JP2020184720A - Planar antenna - Google Patents

Abstract

To provide a flexible planar antenna.SOLUTION: A planar antenna 101 includes a flexible dielectric substrate 102, a radiant conductor layer 103 formed on the first surface of the dielectric substrate 102, and a ground conductor layer 104 formed on the second surface opposite to the first surface of the dielectric substrate 102, and the ground conductor layer 104 is formed by being divided into a plurality of strip portions L by a plurality of slits La extending in a predetermined direction.SELECTED DRAWING: Figure 1B

Description

The present invention relates to a planar antenna.

In recent years, with the progress of IoT, efforts to constantly collect human location and biological information and utilize it for monitoring and health management are attracting attention. In order to constantly acquire biological information, it is necessary to always attach a sensor to the human body, but the operation of the terminal requires replacement or charging of the battery, and it takes time and effort to keep the terminal running for a long period of time.

Wireless power supply methods are attracting attention as a means of solving the problems of battery replacement and charging. In order to perform wireless power supply, it is necessary to use an antenna having a large area and a multi-layer structure in order to convert electromagnetic waves into electric power.

In particular, planar antennas are expected to be applied to this type of application because they are lightweight, easy to manufacture, and have excellent directivity. In this respect, in order to naturally attach the biological information acquisition sensor equipped with a large-area antenna to the human body (for example, to be wrapped around the arm of the human body), the planar antenna needs to be flexible. However, high-efficiency planar antennas generally have a large area and a multi-layer structure, and few of them are flexible.

3A and 3B are views showing the configuration of the planar antenna described in Patent Document 1. Note that FIG. 3A is a diagram showing a state of a flat antenna in the middle of manufacturing, and FIG. 3B is a diagram showing a state of the completed flat antenna.

In this flat antenna, power supply wiring and the like are formed in a dielectric plate 301 which is a multilayer board, and are integrated with an electronic circuit. Further, this flat antenna has a structure in which a bendable antenna plate 302 is attached to one surface of the dielectric plate 301. Then, this flat antenna is deformed and used in a state where the dielectric plate 301 is sandwiched between the antenna plates 302 by bending the antenna plate 302. The flat antenna is configured as a patch antenna so that a radiation element is formed only on one side of the dielectric plate 301 of the antenna plate 302.

In the planar antenna described in Patent Document 1, the area of the antenna plate 302 is increased and the efficiency is improved by such a configuration.

Japanese Unexamined Patent Publication No. 2003-332830

By the way, as a flat antenna according to the prior art, there is known a structure in which an antenna plate made of sheet metal and a ground plate are arranged so as to face each other with an air layer interposed therebetween. Further, as another structure of the planar antenna, a structure is known in which a metal pattern forming an antenna portion is formed on one surface of a dielectric substrate and a metal pattern forming a ground is formed on the other surface.

However, it is difficult to physically bend any of the planar antennas according to the prior art. Therefore, the planar antenna according to the prior art has a problem in terms of wearability to the human body and the like.

The present disclosure has been made in view of the above problems, and an object of the present disclosure is to provide a planar antenna having flexibility.

The main disclosure that solves the above-mentioned problems is
With a flexible dielectric substrate,
A radiation conductor layer formed on the first surface of the dielectric substrate and
A ground conductor layer formed on a second surface of the dielectric substrate opposite to the first surface, and
With
The ground conductor layer is divided into a plurality of strip portions by a plurality of slits extending in a predetermined direction.
It is a flat antenna.

The flat antenna of the present invention can be naturally attached to the human body by making a slit in the ground plate and making the entire antenna flexible.

The figure which shows the whole structure of the plane antenna of this invention The figure which shows the whole structure of the plane antenna of this invention The figure which shows the whole structure of the plane antenna of this invention Enlarged view showing the state of the slit formed in the ground plate of the plane antenna of the present invention. Enlarged view showing the state of the slit formed in the ground plate of the plane antenna of the present invention. The figure which shows the structure of the plane antenna described in Patent Document 1. The figure which shows the structure of the plane antenna described in Patent Document 1.

Preferred embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. In the present specification and the drawings, components having substantially the same function are designated by the same reference numerals, so that duplicate description will be omitted.

<Overall structure>
Hereinafter, an example of the configuration of the planar antenna according to the embodiment will be described with reference to FIGS. 1A, 1B, 1C, 2A, and 2B.

The planar antenna according to the present embodiment is used, for example, as an antenna for microwave wireless power feeding capable of information communication. The flat antenna 101 can be used by wrapping it around an arm, and can operate with high efficiency in the vicinity of a human body or a metal material, and can handle curved surfaces. It should be noted that this planar antenna can be applied to both applications of transmitting electromagnetic waves and applications of receiving electromagnetic waves.

1A, 1B, and 1C are views showing the overall configuration of the planar antenna 101. FIG. 1A is a bottom view of the planar antenna 101. FIG. 1B is a side view of the flat antenna 101 when it is not curved. FIG. 1C is a side view of the flat antenna 101 when curved.

2A and 2B are enlarged views showing the state of the slit La formed in the ground conductor layer 104. FIG. 2A shows the state of the slit La when the flat antenna 101 is in the non-curved state, and FIG. 2B shows the state of the slit La when the flat antenna 101 is in the curved state.

The flat antenna 101 is mounted on the dielectric substrate 102, the radiating conductor layer 103 arranged on the first surface of the dielectric substrate 102, and the second surface of the dielectric substrate 102 opposite to the first surface. The ground conductor layer 104 is provided.

The planar antenna 101 exhibits a planar shape when no external force is applied (see FIG. 1B), and when an external force is applied so as to bend one side and the other side of the dielectric substrate 102 toward the ground conductor layer 104 side. Is configured to be deformable into a curved shape (see FIG. 1C). When the flat antenna 101 is deformed into a curved shape, the flat antenna 101 is elastically deformed with the ground conductor layer 104 on the inside and the radiant conductor layer 103 on the outside.

<Dielectric substrate 102>
The dielectric substrate 102 is used as a base material for the flat antenna 101. Further, the dielectric substrate 102 plays a role of keeping the distance between the radiation conductor layer 103 and the ground conductor layer 104 constant.

In the flat antenna according to the prior art, each of the radiation plate and the ground plate is made of sheet metal, and an air layer is provided between the radiation plate and the ground plate. In such a configuration, it is possible to maintain a distance between the radiation plate and the ground plate, but the application as a flexible planar antenna becomes impossible.

From this point of view, as the dielectric substrate 102 according to the present embodiment, a dielectric material having flexible elastic characteristics is used, and the flexibility of the entire planar antenna 101 is ensured. Further, as the dielectric material used for the dielectric substrate 102, it is desirable that the electrical characteristics are close to those of air, and it is desirable that the dielectric material has as low a dielectric constant and a low dielectric loss tangent as possible. Examples of materials having excellent electrical properties include fluororesins, fluorocarbon resins, and specifically, PTFE (polytetrafluoroethylene) and the like. For example, the dielectric substrate 102 is formed by stretching and containing air in order to further reduce the dielectric constant, reduce the dielectric loss tangent, and make the PTFE more flexible.

Here, flexibility means that it can be curved as shown in FIG. 1C. As a whole, it can be curved like the side surface of a cylinder.

The shape of the dielectric substrate 102 is arbitrary, but for example, it exhibits a substantially square shape in a plan view. The thickness of the dielectric substrate 102 varies depending on the frequency (wavelength) band for wireless power feeding, and is set to, for example, about 2 mm to 5 mm. The length of one side of the dielectric substrate 102 in a plan view is, for example, about 1/6 to 1/2 of the wavelength.

The dielectric substrate 102 may be a multilayer substrate. Further, in the dielectric substrate 102, the high-frequency current received by the radiating conductor layer 103 is propagated, or the high-frequency current is supplied to the radiating conductor layer 103 in order to radiate radio waves from the radiating conductor layer 103. Power lines (eg, microstrip lines) (not shown) may be formed.

<Radiation conductor layer 103>
The radiation conductor layer 103 converts the radio wave radiated from the outside into a current, or converts the fed current into a radio wave radiated to the outside. The radiating conductor layer 103 functions as a patch antenna in cooperation with the ground conductor layer 104, for example.

The radiating conductor layer 103 is formed of a conductor (for example, copper) having a thickness of about 20 to 30 μm on the first surface of the dielectric substrate 102. Examples of the method for forming the radiation conductor layer 103 include plating, printing, and the like. The radiating conductor layer 103 is formed, for example, in a circular shape having a diameter of λ / 2 (where λ represents the wavelength of radio waves transmitted or received).

When the planar antenna 101 is deformed from a planar shape to a curved shape, the radiating conductor layer 103 needs to be extended or the ground conductor layer 104 needs to be contracted. However, since the dimensions of the radiant conductor layer 103 are closely related to the operating frequency of the radiant conductor layer 103, the length of the radiant conductor layer 103 is always constant when the planar antenna 101 is deformed. desirable. Therefore, in the planar antenna 101 according to the present embodiment, by providing the ground conductor layer 104 with a retractable mechanism, the planar antenna 101 can be deformed in a curved shape without changing the dimensions of the radiating conductor layer 103. It is said.

<Ground conductor layer 104>
The ground conductor layer 104 is arranged so as to face the radiation conductor layer 103 via the dielectric substrate 102, and functions as a ground (GND) when the radiation conductor layer 103 operates.

The ground conductor layer 104 is formed on the entire surface of the second surface of the dielectric substrate 102 by a conductor having a thickness of about 20 to 30 μm. Further, the ground conductor layer 104 is on the side to be attached to an object such as a human body or a metal material.

When the ground conductor layer 104 is bent inside, the ground conductor layer 104 needs to shrink in order for the radiation conductor layer 103 to bend as a whole without stretching. As a mechanism for contracting the ground conductor layer 104, the ground conductor layer 104 is formed as a plurality of strip portions L divided from each other by a plurality of slits La extending in one direction.

When the flat antenna 101 has a flat plate shape, the plurality of strip portions L are in a non-contact and non-conducting state, and when the flat antenna 101 is deformed into a curved shape to a predetermined bending radius, all of the strip portions L are in contact with each other and conduct.

The strip portion L is formed, for example, by patterning a copper-plated material formed on one surface.

<Slit La>
The slit La is formed to absorb the difference in the radius of curvature between the radiating conductor layer 103 and the ground conductor layer 104 when the planar antenna 101 is deformed into a curved shape. When the flat antenna 101 bends the ground conductor layer 104 inward, the slit La absorbs the contracted portion, and the plurality of strip portions L separated from each other become conductive. As a result, the planar antenna 101 operates.

It is necessary to specify the width of one slit La in order for the plurality of strip portions L to come into contact with each other when the flat antenna 101 is bent and to conduct electricity as a whole. The width of the slit La is determined by, for example, the thickness of the flat antenna 101 and the radius of curvature of the object to be attached.

In order to increase the radiation efficiency of the flat antenna 101, it is desirable that the distance between the radiation conductor layer 103 and the ground conductor layer 104 is always kept constant (for example, several mm). In this regard, consider a case where a planar antenna is constructed by using a dielectric substrate having a low dielectric constant and a low dielectric loss tangent and forming metal films on both sides thereof in order to keep the distance between the two constant. In this case, bending the planar antenna causes a difference in radius of curvature on both sides of the antenna. Since it is difficult for the metal film to absorb the difference, inconveniences such as loss of flexibility or bending due to the inability to withstand the bending force occur.

In order to solve this problem, the radiant conductor layer 103, which is the outer side when the flat antenna 101 is bent, has a shape corresponding to stretching, or the ground conductor layer 104, which is the inner side when the flat antenna 101 is bent, corresponds to shrinkage. It is necessary to have a shaped shape. However, as described above, if the length of the radiation conductor layer 103 changes, the operating frequency of the antenna changes, so that it is not desirable to cope with stretching. Therefore, in the planar antenna 101 according to the present embodiment, by forming the slit La in the ground conductor layer 104, the planar antenna 101 can be made flexible without stretching the radiating conductor layer 103.

Here, an example of how to set the width of the slit La will be described.

When the thickness of the entire flat antenna 101 when the flat antenna 101 is bent is h and the radius of curvature of the arm to which the flat antenna 101 is mounted is R, the contraction rate inside the dielectric substrate 102 (ground conductor layer 104 side). α is represented by α = R / (R + h). Here, it is assumed that the outside of the dielectric substrate 102 (on the radiation conductor layer 103 side) is not stretched.

Here, assuming that the total length of the ground conductor layer 104 in the flat state is x, if the length of the ground conductor layer 104 when bent at the radius of curvature R is (1-α) x, a plurality of ground conductor layers 104 separated by slits La. The strip portions L of the above are in contact with each other and become conductive as a whole. From this point of view, the total length of the slit La may be αx. That is, when n slits La are formed, the width of one slit La may be αx / n.

For example, when the total length of the flat antenna 101 is 100 [mm], the thickness h is 5 [mm], the antenna is wound around the arm at R = 20 [mm], and 20 slits La are inserted, the inside of the dielectric substrate 102. Shrinks by 20%, so the width of one slit La may be set to 1.0 [mm].

<Operation>
Next, the operation when the flat antenna 101 according to the present embodiment is used will be described.

When the flat antenna 101 has a flat plate shape, slits La separate the plurality of strip portions L from each other. Therefore, the ground conductor layer 104 does not conduct as a whole, and the flat antenna 101 does not operate.

On the other hand, when the flat antenna 101 is wound around the arm or the like, the slit La absorbs the contraction amount inside the flat antenna 101, so that the plurality of strip portions L come into contact with each other. As a result, the planar antenna 101 operates.

<Effect>
As described above, the flat antenna 101 according to the present embodiment includes the flexible dielectric substrate 102, the radiating conductor layer 103 formed on the first surface of the dielectric substrate 102, and the first of the dielectric substrates 102. A ground conductor layer 104 formed on a second surface opposite to the first surface is provided, and the ground conductor layer 104 is divided into a plurality of strip portions L by a plurality of slits La extending in a predetermined direction. Is formed.

Therefore, according to the planar antenna 101 according to the present embodiment, it is possible to realize a planar antenna having flexibility. As a result, it can be mounted on various curved surfaces such as the human body and applied to a biological sensing device or the like.

The flexible planar antenna of the present invention can be widely used as a biological sensing device by mainly attaching it to the human body. This makes it possible to naturally attach an antenna for information communication / wireless power supply to an arm or the like, so that it is possible to apply, for example, to measure biological information on a daily basis without discomfort.

101 Flat antenna 102 Dielectric substrate 103 Radiant conductor layer 104 Ground conductor layer L Strip part La slit 301 Dielectric plate 302 Antenna plate

Claims (5)

With a flexible dielectric substrate,
A radiation conductor layer formed on the first surface of the dielectric substrate and
A ground conductor layer formed on a second surface of the dielectric substrate opposite to the first surface, and
With
The ground conductor layer is divided into a plurality of strip portions by a plurality of slits extending in a predetermined direction.
Planar antenna. It is configured to be deformable from a flat plate shape to a curved shape with the ground conductor layer on the inside and the radiant conductor layer on the outside.
The planar antenna according to claim 1. The plurality of strip portions of the ground conductor layer come into contact with each other and are electrically connected to each other when the planar antenna is deformed from a flat plate shape to a curved shape.
The planar antenna according to claim 2. The dielectric substrate is a fluororesin.
The planar antenna according to any one of claims 1 to 3. A power line was formed in the radiant conductor layer.
The planar antenna according to any one of claims 1 to 4.

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