satisfy the following relationships: 0.1 mm < W1 < 15 mm, 0.1 mm < W2 < 15 mm, 0 mm < W3 < 10 mm, 2 mm < L < 50 mm, and 0.05 mm < G < 5 mm.
Also in this case, the gain reduction by the sheet resistivity and the radiation efficiency equivalent to those of exemplary Embodiment 1 and exemplary Embodiment 2 were obtained. Except for a variation of the reduction of the maximum gain by the sheet resistivity, the radiation pattern was almost the same as that of the antenna made of copper. Exemplary Embodiment 4
The antenna 8 of exemplary Embodiment 3 was film-formed on a surface of a wireless device having a dielectric case 10 as shown in FIG. 25. An upper surface of the wireless device was made of an insulating material. In this case, a radiation characteristic of the antenna 8 is affected by the permittivity of the dielectric case 10 formed on the upper surface of the wireless device. However, in this case compared with a single installation case in exemplary Embodiment 1 and exemplary Embodiment 2, a VSWR characteristic was only slightly varied. Accordingly, this antenna can be installed on a display portion of the wireless device, and can also be installed on a display glass or the backside of a transparent plastic. Exemplary Embodiment 5
The antenna 8 of exemplary Embodiment 3 was film-formed on a surface of a dielectric case 10 of a wireless device as shown in FIG. 26. An upper surface of the wireless device was made of an insulating material, the antenna 8 was formed on a transparent dielectric substrate, for example, but not limited to, glass or plastic, and a dielectric substrate 11 was layered to insert transparent conductive films 9 A and 9B.
In this case, a radiation characteristic of the antenna 8 was affected by the permittivity of the dielectric case 10 formed on the upper surface of the wireless device. However, in this case compared with a single installation case in exemplary Embodiment 1 and exemplary Embodiment 2, a VSWR characteristic was only slightly varied. In this case, the dielectric substrate 11 covered from the upper surface also played a role of protecting the antenna.
While embodiments of the invention have been described and illustrated above, it should be understood that these are exemplary of the invention and are not to be considered as limiting. Additions, omissions, substitutions, and other modifications can be made without departing from the spirit or scope of the present invention. Accordingly, the invention is not to be considered as being limited by the foregoing description, and is only limited by the scope of the appended claims. INDUSTRIAL APPLICABILITY
The transparent antenna of the invention may have transparency in the visible light range, thereby radiating an electromagnetic wave of a frequency band of about 100 MHz to 20 GHz. The antenna can be provided which has sufficient transparency and sufficient radiation characteristics by employing the ITO film in which the sheet resistivity is low and the transparency is high and by designing the shape of the antenna optimally.

Claims

1. A transparent antenna comprising: a radiating element for radiating an electromagnetic wave in a frequency band of 100 MHz to 20 GHz, wherein the radiating element is a transparent conductive film comprising at least one of a tin-doped indium oxide (ITO) thin film and a fluorine-doped tin oxide (FTO) thin film, and wherein the transparent conductive film has a film thickness of 100 nm or more, a transmittance of 40% or more in the visible light wavelength range of about 350 nm to 780 nm, and a sheet resistivity of 20 ohms/square or less.
2. The transparent antenna according to claim 1 , wherein the transparent conductive film is formed on a transparent dielectric substrate.
3. The transparent antenna according to claim 1, wherein the transparent conductive film has a transmittance of 60% or more in the visible light wavelength range.
4. The transparent antenna according to claim 1 , wherein the transparent conductive film has a thickness in a range of 100 nm or more to 1 μm or less.
5. The transparent antenna according to claim 1, wherein the transparent conductive film includes the FTO thin film.
6. The transparent antenna according to claim 2, wherein the transmittance is 30% or more in the visible light wavelength range of about 350 nm to 780 nm when the transparent conductive film is formed on the transparent dielectric substrate.
7. The transparent antenna according to claim 2, wherein the transmittance is 50% or more in the visible light wavelength range of about 350 nm to 780 nm when the transparent conductive film is formed on the transparent dielectric substrate.
8. The transparent antenna according to claim 1 , wherein the transparent conductive firm is formed on a non-transparent dielectric substrate.
9. The transparent antenna according to claim 1 , wherein a reduction of a maximum gain is 6 dB or less and a radiation efficiency is 20% or more in a frequency range of about 1 GHz to 12 GHz, in comparison with an antenna manufactured using an isometric metal thin film.
10. The transparent antenna according to claim 1 , wherein a reduction rate of a maximum gain is 0.5 dB/(ohms/square) or less, and a reduction rate of a radiation efficiency is 5 %/(ohms/square) or less, according to the sheet resistivity of the transparent conductive film at 1 GHz to 12 GHz.
11. The transparent antenna according to claim 1 , wherein the transparent antenna is a monopole antenna in which the transparent conductive film is a four-sided polygon, wherein a lower side thereof is electrically connected to an electrical circuit, and wherein a relationship such that a lower side dimension W1, an upper side dimension W2, and a height L are 0.1 mm < W1 < 15 mm, 0.1 mm < W2 < 15 mm, and 2 mm < L < 50 mm is satisfied in the monopole antenna.
12. The transparent antenna according to claim 1, wherein the transparent antenna is a dipole antenna in which the transparent conductive film comprises: two parallel stripe-shaped bases having first ends connected to an electrical circuit; and two main bodies of externally extended four-sided polygons bent from second ends of the bases, wherein a relationship such that a length W1 of a side of a base of the main body, a length W2 of a side facing W1, a length W3 of the base, a length L of the main body, and an interval of the bases G are 0.1 mm < Wl < 15 mm, 0.1 mm < W2 < 15 mm, 0 mm < W3 < 10 mm, 2 mm < L < 50 mm, and 0.05 mm < G < 5 mm is satisfied.
13. The transparent antenna according to claim 1 , wherein the transparent conductive film is formed on a surface of a wireless device having a dielectric case.
14. The transparent antenna according to claim 13, wherein the dielectric case has a structure in which a dielectric substrate is layered to insert the transparent conductive film.
15. The transparent antenna according to claim 1 , wherein the transparent conductive film is formed on at least one of inner and outer surfaces of a display.
16. The transparent antenna according to claim 15, wherein the display has a structure in which a dielectric substrate is layered to insert the transparent conductive
film.
PCT/JP2007/070965 2006-10-20 2007-10-22 Transparent antenna WO2008047953A1 (en)

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