Antenna device

An antenna device includes a first substrate, a feeder line which is disposed in the first substrate, a grounding conductor which is disposed in the first substrate, a first radiation element which is electrically connected to the feeder line in the first substrate, a second radiation element which is electrically connected to the grounding conductor and is disposed substantially in parallel with the first radiation element in the first substrate, a first reflector which is disposed in the first substrate, and a second reflector which is disposed in the first substrate so as to be separated by a predetermined distance from the first radiation element or the second radiation element in at least one of longitudinal directions of the first radiation element and the second radiation element.

TECHNICAL FIELD

The present disclosure relates to an antenna device.

BACKGROUND ART

While reduction in power consumption is requested in portable wireless device, increase in antenna gain is requested in order to achieve remote distance communication with low power. As one of means for attaining increase in antenna gain, there is an array antenna in which a plurality of antennas are arrayed so that the directivity can be fixed to one direction by control of excitation phases of the respective antennas.

Of array antennas, an array antenna whose directivity is fixed to the array direction is called an end-fire array antenna. A Yagi array antenna which uses dipole type radiation elements, a reflector and a director is known as one of end-fire array antennas.

As to Yagi array antennas, for example, Patent Literature 1 discloses a Yagi array antenna.FIG. 10is a view showing the configuration of the Yagi array antenna disclosed in Patent Literature 1. In the Yagi array antenna shown inFIG. 10, dipoles901and902serving as radiation elements and microstrip lines903and904feeding power to the dipoles901and902are printed in a substrate900consisting of a dielectric substrate.

A director905and a reflector906are printed at a distance from the dipole901in a first surface of the two surfaces of the substrate900. A plane Yagi array antenna is comprised by the director905, the reflector906and the dipoles901and902. A tapered balun907connected to the micro-strip line904disposed in a second surface of the substrate900and a ground plane908connected to the tapered balun line907are printed in the second surface.

PRIOR ART LITERATURE

Patent Document

SUMMARY OF THE INVENTION

Problem that the Invention is to Solve

In the Yagi array antenna disclosed in Patent Literature 1, the antenna gain may be decreased.

The present disclosure has been developed in consideration of the aforementioned circumstances. The present disclosure provides an antenna device capable of suppressing decrease in antenna gain.

Means for Solving the Problem

An antenna device according to the present disclosure includes: a first substrate, a feeding line which is disposed in the first substrate; a ground plane which is disposed in the first substrate; a first radiation element which is disposed in the first substrate so as to be electrically connected to the feeding line; a second radiation element which is disposed in the first substrate so as to extend substantially in parallel with the first radiation element and to be electrically connected to the ground plane; a first reflector which is disposed in the first substrate; and a second reflector which is disposed in the first substrate so as to extend in at least one of longitudinal directions of the first radiation element and the second radiation element and at a predetermined distance from the first radiation element or the second radiation element.

Advantage of the Invention

According to the present disclosure, it is possible to suppress decrease in antenna gain.

MODE FOR CARRYING OUT THE INVENTION

(Circumstances Leading to Achievement of Disclosed Mode)

In recent years, a space where internal parts of a portable wireless device can be disposed has been reduced with miniaturization of the portable wireless device. In addition, an antenna built in the portable wireless device is apt to be affected by an electric structure (also referred to as peripheral structure) disposed near the antenna. The peripheral structure includes, for example, a wiring pattern or a connector for external connection. High technology on design is required for designing the antenna in consideration of the peripheral structure so as to attain excellent antenna performance.

For example, when the Yagi array antenna disclosed in Patent Literature 1 is disposed in a portable wireless device, a remedial measure against decrease in antenna gain is requested because the directivity of the antenna is influenced due to set the peripheral structure.

In the following embodiments, description will be made about antenna devices capable of suppressing decrease in antenna gain.

The antenna devices in the following embodiments are used in wireless communication circuits for high frequencies (e.g. 60 GHz) in millimeter-wave bands, and mounted with various electronic parts (such as antennas and semiconductor chips). In addition, Yagi array antennas which are, for example, mounted on portable wireless device or radar device will be mainly described as the antenna devices by way of example.

FIG. 1(A)toFIG. 1(B)andFIG. 2(A)toFIG. 2(C)are views showing a configuration example of a Yagi array antenna110according to a first embodiment.FIG. 1(A)is a front view showing the configuration example of the Yagi array antenna110, andFIG. 1(B)is a back view showing the configuration example of the Yagi array antenna110.FIG. 2(A)is a sectional view of the A-A′ portion ofFIG. 1(A),FIG. 2(B)is a sectional view of the B-B′ portion ofFIG. 1(A), andFIG. 2(C)is a sectional view of the C-C′ portion ofFIG. 1(A).

The Yagi array antenna110has a dielectric substrate100, a feeding line101, a first radiation element102, a second radiation element103, a first director104a, first reflectors105and106, and second reflectors107and108.

The dielectric substrate100is, for example, a double-sided substrate with thicknesstand a dielectric constant ∈r. In one surface (+Z side, front side) of the dielectric substrate100, a first ground plane109is formed, for example, out of a copper foil pattern. In the other surface (−Z side, back side) of the dielectric substrate100, a second ground plane111is formed, for example, out of a copper foil pattern. The first grounding conductor109and the second grounding conductor111serve as ground.

In addition, a through hole112penetrating the first ground plane109and the second ground plane111is formed in the Yagi array antenna110. The inner wall of the through hole112is, for example, plated with gold so as to electrically connect the first ground plane109and the second ground plane111with each other. In addition, the feeding line101is disposed on the same plane as the second ground plane111in the dielectric substrate100. Thus, a coplanar line with the ground is constituted by use of the first ground plane109, the second ground plane111and the feeding line101.

The first radiation element102is connected to the feeding line101. The second radiation element103is connected to the first ground plane109and disposed substantially in parallel with the first radiation element102. Length Ls1 between an open end of the first radiation element102and an open-end of the second radiation element103is, for example, set at about ½λg, so that a dipole antenna can be formed by use of the first radiation element102and the second radiation element103. Incidentally, “λg” designates an effective wavelength of a signal propagated through the feeding line101, and shows a wavelength corresponding to the working frequency of the Yagi array antenna110in consideration of a wavelength shortening effect within the substrate.

The first director104ais disposed on the same plane as the first radiation element102in the dielectric substrate100. The first director104ais disposed in a predetermined +Y direction position relative to the first radiation element102and substantially in parallel with the first radiation element102and the second radiation element103. A distance Dd1 between the first director104aand each of the first radiation element102and the second radiation element103is, for example, set at about ¼λg so that the first director104acan operate as director. In addition, longitudinal direction length Ld1 of the first director104ais, for example, set to be a little shorter than ½λg.

The Yagi array antenna110which includes the first director104ais capable to increase the gain in the direction of the arrow113. The direction of the arrow113designates the direction of directivity.

The first reflectors105and106are arranged in predetermined −Y direction positions relative to the first radiation element102by the second ground plane111which is partially formed into a convex shape. A distance Dr between each of the first radiation element102and the second radiation element103and each of the first reflectors105and106is, for example, set at about ¼λg so that the first reflectors105and106can operate as reflectors. In addition, Length Lr between opposite end portions of the first reflectors105and106is, for example, set to be a little longer than ½λg.

The Yagi array antenna110which includes the first reflectors105and106is capable to reflect radio waves radiated from the dipole antenna and to provide directivity in the direction (+Y direction) of the arrow113.

The Yagi array antenna110is capable to attain radiation of radio waves in the +Y direction (direction of the arrow113) due to the effect of the reflectors and the director obtained thus.

The second reflectors107and108are disposed on the same plane as the first radiation element102in the dielectric substrate100. The second reflectors107and108are disposed at a predetermined distance D from the first radiation element102or the second radiation element103and substantially perpendicularly to the first radiation element102and the second radiation element103in the substrate surface.

Next, the effect by the second reflectors107and108will be described with reference toFIG. 3(A)toFIG. 3(C).

FIG. 3(A)is a plan view showing a configuration example of a Yagi array antenna211which is not comprised with any peripheral structure and any second reflector.FIG. 3(B)is a plan view showing a configuration example of a Yagi array antenna212which is comprised with a peripheral structure but not comprised with any second reflector.FIG. 3(C)is a plan view showing a configuration example of a Yagi array antenna213which is comprised with a peripheral structure and second reflectors.

In the Yagi array antennas211,212and213, constituents the same as those in the Yagi array antenna110described previously are referenced correspondingly, and detailed description thereof will be omitted. As compared with the Yagi array antenna110, the Yagi array antenna211does not include second reflectors, the Yagi array antenna212does not include second reflectors but has a peripheral structure added thereto, and the Yagi array antenna213has a peripheral structure added thereto.

Assume that each Yagi array antenna211,212,213is, for example, mounted on a portable wireless device, and comprised with a dielectric substrate100of a comparatively large size measuring at least one wavelength in the ±X direction and the ±Y direction. In addition, assume that a second director104band a third director104care disposed in each Yagi array antenna211,212,213in order to take into consideration practical use in the fundamental configuration of the Yagi array antenna110shown inFIG. 1.

Design dimensions resulting from the antenna performance of the Yagi array antenna211are shown inFIG. 3(A). The same design dimensions can be applied to the Yagi array antennas212and213inFIG. 3(B)andFIG. 3(C). Specific examples of the design dimensions will be described below.

dielectric constant ∈r of the dielectric substrate100: 3.6

short direction (Y direction) length W of each of the first director104a, the second director104b, the third director104c, the first radiation element102and the second radiation element103: 0.03λ

distance Dr between each of the first radiation element102and the second radiation element103and each of the first reflectors105and106: 0.17λ

distance Dd1 between the first radiation element102and the first director104a: 0.17λ

distance Dd2 between the first director104aand the second director104b: 0.3λ

distance Dd3 between the second director104band the third director104c: 0.3λ

length Lr between opposite end portions of the first reflectors105and106: 0.72λ

length Ls1 between the open-end of the first radiation element102and the open-end of the second radiation element103: 0.37λ

longitudinal direction (X direction) length Ld1 of the first director104a: 0.22λ

longitudinal direction (X direction) length Ld2 of the second director104b: 0.2λ longitudinal direction (X direction) length Ld3 of the third director104c: 0.2λ

Incidentally, “λ” designates a free space wavelength corresponding to the working frequency of each Yagi array antenna110,211to213.

In the Yagi array antenna212inFIG. 3(B), ground patterns201and202are further added to the Yagi array antenna211inFIG. 3(A)and in its peripheral area. For example, the antenna has a configuration including the first radiation element102, the second radiation element103, the first director104a, the second director104b, the third director104c, and the first reflectors105and106.

InFIG. 3(B), ground patterns201and202are disposed at predetermined distances from the first radiation element102and the second radiation element103in the longitudinal directions of the first radiation element102and the second radiation element103so as to surround a part of the periphery of the antenna. The ground patterns201and202serve as an example of a peripheral structure.

In the Yagi array antenna213ofFIG. 3(C), second reflectors107and108are added to the Yagi array antenna212ofFIG. 3(B). Specific examples of design dimensions resulting from the antenna performance of the Yagi array antenna213will be described below.

longitudinal direction length Ls2 of each of the second reflectors107and108: 0.3λ distance D between each of the second reflectors107and108and each of the first radiation element102and the second radiation element103: 0.47λ

Next, the relationship between each Yagi array antenna211to213and the gain of the antenna will be described.

FIG. 4shows the antenna gain in the configuration of each Yagi array antenna211to213.

With reference toFIG. 4, it is possible to confirm that the gain of the Yagi array antenna212which is comprised with a peripheral structure (for example, the ground patterns201and202) is lower than the gain of the Yagi array antenna211which is not comprised with the peripheral structure. This is because the antenna characteristic deteriorates due to the influence of the peripheral structure.

It is possible to also confirm that the gain of the Yagi array antenna213which is comprised with the peripheral structure and the second reflectors107and108is higher than the gain of the Yagi array antenna212which is not comprised with the second reflectors107and108. This is because the deterioration in gain caused by the influence of the peripheral structure is capable to be suppressed by the second reflectors107and108.

That is, from comparison between a gain301and a gain302inFIG. 4, it is possible to understand that the gain is lowered by disposing the ground patterns201and202in the periphery of the antenna. On the other hand, from comparison between the gain302and a gain303inFIG. 4, it is possible to understand that the gain is improved by the arrangement of the second reflectors107and108.

FIG. 5(A)toFIG. 5(C)show examples of Eφ component (horizontal polarized wave component) radiation patterns on an XY-plane.FIG. 5(A)shows a radiation pattern of the Yagi array antenna211.FIG. 5(B)shows a radiation pattern of the Yagi array antenna212.FIG. 5(C)shows a radiation pattern of the Yagi array antenna213.

As shown inFIG. 5(B)andFIG. 5(C), the Yagi array antenna212and213which is disposed the second reflectors107and108, are capable to reduce radiation of radio waves in directions of about 45 degrees and about 135 degrees, to narrow the directivity around the direction of the arrow113, and to increase the gain. In addition, the Yagi array antenna212and213are capable to reduce the radiation in the substantially ±X directions by narrowing the directivity. Accordingly, for example, as shown inFIG. 3(B), the Yagi array antenna213is capable to reduce the influence of a peripheral structure (such as wiring patterns or ground patterns) disposed in the substantially ±X directions, and to obtain a high gain.

Furthermore, the Yagi array antenna is capable to obtain the aforementioned effect of the second reflectors107and108even when the number of directors changes. The gain becomes higher as the number of directors increases.

Next, the relationship between the longitudinal direction length Ls2 of each second reflector107,108and the gain will be described.

FIG. 6shows a relative value of the gain in the Yagi array antenna213when the longitudinal direction length Ls2 of each second reflector107,108is changed. The relative value designates the gain ratio of the Yagi array antenna213to the Yagi array antenna212when the gain in the Yagi array antenna212is regarded as 0 dB.

InFIG. 6, the gain in the Yagi array antenna213is higher than the gain in the Yagi array antenna212because the second reflectors107and108operate as reflectors in a range where the length Ls2 is larger than 2/10λ and smaller than 7/10λ. Thus, the Yagi array antenna213is capable to obtain the improved antenna gain effect even when the length Ls2 is not ½λ.

Next, the relationship between the gain and the distance D between each of the second reflectors107and108and each of the first radiation element102and the second radiation element103will be described.

FIG. 7shows a relative value of the gain in the Yagi array antenna213when the distance D between each of the second reflectors107and108and each of the first radiation element102and the second radiation element103is changed. The relative value designates the gain ratio of the Yagi array antenna213to the Yagi array antenna212when the gain in the Yagi array antenna212is regarded as 0 dB.

As shown inFIG. 7, the gain in the Yagi array antenna213is higher than the gain in the Yagi array antenna212when the distance D is larger than 1/10λ. This is because the second reflectors107and108made of metal are at a certain distance from the first radiation element102and the second radiation element103. The Yagi array antenna213is capable to suppress the decrease in radiation resistance of the antenna, the decrease in radiation efficiency of the antenna, and the decrease in gain of the antenna. In this case, the Yagi array antenna213is capable to obtain a higher gain improving effect than the Yagi array antenna212.

According to the Yagi array antenna110or213, each second reflector107,108is disposed at a predetermined distance from the first radiation element102or the second radiation element103and, for example, substantially perpendicular to the first director104aso as to reduce the influence of a peripheral structure and obtain a high gain of the antenna. In addition, the Yagi array antenna110,213may suppress an adverse effect of the peripheral structure on the radiation pattern and the deterioration of the gain even when Yagi array antenna110,213is so small in size and the mounting density of electronic parts is high.

This embodiment assumes that an antenna apparatus is mounted on another apparatus (for example, portable wireless device).

FIG. 8(A)andFIG. 8(B)are plan views showing a configuration example of a Yagi array antenna700according to the second embodiment.FIG. 8(A)is a front view showing the configuration example of the Yagi array antenna700, andFIG. 8(B)is a back view showing the configuration example of the Yagi array antenna700. InFIG. 8(A)andFIG. 8(B), constituent parts the same as those in the Yagi array antenna110according to the first embodiment are referenced correspondingly, and detail description thereof will be omitted.

The Yagi array antenna700has a radio unit701connected to the feeding line101in the Yagi array antenna110shown in the first embodiment. In addition, the second reflectors107and108are disposed on the same plane as the first ground plane109, that is, on the other surface of the dielectric substrate100. The second reflectors107and108may be disposed on the one surface of the dielectric substrate100.

When the radio unit701is comprised, the Yagi array antenna700is possible to operate as a radio communication module.

FIG. 11shows an example in which the Yagi array antenna700shown inFIG. 8(A)andFIG. 8(B)is applied to an application of communication. InFIG. 11, a transmitting Yagi array antenna500and a receiving Yagi array antenna600are disposed on the dielectric substrate100. Although the transmitting Yagi array antenna500and the receiving Yagi array antenna600are formed into the same shape inFIG. 11, the two antennas do not have to be formed into the same shape.

The transmitting Yagi array antenna500is connected to a transmitter501with a feeding line502. The receiving Yagi array antenna600is connected to a receiver601with a feeding line602.

Second reflectors503,504and505are disposed on the both ends of the transmitting Yagi array antenna500and the both ends of the receiving Yagi array antenna600. The second reflector504performs as a reflector for both the transmitting Yagi array antenna500and the receiving Yagi array antenna600.

Thus, the Yagi array antenna700applied to the application of communication as shown inFIG. 11is also capable to obtain a similar effect of the Yagi array antennas inFIG. 1,FIG. 3(A)toFIG. 3(C)andFIG. 8(A)toFIG. 8(B).

Incidentally, the second reflector504does not have to be formed into the same shape as the second reflectors503and505, but may be omitted.

FIG. 9(A)toFIG. 9(C)show a configuration example of the Yagi array antenna700disposed on a dielectric substrate800mounted on a portable wireless device.FIG. 9(A)is a plan view showing the Yagi array antenna700and the dielectric substrate800individually.FIG. 9(B)is a plan view in which the Yagi array antenna700is disposed on the dielectric substrate800.FIG. 9(C)is a sectional view taken on the D-D′ portion ofFIG. 8(B).

A first connection area801, a second connection area802, a third connection area803and a fourth connection area804formed out of copper foil patterns are disposed on one surface (+Z side) of the dielectric substrate800. In this manner, the dielectric substrate100and the dielectric substrate800are connected with the connection areas (lands) located at the four points of the substrate corner areas so as to improve the mounting strength.

The pattern shapes of the first connection area801and the second connection area802are, for example, substantially identical to the shapes of the second reflectors107and108in the Yagi array antenna700. In addition, the dielectric substrate100and the dielectric substrate800may be formed out of the same material or different materials. For example, the dielectric substrate100and the dielectric substrate800are formed out of glass epoxy resin.

In a connection process between the Yagi array antenna700and the dielectric substrate800, the first connection area801is superimposed on the second reflector108, the second connection area802is superimposed on the second reflector107, and the third connection area803and the second connection area804are superimposed on the first ground plane109, as shown inFIG. 9(C). Then, the superimposed areas are soldered in a reflow process. Thus, the Yagi array antenna700is connected to the dielectric substrate800and mounted thereon.

In this manner, the second reflectors107and108are electrically or physically connected to connection areas (for example, the first connection area801and the second connection area802). Thus, the Yagi array antenna700mounted on another apparatus (for example, a portable wireless device) is capable to obtain a similar effect of the Yagi array antenna110according to the first embodiment.

In addition, the dielectric substrate100on which an antenna is disposed and the dielectric substrate800which is disposed on a portable wireless device may be configured separately. These configurations eliminate the need to provide a specific design for the antenna in accordance with the material and the thickness of the dielectric substrate which is mounted on the portable wireless device. Thus, the versatility of antenna is improved.

In addition, the second reflectors107and108may be also used as the connection areas with the dielectric substrate800. This configuration eliminate the need to dispose another copper foil pattern for connection on the dielectric substrate100. Thus, the design of antenna becomes easy.

In this manner, according to the Yagi array antenna700, when the Yagi array antenna is mounted on various portable wireless device, an antenna substrate (dielectric substrate) for the Yagi array antenna is comprised by using different dielectric substrate from a dielectric substrate for a portable wireless device. Thus, the versatility of the Yagi array antenna is improved.

For example, due to the antenna substrate which is comprised by using different dielectric substrate, specific optimization for obtaining a desired antenna characteristic is capable to be dispensed with even when there is a difference in material or thickness of a dielectric substrate used for a portable wireless device in accordance with the model or the maker of the portable wireless device. It is therefore possible to universally mount the Yagi array antenna on various portable wireless device.

In addition, when the second reflectors107and108are also used as connection members to another substrate (for example, the dielectric substrate800for the portable wireless device), connection to the other substrate is capable to be made easier.

In addition, when copper foil patterns are disposed as lands on a dielectric substrate for a Yagi array antenna and a dielectric substrate for a portable wireless device in order to connect the Yagi array antenna to the portable wireless device, the copper foil patterns as a peripheral structure may give an adverse effect to the antenna characteristic. The Yagi array antenna700may be reduced the influence of the peripheral structure and suppress the deterioration of the gain.

Incidentally, the present disclosure is not limited to the aforementioned configurations of the embodiments, but it can be applied to any configuration as long as the configuration can achieve the functions shown in the claims or the functions belonging to the configurations of the embodiments.

For example, although the second reflectors107and108are disposed in both the +X directions and −X directions in each of the Yagi array antennas110and213according to the aforementioned embodiments, the second reflector107or108may be disposed on at least one direction, that is, the +X direction or the −X direction. In this case, the influence of a peripheral structure on the side where the second reflector107or108is disposed is capable to be suppressed.

In addition, although the second reflectors107and108and the second ground plane111are disposed on the same plane in each of the Yagi array antennas110and213, the Yagi array antenna is capable to obtain a similar effect even when the second reflectors107and108and the first ground plane109are disposed on the same plane. Further, the second reflectors107and108may be disposed on the both sides of the dielectric substrate100.

In addition, in each of the Yagi array antennas110and213, the first radiation element102is disposed on one surface of the dielectric substrate100and the second radiation element103is disposed on the other surface of the dielectric substrate100. However, the two radiation elements may be disposed on the same surface.

In addition, although rectangles are exemplified as the shapes of the second reflectors107and108in each of the Yagi array antennas110and213, the second reflectors107and108may be formed into other shapes than rectangles. For example, the second reflectors107and108may be conductive members having longitudinal components, such as elliptic conductive members.

In addition, although a Yagi array antenna is exemplified as an antenna apparatus in each of the aforementioned embodiments, another antenna apparatus may be used.

In addition, although the Yagi array antenna having at least one director is exemplified in each of the aforementioned embodiments, the director may be omitted. The Yagi array antenna is capable to suppress to decrease in antenna gain even when the director is omitted.

The present application is based on Japanese Patent Application No. 2013-020536 filed on Feb. 5, 2013, the contents of which are incorporated herein by reference.

(Summary of Embodiments of the Disclosure)

A first antenna apparatus according to the present disclosure includes:

a first substrate;

a feeding line which is disposed in the first substrate;

a ground plane which is disposed in the first substrate;

a first radiation element which is electrically connected to the feeding line in the first substrate;

a second radiation element which is electrically connected to the ground plane and is disposed substantially in parallel with the first radiation element in the first substrate;

a first reflector which is disposed in the first substrate; and

a second reflector which is disposed in the first substrate and is separated by a predetermined distance from the first radiation element or the second radiation element in at least one of longitudinal directions of the first radiation element and the second radiation element.

A second antenna apparatus of the present disclosure according to the first antenna device, further includes:

a director which is disposed in the first substrate and is separated by a predetermined distance from the first radiation element and is disposed on an opposite side to the first reflector with respect to the first radiation element.

A third antenna apparatus of the present invention according to the first or second antenna apparatus, further includes:

a radio unit; wherein:

the radio unit is electrically connected to the feeding line.

A fourth antenna apparatus of the present disclosure according to any one of the first to third antenna apparatus, wherein:

the antenna device is mounted in a wireless device; and

the second reflector is electrically or physically connected to a connection area which is disposed in a second substrate provided in the wireless device.

A fifth antenna apparatus of the present disclosure according to any one of the first to fourth antenna apparatus, wherein:

a longitudinal direction length of the second reflector has an electric length which is longer than 2/10 of a wavelength of a usage frequency of the antenna apparatus and shorter than 7/10 of the wavelength.

A sixth antenna apparatus of the present disclosure according to any one of the first to fifth antenna apparatus, wherein:

a distance between the second reflector and the first radiation element or the second radiation element has an electric length which is longer than 1/10 of a wavelength of a working frequency of the antenna apparatus.

INDUSTRIAL APPLICABILITY

The present disclosure is useful for an antenna apparatus or the like capable of suppressing decrease in antenna gain.

DESCRIPTION OF REFERENCE NUMERALS AND SIGNS