Patent Publication Number: US-2017358860-A1

Title: Antenna device and wireless device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of PCT international application Ser. No. PCT/JP2015/068654 filed on Jun. 29, 2015, which designates the United States; the entire contents of which are incorporated herein by reference. 
    
    
     FIELD 
     The present invention relates to an antenna device and a wireless device. 
     BACKGROUND 
     Conventionally, an antenna in which a loop-shaped antenna element is disposed at a short distance away from a base plate surface has been known. The directivity of the antenna such as the above becomes perpendicular to the base plate surface, by making the circumference length of the loop-shaped antenna element to about a wavelength or less. 
     However, in the conventional antenna, the directivity parallel to the base plate surface has not been taken into consideration, and thus, there is a possibility for the antenna not being able to communicate with a wireless device that is disposed parallel to the base plate surface. In this manner, with the conventional antenna, communication is limited in the direction parallel to the base plate surface. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view illustrating an antenna device according to a first embodiment. 
         FIG. 2  is a top view illustrating the antenna device according to the first embodiment. 
         FIG. 3  is a diagram illustrating radiation characteristics of the antenna device according to the first embodiment. 
         FIG. 4  is a diagram illustrating the radiation characteristics of the antenna device according to the first embodiment. 
         FIG. 5  is a perspective view illustrating an antenna device according to a second embodiment. 
         FIG. 6  is a top view illustrating the antenna device according to the second embodiment. 
         FIG. 7  is a diagram illustrating radiation characteristics of the antenna device according to the second embodiment. 
         FIG. 8  is a diagram illustrating the radiation characteristics of the antenna device according to the second embodiment. 
         FIG. 9  is an explanatory diagram of the radiation characteristics of the antenna device according to the second embodiment. 
         FIG. 10  is an explanatory diagram of the radiation characteristics of the antenna device according to the second embodiment. 
         FIG. 11  is a diagram illustrating the radiation characteristics of the antenna device according to the second embodiment. 
         FIG. 12  is a diagram illustrating the radiation characteristics of the antenna device according to the second embodiment. 
         FIG. 13  is a diagram illustrating an antenna device according to a first modification of the second embodiment. 
         FIG. 14  is a diagram illustrating an antenna device according to a second modification of the second embodiment. 
         FIG. 15  is a top view illustrating an antenna device according to a third embodiment. 
         FIG. 16  is a diagram illustrating VSWR characteristics of the antenna device according to the third embodiment. 
         FIG. 17  is an explanatory diagram of the VSWR characteristics of the antenna device according to the third embodiment. 
         FIG. 18  is a diagram illustrating an antenna device according to a third modification of the third embodiment. 
         FIG. 19  is a diagram illustrating an antenna device according to a fourth modification of the third embodiment. 
         FIG. 20  is a diagram illustrating an antenna device according to a fifth modification of the third embodiment. 
         FIG. 21  is a diagram illustrating a wireless device according to a fourth embodiment. 
         FIG. 22  is a diagram illustrating the wireless device according to the fourth embodiment. 
         FIG. 23  is a diagram illustrating a wireless device according to a sixth modification of the fourth embodiment. 
         FIG. 24  is a diagram illustrating a wireless device according to a seventh modification of the fourth embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     According to an embodiment, an antenna device includes a substrate, a first linear conductive element and a second linear conductive element. The first linear conductive element is disposed on the substrate so as to have a loop shape line-symmetric with respect to a first straight line and a second straight line that is orthogonal to the first straight line, the first linear conductive element having a first electrical length between intersections of the first linear conductive element and the second straight line that is an integer multiple of a wavelength at a resonance frequency. The second linear conductive element is disposed on the substrate and is substantially parallel to the second straight line, first a second electrical length that is a half wavelength of the wavelength at the resonance frequency. 
     First Embodiment 
       FIG. 1  is a perspective view illustrating a configuration of an antenna device  1  according to a first embodiment. To make the explanation easier to understand, 
       FIG. 1  includes a three-dimensional orthogonal coordinate system including a Z-axis the upward direction of which in the drawing is the positive direction, and the downward direction of which in the drawing is the negative direction. Such orthogonal coordinate system may also be illustrated in other drawings used in the following description. 
     The antenna device  1  includes a substrate  100 , a power feeding point  200 , and a linear conductive element  300 . The substrate  100  is a multilayer substrate including a dielectric layer  101  having a rectangular shape and a ground layer  102 . For example, the ground layer  102  is made of a metal layer such as copper and gold. 
     The linear conductive element  300  is an antenna element disposed on the dielectric layer  101  of the substrate  100 . The power feeding point  200  is provided on the linear conductive element  300 . The linear conductive element  300  transmits a signal that is received from a wireless unit, which is not illustrated, via the power feeding point  200 . Alternatively, the linear conductive element  300  outputs a signal received via the power feeding point  200  to the wireless unit. 
     Next, the linear conductive element  300  will be described in detail with reference to  FIG. 2 .  FIG. 2  is a top view illustrating the antenna device  1  according to the present embodiment. The linear conductive element  300  illustrated in  FIG. 2  includes a first linear conductive element  310 , a second linear conductive element  320 , a third linear conductive element  330 , and a fourth linear conductive element  340 . 
     The first linear conductive element  310  is a conductive element having a loop shape that is disposed so as to be in line symmetry with respect to a first straight line A and a second straight line B that is orthogonal to the first straight line A. In this example, the first straight line A and the second straight line B are virtual straight lines parallel to the substrate  100 . In other words, the substrate  100  has a plane parallel to a plane including the first straight line A and the second straight line B, and the first linear conductive element  310  is provided on the plane such as the above. 
     The first linear conductive element  310  includes first to fifth linear elements  311  to  315 . The first linear element  311  and the fifth linear element  315  are disposed on the same straight line. In other words, the first linear element  311  and the fifth linear element  315  connect the power feeding point  200  and the center portion of the straight linear elements, via the third linear conductive element  330  and the fourth linear conductive element  340 . Moreover, the first and the fifth linear elements  311  and  315 , and the second linear element  312  are disposed parallel to one another. 
     In other words, the first and the fifth linear elements  311  and  315 , and the second linear element  312  are parallel to the second straight line B. Moreover, a part of the first linear element  311  and the second linear element  312  are line-symmetric with respect to the second straight line B, and a part of the fifth linear element  315  and the second linear element  312  are line-symmetric with respect to the second straight line B. Furthermore, an electrical length d 1  between the first linear element  311  and the second linear element  312 , and between the second linear element  312  and the fifth linear element  315  is shorter than an integer multiple of a half wavelength of the resonance frequency f (d 1 &lt;mλ/2, m: natural number). 
     An end of the fourth linear element  314  is connected to an end of the first linear element  311 , and the other end of the fourth linear element  314  is connected to an end of the second linear element  312 . Moreover, an end of the third linear element  313  is connected to an end of the fifth linear element  315 , and the other end of the third linear element  313  is connected to the other end of the second linear element  312 . The third linear element  313  and the fourth linear element  314  are line-symmetric with respect to the first straight line A, and are parallel to the first straight line A. As illustrated in  FIG. 2 , similar to the electrical length d 1  between the first linear element  311  and the second linear element  312 , an electrical length of the third linear element  313  and the fourth linear element  314  is shorter than an integer multiple of a half wavelength of the resonance frequency f. 
     The first linear conductive element  310  is a conductive element having a loop shape line-symmetric with respect to the first straight line A and the second straight line B. The first linear conductive element  310  operates as a loop antenna, which will be described below, by connecting to the power feeding point  200  at the intersection between the first linear conductive element  310  and the first straight line A, via the third linear conductive element  330  and the fourth linear conductive element  340 . 
     In the first linear conductive element  310 , an electrical length between the intersections of the first linear conductive element  310  and the first straight line A is an integer multiple of the wavelength λ at the resonance frequency f. In other words, an electrical length D 1  of the first linear conductive element  310 , from the power feeding point  200  to a second intersection (hereinafter, referred to as an intersection  401 ) between the first linear conductive element  310  and the first straight line A is set to the length satisfying 2πD 1 /λ+π=(2n−1)×π. 
     Consequently, the electrical length D 1  of the first linear conductive element  310  is an integer multiple of the wavelength λ at the resonance frequency f of the first linear conductive element  310  (D 1 =nλ, n: natural number). Because the first linear conductive element  310  has a loop shape line-symmetric with respect to the first straight line A, the circumference length D of the first linear conductive element  310  is twice the electrical length D 1  of the first linear conductive element  310  (D=2D 1 =2nλ). 
     Furthermore, in the first linear conductive element  310 , an electrical length between the intersection of the first linear conductive element  310  with the first straight line A, and the intersection of the first linear conductive element  310  with the second straight line B, is an integer multiple of a half wavelength of the resonance frequency f. In other words, an electrical length D 2  from the intersection  401  to a second intersection (hereinafter, referred to as an intersection  403 ) between the first linear conductive element  310  and the second straight line B is an integer multiple of a half wavelength (D 2 =nλ/2). 
     As described above, the first linear conductive element  310  is line-symmetric with respect to the first straight line A, and also line-symmetric with respect to the second straight line B. Thus, the distance from the intersection  401  to an intersection  402  of the first linear conductive element  310  becomes the same as the electrical length D 2 . Moreover, the distance from the power feeding point  200  to the intersection  403  between the first linear conductive element  310  and the second straight line B, and the distance from the intersection  401  to a first intersection (hereinafter, referred to as the intersection  402 ) between the first linear conductive element  310  and the second straight lint B are an integer multiple of a half wavelength (D 2 =nλ/2), which is the same as the electrical length D 2 . 
     The second linear conductive element  320  includes a sixth linear element  321  and a seventh linear element  322 . The sixth linear element  321  and the seventh linear element  322  are disposed on the same straight line. Moreover, the sixth linear element  321  and the seventh linear element  322  are disposed parallel to the second straight line B. 
     In the example illustrated in  FIG. 2 , the second linear conductive element  320  is disposed on the substrate  100 , and outside of the loop shape of the first linear conductive element  310 . The electrical length of the second linear conductive element  320  is a half wavelength of the resonance frequency f. 
     The third linear conductive element  330  includes an eighth linear element  331  and a ninth linear element  332 . An end of the eighth linear element  331  is connected to an end of the sixth linear element  321 , and the other end of the eighth linear element  331  is connected to the other end of the first linear element  311 . An end of the ninth linear element  332  is connected to an end of the seventh linear element  322 , and the other end of the ninth linear element  332  is connected to the other end of the fifth linear element  315 . The third linear conductive element  330  electrically connects between the first linear conductive element  310  and the second linear conductive element  320 . 
     The fourth linear conductive element  340  includes a tenth linear element  341  and an eleventh linear element  342 . An end of the tenth linear element  341  is connected to the eighth linear element  331 , and the other end of the tenth linear element  341  is connected to the power feeding point  200 . An end of the eleventh linear element  342  is connected to the ninth linear element  332 , and the other end of the eleventh linear element  342  is connected to the power feeding point  200 . 
     Consequently, the first linear conductive element  310  is connected to the power feeding point  200 , via the third linear conductive element  330  and the fourth linear conductive element  340 . Thus, the first linear conductive element  310  operates as a loop antenna. Moreover, the second linear conductive element  320  is connected to the power feeding point  200 , via the third linear conductive element  330  and the fourth linear conductive element  340 . Thus, the second linear conductive element  320  operates as a dipole antenna. 
     Next, the operating principle of the antenna device  1  will be described in detail with reference to  FIG. 2 . The electric current input via the power feeding point  200  flows to the first linear conductive element  310 . Because the electrical length D 1  from the power feeding point  200  to the intersection  401  of the first linear conductive element  310  is an integer multiple of the wavelength λ at the resonance frequency f, the direction of the electric current that flows through the power feeding point  200  and the direction of the electric current that flows through the intersection  401  are opposite from each other in  FIG. 2 . In other words, the phase of the electric current that flows through the first and the fifth linear elements  311  and  315 , and the phase of the electric current that flows through the second linear element  312  are opposite from each other in  FIG. 2 . 
     Thus, the transmission of radio waves caused by the electric current that flows through the first and the fifth linear elements  311  and  315 , and the transmission of radio waves caused by the electric current that flows through the second linear element  312  cancel out with each other. Consequently, in the radiation pattern of the first linear conductive element  310 , the radio waves are prevented from transmitting in the direction where the linear conductive element  300  is arranged (Z-axis positive direction in  FIGS. 1 and 2 ) from the substrate  100 , and the radio waves are properly transmitted in the direction parallel to the substrate  100  (X-axis direction in  FIGS. 1 and 2 ). 
     Moreover, the electric current input via the power feeding point  200  flows to the second linear conductive element  320 . The electrical length of the second linear conductive element  320  is a half wavelength at the resonance frequency f. Thus, in the radiation pattern of the second linear conductive element  320 , the radio waves can be properly transmitted in the direction where the linear conductive element  300  is arranged (Z-axis positive direction in  FIG. 2 ) from the substrate  100 , and in the direction perpendicular to the second linear conductive element  320  (Y-axis direction in  FIG. 2 ). 
     Consequently, the radiation pattern of the antenna device  1  is a combination of the radiation pattern of the first linear conductive element  310  and the radiation pattern of the second linear conductive element  320 . Hence, the radio waves can be properly transmitted in the direction where the linear conductive element  300  is arranged (Z-axis positive direction in  FIG. 2 ) from the substrate  100 , and in the direction parallel to the substrate  100  (X-axis direction and Y-axis direction in  FIG. 2 ). 
       FIG. 3  and  FIG. 4  are diagrams each illustrating radiation characteristics of the antenna device  1  according to the present embodiment.  FIG. 3  is a diagram illustrating the radiation characteristics of the antenna device  1  according to the present embodiment in an X-Z plane, and  FIG. 4  is a diagram illustrating the radiation characteristics of the antenna device  1  in a Y-Z plane. 
     As illustrated in  FIG. 3 , in the X-Z plane, a range where the antenna device  1  gains 2 dBi or more is a range from approximately +130 degrees to approximately −38 degrees. As illustrated in  FIG. 4 , in the Y-Z plane, a range where the antenna device  1  gains 2 dBi or more is a range of approximately ±45 degrees. In this manner, with the antenna device  1  according to the present embodiment, the radio waves can be properly transmitted in the X-axis direction and the Y-axis direction. 
     In this manner, the antenna device  1  according to the present embodiment includes the first linear conductive element  310  and the second linear conductive element  320 . The first linear conductive element  310  is formed in a loop shape that is line-symmetric with respect to the first straight line A and the second straight line B, and the electrical length D 1  of the first linear conductive element  310  is an integer multiple of a wavelength. Moreover, the second linear conductive element  320  is disposed in parallel with respect to the second straight line B, and the electrical length of the second linear conductive element  320  is a half wavelength. In this manner, it is possible to increase the amount of radio waves to be transmitted in the direction where the first linear conductive element  310  is arranged from the substrate  100 , and in the direction parallel to the substrate  100 . Consequently, for example, the antenna device  1  can communicate with a wireless device that is disposed in the direction parallel to the substrate  100 . Hence, it is possible to improve communication flexibility. 
     As described above, the antenna device  1  according to the present embodiment can increase the amount of radio waves to be transmitted in the direction parallel to the substrate  100 . Thus, for example, the antenna device  1  is suitable for what is called on-body communication that is communication performed between wireless devices worn on human bodies, or for communication performed between wireless devices disposed on the surface of a structure such as a wall. 
     Second Embodiment 
       FIG. 5  is a perspective view illustrating a configuration of an antenna device  2  according to a second embodiment.  FIG. 6  is a top view illustrating the configuration of the antenna device  2  according to the second embodiment. The antenna device  2  according to the present embodiment has the same configuration as that of the antenna device  1  illustrated in  FIG. 1 , except the configuration of a second linear conductive element  325 . 
     The second linear conductive element  325  of the antenna device  2  includes a sixth linear element  323  and a seventh linear element  324 . The sixth linear element  323  and the seventh linear element  324  are disposed on the same straight line. Moreover, the sixth linear element  323  and the seventh linear element  324  are disposed parallel to the second straight line B. 
     In the example illustrated in  FIG. 6 , the second linear conductive element  325  is disposed on the substrate  100  and inside of the loop shape of the first linear conductive element  310 . It is preferable that the second linear conductive element  325  is disposed between the second straight line B and the first and the fifth linear elements  311  and  315 . The electrical length of the second linear conductive element  325  is a half wavelength of the resonance frequency f. 
       FIGS. 7 and 8  are diagrams each illustrating the radiation characteristics of the antenna device  2  according to the present embodiment.  FIG. 7  is a diagram illustrating the radiation characteristics of the antenna device  2  according to the present embodiment in the X-Z plane, and  FIG. 8  is a diagram illustrating the radiation characteristics of the antenna device  2  in the Y-Z plane. 
       FIGS. 9 and 10  are explanatory diagrams of the radiation characteristics of the antenna device  2  according to the present embodiment.  FIGS. 9 and 10  are diagrams each illustrating the radiation characteristics of the antenna device that has a loop shape and the circumference length of which is an integer multiple of a wavelength. In other words,  FIGS. 9 and 10  are diagrams each illustrating the radiation characteristics of the antenna device  2  of the first linear conductive element  310  the electrical length of which corresponding to the electrical length D 1  is an integer multiple of a half wavelength.  FIG. 9  is a diagram illustrating the radiation characteristics of the antenna device such as above in the X-Z plane, and  FIG. 10  is a diagram illustrating the radiation characteristics of the antenna device such as above in the Y-Z plane. 
     As illustrated in  FIG. 7  and  FIG. 8 , the antenna device  2  according to the present embodiment has the radiation characteristics capable of properly transmitting the radio waves in the X-axis direction and the Y-axis direction. 
     On the other hand, in the antenna device illustrated in  FIG. 9  and  FIG. 10 , the electrical length corresponding to the electrical length D 1  of the first linear conductive element  310  is an integer multiple of a half wavelength. Thus, the phase of the electric current that flows through the first and the fifth linear elements  311  and  315 , and the phase of the electric current that flows through the second linear element  312  of the first linear conductive element  310  are the same. Consequently, the transmission of radio waves caused by the electric current that flows through the first and the fifth linear elements  311  and  315  of the first linear conductive element  310 , and the transmission of radio waves caused by the electric current that flows through the second linear element  312  strengthen each other. Hence, as illustrated in  FIG. 9  and  FIG. 10 , in the radiation characteristics of the antenna device such as the above, the radio waves are properly transmitted in the Z-axis positive direction, but the radio waves are prevented from transmitting in the X-axis direction and the Y-axis direction. 
     In the radiation characteristics of the antenna device  2  of the present embodiment illustrated in  FIG. 7  and  FIG. 8 , the transmission of radio waves in the direction parallel to the substrate  100  (X-axis direction and Y-axis direction) is improved compared with that in FIG.  9  and  FIG. 10 . When comparing  FIG. 7  with  FIG. 9 , the range where the antenna device gains 2 dBi or more in  FIG. 9  is a range of ±44.4 degrees, but the range where the antenna device  2  gains 2 dBi or more in  FIG. 7  is a range from −67.7 degrees to +72.0 degrees. Thus, the directivity in the X-Z plane is improved. 
     When comparing  FIG. 8  with  FIG. 10 , the range where the antenna device gains 2 dBi or more in  FIG. 10  is a range of ±33.2 degrees, but the range where the antenna device  2  gains 2 dBi or more in  FIG. 8  is a range of ±46.8 degrees. Thus, the directivity in the Y-Z plane is improved. 
     Next, another example of the radiation characteristics of the antenna device  2  according to the present embodiment will be described with reference to  FIG. 11  and  FIG. 12 .  FIG. 11  and  FIG. 12  are diagrams each illustrating the radiation characteristics when a rectangular parallelepiped phantom (not illustrated) is disposed at the vicinity of the substrate  100  of the antenna device  2  according to the present embodiment. The examples in  FIG. 11  and  FIG. 12  illustrate the radiation characteristics of the antenna device  2 , when the rectangular parallelepiped phantom is disposed at a location approximately  10  mm away from the ground layer  102  of the antenna device  2 .  FIG. 11  is a diagram illustrating the radiation characteristics of the antenna device  2  such as above in the X-Z plane, and  FIG. 12  is a diagram illustrating the radiation characteristics of the antenna device  2  such as above in the Y-Z plane. 
     As illustrated in  FIG. 11  and  FIG. 12 , similar to  FIG. 7  and  FIG. 8 , in the radiation characteristics of the antenna device  2 , the radio waves are properly transmitted in the direction parallel to the substrate  100  (X-axis direction and Y-axis direction). Moreover, the radio waves are prevented from transmitting in the direction where the substrate  100  is arranged from the linear conductive element  300  (Z-axis negative direction). Consequently, for example, even when a human body is located at the side of the substrate  100 , the antenna device  2  is hardly affected by the human body. 
     In this manner, the antenna device  2  according to the second embodiment can obtain the same effects as those of the antenna device  1  according to the first embodiment. Furthermore, by disposing the second linear conductive element  325  inside the loop shape of the first linear conductive element  310 , it is possible to further improve the radiation characteristics of the antenna device  2 . 
     For example, when comparing the radiation characteristics of the antenna device  2  in the X-Z plane illustrated in  FIG. 7  with the radiation characteristics of the antenna device  1  in the X-Z plane illustrated in  FIG. 3 , the gains in the Z-axis positive direction as well as in the X-axis negative direction are improved. 
     This is because it is assumed that the influence applied to the linear elements  311  to  315  of the first linear conductive element  310  by the second linear conductive element  325  is reduced, by disposing the second linear conductive element  325  inside the loop shape of the first linear conductive element  310 . 
     First Modification 
       FIG. 13  is a diagram illustrating an antenna device  3  according to a first modification of the present embodiment. The antenna device  3  has the same configuration as that of the antenna device  2  according to the second embodiment, except that at least a part of a first linear conductive element  350  has a meander shape. 
     The first linear conductive element  350  of the antenna device  3  includes a first linear element  351  to a fifth linear element  355 . The first linear element  351  and the fifth linear element  355  each have a meander shape. The second linear element  352  has a meander shape, and is disposed so as to be line-symmetric with respect to the first and the fifth linear elements  351  and  355 , and the second straight line B. 
     The fourth linear element  354  is a straight line an end of which is connected to an end of the first linear element  351 , and the other end of which is connected to an end of the second linear element  352 . The third linear element  353  is a straight line an end of which is connected to an end of the fifth linear element  351 , and the other end of which is connected to the other end of the second linear element  352 . The third linear element  353  and the fourth linear element  354  are disposed so as to be line symmetric with respect to the first straight line A. 
     In the antenna device  3  according to the present modification, the first linear element  351 , the second linear element  352 , and the fifth linear element  355  are each formed in a meander shape. Hence, it is possible to reduce the physical length of the first linear conductive element  350 , while keeping the electrical length D 1  of the first linear conductive element  350  to an integer multiple of a wavelength. Thus, it is possible to reduce the size of the first linear conductive element  350 . Consequently, it is possible to reduce the size of the antenna device  3  according to the present modification. 
     In the present modification, the first linear element  351 , the second linear element  352 , and the fifth linear element  355  are each formed in a meander shape. However, the third linear element  353  and the fourth linear element  354  may also be formed in a meander shape, and the second linear conductive element  325  may also be formed in a meander shape. Moreover, at least a part of the linear conductive elements of the antenna device according to the other embodiments, which will be described later, may be formed in a meander shape. 
     Second Modification 
       FIG. 14  is a diagram illustrating an antenna device  8  according to a second modification of the present embodiment. The antenna device  8  has the same configuration as that of the antenna device  2  according to the second embodiment, except that the antenna device  8  further includes an impedance adjustment unit  370 . 
     The impedance adjustment unit  370  of the antenna device  8  is connected to the third linear conductive element  330  that connects between the first linear conductive element  310  and the second linear conductive element  325 . The impedance adjustment unit  370  is connected to the third linear conductive element  330 , and adjusts an impedance value of the first linear conductive element  310  and the second linear conductive element  320 . 
     The impedance adjustment unit  370  includes an inductor  371  and a capacitive element  372 . An end of the inductor  371  is connected to the eighth linear element  331 , and the other end of the inductor  371  is connected to the ninth linear element  332 . Moreover, an end of the capacitive element  372  is connected to the eighth linear element  331 , and the other end of the capacitive element  372  is connected to the ninth linear element  332 . In other words, the inductor  371  and the capacitive element  372  are each connected to the power feeding point  200  in parallel. 
     Thus, for example, even if a manufacturing error occurs during the manufacturing process of the linear conductive element  300 , it is possible to easily adjust the impedance mismatch of the linear conductive element  300 . 
     Third Embodiment 
       FIG. 15  is a top view illustrating a configuration of an antenna device  4  according to a third embodiment. The antenna device  4  according to the present embodiment further includes an adjustment unit  360  that adjusts a capacitor value between the first linear conductive element  310  and the second linear conductive element  325 , in addition to the antenna device  2  illustrated in  FIG. 5 . 
     The adjustment unit  360  includes a first L-shaped conductive element  361  and a second L-shaped conductive element  362 . One end of the first L-shaped conductive element  361  is connected to the other end of the sixth linear element  323 . The first L-shaped conductive element  361  is disposed between the first linear element  311  and the sixth linear element  323 . 
     Moreover, an end of the second L-shaped conductive element  362  is connected to the other end of the seventh linear element  324 . The second L-shaped conductive element  362  is disposed between the fifth linear element  315  and the seventh linear element  324 . 
       FIG. 16  is a diagram illustrating voltage standing wave ratio (VSWR) characteristics of the antenna device  4  according to the present embodiment. Moreover,  FIG. 17  is a diagram illustrating the VSWR characteristics of the antenna device  2  illustrated in  FIG. 5 . 
     As illustrated in  FIG. 16 , the antenna device  4  according to the present embodiment has a wide frequency bandwidth where the VSWR is equal to or less than “3”. Consequently, the antenna device  4  according to the present embodiment has excellent VSWR characteristics. When comparing  FIG. 16  with  FIG. 17 , for example, the frequency bandwidth where the VSWR is equal to or less than “2” is approximately 4 MHz in the antenna device  2 , while the frequency bandwidth where the VSWR is equal to or less than “2” is approximately 10 MHz in the antenna device  4 . 
     In this manner, the antenna device  4  according to the present embodiment can further improve the VSWR characteristics of the antenna device  2  illustrated in  FIG. 5 , by including the adjustment unit  360 . When the VSWR characteristics are improved, it is possible to easily match the impedance of the antenna device  4 , and increase the bandwidth of the antenna device  4 . 
     In this manner, the antenna device  4  according to the third embodiment can obtain the same effects as those of the antenna device  2  according to the second embodiment, and by further including the adjustment unit  360 , it is possible to easily match the impedance. Furthermore, it is possible to increase the bandwidth of the antenna device  4 . 
     Third Modification 
       FIG. 18  is a diagram illustrating an antenna device  5  according to a third modification of the present embodiment. The antenna device  5  has the same configuration as that of the antenna device  4  according to the third embodiment, except that the adjustment unit  360  is a first plate-like element  363  and a second plate-like element  364 . 
     The adjustment unit  360  of the antenna device  5  includes the first plate-like element  363  and the second plate-like element  364 . The first plate-like element  363  and the second plate-like element  364  are rectangular conductive elements the length of which in the X-axis direction is W 1 , and the length of which in the Y-axis direction is W 2 . 
     One side of the first plate-like element  363  is connected to the other end of the sixth linear element  323 . The first plate-like element  363  is disposed between the first linear element  311  and the sixth linear element  323 . 
     One side of the second plate-like element  364  is connected to the other end of the seventh linear element  324 . The second plate-like element  364  is disposed between the fifth linear element  315  and the seventh linear element  324 . 
     In this manner, the adjustment unit  360  may be configured by the first plate-like element  363  and the second plate-like element  364 . The plate-like elements are easy to manufacture, and the capacitor value between the first linear conductive element  310  and the second linear conductive element  325  can be easily adjusted, by adjusting the length of the sides of the plate-like elements. 
     Fourth Modification 
     The shape of the first plate-like element  363  and the second plate-like element  364  is not limited to the rectangular shape. For example, as illustrated in  FIG. 19 , the shape of a first plate-like element  365  and a second plate-like element  366  may be a triangle.  FIG. 19  is a diagram illustrating an antenna device  6  according to a fourth modification of the third embodiment. 
     As illustrated in  FIG. 19 , the first plate-like element  365  and the second plate-like element  366  may have a tapered shape in which the length in the Y-axis direction is increased as the first plate-like element  365  and the second plate-like element  366  are away from the power feeding point  200 . 
     Fifth Modification 
     Moreover, the adjustment unit  360  is not limited to the L-shaped conductive elements  361  and  362 , and the plate-like elements  363  to  366 . For example, as illustrated in  FIG. 20 , the adjustment unit  360  may be a capacitive element.  FIG. 20  is a diagram illustrating an antenna device  7  according to a fifth modification of the third embodiment. 
     The adjustment unit  360  of the antenna device  7  includes a first capacitive element  367  and a second capacitive element  368 . One end of the first capacitive element  367  is connected to the other end of the sixth linear element  323 , and the other end of the first capacitive element  367  is connected to the first linear element  311 . One end of the second capacitive element  368  is connected to the other end of the seventh linear element  324 , and the other end of the second capacitive element  368  is connected to the fifth linear element  315 . 
     In this manner, the adjustment unit  360  may be configured by the first capacitive element  367  and the second capacitive element  368 . Moreover, for example, by making the first capacitive element  367  and the second capacitive element  368  to be variable capacitive elements, the capacitor values of the first capacitive element  367  and the second capacitive element  368  can be adjusted according to the changes in the communication environment of the antenna device  7  and the like. 
     Fourth Embodiment 
       FIG. 21  is a diagram illustrating a wireless device  10  according to a fourth embodiment. The wireless device  10  according to the present embodiment is mounted with the antenna device  2  illustrated in  FIG. 5 . However, the wireless device  10  according to the present embodiment may also be mounted with the antenna device  1  and the antenna devices  3  to  8  that are illustrated in the other embodiments and the other modifications. 
     The wireless device  10  includes the antenna device  2  and a wireless unit  600  that receives or transmits a signal via the antenna device  2 . The wireless unit  600  includes a substrate  610 , a wireless circuit  620 , a signal line  630 , a terminal  640 , and a power feeding line  650 . 
     The substrate  610  includes a dielectric layer  611  and a ground layer  612 . The wireless circuit  620  is provided on the dielectric layer  611  of the substrate  610 . The wireless circuit  620  generates a signal, and transmits the signal via the antenna device  2 . Alternatively, the wireless circuit  620  receives a signal via the antenna device  2 . The signal line  630  connects between the wireless circuit  620  and the terminal  640 . One end of the power feeding line  650  is connected to the terminal  640 , and the other end of the power feeding line  650  is connected to the power feeding point  200 . 
     Next, an example of on-body communication by putting the wireless device  10  on a finger will be described with reference to  FIG. 22 . For example, the wireless device  10  may be installed in a ring (not illustrated), and the wireless device  10  is put on a finger, by wearing the ring. Alternatively, the wireless device  10  may be put on a finger using a belt. 
     For example, it is assumed that the wireless device  10  worn on a finger and the wireless device  10  worn on the chest (not illustrated) communicate with each other. When on-body communication is performed between the wireless devices  10  that are worn on human bodies in this manner, there are more instances in which wireless devices  10  communicate with each other on substantially the same plane compared with those of general wireless communication. 
     The wireless device  10  according to the present embodiment includes the antenna device  2  that can properly transmit the radio waves toward the same plane as the substrate  100 . Thus, the on-body communication can be properly executed even when the wireless device  10  is worn on the human body. 
     In this manner, the wireless device  10  according to the present embodiment can obtain the same effects as those of the second embodiment, by communicating via the antenna device  2 . Moreover, it is possible to improve communication flexibility of the wireless device  10 . Furthermore, the wireless device  10  can properly communicate with the other wireless device that is arranged on the same plane, such as when the wireless device  10  is worn on the human body for the on-body communication. 
     In the present embodiment, the antenna device  2  transmits and receives a signal. However, the antenna device  2  may only transmit a signal, or only receive a signal. 
     Moreover, in the present embodiment, the antenna device  2  and the wireless unit  600  are disposed on the same plane. However, the arrangement of the antenna device  2  and the wireless unit  600  is not limited thereto. The antenna device  2  and the wireless unit  600  may be disposed on different planes. 
     Sixth Modification 
       FIG. 23  is a diagram illustrating a wireless device  20  according to a sixth modification of the present embodiment. The wireless device  20  illustrated in  FIG. 23  is different from the wireless device  10  in  FIG. 21  in providing the wireless circuit  620  on the substrate  100  of the antenna device  2 . Consequently, the wireless device  20  does not include the signal line  630  and the terminal  640 , and one end of the power feeding line  650  of the wireless device  20  is connected to the wireless circuit  620 , and the other end of the power feeding line  650  is connected to the power feeding point  200 . 
     In this manner, it is possible to reduce the parts of the wireless device  20 , by providing the wireless circuit  620  of the wireless device  20  on the substrate  100  of the antenna device  2 . 
     Seventh Modification 
       FIG. 24  is a diagram illustrating a wireless device  30  according to a seventh modification of the present embodiment. The wireless device  30  illustrated in  FIG. 24  includes a wireless unit  700  instead of the power feeding point  200 . The other components are the same as those in the antenna device  2  illustrated in  FIG. 5  and are denoted by the same reference numerals, and a detailed description thereof will be omitted. 
     The wireless unit  700  is, for example, an integrated circuit (IC) of a radio frequency identifier (RFID) tag or a sensor IC with a wireless function. The wireless unit  700  transmits a signal via the linear conductive element  300 , by inputting the signal directly to the linear conductive element  300 . Alternatively, the wireless unit  700  receives a signal via the linear conductive element  300 , by receiving the signal directly from the linear conductive element  300 . In this manner, it can be assumed that the wireless unit  700  also operates as the power feeding point  200 , by transmitting and receiving a signal directly with the linear conductive element  300 . 
     In this manner, the antenna devices  1  to  8  of the embodiments may be provided in the wireless device  30  that is directly connected to an antenna element such as the IC of the RFID tag. Consequently, the wireless device  30  can communicate in a large angle range, and can improve communication flexibility. 
     While some embodiments of the present invention have been described, these embodiments are merely examples, and are not intended to limit the scope of the invention. These novel embodiments may be implemented in various other forms, and various omissions, replacements, and modifications may be made without departing from the scope and spirit of the invention. These embodiments and modifications are included in the scope and spirit of the invention, and are included in the invention described in the claims and their equivalents.