Antenna device

Patch antennas include four radiation elements arrayed in a rectangular lattice pattern at four positions around a feeding point in the electrode, and wiring which electrically couples each of the radiation elements and the feeding point with an equal wiring length, and is fed by a line-shaped feeding conductor arranged at a position intersecting slots formed at a ground conductor plate, where the feeding conductor has a repetitive branch pattern in which multiple pieces of line-shaped wiring are connected in T-shapes being perpendicular to each other at a total of 2N−1 branch points from a base end to each of the tips, and each of the tips is bent in a same direction in the second direction from a terminal end of the line-shaped wiring to which the tip is connected.

TECHNICAL FIELD

The present invention relates to an antenna device.

This application is a National Stage Application filed under 35 U.S.C. § 371 of International Application No. PCT/JP2018/033784 filed on Sep. 12, 2018 which claims the benefit of priority under 35 U.S.C. § 119(a) of Japanese Patent Application No. 2017-181339 filed on Sep. 21, 2017, the contents of which are incorporated herein by reference.

BACKGROUND ART

In the field of high-speed wireless communication, antenna devices including planar antennas of an electromagnetic coupling feeding system are known.

For example, Patent Document 1 describes a phased array antenna device in which a rectangular feeding slot is formed in a feeding slot layer that is a ground layer, and a distribution synthesizer is electromagnetically coupled to circular radiation elements via the feeding slot layer.

In Patent Document 1, the radiation elements are arrayed in a staggered pattern in a plan view, and the branch wiring pattern of the distribution synthesizer pairs two radiation elements adjacent to each other as one set and thereby supplies power simultaneously to the radiation elements.

PRIOR ART DOCUMENTS

Patent Documents

DISCLOSURE OF INVENTION

Problems to be Solved by the Invention

However, in a case where power is supplied to a large number of radiation elements using a branch wiring pattern as in the technology described in Patent Document 1, the impedance at the feeding source and the impedance at electromagnetic coupling feeding portions with the radiation elements are required to be set at constant values depending on the specifications of the device, such as 50Ω for the feeding source and 120Ω for the electromagnetic coupling feeding portions. It is also necessary to make the line lengths from the feeding source to feeding points correspond in order to make the phase of the electric current in each of the radiation elements correspond.

For this reason, in a case where the feeding wiring is a branch wiring pattern, it is necessary to first match the impedance at branch points. It is further necessary that the branch wiring pattern be laid out so that the line lengths match.

For this reason, the array of radiation elements and the layout design of the branch wiring pattern become complicated, and thus it takes time to design.

Furthermore, if impedance matching at the branch points is insufficient, reflection of a current occurs in the branch wiring pattern, and thus the gain of the antenna device is reduced.

The present invention has been made in view of the above disadvantages, and provides an antenna device that enables efficient design with improved gain.

Means for Solving the Problems

A first aspect of the present invention is an antenna device including: a first dielectric layer; flat-plate-shaped 2Npatch antennas where N is an integer greater than or equal to 2 arranged on a first surface of the first dielectric layer, the patch antennas each including an electrode for electromagnetic coupling; a ground conductor plate arranged on a second surface opposite to the first surface of the first dielectric layer, the ground conductor plate formed with slots, which are non-conductive portions, extending in a first direction at positions facing the electrodes; a second dielectric layer secured to the ground conductor plate so as to face the first dielectric layer with the ground conductor plate sandwiched therebetween; and a line-shaped feeding conductor formed on the second dielectric layer so as to face the ground conductor plate with the second dielectric layer sandwiched therebetween, the feeding conductor arranged in a positional relationship intersecting the slots when viewed from a normal direction of the patch antennas with tips extending in a second direction intersecting with the first direction when viewed from the normal direction, in which the patch antennas each further include: four radiation elements arrayed in a rectangular lattice pattern at four positions around a feeding point in the electrode; and wiring which electrically couples each of the radiation elements and the feeding point with an equal wiring length, the feeding conductor has a repetitive branch pattern in which multiple pieces of line-shaped wiring are connected in T-shapes being perpendicular to each other at a total of 2N−1 branch points from a base end to each of the tips, and each of the tips is bent in a same direction in the second direction from a terminal end of the line-shaped wiring to which the tip is connected.

According to a second aspect of the present invention, in the antenna device according to the first aspect, an impedance matcher having a line width widened by two or more stages toward a terminal end may be provided at an end of the line-shaped wiring.

According to a third aspect of the present invention, in the antenna device according to the second aspect, a change in impedance at each of the stages of the impedance matcher may be less than or equal to 50Ω.

According to a fourth aspect of the present invention, in the antenna device according to the third aspect, among the impedance matchers, an impedance matcher provided at the base end of the feeding conductor may have less than or equal to 30Ω of a change in impedance at a widening stage closest to the terminal end of the base end.

According to a fifth aspect of the present invention, in the antenna device according to any one of the first to fourth aspects, the second direction may be perpendicular to the first direction, and the tips of the feeding conductor may be perpendicular to the slots when viewed from the normal direction.

Effects of the Invention

According to an antenna device of the present invention, efficient design is enabled with improved gain.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

Hereinafter, an antenna device according to an embodiment of the present it will be described with reference to the drawings.

FIG. 1is a schematic exploded perspective view showing an example of an antenna device of the present embodiment.FIG. 2is a schematic vertical sectional view showing an exemplary example of a configuration of the main part of the antenna device of the present embodiment.FIG. 3is a schematic plan view showing an exemplary example of a patch antenna of the antenna device of the present embodiment.FIG. 4is a schematic plan view showing an exemplary example of an opening shape of a slot used in the antenna device of the present embodiment.FIG. 5is a schematic plan view showing an exemplary example of a wiring pattern of a feeding conductor of the antenna device of the present embodiment.FIG. 6is a schematic plan view showing an exemplary example of a wiring pattern of the feeding conductor that feeds power to antenna blocks in the antenna device of the present embodiment.FIG. 7is a schematic plan view showing an exemplary example of an impedance matcher on the base end side of the feeding conductor in the antenna device of the present embodiment.

The drawings are schematic diagrams, in which dimensions or shapes are exaggerated or simplified (the same applies to other drawings below).

An antenna device20of the present embodiment shown inFIG. 1includes planar antennas of an electromagnetic coupling feeding system. For example, the antenna device20can be used as an antenna device for communication in the field of internet of things (IoT) or high-speed wireless communication such as wireless gigabit (WiGig).

As shown inFIGS. 1 and 2, the antenna device20includes patch antennas1, a first dielectric layer2, a ground conductor plate4, a second dielectric layer5, and a feeding conductor60that are stacked in the order mentioned.

Hereinafter, the stacking direction is defined as a Z-axis direction, and two axial directions perpendicular to the Z-axis direction and perpendicular to each other are referred to as an X-axis direction (second direction) and a Y-axis direction (first direction). The coordinate system here is a right-handed system.

As shown inFIG. 1, the patch antennas1are patterned on a first surface2a(first surface) of the first dielectric layer2to be described later on the basis of a predetermined array pattern. The normal directions of the patch antennas1and the first surface2aare the Z-axis direction.

The patch antennas1are planar antennas that are electromagnetically coupled and fed from the feeding conductor60which will be described later. In the present embodiment, as an example, a plurality of patch antennas1is arrayed in a square lattice pattern arranged in the X-axis direction and the Y-axis direction. Specifically, 64 (=26) patch antennas1are arrayed in an 8×8 square lattice pattern.

As shown inFIG. 3, in the present embodiment, each of the patch antennas1includes, as an example, four radiation elements1aand a divided circuit pattern1dwhich is a divider for arraying the radiation elements1a.

Bach of the radiation elements1ais formed into a square shape having sides each extending in the X-axis direction and the Y-axis direction. The radiation elements1aare arrayed into a rectangular lattice pattern having a substantially square lattice pattern arranged in the X-axis direction and the Y-axis direction.

The divided circuit pattern1dincludes an electrode1bfor electromagnetic coupling and four pieces of wiring1cfor electrically coupling the electrode1band the radiation elements1ato each other.

The electrode1bis formed into a rectangular shape that extends in the X-axis direction centered at a point P that is an intersection of diagonal lines connecting the centers of the arrangement positions of the radiation elements1a. A feeding point in the electrode1bis formed at the center of the electrode1b.

The wiring1ceach extends from a side portion in the Y-axis direction at each of the four corners of the electrode1btoward a radiation element1ato which it is coupled. Specifically, the wiring1ceach extends in the Y-axis direction toward a radiation element1ato which it is coupled, and then is bent at a right angle at a position facing the center of the sides in the X-axis direction of the radiation element1ato which it is coupled so as to extend in the X-axis direction. The path lengths of the wiring1care equal to each other. A chamfered portion1fthat intersects with the X axis at 45 degrees is formed at a corner of a bent portion of each piece of the wiring1c.

As shown inFIG. 3, each of the patch antennas1having such a configuration is arranged at corners of a rectangular area having a width in the X-axis direction of WXand a width in the Y-axis direction of WY.

For example, in application to 60 GHz band wireless communication, WXand WYmay be 4.4 mm and 4.52 mm, respectively.

In this case, the width WaXin the X-axis direction and the width WaYin the Y-axis direction of each of the radiation elements1amay be 1.15 mm and 1.15 mm, respectively. The width WbXin the X-axis direction and the width WbYin the Y-axis direction of the electrode1bmay be 0.8 mm and 0.4 mm, respectively. The width of each piece of the wiring1cmay be 0.13 mm.

The quarter effective length (hereinafter simply referred to as effective length) of such a patch antenna1is 1.15 mm, for example.

The patch antennas1are made of a metal material such as copper.

In the patch antenna1, the impedances from the point P to the respective radiation elements1aare set in such a manner that current directions in the respective radiation elements1abecome the same. In the present embodiment, the current directions in the respective radiation elements1aas a whole flow in the same direction in the X-axis direction, which is a direction parallel to a tip line6edescribed later.

As shown inFIGS. 1 and 2, the first dielectric layer2is a flat plate member whose dielectric constant and layer thickness are defined depending on required radiation characteristics. The first dielectric layer2may be a single-layer dielectric or a plurality of dielectrics bonded together. Whether to use a single layer or a plurality of layers may be determined in consideration of the cost of materials, for example.

In the example shown inFIG. 2, an example is shown in which dielectrics2A having a certain thickness are joined by resin adhesive layers2B that are dielectrics. A second surface2b(second surface), which is the surface opposite to the first surface2ain the first dielectric layer2, is formed by a resin adhesive layer2B. The resin adhesive layer2B forming the second surface2bjoins the ground conductor plate4described later.

In the case where the first dielectric layer2includes a plurality of layers as described above, the dielectric constant and the thickness of the first dielectric layer2can be easily changed. Thus, it becomes easier to set the impedance of each component to a predetermined value together with the conductor shape of each component in the patch antennas1.

As shown inFIGS. 1 and 2, the ground conductor plate4is a conductor plate-like member in which slots7are formed at positions facing the patch antennas1. The ground conductor plate4is grounded.

The ground conductor plate4is secured to the first dielectric layer2via a resin adhesive layer2B forming the second surface2b.

The slots7are a non-conductive portions in the ground conductor plate4. As shown inFIGS. 3 and 4, a slot7extends in the Y-axis direction which is the first direction. The opening shape of a slot7enables impedance matching between the impedance of the patch antenna1and the impedance of the feeding conductor60described later.

As shown inFIG. 4, a slot7in the present embodiment is H-shaped when viewed from the Z-axis direction. Specifically, the slot7includes a rectangular first opening7aand second openings7bformed at both ends in the longitudinal direction (first direction) of the first opening7a.

As shown inFIG. 3, the center (centroid) of the slot7is arranged so as to overlap with the point P that is the center (centroid) of the electrode1bin the patch antenna1. Therefore, the slot7is orthogonal to the electrode1bat the center of the electrode1band crosses the electrode1bin the Y-axis direction when viewed from the Z-axis direction.

The first opening7aforms a signal passing portion through which a signal passes. The second openings7beach increase the impedance at both ends of the signal passing portion.

It is more preferable that the length d3of the slot7in the longitudinal direction (first direction) be matched to the effective length of the patch antenna1.

The first opening7aopens in a rectangular shape having a width of W2in the X-axis direction (first width) that is the lateral direction (second direction) and a length of d1(where d1>W2) in the Y-axis direction (first direction) that is the longitudinal direction.

It is more preferable that the width W2of the first opening7ain the lateral direction be 0.75 mm in order to set the coupling impedance at 112Ω, for example. For example in a case where the impedance of a patch antenna1is 220Ω, W2is more preferably 0.2 mm.

Each of the second openings7bis widened from the width W2in the lateral direction of the first opening7ain order to form an impedance larger than the coupling impedance by the first opening7a.

In the example shown inFIG. 4, each of the second openings7bopens in a rectangular shape with a length of d2in the Y-axis direction and a width of W3in the X-axis direction (where W3>W2).

For example, in the second openings7b, d2and W3may be 0.2 mm and 0.4 mm, respectively. In this case, the length d1of the first opening7ais 0.75 mm (=1.15 mm−2×0.2 mm).

According to the more preferable numerical example of the slot7described above, the coupling impedance of the electromagnetic coupling feeding portion is 112Ω at the center of the electrode1b.

As shown inFIG. 2, the second dielectric layer5is provided to separate the ground conductor plate4and the feeding conductor60described later by a certain insulation distance so that electromagnetic coupling feeding can be performed from the feeding conductor60described later to the patch antennas1through the slots7.

Therefore, the ground conductor plate4is disposed on a first surface5aof the second dielectric layer5, and the feeding conductor60described later is disposed on the second surface5bof the second dielectric layer5.

In order to improve the feeding efficiency, it is preferable that the relative dielectric constant εrof the second dielectric layer5be as small as possible. For example, the relative dielectric constant εrof the second dielectric layer5is more preferably within a range of 1 to 2.5.

For example, in the case where the relative dielectric constant εrof the second dielectric layer5is 2.2, the thickness of the second dielectric layer5is more preferably 130 μm.

As a material of the second dielectric layer5, quartz glass may be used. In this case, the quartz glass may be bonded to the ground conductor plate4by an adhesive sheet that is a dielectric. The thickness of the quartz glass and the adhesive sheet may be set depending on its own relative dielectric constant.

As shown inFIG. 2, the feeding conductor60is patterned on the second surface5bof the second dielectric layer5. The feeding conductor60can be electrically coupled to an external circuit (not shown) via a connection path having a predetermined impedance.

As shown inFIG. 5, the feeding conductor60includes first block wiring6, second block wiring16, third block wiring26, and base end wiring36.

First block wiring6is a wiring pattern which groups 2×2 patch antennas1adjacent to each other in the X-axis direction and the Y-axis direction as one antenna block to form a first feeding block in which power is fed simultaneously to each of the patch antennas1in the antenna block.

In the antenna device20, the patch antennas1are arrayed in an 8×8 square lattice pattern, and the patch antennas1are divided into blocks Bij (i=1, . . . , 4, j=1, . . . , 4) that are antenna blocks of 2×2 square lattices. Here, the subscript i represents the arrangement order in the Y-axis direction, and an increase of i from 1 means that the arrangement position is shifted in the Y-axis negative direction. The subscript j represents the arrangement order in the X-axis direction, and an increase of j from 1 means that the arrangement position is shifted in the X-axis positive direction. An array pitch PXin the X-axis direction and an array pitch PYin the Y-axis direction of each of the blocks Bij are both 14 mm in the present embodiment.

Thus, four pieces of first block wiring6are arrayed at the array pitch PXin the X axis direction corresponding to the arrangement of the blocks Bij in the X axis direction, and four pieces of first block wiring6are arrayed at an array pitch PYin the Y axis direction corresponding to the arrangement in the Y axis direction.

Since the configuration of first block wiring6in each of the blocks Bij is the same, the example of first block wiring6corresponding to a block B11shown inFIG. 5will be described.

At tips of the first block wiring6, four tip lines6e(tips) are formed so as to overlap with four slots7and electrodes1bof the four patch antennas1corresponding to the block B11when viewed from the Z-axis direction.

Each of the tip lines6eis a line-shaped conductor forming an open end of the feeding conductor60. In the present embodiment, each of the tip lines6eextends in the X-axis direction passing through the center in the longitudinal direction of a first opening7aof each of the slots7when viewed from the Z-axis direction as shown inFIG. 6. Thus, a tip line6ecrosses a first opening7aso as to be perpendicular to a first opening7awhen viewed from the Z-axis direction.

The width W1of the tip lines6eis determined so as to enable manufacturing and to allow back radiation to be minimized since a quite wide line width results in more loss and radiation, whereas a quite thin line width is difficult to manufacture. For example, the width W1of the tip lines6emay be 0.1 mm.

As shown inFIG. 4, the length (stub length) from a central axis O of the first opening7ato a tip6fof the tip line6eis ds. In the present embodiment, the stub length ds matches the length d1of the first opening7ain order to match the reactance components. In the numerical example of the slot7described above, the stub length ds is 0.75 mm.

As shown inFIG. 6, two tip lines6eadjacent in the Y-axis direction, of the respective tip lines6e, are coupled to each other by a first line6d(line-shaped wiring) extending in the Y-axis direction at the end portions located on the opposite sides to the tips6f. The width of each of the first lines6dis equal to the width W1of the tip lines6e.

Two first lines6dadjacent in the X-axis direction are coupled to each other by a second line6c(line-shaped wiring) extending in the X-axis direction at a position bisecting the lengths thereof in the longitudinal direction. The width of each second line6cis equal to the width W1of the tip lines6eexcept for both ends in the longitudinal direction.

In this manner, a first line6dand the second line6care coupled in a T-shape being perpendicular to each other. A first line6dis a branch line when viewed from the second line6c, and the midpoint in the longitudinal direction of the first line6dis a branch point. Hereinafter, unless there is a risk of misunderstanding, the “midpoint” of a line refers to the “midpoint in the longitudinal direction” of the line.

At both ends of the second line6c, impedance matchers6bare formed in which the line width gradually increases from W1from the center of the second line6ctoward the branch points.

An impedance matcher6bin the present embodiment performs impedance matching with the second line6cat a branch point of a first line6d.

An impedance matcher6bhas a line width that is widened in three stages of W11, W12, and W13(where W11<W12<W13) from the middle portion to an end portion of the second line6c. The lengths of the respective portions having the line widths W11, W12, and W13are L11, L12, and L13, respectively.

Specific numerical examples for the impedance matcher6binclude 0.12 mm, 0.22 mm, and 0.3 mm for the line widths W11, W12, and W13, respectively. In this case, the impedances of the respective portions having the line widths W11, W12, and W13are 96Ω, 70Ω, and 58Ω, respectively.

Since the impedance of the main body of the second line (the portion having the width W1excluding the impedance matchers6bat both ends) is 112Ω and the impedance at the branch points are 56Ω (=112Ω/2), the impedance gradually changes from the main body of second line6ctoward the branch points of the first lines6d, such as 112Ω, 96Ω, 70Ω, and 58Ω, and is matched with the impedance 56Ω at the branch points.

In this example, the amounts of change in impedance by an impedance matcher6bare 16Ω, 26Ω, and 12Ω for each portion where the line width changes toward the branch point.

According to an examination result of the inventors, for example in a case where a frequency band used by the antenna device20is a 60 GHz band, if the amount of change in impedance in the portions where the line width changes in the impedance matcher6bis less than or equal to 50Ω, a return loss due to a current reflection at a branch point is preferably suppressed. As in the above numerical example, it is more preferable that the amount of change in impedance at portions where the line width changes is less than or equal to 30Ω.

For example, in order to match the impedance of the 112Ω wiring to the impedance at a branch point (56Ω) within a range of amount of change in impedance less than or equal to 30Ω, the number of stages of widening width in an impedance matcher6bis only required to be greater than or equal to two ((112Ω−56Ω)/30Ω=1.86<2). However, if the number of steps is too many, it becomes difficult to form a minute line width difference with high accuracy m manufacturing, and thus it is particularly preferable that the number of stages of widening width be three.

In such first block wiring6, the lengths of the four lines from the midpoint of the second line6cto the respective feeding points are equal to each other. Therefore, a current flowed into the midpoint of the second line6cis divided into four and thereby distributed to each of the tip lines6e.

Moreover, each of the tip lines6eextends from a first line6din the X-axis positive direction. Thus, the currents distributed to each of the tip lines6eflow in the same direction in the same phase.

Each of such tip lines6eis impedance-matched with a slot7that the tip line6efaces.

As shown inFIG. 5, a second block wiring16electrically couples respective pieces of first block wiring6in four blocks Bij arranged adjacent to each other in a square lattice pattern. Second block wiring16is a substantially H-shaped wiring pattern that groups four blocks of four patch antennas1that form a block Bij to form a second feeding block in which power is fed collectively.

Specifically, second block wiring16is formed at four locations in similar wiring patterns so as to mutually couple first block wiring6corresponding to blocks B11, B12, B21, and B22, and first block wiring6corresponding to blocks B13, B14, B23, and B24, first block wiring6corresponding to blocks B31, B32, B41, and B42, and first block wiring6corresponding to blocks B33, B34, B43, and B44.

Hereinafter, as an example, the structure of the second block wiring16that mutually connects the first block wiring6corresponding to the blocks B11, B12, B21, and B22will be described.

The second block wiring16includes a first line16a(line-shaped wiring), a second line16b(line-shaped wiring), and a third line16c(line-shaped wiring).

The first line16aelectrically couples, in the Y-axis direction, the midpoint of the second line6cof the first block wiring6corresponding to the block B11and the midpoint of the second line6cof the first block wiring6corresponding to the block B21.

For example, as shown inFIG. 6, the end of the first line16acoupled to the second line6cof the first block wiring6corresponding to the block B11is bent in the X-axis negative direction, and then is coupled to the second line6cat a position facing the midpoint of the second line6cvia an impedance matcher6bextending in the Y-axis direction.

The second line6cis a branch line when viewed from the first line16a, and the midpoint of the second line6cis a branch point.

Although no enlarged view is particularly shown, as shown inFIG. 5, the end of the first line16acoupled to the second line6cof the first block wiring6corresponding to the block B21is similarly structured.

The second line16belectrically couples, in the Y-axis direction, the midpoint of the second line6cof the first block wiring6corresponding to the block B12and the midpoint of the second line6cof the first block wiring6corresponding to the block B22.

The shape and arrangement of the second line16bare similar to as those of the first line16aexcept that the second line6cto be coupled is different.

The third line16celectrically couples the midpoint of the first line16aand the midpoint of the second line16beach via an impedance matcher6b. The third line16cis formed into a straight line extending in the X-axis direction.

The first line16aand the second line16bare branch lines when viewed from the third line16c, and the midpoints of the first line16aand the second line16bare branch points.

In the second block wiring16, the line width of the main body of the first line16a, the second line16b, and the third line16cexcluding the respective impedance matchers6bis W1.

Therefore, at each branch point in the second block wiring16, impedance matching is performed by the impedance matchers6blike in the first block wiring6described above.

In such second block wiring16, the lengths of the four lines from the midpoint of the third line16cto the branch points of the respective second lines6care equal to each other. Therefore, a current flowed into the midpoint of the third line16cis divided into four and thereby distributed to each of the first block wiring6.

As shown inFIG. 5, the third block wiring26electrically couples four second power feeding blocks electrically coupled by the second block wiring16to each other. The third block wiring26is a substantially H-shaped wiring pattern that forms a third feeding block in which power is fed to the four second feeding blocks collectively.

Specifically, the third block wiring26is formed in the center of the second dielectric layer5so as to couple the second block wiring16coupled to each piece of the first block wiring6corresponding to the blocks B11, B12, B21, and B22, the second block wiring16coupled to each piece of the first block wiring6corresponding to the blocks B13, B14, B23, and B24, the second block wiring16coupled to each of the first block wiring6corresponding to the blocks B31, B32, B41, and B42, and the second block wiring16coupled to each of the first block wiring6corresponding to the blocks B33, B34, B43, and B44.

The third block wiring26includes a first line26a(line-shaped wiring), a second line26b(line-shaped wiring), and a third line26c(line-shaped wiring).

The first line26aelectrically couples the midpoint of the third line16ethat is interposed between the blocks B11and B12and the blocks B21and B22and extends in the X-axis direction and the midpoint of the third line16cthat is interposed between the blocks B31and B32and the blocks B41and B42and extends in the X-axis direction, each via an impedance matcher6b. The first line26ais formed into a straight line extending in the Y-axis direction.

Each of the third lines16ccoupled to the first line26ais a branch line when viewed from the first line26a, and the midpoints of the third lines16eare branch points.

The second line26belectrically couples the midpoint of the third line16cthat is interposed between the blocks B13and B14and the blocks B23and B24and extends in the X-axis direction and the midpoint of the third line16cthat is interposed between the blocks B33and B34and the blocks B43and B44and extends in the X-axis direction, each via an impedance matcher6b. The second line26bis formed into a straight line extending in the Y-axis direction.

Each of the third lines16ccoupled to the second line26bis a branch line when viewed from the second line26b, and the midpoints of the third lines16care branch points.

The third line26celectrically couples the midpoint of the first line26aand the midpoint of the second line26beach via an impedance matcher6b. The third line26cis formed into a straight line extending in the X-axis direction.

The first line26aand the second line26bare branch lines when viewed from the third line26c, and the midpoints of the first line26aand the second line26bare branch points.

In the third block wiring26, the line width of the main body of the first line26a, the second line26b, and the third line26cexcluding the respective impedance matchers6bis W1.

Therefore, at each branch point in the third block wiring26, impedance matching is performed by the impedance matchers6blike in the first block wiring6described above.

In such third block wiring26, the lengths of the four lines from the midpoint of the third line26cto the branch points of the respective third lines16care equal to each other. Therefore, a current flowed into the midpoint of the third line26cis divided into four and thereby distributed to each of the second block wiring16.

The base end wiring36includes a substantially straight base end line36a(line-shaped wiring) extending in the Y-axis direction between the blocks B32and B42and the blocks B33and B43in order to electrically couple the outside of the antenna device20and the third block wiring26.

The upper end of the base end line36ain the figure is coupled to the third line26cof the third block wiring26. Specifically, like the end of the first line16a, the upper end of the base end fine36ais bent in the negative X-axis direction and then is coupled to the midpoint of the third line26cvia an impedance matcher6bextending in the Y-axis direction.

The third line26cis a branch line when viewed from the base end line36a, and the midpoint of the third line26cis a branch point.

An impedance matcher36bis formed at the lower end of the base end line36ain the figure.

The impedance matcher36bis provided at the base end of the feeding conductor60and is a feeding source of the feeding conductor60. For example, a feeding coaxial cable (not shown) having an impedance of 50Ω is electrically coupled to the impedance matcher36b.

The line width of the main body of the base end line36aexcluding the impedance matchers6band36bis W1as in the main body of the third line26c.

As shown inFIG. 7, the impedance matcher36bhas a line width that is widened in three stages of W21, W22, and W23(where W21<W22<W23) from the middle portion to the lower end of the base end line36ain the figure. The lengths of the respective portions having the line widths W21, W22, and W23are L21, L22, and L23, respectively.

According to an examination result of the inventors, for example in a case where a frequency band used by the antenna device20is a 60 GHz band, it is more preferable that the amount of change in impedance in the portions where the line width changes in the impedance matcher36bin the base end of the feeding conductor60be less than or equal to 50Ω and that the amount of change in impedance in the widening stage closest to the terminal end in the base end be less than or equal to 30Ω. In this case, a return loss due to current reflection at the base end of the feeding conductor60is more preferably suppressed.

Specific numerical examples for the impedance matcher36binclude 0.18 mm, 0.28 mm, and 0.38 mm for the line widths W21, W22, and W23, respectively. In this case, the impedances of the respective portions having the line widths W21, W22, and W23are 78Ω, 60Ω, and 50Ω, respectively.

The impedance matcher36bis widened in three stages like the impedance matcher6b, and the impedance gradually changes from the main body of the base end line36atoward the feeding source in multiple stages such as 112Ω, 78Ω, 60Ω, and 50Ω and is matched with the impedance of the coaxial cable of 50Ω.

In this example, the amounts of change in impedance by the impedance matcher36bare 42Ω, 18Ω, and 10Ω for each of the portions where the line width changes toward the feeding source.

With such a structure, the feeding conductor60has a repetitive branch pattern in which the multiple pieces of line-shaped wiring, which are extending along the Y-axis direction that is the first direction or along the X-axis direction that is the second direction, are connected in T-shapes being perpendicular to each other at a total of 2N−1 branch points (N=6 in the present embodiment) from the base end (impedance matcher36b) that is the feeding source to connection with each of the tips (tip lines6e). Tracing each of the 2Nbranched wiring paths extending from the base end wiring36to each of the tip lines6e, N branch points are formed on each of the wiring paths in the feeding conductor60.

The antenna device20having such a structure is manufactured in the following manner, for example.

First, a conductor film is formed on each of the first surface5aand the second surface5bof the second dielectric layer5, and then the ground conductor plate4and the feeding conductor60are each patterned by etching, for example. Then, the first dielectric layer2, in which the dielectrics2A are bonded, is bonded onto the ground conductor plate4. Thereafter, a conductor film is formed on the first surface2aof the first dielectric layer2, and the patch antennas1are patterned by, for example, etching.

After the patch antennas1are patterned on the first dielectric layer2, the first dielectric layer2and the ground conductor plate4may be bonded together.

Next, the operation of the antenna device20of the present embodiment will be described.

FIG. 8Ais a simulation diagram of an example explaining the wiring pattern of the feeding conductor in the antenna device of the present embodiment.FIG. 8Bis a simulation diagram of a comparative example.

According to the shape of the patch antennas1of the present embodiment and the wiring pattern of the feeding conductor60, when power is fed from the impedance matcher36bof the feeding conductor60, the current is equally distributed to each of the tip lines6eby the T-shaped branch wiring pattern of the feeding conductor60.

At this point, since the line lengths from the feeding source to each of the tip lines6eare equal to each other, and the directions of the tips of the tip lines6eare uniformly oriented in the positive X-axis direction in the feeding conductor60, the electrodes1bof the patch antennas1are electromagnetically coupled and fed with the same amount of current of the same phase in the same direction.

It is also necessary that the coupling impedance be matched in the electromagnetic coupling feeding portion from the tip lines6eto the electrodes1bof the patch antennas1.

In the present embodiment, the coupling impedance is matched through optimization of the arrangement and the opening shape of the first openings7aof the slots7in the ground conductor plate4, formation of the second openings7bin the slots7, and optimization of ds that is the stub length of the tip lines6e.

In particular, by providing widened second openings7bat both ends of a first opening7a, high-impedance areas are formed outside the both ends of the first opening7a. Therefore, signals efficiently pass through the first opening7a, and thus the reflection loss is reduced as a whole.

A current fed to an electrode1bis equally divided in the same phase and distributed to respective radiation elements1aby a divided circuit pattern1dof a patch antenna1.

In this manner, in the antenna device20, a current flows in each of the radiation elements1ain the same phase and in substantially the same direction. For this reason, the gain of a radio wave radiated from each of the patch antennas1is improved.

In order to examine such a feeding conductor60, simulation of the current direction was performed on an example in which the power is directly fed to the midpoints of the second lines6cof the first block wiring6and a comparative example in which directions of the tip lines6eare different despite the same line length.

For specific numerical values used in the following numerical simulation, the numerical values exemplified in the above embodiment are used.

InFIG. 8A, the configuration of an antenna device101of the example and a simulation result are shown. Note thatFIG. 8Ais a schematic diagram, and thus the shape is partially simplified.

In the antenna device101, for example, the 64 patch antennas1in the antenna device20are replaced with four patch antennas1, and accordingly, instead of the feeding conductor60, a feeding conductor106including a first block wiring6and a base end wiring36is included. The other configuration is the same as that of the antenna device20.

The base end wiring36in the antenna device101extends in the Y-axis direction and is connected to the midpoint of a second line6c.

InFIG. 8B, a configuration of an antenna device111of a comparative example and a simulation result are shown. Note thatFIG. 8Bis a schematic diagram, and thus the shape is partially simplified.

The antenna device111includes a feeding conductor126instead of the feeding conductor106of the antenna device101. The feeding conductor126includes first block wiring116instead of the first block wiring6of the feeding conductor106.

Hereinafter, description will be given focusing on differences from the antenna device101.

The first block wiring116is different from the pattern of the first block wiring6in that the first line6dand each of the tip lines6ethat feed the two patch antennas1in the lower part of the figure are inverted in the X-axis direction and that the inverted first line6dand the first line6din the upper part of the figure are connected by a second line116cincluding impedance matchers6bat both ends. The second line116chas a shorter length than that of the second line6e.

The base end wiring36in the feeding conductor126is formed at a position facing the midpoint of the second line116c, and is translated in the X-axis positive direction from the base end wiring36in the feeding conductor106.

The current flowing in the patch antennas1and the radiation pattern were simulated in the case where the antenna devices101and111having the above configurations are respectively fed from the base end wiring36.

In the antenna device101, current directions in the radiation elements1awere aligned in a substantially constant direction (X-axis positive direction in the example shown) as indicated by solid arrows inFIG. 8A. Therefore, in the respective patch antennas1, the current flowed in substantially the same direction in the patch antennas1as a whole as indicated by white arrows C1in the figure.

On the other hand, in the antenna device111, as shown inFIG. 8B, although current directions of radiation elements1aof the two patch antennas1in the lower part of the figure were similar to those of the antenna device101, current directions of radiation elements1aof the two patch antennas1in the upper part of the figure were opposite to those of the antenna device101.

In the antenna device111, as indicated by white arrows C1and C2in the figure, the direction of a current flowing through each of the patch antennas1as a whole was opposite to the direction of the tip of the tip line6e.

FIG. 9Ais a graph showing the radiation pattern of the example, andFIG. 9Bis a graph showing the radiation pattern of the comparative example. InFIGS. 9A and 9B, the horizontal axis represents the elevation angle θ (degrees), and the vertical axis represents the gain (dBi). InFIGS. 9A and 9B, broken lines (curves201and203) represent the total gain on the XZ plane, and solid lines (curves202and204) represent the total gain on the YZ plane. Here, the XZ plane is an electrical plane (E plane), and the YZ plane is a magnetic plane (H plane).

In the antenna device101of the example, as shown inFIG. 9A, the radiation pattern on the XZ plane (see the curve201) and the radiation pattern on the YZ plane (see the curve202) were substantially the same. At θ=0 (degrees), the gains on the XZ plane and the YZ plane were maximized.

On the other hand, in the antenna device111of the comparative example, as shown inFIG. 9B, the radiation pattern on the XZ plane (see the curve203) is a bimodal radiation pattern having peaks at θ=±18 (degrees), and almost no radio wave was radiated at θ=0 (degrees).

In addition, the gain of the radiation pattern on the YZ plane (see the curve204) was significantly lower than that of the curve203. This is considered to be because, since directions of currents flowing through radiation elements1aare opposite in patch antennas1facing each other in the X-axis direction, radio waves interfere with each other and cancel each other.

As described above, radiation characteristics of the antenna in the comparative example were significantly inferior to those of the example since the directions of the tip lines6eare not uniform even though the feeding conductor126having the T-shaped branch wiring pattern is included.

Next, antenna characteristics of the antenna device20will be described.

FIG. 10is a graph showing the total gain in the antenna device of the present embodiment.FIG. 11is a graph showing a reflection loss (S11) in the antenna device of the present embodiment.

InFIG. 10, simulation results of all gains on the XZ plane and the YZ plane are shown.

InFIG. 10, the horizontal axis represents the elevation angle θ (degrees), and the vertical axis represents the gain (dBi). InFIG. 10, a curve210(broken line) represents the total gain on the XZ plane, and a curve211(solid line) represents the total gain on the YZ plane. Here, the XZ plane is an electrical plane (E plane), and the YZ plane is a magnetic plane (H plane).

As indicated by the curves210and211inFIG. 10, improved gain is obtained on both the XZ plane and the YZ plane within the range of elevation angles of 0 to ±4 degrees in the antenna device20.

InFIG. 11, frequency characteristics of a reflection loss (S11) are shown. InFIG. 11, the horizontal axis represents the frequency (GHz) and the vertical axis represents the reflection loss (dB).

As indicated by a curve212inFIG. 1, the reflection loss is less than or equal to −10 dB within the range from about 56 GHz to about 64 GHz. Thus, the antenna device20has preferable reflection loss characteristics in 60 GHz hand wireless communication applications.

Moreover, the antenna device20of the present embodiment is excellent in design work efficiency since it is easy to change the design according to other specifications when an antenna device with different specifications is designed.

For example in a case where the number of patch antennas1is modified, as long as the number of patch antennas1is 2N, the modification can be implemented by increasing/decreasing a T-shaped branch wiring pattern including similar repetitive patterns without newly examining the optimal wiring layout of the feeding conductor.

For example, in the present embodiment, the patch antennas1and the radiation elements1aare arrayed in a square lattice and a substantially square lattice, respectively, and the tip lines6eare arranged in a predetermined positional relationship with the respective patch antennas1when viewed from the normal direction. Since the line-shaped wiring excluding the tip lines6eis only required to be provided so as to extend in the X-axis direction or the Y-axis direction in an area between adjacent patch antennas1, no shortage of arrangement space occurs even if the wiring pattern increases.

The line-shaped wiring of the present embodiment has a constant width in the main body, and a predetermined impedance matcher is formed only at an end connected to a branch point, thereby performing impedance matching with a small return loss. Therefore, it is easy to design each piece of the line-shaped wiring, and the antenna can be miniaturized.

As described above, according to the antenna device20of the present embodiment, efficient design is enabled with improved gain.

In the description of the above embodiment, the examples of 64 and 4 patch antennas1have been described; however, the number of patch antennas1is only required to be 2N(where N is an integer greater than or equal to 2) and is not limited to 64 or 4.

In the description of the above embodiment, the example has been described in which four radiation elements1aare arrayed in a rectangular lattice pattern of a substantially square lattice to form a patch antenna1, and patch antennas1are further arrayed in a square lattice pattern.

However, the four radiation elements1amay be arrayed in a rectangular lattice pattern in which array pitches in the first direction and the second direction are significantly different. Similarly, the patch antennas1are not limited to a square lattice array, and may be arrayed in a rectangular lattice pattern.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments. Additions, omissions, substitutions, and other modifications can be made within a scope not departing from the spirit of the present invention.

Moreover, the present invention is not limited by the above description, and is limited only by the appended claims.

DESCRIPTION OF THE REFERENCE SYMBOLS

1dDivided circuit pattern

36aBase end line