Invisible antenna

An invisible antenna with excellent antenna characteristics that cannot be visually recognized by naked eyes. A pair of linear conductors 11 are connected to a feeding line 12, and a plurality of the linear conductors 11 are disposed on and/or within a transparent insulating layer 14. The linear conductor 11 cannot be visually recognized by human naked eyes.

The present application is based on Japanese Patent Application No. 2004-328839 filed on Nov. 12, 2004, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an invisible antenna for radio communication, which receives a VHF band, UHF band, etc., in more particularly, to an invisible antenna with a reduced visibility of an antenna device.

2. Description of the Related Art

Conventionally, when considering a half wavelength dipole antenna as antenna device for transmitting and receiving a VHF band (30 to 300 MHz), UHF band (300 MHz to 3 GHz), etc., an antenna device30comprising a pair of conductor plates31,31and a feeder part32connected to the conductor plates31,31may be provided as shown inFIG. 1.

Herein, the conductor plate31can be composed of a pipe material or wire rod. A total length L of the conductor plates is various, however, as for a most theoretical length, the length L is the ½ wavelength. For example, the length L becomes about 300 mm (L=300 mm) for a 500 MHz band, since the wavelength is 600 mm. For this case, a width W of the conductor plate is generally more than several millimeters for the practical dimension.

In addition,FIG. 2shows another type of a conventional antenna device30in which a passive element33is disposed with a predetermined distance from conductor plates31,31to adjust directional characteristics.FIG. 3shows an antenna device30, in which a pair of triangular conductor plates31a,31aare positioned in symmetry to provide a bow tie configuration, so as to broaden a bandwidth of a resonance frequency.FIG. 4shows a conventional antenna device30, in which a pair of fan-shaped conductor plates31b,31bare positioned in symmetry to provide a bow tie configuration, so as to broaden a bandwidth of the resonance frequency.

However, in the conventional antenna device30for example shown inFIG. 1, the width W of the conductor plate31is several millimeters and the length L is about 300 mm for the 500 MHz band. Since the width N and the length L are large, the antenna device30is visible by human naked eyes. For example, if an installation site of the antenna device30is a perimeter of a television receiver or inside of a car, the existence of the antenna device may be an issue in a total design matching.

In addition, film-shaped antennae have been commercialized. However, when the film-shaped antenna is stuck on a glass window of a house or car, the existence of the antenna device may become an issue in the total design matching. When the antenna device occupies a large area, it may become one of visual field blockage factors. Conventional film-shaped antennae are disclosed in Japanese Patent Laid-Open (Kokai) Nos. 2000-174529 (JP-A-2000-174529), 11-145717 (JP-A-11-145717), and 8-242114 (JP-A-8-242114).

For solving the above problems, as shown inFIG. 5, it is necessary to make a width of linear conductors21,21extremely small, such that the linear conductors21,21are not in a visible state. However, such a configuration is accompanied with an increase in a conductor resistance, thereby occurring a loss in electric wave transmission and reception characteristics, which is an important function of the antenna device.

In other words, it is necessary for the length L of the linear conductors21,21to be about ½ wavelength to tune the resonance frequency in the dipole antenna. However, when the width W of the linear conductor21is made small, the conductor resistance is increased, so that the conductor resistance becomes dominant in an input impedance of the antenna. As a result, there is a disadvantage in that an impedance matching with a feeder part22becomes impossible, thereby deteriorating the antenna characteristics.

Accordingly, it is an object of the invention to provide an invisible antenna with excellent antenna characteristics, which cannot be recognized visually by the human naked eyes.

According to a first feature of the invention, an invisible antenna, comprises:

a transparent insulating layer; and

a plurality of conductors disposed on and/or in the transparent insulating layer for radiating or receiving electric wave, the conductor being invisible by human eyes.

Further, the conductor may be a linear conductor.

It is preferable that a diameter of the conductor is 0.1 mm or less. It is more preferable that a diameter of the conductor is 0.08 mm or less.

Still further, the invisible antenna may further comprise a feeding line connected to a pair of the conductors, wherein the conductors are disposed in parallel with each other.

In addition, the invisible antenna may further comprise a feeding line connected to a pair of the conductors, wherein each of the conductors is provided with an angle different with each other to a reference line.

An angle between adjacent ones of the conductors may be different with each other. The angle between adjacent ones of the conductors may be equal to each other. Each of the conductors may be provided with a length different with each other.

Further, the conductors may be crisscrossed with each other.

Still further, the conductors may be formed on and/or in the insulating layer by a mechanical process. The conductors may be formed on and/or in the insulating layer by a chemical process.

Furthermore, it is preferable that a projection width of the conductor on a plane observed by human eyes is 0.1 mm or less, and a pitch between adjacent ones of the conductors on the plane is more than ten times of the diameter of the conductor or the projection width of the conductor at the narrowest.

The projection width of the conductor may be 0.08 mm or less.

According to an invisible antenna of the present invention, since extremely thin linear conductors are disposed planarly with a large pitch, a visual recognition of the antenna device by human naked eyes becomes almost impossible, so that the installation condition of the antenna device will not become an issue in the total design matching. In addition, while the antenna device may be provided in various shapes in accordance with its application, the invisible antenna of the present invention can be freely formed in any shape, since the visibility of the antenna device becomes almost none.

DETEILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Next, an invisible antenna in preferred embodiments of the present invention will be explained in conjunction with the appended drawings.

Firstly, in the present application, a term “invisible” means at least two following states.

(1) where the conductors are difficult to be visually recognized, and

(2) where the conductors are not possible to be visually recognized.

FIGS. 6A and 6Bare diagrams showing an invisible antenna in a first preferred embodiment according to the present invention, whereinFIG. 6Ais a plan view of the invisible antenna1andFIG. 6is a cross sectional view of the invisible antenna1shown inFIG. 6Acut along line A-A′.

In an invisible antenna1shown inFIG. 6A, the number N of thin linear conductors11having a wire diameter of 0.1 mm, preferably 0.08 mm or less are disposed in an insulating layer14with an excellent optical transparency to form an antenna element part10. This antenna element part10is connected collectively to a feeding line12, which is connected to a receiver (not shown) or a power source (not shown) to provide the invisible antenna1.

The linear conductors11are composed of plural thin lines (wires), and the linear conductors11are disposed symmetrically as to regard the feeding line12. A length L of a pair of the linear conductors11is determined as e.g. about ½ wavelength of a frequency of a receiving/radiating electric wave of the invisible antenna1.

For example, assuming this invisible antenna1as a receiving antenna, electric current is induced in each one of the thin lines, and a receiving electric power can be provided through the feeding line12.

The linear conductors11with the number N have an equal length, so that the electric powers supplied from respective lines are synthesized to have a common mode (in-phase) in the feeding line12.

If the number N becomes large, the antenna element part10comprising a batch of the linear conductors11will become approximately equivalent with a conductor plate31shown inFIG. 1, and electric wave receiving functions of both the antenna devices will approach to each other. From this fact, an operation of the antenna element part10inFIG. 6Awill be understood.

Herein, the linear conductor11has a high resistance value since the respective lines are thin. However, the linear conductors11with the number N are connected collectively by the feeding line12, thereby providing a parallel circuit.

Therefore, considering the antenna device1as an antenna composed of the antenna element part10comprising the linear conductors11with the number N and a feeding line12, a resistance value of each of the linear conductors11providing a heat loss will be synthesized parallel and will be reduced to 1/N Accordingly, the impedance matching of the antenna element part10and the feeding line12can be realized easily by choosing the number of the linear conductors11appropriately.

For example, assuming an antenna device for 500 MHz band (a wavelength of 600 mm) with a length L of ½ wavelength (wavelength/2=300 mm) by using a copper wire with a diameter d of 0.01 mm (d=0.01 mm), a high frequency resistance along the length L of the conductors11will be 263Ω, wherein N=1. This high frequency resistance value is much greater than 73.13Ω that is a radiation resistance of the antenna device1, so that a heat loss will become large. When the number N is 100 (N=100), the high frequency resistance will be reduced to be 2.6Ω, so that the heat loss becomes to a level that can be ignored. At this time, if a conductor pitch P is assumed e.g. 0.2 mm, a width occupied by the linear conductors11is 19.81 mm, so that a dimension of the antenna device1becomes a dimension of a general antenna.

FIGS. 7A and 7Bare enlarged cross sectional views of the invisible antenna shown inFIG. 6A, whereinFIG. 7Ashows a state the linear conductors are formed in an insulating layer, andFIG. 7Bshows a state that the linear conductors are formed on the insulating layer.FIG. 7Ais a diagram for explaining the visibility of the antenna device1, wherein a cross section of the linear conductor11has a circular shape, a conductor diameter is d, a conductor pitch is P, a number of conductors is N, and a width of the insulating layer14is A.

Herein, the diameter d is 0.1 mm or less, more preferably 0.08 mm or less, since the visual recognition becomes difficult with an ordinary recognition capacity of human naked eyes under this condition. Therefore, a projection width of the linear conductor11on a plane to be visually observed is 0.1 mm or less, preferably 0.08 mm or less.

In addition, when a part of a light transmitting through the insulating layer14having a width A is obstructed by the linear conductors11with the number N, shadows of the linear conductors11are formed, so that the linear conductors11will become visible as a result.

A degree of this shadow can be expressed as SR as follows:

In general, due to the human vision capacity, if the diameter d is greater than SR=10 dB, the visual recognition by the human naked eyes will become difficult. For this reason, it is necessary to satisfy that P/d is 10 or more (P/d≧10). In other words, the pitch P between the adjacent linear conductors on a plane visually observed should be more than 10 times the diameter d or the projection width of the linear conductor at the narrowest.

In addition, a technique of composing an antenna device by using plural conductors is generally used in the field of antenna device for a short wavelength band using a low frequency. However, the object of such an antenna device is to prevent an increase in a device weight or an increase in a received wind pressure due to a device dimension for the long wavelength, rather than reducing the heat loss due to the conductor resistance. Therefore, the technical role of the antenna device according to the present invention is completely different from that of the antenna device for the short wavelength band

FIG. 7Ashows an example in which the plural linear conductors11are disposed coplanarly in the insulating layer14, so that the plural linear conductors11are arranged in a same plane. However, the present invention is not limited thereto. The respective linear conductors11may not be disposed in the same plane.

FIG. 7Bshows an example where the plural linear conductors11are provided on a surface of the insulating layer14. The linear conductors11may be provided anywhere including a front surface and a back surface. Accordingly, the linear conductors11can be disposed on and/or in the insulating layer14,

In addition, the feeding line12does not have an adverse effect, since the length thereof is short even if the feeding line12is visible by human naked eyes However, for making the feeding line12invisible, a diameter of the feeding line12should be 0.1 mm or less. For this case, the feeding lines12should be arranged in parallel since the resistance value at an input side is increased.

FIG. 8is a plan view showing an invisible antenna in a second preferred embodiment according to the invention.

InFIG. 8, each of linear conductors11with a diameter of 0.1 mm or less composing an antenna element part10is provided with an angle different with each other to provide a bow tie configuration. In other words, the linear conductors11are arrayed on the insulating layer14. Simultaneously, each pair of the linear conductors11is provided with an equal length L (for example, ½ wavelength), and disposed on the insulating layer14to constitute an invisible antenna device1. Herein, the length L is a distance between both ends of the pair of the linear conductors11.

Herein, the angle of the each linear conductor11is an angle as regard to a predetermined reference line provided on an insulating layer14. InFIG. 8, a centerline CL is provided for example at a center of the insulating layer14that is parallel with the feeding lines12.

Further, the angles between the adjacent linear conductors11might be different with each other. For example, adjacent linear conductors11-1and11-2are positioned with an angle θ1, and adjacent linear conductors11-2and11-3are positioned with an angle θ2, wherein the angles θ1and θ2are different with each other.

Still further, the angles between the adjacent linear conductors11might be equal with each other. For example, the angle θ1between the linear conductors11-1and11-2and the angle θ2between the linear conductors11-2and11-3might be equal to each other.

According to the invisible antenna1in the second preferred embodiment, it is possible to achieve an operation similar to that of the conventional antenna device30(half wavelength dipole antenna) having a bow tie configuration shown inFIG. 3, which comprises the triangular conductor plates31a,31aand the feeder part32.

FIG. 9is a plan view showing an invisible antenna in a third preferred embodiment according to the invention

InFIG. 9, each of linear conductors11composing an antenna element part10is provided with an angle and a length different with each other to provide a substantially fan shape configuration to constitute an invisible antenna1.

Similarly to the second preferred embodiment shown inFIG. 8, the angle of the each linear conductor11is an angle as regard to a predetermined reference line (e.g. centerline CL) provided on an insulating layer14.

Further, the angles between the adjacent linear conductors11might be different with each other For example, adjacent linear conductors11-1and11-2are positioned with an angle θ1, and adjacent linear conductors11-2and11-3are positioned with an angle θ2, wherein the angles θ1and θ2are different with each other.

Still further, the angles between the adjacent linear conductors11might be equal with each other For example, the angle θ1between the linear conductors11-1and11-2and the angle θ2between the linear conductors11-2and11-3might be equal to each other.

According to the invisible antenna1in the third preferred embodiment, it is possible to achieve an operation similar to that of the conventional antenna device30(half wavelength dipole antenna) having a bow tie configuration shown inFIG. 4, which comprises the fan shape conductor plates31b,31band the feeder part32.

FIGS. 10A and 10Bare diagrams showing an invisible antenna in a fourth preferred embodiment according to the present invention, whereinFIG. 10Ais a plan view of the invisible antenna andFIG. 10Bis a cross sectional view of the invisible antenna shown inFIG. 10Acut along line A-A′.

InFIG. 10A, a passive element15comprising thin linear conductors16disposed in parallel with an antenna element part10configured similarly to that inFIG. 6Ais provided to form an invisible antenna1.

According to the invisible antenna1in the fourth preferred embodiment, it is possible to achieve an operation similar to the conventional antenna device30shown inFIG. 2.

FIG. 11is an enlarged perspective view showing the linear conductors of an invisible antenna2na fifth preferred embodiment according to the present invention.

InFIG. 11, linear conductors11a,11bare positioned in crisscross arrangement. The linear conductors11aare positioned in parallel with a conductor pitch P1, and the linear conductors11bare positioned in parallel with a conductor pitch P2.

The antenna element10inFIGS. 6A,8and9and an antenna element comprising the linear conductors21inFIG. 5may be replaced with these linear conductors11a,11bwith appropriately connecting to a feeding line (not shown inFIG. 11).

Further, the passive element15inFIG. 10Amay be replaced with these linear conductors11a,11bwithout connecting the feeding line.

According to an invisible antenna1using the crisscrossed linear conductors11a,11bin the fifth preferred embodiment, it is possible to achieve an operation similar to those in the antenna devices shown inFIGS. 5,6A,8and9.

For realizing the antenna devices in the first to fifth preferred embodiments in a manufacturing process, the thin linear conductors11may be disposed on and/or in the insulating layer14by a mechanical process. For example, the linear conductors11may be laminated between two layers of the insulating layers14. The thin linear conductors11may be formed on and/or in the insulating layer14by a chemical process such as etching.

The invisible antenna of the present invention can be stuck on a glass window of a house, car, etc. as an antenna for receiving FM broadcasting, television broadcasting or antenna for wireless LAN transmission and reception.

Although the invention has been described with respect to specific embodiment for complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modification and alternative constructions that may be occurred to one skilled in the art which fairly fall within the basic teaching herein set forth.