Antenna device

An antenna device includes a substrate; a first ground element that is arranged on the substrate; an antenna element that is arranged on the substrate and extends from its first end positioned near a side edge of the first ground element to its second end positioned away from the side edge; and a non-feed element that is arranged on the substrate, connected to the first ground element, and insulated from the antenna element. The non-feed element extends from its first end portion positioned near the side edge of the first ground element to a bending portion in a direction away from the side edge and extends from the bending portion to its second end portion along the side edge. A portion between the bending portion and the second end portion of the non-feed element intersects with the antenna element.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an antenna device.

2. Description of the Related Art

A wideband array antenna is known that has an inverted-F antenna as a feed element and a non-feed element having a prescribed length erected on a ground plate. In such a wideband array antenna, a part of the non-feed element is disposed at an upper side at a prescribed distance from the feed element, and the respective element lengths of the non-feed element and the feed element are arranged to be different from each other (See e.g., Japanese Laid-Open Patent Publication No. 2001-160710).

It has been difficult to miniaturize antenna devices such as the wideband array antenna described above because of the arrangement of the inverted-F antenna and the non-feed element on the ground plate.

SUMMARY

It is an object of at least one embodiment of the present invention to provide a miniaturized antenna device.

According to an embodiment of the present invention, an antenna device includes a substrate; a first ground element that is arranged on the substrate; an antenna element that is arranged on the substrate and extends from its first end positioned near a side edge of the first ground element to its second end positioned away from the side edge; and a non-feed element that is arranged on the substrate, connected to the first ground element, and insulated from the antenna element. The non-feed element extends from its first end portion positioned near the side edge of the first ground element to a bending portion in a direction away from the side edge and extends from the bending portion to its second end portion along the side edge. A portion between the bending portion and the second end portion of the non-feed element intersects with the antenna element.

According to an aspect of the present invention, a miniaturized antenna device may be provided.

DESCRIPTION OF EMBODIMENTS

FIG. 1is a perspective view of an antenna device100according to an embodiment of the present invention.FIGS. 2A and 2Brespectively illustrate a front surface and a back surface of the antenna device100. Note thatFIGS. 1,2A, and2B illustrate the antenna device100with respect to an XYZ orthogonal coordinate system.

The antenna device100includes a substrate110, an antenna element120, ground elements130A and130B, and a non-feed element140.

The substrate110may be a printed circuit board that complies with a standard such as FR-4 (Flame Retardant Type 4), for example. Alternatively, the substrate110may be a flexible substrate made of a polyimide film, for example.

The substrate110has a rectangular shape in plan view with its longer sides extending in the Y-axis direction. Specifically, as illustrated inFIGS. 2A and 2B, the substrate110of the present embodiment is arranged into a rectangle having four side edges110X1,110X2,110Y1, and110Y2.

The antenna element120is formed on one surface (front surface illustrated inFIG. 2A) of the substrate110. A feed point121is arranged at one end of the antenna element120. The feed point121is arranged near a side edge131A of the ground element130A, which has a rectangular shape in plan view.

The antenna element120extends from the feed point121, which is arranged near the side edge131A of the ground element130A, to an end point122at the other end of the antenna element120located toward the Y-axis positive direction side and away from the side edge131A.

The antenna element120is a monopole antenna that is fed at the feed point121. The length between the feed point121and the end point122may be set to λ/4; i.e., ¼ of the wavelength λ at a communication frequency (resonant frequency of the antenna device100), for example.

However, because the effective length of a monopole antenna may vary depending on factors such as the dielectric constant of the substrate110, the length of the antenna element120(i.e., length between the feed point121and the end point122) may be set to approximately λ/4 taking into account the dielectric constant of the substrate110, for example.

The feed point121of the antenna element120may be fed by connecting the feed point121to a cable core of a coaxial cable that is connected to a transceiving terminal of a transceiver, for example. In this case, a shield line of the coaxial cable may be connected to a point of the ground element130A near the side edge131A, which is located at the Y-axis negative direction side of the feed point121, for example. Such a point to which the shield line of the coaxial cable is connected is illustrated as feed point132inFIG. 2A. The feed point132may be located at a position corresponding to the position of the feed point121.

Alternatively, instead of feeding the feed point121using a coaxial cable, a transceiver may be arranged at the ground element130A and a transceiving terminal of the transceiver may be connected to the feed point121, for example. In this case, a ground terminal of the transceiver may be connected to the ground element130A.

The antenna element120intersects with the non-feed element140at a point123(“intersecting point”) between the feed point121and the end point122in plan view.

The antenna120as described above may be fabricated by etching a pattern on a copper foil that is laminated on one surface of the substrate110, for example. Note that although an exemplary case where the antenna element120is made of copper is described below, the antenna element120is not limited to copper but may be made of some other type of metal such as aluminum, for example.

The ground element130A is formed at the Y-axis negative direction side of one surface of the substrate110within an area substantially half the size of the entire surface of the substrate110. The ground element130A extends along substantially the entire X-axis direction range of the substrate110other than the X-axis direction side edges of the substrate110.

The antenna element120extends along the Y-axis direction and may be located at the X-axis positive direction side of the longitudinal central axis of the substrate110, for example. The position of the antenna element120with respect to the X-axis direction is described in detail below.

InFIG. 2B, a corresponding position of the antenna element120at the back surface of the substrate110is indicated by broken lines.

As described above, the ground element130A has a rectangular shape in plan view and is arranged at the X-axis negative direction side of one surface (front surface illustrated inFIG. 2A) of the substrate110. That is, the ground element130A is arranged into a rectangular shape. Note that the ground element130A may be an exemplary embodiment of a first ground element or a second ground element.

The ground element130A includes four side edges131A,132A,133A, and134A. The side edges132A,133A, and134A extend along the edges of the substrate110.

The side edge131A extends across the surface of the substrate110in the X-axis direction along a boundary between the area where the ground element130A is arranged and the area where the ground element130A is not arranged.

The feed point132to which the shield line of a coaxial cable is connected is arranged near the side edge131A at a position corresponding to the position of the feed point121. The ground element130A is connected to the coaxial cable via the feed point132.

The ground element130A as described above may be fabricated by etching a pattern on a copper foil that is laminated on one surface of the substrate110, for example. Note that although an exemplary case where the ground element130A is made of copper is described below, the ground element130A is not limited to copper but may be made of some other type of metal such as aluminum, for example.

The ground element130B is formed on the other surface (back surface shown inFIG. 2B) of the substrate110within an area overlapping the area of the ground element130A in plan view. The ground element130B may be an exemplary embodiment of the first ground element or the second ground element. That is, when the ground element130A corresponds to an exemplary embodiment of the first ground element, the ground element130B may correspond to an exemplary embodiment of the second ground element. On the other hand, when the ground element130A corresponds to an exemplary embodiment of the second ground element, the ground element130B may correspond to an exemplary embodiment of the first ground element.

The ground element130B is connected to the ground element130A by vias150that penetrate through the substrate110so that the ground element130B may be maintained at ground potential. The vias150are arranged within the areas where the ground element130A and the ground element130B are formed.

The ground element130B includes four side edges131B,132B,133B, and134B. The side edges131B,132B,133B, and134B are respectively arranged at positions overlapping the positions of the side edges131A,132A,133A, and134A in plan view.

The ground element130B has a corner portion130B1located at the X-axis positive direction side and Y-axis positive direction side of the ground element130B. An end portion141of the non-feed element140is connected to the corner portion130B1. The corner portion130B1is located at a point where the side edge131B and the side edge132B intersect.

The ground element130B as described above may be fabricated by etching a pattern on a copper foil that is laminated on the other surface of the substrate110, for example. Note that although an exemplary case where the ground element130B is made of copper is described below, the ground element130B is not limited to copper but may be made of some other type of metal such as aluminum, for example. Also, in certain preferred embodiments, the ground element130B and the non-feed element140may be fabricated at the same time.

As illustrated inFIG. 2B, the non-feed element140is an L-shaped non-feed element having the end portion141connected to the corner portion130B1of the ground element130B.

The non-feed element140includes the end portion141as one end of the non-feed element140; a portion extending in the Y-axis direction from the end portion141, to a bending portion142at which the non-feed element140bends at a 90-degree angle; a portion extending in the X-axis direction from the bending portion142to an end portion143along the side edge131B; and the end portion143as the other end of the non-feed element140. The end portion143is located near the side edge110Y1.

The non-feed element140is connected to the ground element130B and does not directly receive power. Thus, the non-feed element140may be regarded as a parasitic element.

The length between the bending portion142and the end portion143of the non-feed element140may be set to λ/4; i.e., ¼ of the wavelength λ of the communication frequency (resonant frequency of the antenna device100), for example.

However, because the length of the non-feed element140may depend on factors such as the dielectric constant of the substrate110, the length between the bending portion142and the end portion143may be set to approximately λ/4 taking into account the dielectric constant of the substrate110, for example.

The portion between the bending portion142and the end portion143of the non-feed element140intersects with the antenna element120. In the example illustrated inFIGS. 2A and 2B, the portion between the bending portion142and the end portion143of the non-feed element140intersects with the antenna element120at a right angle. InFIG. 2B, the non-feed element140intersects with the antenna element120at point144.

Note that the angle at which the portion between the bending portion142and the end portion143of the non-feed element140intersects with the antenna element120is not limited to a right angle. InFIG. 2A, a corresponding position of the non-feed element140at the front surface of the substrate110is indicated by broken lines.

In the antenna device100having the above-described configuration, the antenna element120receives power via the feed point121and functions as a monopole antenna.

By coupling the antenna element120to the non-feed element140, a band may be widened at the lower frequency side. That is, by widening the band, favorable antenna characteristics may be obtained at a lower frequency range.

Note that the above-described effect may similarly be obtained even when the length of the antenna element120is shortened and a high frequency (resonant frequency) is used.

That is, even when the length of the antenna element120is shortened and a high frequency is used, the band may be widened at the lower frequency side and favorable antenna characteristics may be obtained at the frequency used.

By shortening the length of the antenna element120as described above, the antenna device100may be miniaturized. The resonant frequency used by the antenna element120may be set to a suitable frequency according to the intended use of the antenna device100.

Also, in the antenna device100of the present embodiment, the positional relationship between the antenna element120and the non-feed element140may preferably be arranged in the following manner, for example.

The position of the antenna element120with respect to the X-axis is preferably arranged such that the length between intersecting point123and the bending porting143is equal to λ/20; i.e., 1/20 of the wavelength λ of the communication frequency.

Also, the distance in the Y-axis from the side edge131B of the ground element130B (or side edge131A of the ground element130A) to the portion between the bending portion142and the end portion143of the non-feed element140is preferably set to λ/20; i.e., 1/20 of the wavelength λ of the communication frequency. In other words, the distance from the end portion141to the bending portion142of the non-feed element140is preferably set to λ/20.

For example, in a case where the communication frequency is set to 2.45 GHz for use in a wireless LAN (local area network), the length between the feed point121and the end point122of the antenna element120may be arranged to be 20 mm so that the above value λ/20 may be 4 mm.

Also, the lengths of the ground elements130A and130B in the X-axis direction may be 20 mm, and the lengths of the ground elements130A and130B in the Y-axis direction may be 25 mm.

Also, the respective lengths between the side edges132A,133A, and134A of the ground element130A and the side edges110Y2,110X1, and110Y1of the substrate110(i.e., margins between the edges of the substrate110and the edges of the ground element130A where the ground element130A is not arranged) may be set to 0.5 mm, for example. The same arrangements may be made for the ground element130B.

Although the line width of the antenna element120and the line width of the non-feed element140may be set to suitable values in view of various factors such as the communication characteristics of the antenna device100, in one example, the line widths may be set to 0.5 mm.

In the following, referring toFIGS. 3-11, VSWR (voltage standing-wave ratio) characteristics of the antenna device100are described in various cases where the dimensions of its components are changed.

FIG. 3is a graph illustrating VSWR characteristics of the antenna device100of the present embodiment and VSWR characteristics of an antenna device that does not include the non-feeding element140of the antenna device100.

InFIG. 3, the VSWR characteristics of the antenna device100of the present embodiment are represented by a solid line, and the VSWR characteristics of the antenna device without the non-feed element140are represented by a broken line.

The VSWR characteristics represented by the solid line inFIG. 3are obtained in a case where the dimensions of the antenna device100of the present embodiment were set up as follows:Length between intersecting point123and the bending portion142: λ/20 (4 mm)Distance in the Y-axis direction from the side edge131B of the ground element130B to the portion between the bending portion142and the end portion143of the non-feed element140: λ/20 (4 mm)Length between the feed point121and the end point122of the antenna element120: 20 mmLengths of the ground elements130A and130B in the X-axis direction: 20 mmLengths of the ground elements130A and130B in the Y-axis direction: 25 mm

The antenna device without the non-feed element140has other components of the antenna device100(i.e., components other than the non-feed element140) with the same dimensions.

That is, the difference in the VSWR characteristics represented by the solid line and the broken line inFIG. 3may be solely attributed to the presence or absence of the non-feed element140. Note that the VSWR characteristics illustrated inFIG. 3were obtained through electromagnetic simulation.

As illustrated by the solid line inFIG. 3, in the antenna device100of the present embodiment, favorable VSWR characteristics of 2.0 or less can be obtained at a frequency range from approximately 2.43 GHz to approximately 3.15 GHz. The minimum value of the VSWR is approximately 1.1, and the VSWR is approximately 1.2 at 2.45 GHz.

On the other hand, as illustrated by the broken line inFIG. 3, in the antenna device without the non-feed element140, VSWR characteristics of 2.0 or less can be obtained at a frequency range from approximately 2.57 GHz to approximately 3.1 GHz. The minimum value of the VSWR is approximately 1.4, and the VSWR is approximately 3.2 at 2.54 GHz.

As can be appreciated from above, the band of the antenna device100may be widened by providing the non-feed element140.

Also, when the non-feed element140is added, the band at which the VSWR equals its minimum value is shifted toward the lower frequency side. This may be attributed to band widening at the lower frequency side as a result of coupling the antenna element120to the non-feed element140.

On the other hand, the VSWR characteristics may shift toward the higher frequency side when the length of the antenna element120is shortened.

Thus, by adding the non-feed element140to shift the VSWR characteristics toward the lower frequency side and shortening the length of the antenna element120, VSWR characteristics at the desired frequency of 2.45 GHz may be improved and the antenna device100may be miniaturized. Note that the VSWR characteristics may be affected by the length of the non-feed element140in a similar manner as described in detail below.

As can be appreciated from above, the antenna device100including the non-feed element140may be miniaturized by shortening the antenna element120.

In the following, referring toFIGS. 4A-5D, VSWR characteristics of the antenna device100are described in various cases where the position of the antenna element120is shifted (changed) in the X-axis direction.

FIGS. 4A-4Fare perspective views of the antenna device100having the antenna element120arranged at different positions in the X-axis direction.

Note that shifting the position of the antenna element120in the X-axis direction corresponds to changing the length between the intersecting point123and the bending portion142. Also, because intersecting point123(seeFIG. 2A) and point144(seeFIG. 2B) are located at the same position with respect to the X-axis direction, altering the length between intersecting point123and the bending portion142corresponds to altering the length between point144and the bending portion142.

InFIG. 4C, the antenna element120is shifted in the X-axis negative direction so that the length between intersecting point123and the bending portion142is λ/8 (10 mm).

InFIGS. 4B and 4A, the antenna element120is shifted farther in the X-axis negative direction so that the length between intersecting point123and the bending portion142is 15 mm and 20 mm, respectively.

InFIGS. 4E and 4F, the antenna element120is shifted in the X-axis positive direction so that the length between intersecting point123and the bending portion142is 2 mm and 1 mm, respectively.

FIGS. 5A-5Dare graphs illustrating VSWR characteristics of the antenna device100in various cases where the length between intersecting point123and the bending portion142is incremented by 1 mm from 1 mm to 20 mm. For the sake of improving visibility, illustrations of the VSWR characteristics of the antenna device100incremented in the above manner are divided into four separate graphs inFIGS. 5A-5D. That is,FIG. 5Aillustrates cases where the length between intersecting point123and the bending portion142is from 1 mm to 5 mm;FIG. 5Billustrates cases where the length between intersecting point123and the bending portion142is from 6 mm to 10 mm;FIG. 5Cillustrates cases where the length between intersecting point123and the bending portion142is from 11 mm to 15 mm; andFIG. 5Dillustrates cases where the length between intersecting point123and the bending portion142is from 16 mm to 20 mm.

Upon reviewing the VSWR values at 2.45 GHz inFIGS. 5A-5D, it can be appreciated that favorable VSWR characteristics can be obtained when the length between intersecting point123and the bending portion142is 4 mm, 5 mm, and 6 mm. Further, of these cases, the band widening effect is greatest when the length between intersecting point123and the bending portion142is 4 mm.

Note that when the length between intersecting point123and the bending portion142is 7 mm or more, the VSWR value tends to increase and the band tends to become narrower.

As can be appreciated from the above, by arranging the length between intersecting point123and the bending portion142to be within a range of 4 mm to 6 mm in the antenna device100of the present embodiment, the band may be widened around the desired frequency of 2.45 GHz and favorable VSWR values may be obtained. The above range from 4 mm to 6 mm may be expressed as λ/20 to 3λ/40 using the wavelength λ at the frequency 2.45 GHz, which is approximately 80 mm.

As described above, the VSWR characteristics of the antenna device100tend to shift toward the higher frequency side when the length of the antenna element120is shortened.

Thus, by arranging the length between intersecting point123and the bending portion142to be within a range of 4 mm to 6 mm (λ/20 to 3λ/40) to widen the band toward the lower frequency side in the antenna device100including the non-feed element140of the present embodiment, the length of the antenna element120may be shortened and the antenna device100may be miniaturized.

In the following, VSWR characteristics of the antenna device100are described in various cases where the distance from the side edge131B of the ground element130B to the portion between the bending portion142and the end portion143of the non-feed element140is changed by adjusting the length between the end portion141and the bending portion142of the non-feed element140.

In the exemplary cases described below, it is assumed that the length between the bending portion142and the end portion143of the non-feed element140is fixed at λ/4 (20 mm).

FIGS. 6A-6Eare perspective views of the antenna device100having the non-feed element140arranged at different positions.

The antenna device100illustrated inFIG. 6Ccorresponds to the antenna device100illustrated inFIG. 1. That is, in the antenna device100ofFIG. 6C, the length between the end portion141and the bending portion142(seeFIG. 2B) is arranged to be λ/4 (20 mm).

InFIGS. 6A and 6B, the portion between the bending portion142and the end portion143is moved in the Y-axis negative direction so that the length between the end portion141and the bending portion142(seeFIG. 2B) is 2 mm and 1 mm, respectively.

InFIGS. 6D and 6E, the portion between the bending portion142and the end portion143is moved in the Y-axis positive direction so that the length between the end portion141and the bending portion142(seeFIG. 2B) is 10 mm and 15 mm, respectively.

FIGS. 7A-7Care graphs illustrating VSWR characteristics of the antenna device100in various cases where the length between the end portion141and the bending portion142is incremented by 1 mm from 1 mm to 15 mm.

Note that for the sake of improving visibility, the illustrations of the VSWR characteristics in the various cases are divided into separate graphs inFIGS. 7A-7C. That is,FIG. 7Aillustrates cases where the length between the end portion141and the bending portion142is from 1 mm to 5 mm;FIG. 7Billustrates cases where the length between the end portion141and the bending portion142is from 6 mm to 10 mm; andFIG. 7Cillustrates cases where the length between the end portion141and the bending portion142is from 11 mm to 15 mm.

Upon reviewing the VSWR values at the frequency 2.45 GHz inFIGS. 7A-7C, it can be appreciated that favorable VSWR characteristics can be obtained when the length between the end portion141and the bending portion142is 3 mm, 4 mm, and 5 mm. Of these cases, the band widening effect is greatest when the length between the end portion141and the bending portion142is 4 mm.

Note that when the length between the end portion141and the bending portion142is 6 mm or more, the VSWR value tends to increase and the band tends to become narrower.

As can be appreciated from the above, by arranging the length between the end portion141and the bending portion142to be within a range of 3 mm to 5 mm in the antenna device100of the present embodiment, the band may be widened around the desired frequency of 2.45 GHz and favorable VSWR values may be obtained.

Note that the above range of 3 mm to 5 mm may be expressed as 3λ/80 to 5λ/80 using the wavelength λ at the frequency 2.45 GHz, which is approximately 80 mm.

As described above, the VSWR characteristics of the antenna device100tend to shift toward the higher frequency side when the length of the antenna element120is shortened.

Thus, by arranging the length between end portion141and the bending portion142to be within a range of 3 mm to 5 mm (3λ/80 to 5λ/80) to widen the band toward the lower frequency side in the antenna device100including the non-feed element140of the present embodiment, the length of the antenna element120may be shortened and the antenna device100may be miniaturized.

In the following, VSWR characteristics of the antenna device100are described in various cases where the length between the bending portion142and the end portion143of the non-feed element140is adjusted.

In the exemplary cases described below, it is assumed that the length between the end portion141and the bending portion142is fixed at λ/20 (4 mm), and the length between the bending portion142and the end portion143of the non-feed element140is adjusted.

FIGS. 8A-8Fare perspective views of the antenna device100having the non-feed element140adjusted to different lengths.

The antenna device100illustrated inFIG. 8Bcorresponds to the antenna device100illustrated inFIG. 1. That is, in the antenna device100ofFIG. 8B, the length between the bending portion142and the end portion143(seeFIG. 2B) is arranged to be λ/4 (20 mm).

InFIG. 8A, the end portion143is extended in the Y-axis negative direction so that the length between the bending portion142and the end portion143is 21 mm. Note that in conducting electromagnetic simulation of the antenna device100in this case, the width of the substrate110was widened in the X-axis direction by moving the side edge110Y1of the substrate110(seeFIG. 2A) 1 mm toward the X-axis negative direction side.

InFIGS. 8C,8D,8E, and8F, the end portion143is moved in the X-axis positive direction so that the length between the bending portion142and the end portion143is 15 mm, 10 mm, 5 mm, and 0 mm, respectively.

FIG. 9is a graph illustrating VSWR characteristics of the antenna device100in cases where the length between the bending portion142and the end portion143is set to 21 mm (A), 20 mm (B), 15 mm (C), 10 mm (D), 4 mm (E), and 0 mm (F).

Upon reviewing the VSWR values at the frequency 2.45 GHz inFIG. 9, it can be appreciated that favorable VSWR characteristics can be obtained when the length between the bending portion142and the end portion143is 21 mm and 20 mm. Of these cases, the VSWR value is lower and more favorable when the length between the bending portion142and the end portion143is 20 mm.

Also, when the length between the bending portion142and the bending portion is 15 mm or less, the VSWR value tends to increase and the band tends to shift toward the higher frequency side.

As can be appreciated from the above, by arranging the length between the bending portion142and the end portion143to be approximately 20 mm in the antenna device100of the present embodiment, the band may be widened around the desired frequency of 2.45 GHz and favorable VSWR values may be obtained.

As described above, the VSWR characteristics of the antenna device100tend to shift toward the higher frequency side when the length of the antenna element120is shortened.

Thus, by arranging the length between the bending portion142and the end portion143to be approximately 20 mm to widen the band toward the lower frequency side in the antenna device100including the non-feed element140of the present embodiment, the length of the antenna element120may be shortened and the antenna device100may be miniaturized.

In the following, VSWR characteristics of the antenna device100are described in various cases where the width of the portion between the bending portion142and the end portion143of the non-feed element140is adjusted.

In the exemplary cases described below, the width of the portion between the bending portion142and the end portion143is adjusted so that the length between the end portion141and the bending portion142is shorter than λ/20 (4 mm).

FIGS. 10A-10Care perspective views of the antenna device100having the non-feed element140adjusted to different widths.

The antenna device100illustrated inFIG. 10Acorresponds to the antenna device100illustrated inFIG. 1. That is, in the antenna device100ofFIG. 10A, the width of the portion between the bending portion142and the end portion143(seeFIG. 2B) is arranged to be 0.5 mm.

InFIG. 10B, the width of the portion between the bending portion142and the end portion143is arranged to be 3 mm, and the length of the portion between the end portion141and the bending portion142is arranged to be 1 mm.

InFIG. 10C, the width of the portion between the bending portion142and the end portion143is arranged to be 10 mm, and the length of the portion between the end portion141and the bending portion142is arranged to be 1 mm.

InFIG. 10D, the width of the portion between the bending portion142and the end portion143is arranged to be 15 mm, and the length of the portion between the end portion141and the bending portion142is arranged to be 1 mm.

FIG. 11is a graph illustrating VSWR characteristics of the antenna device100in cases where the width of the portion between the bending portion142and the end portion143is set to 0.5 mm (A), 3 mm (B), 10 mm (C), and 15 mm (D).

Upon reviewing the VSWR values at the frequency 2.45 GHz inFIG. 11, it can be appreciated that favorable VSWR values of less 2.0 can be obtained at 2.45 GHz in all of the above cases (A)-(D).

Of the above cases, particularly favorable characteristics can be obtained when the width of the portion between the bending portion142and the end portion143is 0.5 mm.

As can be appreciated from the above, by arranging the width of the portion between the bending portion142and the end portion143to be 0.5 mm in the antenna device100of the present embodiment, the band may be widened around the desired frequency of 2.45 GHz and favorable VSWR values may be obtained.

As described above, the VSWR characteristics of the antenna device100tend to shift toward the higher frequency side when the length of the antenna element120is shortened.

Thus, by arranging the width of the portion between the bending portion142and the end portion143to be approximately 0.5 mm to widen the band toward the lower frequency side in the antenna device100including the non-feed element140of the present embodiment, the length of the antenna element120may be shortened and the antenna device100may be miniaturized.

According to an aspect of the present embodiment, the antenna device100may be miniaturized by arranging the non-feed element140and the antenna element120in the manner described above.

Note that although the antenna device100includes two ground elements130A and130B in the above-described embodiment, the antenna device100may alternatively include only one of the ground element130A or the ground element130B.

For example, in a case where the antenna device100only includes the ground element130A, the end portion141of the non-feed element140may be connected to the ground element130A by a via that penetrates through the substrate110.

In a case where the antenna device100only includes the ground element130B, the shield line of a coaxial cable may be connected to the ground element130B by a via that penetrates through the substrate110, for example.

Also, in the antenna device100described above, the antenna element120and the ground element130A are arranged on one surface of the substrate110and the non-feed element140and the ground element130B are arranged on the other surface of the substrate110.

However, the antenna element120, the ground elements130A and130B, and the non-feed element140do not necessarily have to be arranged on one surface and the other surface of the substrate110as long as their plan-view positional relationship is maintained.

For example, in certain embodiments, the substrate110may be a multilayer substrate including a conductive inner layer. In this case, the antenna element120, the ground elements130A and130B, and the non-feed element140may be arranged on the front surface, the back surface or an inner layer of the substrate110.

FIG. 12illustrates an exemplary configuration of an antenna device with the substrate110having a multilayer structure. InFIG. 12, the antenna element120is arranged on an inner layer of the substrate110. Note that inFIG. 12, the inner layer of the substrate110is illustrated at an upper portion above the section line drawn across the substrate110where the antenna element120is indicated by a solid line. At the portion below this section line, the inner layer is covered by a top layer of the substrate110, and the corresponding positions of the antenna element120and the ground element130A are indicated by broken lines.

In the case where the substrate110is a multilayer substrate, vias that penetrate through an insulating layer of the multilayer substrate may be used to establish electrical connection between the antenna element120, the ground elements130A and130B, and the non-feed element140, for example.

Also, in the above case, the antenna device100may include only one of the ground element130A or the ground element130B, for example.

Also, although the end portion141of the non-feed element140is connected to the corner portion130B1of the ground element130B in the above-described embodiment, the present invention is not limited to such an arrangement and the end portion141may be grounded at some other location.

For example, in the case where the antenna device100includes only the ground element130A, the position of the end portion141of the non-feed element140may be extended in the Y-axis negative direction from the position illustrated inFIGS. 2A and 2B. In this case, the non-feed element140may be connected to the ground element130A at the position of the end portion141illustrated inFIG. 2Bby a via that penetrates through the substrate110, for example.

Also, in the above-described embodiment, the feed point121at one end of the antenna element120is arranged near the side edge131A of the ground element130A, and the side edge130A is linear. However, in other embodiments, a concave portion may be provided at the side edge131A by notching the side edge131A in the Y-axis negative direction, and the feed point121may be drawn into this concave portion, for example. Such an arrangement may be advantageous in a case where a coaxial cable is used to feed the feed point121, for example.

Further, although the antenna device of the present invention is described above with respect to certain illustrative embodiments, the present invention is not limited to these embodiments but encompasses numerous other variations and modifications that may be made without departing from the scope of the present invention.

The present application is based on and claims priority to Japanese Patent Application No. 2012-276101 filed on Dec. 18, 2012, the entire contents of which are hereby incorporated by reference.