JP6983613B2 - Microwave band antenna - Google Patents

Description

The present invention relates to a microwave band antenna using graphene as an antenna element.

A transparent antenna in which an antenna element made of a transparent conductive film is formed on a transparent substrate is known. At present, ITO (indium tin oxide), which is the mainstream as a transparent conductive film, has problems such as containing a rare metal and low plasticity, and a transparent conductive film replacing ITO is required.

Patent Document 1 proposes various electronic devices including a graphene-based layer, and an antenna is exemplified as one of the electronic devices. In Patent Document 1, a graphene-based layer is supported on a substrate, a part of the graphene-based layer is etched, and the graphene-based layer is made thinner than other parts to form an antenna.

Japanese Patent Publication No. 2013-502049

However, the specific structure of the antenna of Patent Document 1 is unknown, and it is not described so that a person skilled in the art can make this antenna. Moreover, when graphene is used as an antenna element, the band that can be used as an antenna has not been clarified at all. The inventors of the present application have been diligently studying the application of graphene to antenna elements.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an antenna using graphene as an antenna element.

In order to achieve the above object, the present invention provides a microwave band antenna having a substrate and a transparent antenna element formed on the substrate and composed of graphene having a single layer or graphene laminated in a plurality of layers. .. The inventors of the present application have experimentally confirmed that graphene operates as an antenna element of a microwave band antenna.

In the microwave band antenna, the substrate may be transparent.

In the microwave band antenna, the antenna element may be made of a single layer of graphene.

In the microwave band antenna, the microwave band antenna may be a dipole antenna.

According to the present invention, graphene can be used as an antenna element for a microwave band antenna.

It is a top view of the microwave band antenna which shows one Embodiment of this invention. It is explanatory drawing which shows the manufacturing process of a microwave band antenna. It is a top view of the microwave band antenna of the comparative example. It is a graph which shows the measurement result of the reflection characteristic of an Example and a comparative example. It is a graph which showed the measurement result of the radiation characteristic of an Example superimposed on the measurement result of the reflection characteristic of an Example.

1 and 2 show an embodiment of the present invention, FIG. 1 is a plan view of a microwave band antenna, and FIG. 2 is an explanatory view showing a manufacturing process of the microwave band antenna. In FIGS. 1 and 2, the transparent graphene portion is shown in a honeycomb pattern for easy understanding.

As shown in FIG. 1, the microwave band antenna 1 has a substrate 2 as a substrate, an antenna element 3 formed on the substrate 2, and a feeder line 4. The microwave band antenna 1 of the present embodiment is a dipole antenna.

The substrate 2 is made of a transparent material having a rectangular shape in a plan view. In this embodiment, the substrate 2 is made of quartz glass. In the present specification, "transparent" means that the transmittance is 80% or more. The substrate 2 may be made of a glass material other than quartz glass. Further, the substrate 2 can be made of a transparent material other than the glass material, such as a transparent resin material such as polyethylene terephthalate. In the present embodiment, the arithmetic average surface roughness (Ra) of the surface of the substrate 2 is 2.0 nm or less. This is because if Ra on the surface of the substrate 2 exceeds 2.0 nm, the electrical characteristics of the antenna element 3 made of graphene may be impaired. Considering the electrical characteristics of the antenna element 3 as an antenna, Ra on the surface of the substrate 2 is preferably 1.0 nm or less, more preferably 0.8 nm or less.

The antenna element 3 is transparent and consists of a single layer of graphene or a plurality of layers of graphene. The inventors of the present application have experimentally confirmed that graphene operates as the antenna element 3 of the microwave band antenna 1. The surface on the substrate 2 on which the graphene is formed is preferably hydrophilic in order to achieve good adhesion of the graphene to the substrate 2. The antenna element 3 has two linear portions 31 provided symmetrically with respect to the virtual line 21 on the substrate 2. In the present embodiment, the two straight lines 31 are formed side by side in the longitudinal direction with the virtual line interposed therebetween. The transmittance T (%) of graphene is T (%) = 100-2.3N, where N is the number of layers. Therefore, for example, in order to make the transmittance of the antenna element 3 80% or more, graphene laminated in 8 layers or less may be used, and in the case of 90% or more, graphene laminated in 4 layers or less may be used. good. In the present embodiment, the antenna element 3 is a single layer graphene and has a transmittance of 97.7%.

The feeder line 4 is made of a conductive material and is used for transmitting high frequency power to and / or for transmitting high frequency power from the antenna element 3. In this embodiment, the feeder line 4 is made of Au / graphene. In the present embodiment, the feeder line 4 has a coplanar line portion 41 and a transmission line portion 42 connecting the coplanar line portion 41 and the antenna element 3. The coplanar line 41 is composed of a signal line 41a and a pair of grounding lines 41b formed at intervals from the signal line 41a. In the present embodiment, the transmission line unit 42 is configured by extending the signal line 41a of the coplanar line 41 and one of the ground lines 41b toward the antenna element 3.

Next, a method of manufacturing the microwave band antenna 1 of the present embodiment will be described with reference to FIG.
First, as shown in FIG. 2A, a single-layer graphene film 103 is produced on a copper foil 101 by a chemical vapor deposition method (CVD method). Then, as shown in FIG. 2B, the produced graphene film 103 is transferred onto the substrate 2. Specifically, in the transfer, for example, a support layer made of a resin material is formed on the copper foil 101, the copper foil 101 is removed with an acid or the like to form a laminate composed of the graphene film 103 and the support layer, and then the substrate 2 is formed. This is done by placing a laminate on top and melting the support layer. Here, the substrate 2 is made of quartz glass and is surface-treated in advance so as to be hydrophilic prior to transfer.

After that, as shown in FIG. 2C, the Au film 104 is vapor-deposited on the graphene film 103. Then, as shown in FIG. 2D, the antenna element 3 and the feeder line 4 are patterned on the Au film 104 by the photolithography technique and the etching technique, and unnecessary portions of the Au film 104 are removed. Further, as shown in FIG. 2 (e), the exposed graphene film 103 is removed by UV-ozone treatment. Then, as shown in FIG. 2 (f), the feed line 4 is patterned on the Au film 104 by the photolithography technique and the etching technique, the Au film 104 on the antenna element 3 is removed, and the microwave band antenna 1 is removed. Is completed.

According to the microwave band antenna 1 configured as described above, since the antenna element 3 is graphene, a transparent antenna element 3 can be realized without using a rare metal like ITO. Further, since graphene is rich in plasticity as compared with ITO, it is possible to form the antenna element 3 not only on a flat surface but also on a curved surface. Further, even when the substrate 2 is made of a flexible resin material, the antenna element 3 can be made to follow the deformation of the substrate 2, and the flexibility can be imparted to the entire antenna.

In the above embodiment, the microwave band antenna 1 configured as a dipole antenna is shown, but if the shape, arrangement, etc. of the antenna element 3 are changed, for example, a monopole antenna, a loop antenna, or a logperiodic antenna. It is also possible to use a linear antenna other than a dipole antenna. Further, it may be a planar antenna such as a patch antenna, and the type of antenna is not particularly limited.

Further, in the above-described embodiment, the feeding line 4 is formed on the substrate 2, but the feeding line 4 is not formed on the substrate 2 and the feeding line 4 is supplied to the antenna element 3 from the outside of the antenna in a non-contact manner. It may be configured. In this case, the microwave band antenna 1 composed of the transparent substrate 2 and the transparent antenna element 3 can be made transparent as a whole. Even if the feeder line 4 is opaque, it is possible to make the feeder line 4 inconspicuous by arranging the feeder line 4 near the outer edge of the substrate 2.

Further, in the above-described embodiment, the antenna element 3 is formed on the substrate 2, but it is also possible to form the antenna element 3 on a substrate other than the substrate 2 to form the microwave band antenna 1. .. Further, although the substrate 2 is shown to be transparent, the substrate 2 may be opaque.

Although the embodiments of the present invention have been described above, the embodiments described above do not limit the invention according to the claims. It should also be noted that not all combinations of features described in the embodiments are essential to the means for solving the problems of the invention.

As an example, the microwave band antenna 1 shown in FIG. 1 was actually manufactured, and the reflection characteristics and the radiation characteristics with respect to the input power of the microwave band antenna 1 were measured.

In producing the microwave band antenna 1, first, a single-layer graphene film 103 was produced on a copper foil 101 by a chemical vapor deposition method (CVD method). Graphene was grown at a temperature of 1000 ° C. and a pressure of 1500 Pa, and _{2 sccm of CH 4} gas and 20 sccm of H 2 gas were circulated for 30 minutes. Then, the graphene film 103 was transferred onto the quartz glass substrate 2 using the support layer of methyl polymetalcrylate. When the Raman spectrum of the graphene film 103 after transfer was measured, the intensity ratio of the 2D band to the G band was 3.5, and the 2D band could be fitted by the Lorentz function, so that the graphene was a single layer. Was confirmed.

Subsequently, an Au film 104 having a diameter of 700 nm was formed on the graphene film 103 by using an electron beam vapor deposition method. Then, the antenna element 3 and the feeder line 4 were patterned on the Au film 104 by photolithography, and the Au film 104 was etched using the KI aqueous solution at 60 ° C. Further, the exposed graphene film 103 was removed by UV-ozone treatment at 120 ° C. by passing _{300 sccm of O 2 gas.} Then, the feeder line 4 was patterned on the Au film 104 by photolithography, and the Au film 104 on the antenna element 3 was removed at 60 ° C. using a KI aqueous solution. When the region where graphene was present on the substrate 2 in the microwave band antenna 1 thus produced was confirmed by Raman imaging, it almost coincided with the region of the antenna element 3 in the design.

The specific dimensions of the antenna element 3 are 10.7 mm in the longitudinal direction and 1.0 mm in the width direction as a whole including the two straight portions. Further, the characteristic impedance of the coplanar wire portion 41 of the feeding portion 4 is set to 50Ω.

Further, as a comparative example, a microwave band antenna 201 using Au for the antenna element 203 on the quartz glass substrate 202 as shown in FIG. 3 was manufactured. As shown in FIG. 3, the pattern of the antenna element 203 of the comparative example has two linear portions 231 as in the embodiment. The pattern of the feeding unit 204 of the comparative example includes a coplanar wire unit 241 and a transmission line unit 242 connecting the coplanar wire unit 241 and the antenna element 203, as in the embodiment. The material of the antenna element 203 and the feeding portion 204 was Au / Cr (700 nm / 50 nm), and the antenna element 203 and the feeding portion 204 were manufactured by an electron beam vapor deposition method and a thermal vapor deposition method.

FIG. 4 is a graph showing the measurement results of the reflection characteristics of Examples and Comparative Examples. In FIG. 4, the horizontal axis is the frequency and the vertical axis is the reflection coefficient. Specifically, the input power to the feeding units 4, 204 was set to 0.32 mW, and the reflectance coefficient was measured at a frequency of 100 MHz to 30 GHz.

As shown in FIG. 4, it was confirmed that in the antenna of the example, the operating frequency at which the reflection loss is minimized is 20.7 GHz. In the antenna of the comparative example, the operating frequency was 9.2 GHz. Further, in both the examples and the comparative examples, since the operating frequency was lower than -10 dB, it was confirmed that 90% or more of the electric power was supplied.

FIG. 5 is a graph showing the measurement results of the reflection characteristics of the examples and the measurement results of the radiation characteristics of the examples superimposed. For the radiation characteristics, the main polarization horizontal to the antenna element 3 and the cross polarization perpendicular to the antenna element 3 were measured separately. In FIG. 5, the horizontal axis is the frequency, and the vertical axis is the reflection coefficient and the transmission coefficient.

As shown in FIG. 5, in the antenna of the embodiment, since the amount of radiation of the main polarization in the operating frequency band is relatively larger than that of the other frequency bands, it is understood that microwaves are radiated from the antenna. In particular, in the operating frequency band, the radiation amount of the main polarization is about 20 dB larger than that of the cross polarization, so that it is shown that the antenna operates as a dipole antenna.

1 Microwave band antenna 2 Board 3 Antenna element 4 Feeding part 21 Virtual line 31 Straight line part 41 Coplanar line part 41a Signal line 41b Ground wire 42 Transmission line part 101 Copper foil 103 Graphene film 104 Au film 201 Microwave band antenna 202 Board 203 Antenna element 204 Feeding part 231 Straight line part 241 Coplanar line part 242 Transmission line part

Claims (4)

With the substrate
A microwave band antenna having a transparent antenna element formed on the substrate and composed of graphene having a single layer or graphene laminated in a plurality of layers. The microwave band antenna according to claim 1, wherein the substrate is transparent. The microwave band antenna according to claim 1 or 2, wherein the antenna element is made of a single layer of graphene. The microwave band antenna according to any one of claims 1 to 3, wherein the microwave band antenna is a dipole antenna.

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