Patent Publication Number: US-2023145638-A1

Title: Antenna device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 U.S.C. §119 to Japanese Patent Application 2021-183246, filed on Nov. 10, 2021, the entire content of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     This disclosure relates to an antenna device. 
     BACKGROUND DISCUSSION 
     In related art, an antenna device is used for transmission and reception of radio waves. Techniques related to such an antenna device include, for example, those disclosed in JP 2009-225068A (Reference 1), JP 2016-116016A (Reference 2) and WO 2017/138800 (Reference 3). 
     Reference 1 discloses a circularly polarized composite monopole antenna. The circularly polarized composite monopole antenna includes a ground plate formed of a plate-shaped conductor, and the ground plate is provided with a power feeding element and a parasitic element formed by bending in an inverted L shape. The power feeding element and the parasitic element are erected from the ground plate by allowing a rising side of the power feeding element and a rising side of the parasitic element to pass through a through hole formed in a dielectric on the ground plate. 
     Reference 2 discloses a wide-band circularly polarized wave antenna. The wide-band circularly polarized wave antenna is implemented such that a first antenna element and a second antenna element both having a trapezoidal shape are arranged point-symmetrically with respect to a power feeding portion. 
     Reference 3 discloses a monopole antenna. The monopole antenna includes a circular disk-shaped coplanar waveguide transmission line. 
     In the technique disclosed in Reference 1, since the power feeding element and the parasitic element are formed in a state of being erected from the ground plate via the dielectric, a three-dimensional shape is formed. Therefore, the antenna device may not be used when there is a height limit in a region where the antenna device is disposed. Since the technique disclosed in Reference 2 is a so-called parallel antenna device, a pair of antenna elements are required. Therefore, an area occupied by the antenna device increases. As described above, the techniques disclosed in References 1 and 2 have room for improvement in reducing a size of the antenna device. 
     Polarized radio waves include, for example, horizontally polarized waves, vertically polarized waves, and circularly polarized waves. The technique disclosed in Reference 3 is a technique related to the monopole antenna, and thus can be used only for transmission and reception of one of the vertically polarized radio waves and the horizontally polarized radio waves. Therefore, the technique disclosed in Reference 3 cannot be used for transmission and reception of the circularly polarized radio waves. 
     A need thus exists for an antenna device which is not susceptible to the drawback mentioned above. 
     SUMMARY 
     A characteristic configuration of an antenna device according to this disclosure is an antenna device including: a ground portion including a linear portion connecting a first point and a second point to each other along a predetermined first direction parallel to a surface of a substrate, the ground portion being formed by grounding a conductor portion of the substrate on one side in a second direction orthogonal to the first direction and parallel to the surface of the substrate; a power feeding portion provided in a first range including the first point among the first range, a second range, and a third range that are obtained by dividing the linear portion of the ground portion into three equal parts along the first direction; and an element portion configured to receive power from the power feeding portion and formed in a conductor portion of the substrate that is insulated from the ground portion in a state in which the element portion protrudes from the first range toward the other side in the second direction with respect to the linear portion. The element portion includes a first element portion protruding from the linear portion in the first range toward the other side in the second direction, and a second element portion extending along the first direction from the first element portion toward the second point, spaced apart from the linear portion toward the other side in the second direction, and having at least one linear side. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and additional features and characteristics of this disclosure will become more apparent from the following detailed description considered with the reference to the accompanying drawings, wherein: 
         FIG.  1    is a plan view of a substrate on which an antenna device is provided; 
         FIG.  2    is an enlarged view of the antenna device; 
         FIGS.  3 A to  3 D  are diagrams showing charge distribution in the antenna device; 
         FIGS.  4 A to  4 C  are diagrams showing radio waves radiated by the antenna device; 
         FIG.  5    shows VSWR data of the antenna device; 
         FIGS.  6 A to  6 H  are plan views of antenna devices according to other embodiments; 
         FIG.  7    is a plan view of an antenna device according to another embodiment; and 
         FIGS.  8 A to  8 D  are diagrams showing radio waves radiated by the antenna device according to the other embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     An antenna device according to this disclosure is configured to transmit and receive circularly polarized radio waves. Hereinafter, an antenna device  1  according to the present embodiment will be described. 
     The antenna device  1  is provided on a substrate  2 .  FIG.  1    shows a plan view of the substrate  2 .  FIG.  2    shows an enlarged view of the vicinity of a power feeding portion  20 . Here, in the following description, a predetermined direction parallel to a surface of the substrate  2  is referred to as a first direction A, and a direction orthogonal to the first direction A and parallel to the surface of the substrate  2  is referred to as a second direction B. In the present embodiment, the substrate  2  is formed in a rectangular shape with chamfered corners. In the present embodiment, the first direction A is a direction along a direction (hereinafter referred to as a lateral direction) in which short sides of the rectangular substrate  2  extend, and the second direction B is a direction along a direction (hereinafter referred to as a longitudinal direction) in which long sides of the rectangular substrate  2  extend. When a wavelength corresponding to the highest frequency in a frequency band used in the antenna device  1  is λ, a length of the substrate  2  along the first direction A is 0.48 λ, and a length of the substrate  2  along the second direction B is 2.3 λ in the present embodiment. 
     As shown in  FIG.  1   , the antenna device  1  includes a ground portion  10 , a power feeding portion  20 , and an element portion  30 . 
     As shown in  FIG.  2   , the ground portion  10  includes a linear portion  13  connecting a first point  11  and a second point  12  to each other along the first direction A, and is formed by grounding a conductor portion of the substrate  2  on one side in the second direction B. The linear portion  13  connecting the first point  11  and the second point  12  along the first direction A means that the linear portion  13  is parallel to the first direction A and the first point  11  and the second point  12  are present on the linear portion  13 . In the present embodiment, the first point  11  is set at a position spaced apart from an outer edge portion  2 A of the substrate  2  on one side in the first direction A toward a center side of the substrate  2  along the first direction A, and the second point  12  is set at a position spaced apart from an outer edge portion  2 B of the substrate  2  on the other side in the first direction A toward the center side of the substrate  2  along the first direction A. Therefore, the first point  11  and the second point  12  are set at positions that approaches the center side of the substrate  2  along the first direction A from the outer edge portion  2 A and the outer edge portion  2 B, respectively. The linear portion  13  corresponds to a line virtually connecting the first point  11  and the second point  12  as described above. The first point  11  and the second point  12  are not provided as actually drawn points on the substrate  2 , but are defined to facilitate understanding of the linear portion  13 . 
     The one side in the second direction B is one end portion side of both end portions of the substrate  2  in the longitudinal direction. That is, in an example in  FIG.  1   , the one side in the second direction B is the outer edge portion side of one of an outer edge portion  2 C and an outer edge portion  2 D of the substrate  2 . In the present embodiment, the one side in the second direction B is an outer edge portion  2 D side in the outer edge portion  2 C and the outer edge portion  2 D of the substrate  2 . 
     Here, the substrate  2  is formed by laminating a conductor and a dielectric. The conductor portion of the substrate  2  corresponds to the conductor that is laminated with such a dielectric to form the substrate  2 . The ground portion  10  is formed by patterning such a conductor portion of the substrate  2  so as to include the linear portion  13 , and is grounded. The linear portion  13  virtually connects the first point  11  set at the position spaced apart from the outer edge portion  2 A of the substrate  2  on the one side in the first direction A toward the center side of the substrate  2  along the first direction A, and the second point  12  set at the position spaced apart from the outer edge portion  2 B of the substrate  2  on the other side in the first direction A toward the center side of the substrate  2  along the first direction A. 
     In the present embodiment, the ground portion  10  includes a protruding portion  17  protruding from a second point  12  side of the linear portion  13  toward the other side in the second direction B with a predetermined width. The second point  12  side of the linear portion  13  means a side that is closer to the second point  12  than is a central portion of the linear portion  13  between the first point  11  and the second point  12 . 
     Here, as described above, the linear portion  13  is provided between the first point  11  and the second point  12 . The linear portion  13  is divided into three equal parts along the first direction A, and the three equal parts are referred to as a first range D1, a second range D2, and a third range D3. In this case, two points are required between the first point  11  and the second point  12 . Of the two points, when a point closer to the first point  11  is referred to as a first auxiliary point  14  and a point closer to the second point  12  is referred to as a second auxiliary point  15 , a portion of the linear portion  13  between the first point  11  and the first auxiliary point  14  corresponds to the first range D1. A portion of the linear portion  13  between the first auxiliary point  14  and the second auxiliary point  15  corresponds to the second range D2, and a portion of the linear portion  13  between the second auxiliary point  15  and the second point  12  corresponds to the third range D3. 
     In the present embodiment, the protruding portion  17  having the predetermined width and protruding toward the other side in the second direction B is provided in the third range D3 that is a range between the second auxiliary point  15  and the second point  12 . The predetermined width is a width set according to a frequency of the radio waves transmitted and received by the antenna device  1 . The other side in the second direction B is an outer edge portion  2 C side as viewed from the linear portion  13  along the first direction A. Therefore, the ground portion  10  includes the protruding portion  17  protruding from the third range D3, which is the range between the second auxiliary point  15  and the second point  12 , toward the outer edge portion  2 C side, with the width set according to the frequency of the radio waves transmitted and received by the antenna device  1 , as viewed from the linear portion  13  along the first direction A. In the present embodiment, the protruding portion  17  is formed in a rectangular shape in which a side along the first direction A is a short side and a side along the second direction B is a long side. In the shape of the protruding portion  17 , a corner portion on an outer edge portion  2 B side and an outer edge portion  2 D side coincides with the second point  12 . Similar to the ground portion  10 , such a protruding portion  17  is formed by patterning a conductor portion of the substrate  2 , and is formed of a conductor having the same potential in terms of direct current as a portion of the ground portion  10  formed on the one side with respect to the linear portion  13  in the second direction B. 
     As shown in  FIG.  1   , in the present embodiment, the ground portion  10  is formed such that the length along the second direction B is greater than the length along the first direction A. The length along the second direction B is a length of the ground portion  10  along the second direction B, and in the present embodiment, is a length L1 from the linear portion  13  to an end portion of the ground portion  10  on the outer edge portion  2 D side. The length along the first direction A is a length of the ground portion  10  along the first direction A, and in the present embodiment, is a length L2 from an end portion of the ground portion  10  on an outer edge portion  2 A side to an end portion of the ground portion  10  on the outer edge portion  2 B side. In  FIG.  1   , the ground portion  10  is formed such that a length of the linear portion  13  along the first direction A is smaller than the length L2, but the length of the linear portion  13  along the first direction A may be formed to be the length L2. 
     In the present embodiment, a distance between the first point  11  and the second point  12  is 0.33 λ, a length of the protruding portion  17  along the first direction A is 0.03 λ, and a length of the protruding portion  17  along the second direction B is 0.11 λ. 
     The power feeding portion  20  is provided in the first range D1 including the first point  11  among the first range D1, the second range D2, and the third range D3 that are obtained by dividing the linear portion  13  of the ground portion  10  into three equal parts along the first direction A. The first range D1 is between the first point  11  and the first auxiliary point  14  in the linear portion  13 . The power feeding portion  20  is provided in the first range D1. The power feeding portion  20  feeds power to the ground portion  10  described above and the element portion  30  to be described later such that the antenna device  1  transmits and receives radio waves propagating in the air. Specifically, the power feeding portion  20  applies a reference potential (0 V) from a power feeding point  21 N to (grounds) the ground portion  10 , and applies AC power of a predetermined frequency from a power feeding point  21 L to the element portion  30 . Therefore, the power feeding portion  20  is provided in the first range D1 of the linear portion  13  between the first point  11  and the first auxiliary point  14 , applies the reference potential (0 V) to (grounds) the ground portion  10 , and applies AC power of the predetermined frequency to the element portion  30 . In the present embodiment, the power feeding point  21 N and the power feeding point  21 L are provided at positions that are 0.06 λ away from the first point  11 . 
     The element portion  30  receives power from the power feeding portion  20  and is formed in a conductor portion of the substrate  2  that is insulated from the ground portion  10  in a state in which the element portion  30  protrudes from the first range D1 toward the other side with respect to the linear portion  13  in the second direction B. “Receiving power from the power feeding portion 20” means receiving power fed from the power feeding portion  20  as described above. The first range D1 is a range from the first point  11  to the first auxiliary point  14  in the linear portion  13 . The state in which the element portion  30  protrudes toward the other side with respect to the linear portion  13  in the second direction B means a state in which the element portion  30  protrudes from the linear portion  13  toward a side opposite to the ground portion  10  provided on the outer edge portion  2 D side of the substrate  2  with respect to the linear portion  13 , that is, toward the outer edge portion  2 C side of the substrate  2  with respect to the linear portion  13 , on the one side with respect to the linear portion  13  in the second direction B. The conductor portion of the substrate  2  that is insulated from the ground portion  10  refers to a conductor portion formed by patterning in a manner of being spaced apart, with a predetermined insulation distance, from the ground portion  10  formed by patterning the conductor portion of the substrate  2 . Therefore, the element portion  30  receives power from the power feeding portion  20  at the power feeding point  21 L and is formed in the conductor portion formed by patterning in a manner of being spaced apart, with the predetermined insulation distance, from the ground portion  10  formed by patterning the conductor portion of the substrate  2 , in a state in which the element portion  30  protrudes from the linear portion  13  in a range of the linear portion  13  from the first point  11  to the first auxiliary point  14 , toward the outer edge portion  2 C side of the substrate  2  with respect to the linear portion  13 . 
     In the present embodiment, the power feeding point  21 L at which power is fed from the power feeding portion  20  to the element portion  30  is provided on the linear portion  13 , and the element portion  30  includes a portion protruding toward the one side in the second direction B from the power feeding point  21 L. Therefore, the ground portion  10  is formed by cutting in a manner of surrounding the portion of the element portion  30  including the power feeding point  21 L. That is, the ground portion  10  includes a cutout portion  16  in the first range D1. In the element portion  30 , the power feeding point  21 L at which power is fed from the power feeding portion  20  may be provided on the other side with respect to the linear portion  13  in the second direction B, or may be provided on the one side with respect to the linear portion  13  in the second direction B. 
     The element portion  30  includes a first element portion  31  and a second element portion  32 . The first element portion  31  protrudes from the first range D1 toward the other side in the second direction B. The first range D1 is the range between the first point  11  and the first auxiliary point  14  in the linear portion  13 , and the first range D1 is provided with the power feeding point  21 L of the element portion  30 , at which power is fed from the power feeding portion  20 . The other side in the second direction B is the outer edge portion  2 C side of the substrate  2  as viewed from the linear portion  13 . Therefore, the first element portion  31  includes the power feeding point  21 L at which power is fed from the power feeding portion  20 , and protrudes from the first range D1, which is the range between the first point  11  and the first auxiliary point  14  in the linear portion  13 , toward the outer edge portion  2 C side of the substrate  2  as viewed from the linear portion  13 . In the present embodiment, as shown in  FIG.  2   , the first element portion  31  has a width corresponding to the cutout portion  16 , and is formed in a rectangular shape in which a side along the first direction A is a short side and a side along the second direction B is a long side. 
     The second element portion  32  extends along the first direction A from the first element portion  31  toward the second point  12 . As described above, the first element portion  31  protrudes from the first range D1 toward the outer edge portion  2 C side of the substrate  2  as viewed from the linear portion  13 . “Along the first direction A” means “so as to have a portion parallel to the linear portion  13 ”. “Toward the second point  12 ” means “toward the outer edge portion  2 B side of the substrate  2  as viewed from the first element portion  31 ”. Therefore, the second element portion  32  extends from the first element portion  31 , which protrudes from the first range D1 toward the outer edge portion  2 C side of the substrate  2  when viewed from the linear portion  13 , toward the outer edge portion  2 B side of the substrate  2  when viewed from the first element portion  31  so as to have the portion parallel to the linear portion  13 . Therefore, the second element portion  32  extends, along the second direction B, from a portion  41  of the rectangular first element portion  31  on the outer edge portion  2 B side. 
     In the present embodiment, the ground portion  10  includes the protruding portion  17 . As shown in  FIG.  2   , an outer edge  51  of the protruding portion  17  on the outer edge portion  2 C side is closer to the outer edge portion  2 C of the substrate  2  in the second direction B than is an outer edge  52  of the second element portion  32  on the outer edge portion  2 C side. In the present embodiment, the second element portion  32  extends from the first element portion  31  toward the protruding portion  17 . 
     The first element portion  31  and the second element portion  32  described above are formed by patterning one conductor portion. Therefore, the first element portion  31  and the second element portion  32  are formed of conductors having the same potential in terms of direct current. 
     In the present embodiment, the second element portion  32  is gradually spaced apart from the linear portion  13  as the second element portion  32  approaches the second point  12  from the first element portion  31 . “As the second element portion  32  approaches the second point  12  from the first element portion  31 ” means “as the second element portion  32  approaches the protruding portion  17  from the first element portion  31 ” in the present embodiment. “Gradually spaced apart from the linear portion  13 ” means that an outer edge portion  33  of the second element portion  32  on a linear portion  13  side is formed such that a distance between the outer edge portion  33  and the linear portion  13  gradually increases from a boundary portion  34  with the first element portion  31  along the first direction A to a closest portion  35  of the second element portion  32  closest to the protruding portion  17 . Therefore, the outer edge portion  33  of the second element portion  32  on the linear portion  13  side is formed such that the distance between the outer edge portion  33  and the linear portion  13  gradually increases as the second element portion  32  approaches the protruding portion  17  from the first element portion  31 . 
     In the present embodiment, the second element portion  32  is formed in a right-angled triangular shape, and a right-angled corner portion of the second element portion  32  coincides with a corner portion of the rectangular first element portion  31  on the outer edge portion  2 B side and the outer edge portion  2 C side. One of two sides of the right-angled triangle sandwiching the corner portion coincides with a side (portion  41 ) of the first element portion  31  on the outer edge portion  2 B side, and the other of the two sides of the right-angled triangle sandwiching the corner portion is parallel to the linear portion  13 . Therefore, an oblique side (corresponding to the outer edge portion 33) of the right-angled triangle faces the linear portion  13  side. Accordingly, as described above, the second element portion  32  can be formed such that the distance between the outer edge portion  33  and the linear portion  13  gradually increases as the second element portion  32  approaches the protruding portion  17  from the first element portion  31 . 
     In other words, the second element portion  32  includes a reduced width portion  18  in which a width along an orthogonal direction orthogonal to an extending direction of the second element portion  32  extending from the first element portion  31  gradually decreases as the second element portion  32  approaches the second point  12  from the first element portion  31 . The extending direction extending from the first element portion  31  is the first direction A. Therefore, the orthogonal direction orthogonal to the extending direction extending from the first element portion  31  corresponds to the second direction B orthogonal to the first direction A. Therefore, the second element portion  32  is formed such that the width along the second direction B gradually decreases as the second element portion  32  approaches the second point  12  from the first element portion  31 . Such a portion may also be referred to as the reduced width portion  18 . 
     In the present embodiment, a length of the element portion  30  along the first direction A is 0.17 λ, and a length of the element portion  30  along the second direction B is  0  · 1 λ. A distance X between an end portion of the reduced width portion  18  closest to the protruding portion  17  (closest portion  35 ) and the linear portion  13  may be equal to or greater than 0.04 λ (preferably equal to or greater than 0.06 λ). 
       FIGS.  3 A to  3 D  show charge distribution generated between the ground portion  10  and the element portion  30  when power is fed to the ground portion  10  and the element portion  30  in the antenna device  1  formed as described above. 
     As described above, the power feeding portion  20  grounds the ground portion  10  and feeds AC power to the element portion  30 .  FIG.  3 A  shows the charge distribution when a phase of the AC power is 60 degrees. In this case, a portion of the ground portion  10  on a side opposite to a side where the element portion  30  protrudes from the linear portion  13  (referred to as a ground main body  10 A) is positively charged, while the protruding portion  17  and the element portion  30  are negatively charged. In  FIGS.  3 A to  3 D , a positively charged state is indicated by E+, and a negatively charged state is indicated by E-. Therefore, an electric field in a direction from the ground main body  10 A toward the element portion  30  is generated between the ground main body  10 A and the element portion  30  as indicated by an arrow C. 
       FIG.  3 B  shows the charge distribution when the phase of the AC power is 150 degrees. In this case, the protruding portion  17  is positively charged, and the ground main body  10 A and the element portion  30  are negatively charged. Therefore, an electric field in a direction from the protruding portion  17  toward the element portion  30  is generated between the protruding portion  17  and the element portion  30  as indicated by the arrow C. 
       FIG.  3 C  shows the charge distribution when the phase of the AC power is 240 degrees. In this case, the protruding portion  17  and the element portion  30  are positively charged, and the ground main body  10 A is negatively charged. Therefore, an electric field in a direction from the element portion  30  toward the ground main body  10 A is generated between the ground main body  10 A and the element portion  30  as indicated by the arrow C. 
       FIG.  3 D  shows the charge distribution when the phase of the AC power is 330 degrees. In this case, the ground main body  10 A and the element portion  30  are positively charged, and the protruding portion  17  is negatively charged. Therefore, an electric field in a direction from the element portion  30  toward the protruding portion  17  is generated between the protruding portion  17  and the element portion  30  as indicated by the arrow C. 
     By continuously feeding such AC power, an electric field rotating about an axis along a direction orthogonal to both the first direction A and the second direction B as a rotation axis can be generated from the substrate  2 . Therefore, by erecting the substrate  2 , it is possible to transmit and receive circularly polarized radio waves as shown in  FIG.  4 A . When the antenna device  1  is used as a reception antenna device, it is possible to receive vertically polarized radio waves as shown in  FIG.  4 B , and to receive horizontally polarized radio waves as shown in  FIG.  4 C . When the antenna device  1  is used as a transmission antenna device, an antenna device capable of receiving only the vertically polarized radio waves as shown in  FIG.  4 B  can receive radio waves transmitted from the antenna device  1 , and an antenna device capable of receiving only the horizontally polarized radio waves as shown in  FIG.  4 C  can receive radio waves transmitted from the antenna device  1 . 
       FIG.  5    shows VSWR characteristics of the antenna device  1 . In  FIG.  5   , a vertical axis represents a VSWR value, and a horizontal axis represents a frequency. In general, an antenna device is desired to have a VSWR value of  3  or smaller. With a configuration described above, it is possible to implement the antenna device  1  having a VSWR value of  3  or smaller in a wide frequency range as shown in  FIG.  5   . 
     Other Embodiments 
     In the above embodiment, the element portion  30  includes the first element portion  31  having the rectangular shape in a plan view and the second element portion  32  having the right-angled triangular shape in the plan view. For example, as shown in  FIG.  6 A , the first element portion  31  may include a rectangular first portion  37  and a triangular second portion  38  in a plan view. In this case, an edge portion  37 A of the first portion on the outer edge portion  2 A side and an edge portion  38 A of the second portion on the outer edge portion  2 B side may coincide with each other. 
     As shown in  FIG.  6 B , the second element portion  32  may have a shape in which a central angle of an elliptical shape is 90 degrees in a plan view. In this case, an arc-shaped portion may face the linear portion  13 . The convex arc-shaped portion in  FIG.  6 B  may be formed in a concave shape as shown in  FIG.  6 C . 
     The second element portion  32  may have a quadrangular shape in a plan view. In this case, as shown in  FIG.  6 D , the second element portion  32  may extend toward the protruding portion  17  along the first direction A from the first element portion  31  on the outer edge portion  2 C side of the substrate  2 . As shown in  FIG.  6 E , a length of the first element portion  31  along the second direction B may be approximately on the linear portion  13 , and the second element portion  32  may have a quadrangular shape in a plan view from the first element portion  31  toward the protruding portion  17 . 
     As shown in  FIG.  6 F , the second element portion  32  may include a constant width portion  19  that is electrically connected to the reduced width portion  18  on a second point  12  side of the reduced width portion  18  and has a constant width. The reduced width portion  18  is a portion in which a width along the second direction B gradually decreases as the reduced width portion  18  approaches the second point  12  from the first element portion  31 . The constant width portion  19  having the constant width along the second direction B may be provided on a side of the reduced width portion  18  opposite to the first element portion  31  in the first direction A, that is, on a side close to the protruding portion  17  in the first direction A. 
     In the above embodiments, the protruding portion  17  is described as being provided such that a corner portion on the outer edge portion  2 B side and the outer edge portion  2 D side coincides with the second point  12 , but the protruding portion  17  may be provided such that the corner portion on the outer edge portion  2 B side and the outer edge portion  2 D side of the substrate  2  does not coincide with the second point  12 . In this case, as shown in  FIG.  6 G , a corner portion of the protruding portion  17  on the outer edge portion  2 B side and the outer edge portion  2 D side of the substrate  2  may be spaced apart from the second point  12  toward the first point  11  of the linear portion  13  along the first direction A. However, it is preferable that the protruding portion  17  is within the third range D3. As shown in  FIG.  6 H , the ground portion  10  may be formed such that the protruding portion  17  on the outer edge portion  2 D side has a cutout portion  60  along a width of the protruding portion  17 . Also in this case, it is preferable that the protruding portion  17  is within the third range D3. 
     In the above embodiments, a length of the ground portion  10  along the second direction B is greater than a length of the ground portion  10  along the first direction A, but a length of the ground portion  10  along the second direction B may be equal to or smaller than half of a length of the ground portion  10  along the first direction A as shown in  FIG.  7   . For example, when a wavelength corresponding to the highest frequency in the frequency band used in the antenna device  1  is λ, and a length T of the ground portion  10  along the second direction B is 0.17 λ, a length S along the first direction A may be equal to or greater than 0.34 λ. In this case, the ground portion  10  may not include the protruding portion  17 . 
       FIGS.  8 A to  8 D  show charge distribution generated between the ground portion  10  and the element portion  30  when power is fed to the ground portion  10  and the element portion  30  in the antenna device  1  formed as described above. 
       FIG.  8 A  shows the charge distribution when a phase of the AC power is 60 degrees. In this case, the entire ground portion  10  is positively charged, and the element portion  30  is negatively charged. Therefore, an electric field in a direction from the ground portion  10  toward the element portion  30  is generated between the ground portion  10  and the element portion  30  as indicated by the arrow C. 
       FIG.  8 B  shows the charge distribution when the phase of the AC power is 150 degrees. In this case, a portion of the ground portion  10  on a side (second point  12  side) far from the power feeding portion  20  is positively charged, and a portion of the ground portion  10  on a side (first point  11  side) close to the power feeding portion  20 , and the element portion  30  are negatively charged. Therefore, an electric field in a direction from the portion of the ground portion  10  on the side (second point  12  side) far from the power feeding portion  20  toward the element portion  30  is generated between the portion of the ground portion  10  on the side far from the power feeding portion  20 , and the element portion  30  as indicated by the arrow C. 
       FIG.  8 C  shows the charge distribution when the phase of the AC power is 240 degrees. In this case, the element portion  30  is positively charged, and the entire ground portion  10  is negatively charged. Therefore, an electric field in a direction from the element portion  30  toward the ground portion  10  is generated between the element portion  30  and the ground portion  10  as indicated by the arrow C. 
       FIG.  8 D  shows the charge distribution when the phase of the AC power is 330 degrees. In this case, the portion of the ground portion  10  on the side (first point  11  side) close to the power feeding portion  20 , and the element portion  30  are positively charged, and a portion of the ground portion  10  on the side (second point  12  side) far from the power feeding portion  20  is negatively charged. Therefore, an electric field in a direction from the element portion  30  toward the portion of the ground portion  10  on the side (second point  12  side) far from the power feeding portion  20  is generated between the element portion  30  and the portion of the ground portion  10  on the side far from the power feeding portion  20  as indicated by the arrow C. By continuously feeding such AC power, an electric field rotating about an axis along a direction orthogonal to both the first direction A and the second direction B as a rotation axis can be generated from the substrate  2 , and circularly polarized radio waves can be transmitted and received as shown in  FIG.  4 A . 
     In the above embodiments, each size of the antenna device  1  is described using the wavelength λ corresponding to the highest frequency in the frequency band used in the antenna device  1 , which is only an example, and other values may be set. 
     In the above embodiments, the length of the protruding portion  17  along the first direction A is 0.03 λ, and the length of the protruding portion  17  along the second direction B is 0.11 λ. For example, a length of the protruding portion  17  along the first direction A may be 0.03 λ and a length of the protruding portion  17  along the second direction B may be 0.23 λ, or a length of the protruding portion  17  along the first direction A may be 0.085 λ and a length of the protruding portion  17  along the second direction B may be 0.23 λ. In this case, a distance between the protruding portion  17  and the element portion  30  may be 0.2 λ or smaller (preferably 0.02 λ to 0.07 λ). 
     This disclosure can be applied to an antenna device. 
     A characteristic configuration of an antenna device according to this disclosure is an antenna device including: a ground portion including a linear portion connecting a first point and a second point to each other along a predetermined first direction parallel to a surface of a substrate, the ground portion being formed by grounding a conductor portion of the substrate on one side in a second direction orthogonal to the first direction and parallel to the surface of the substrate; a power feeding portion provided in a first range including the first point among the first range, a second range, and a third range that are obtained by dividing the linear portion of the ground portion into three equal parts along the first direction; and an element portion configured to receive power from the power feeding portion and formed in a conductor portion of the substrate that is insulated from the ground portion in a state in which the element portion protrudes from the first range toward the other side in the second direction with respect to the linear portion. The element portion includes a first element portion protruding from the linear portion in the first range toward the other side in the second direction, and a second element portion extending along the first direction from the first element portion toward the second point, spaced apart from the linear portion toward the other side in the second direction, and having at least one linear side. 
     According to such a characteristic configuration, it is possible to generate a difference between charge distribution in the ground portion including a conductor portion of the substrate and charge distribution in the element portion including another conductor portion of the substrate, the ground portion including the linear portion and being provided on the one side in the second direction, according to a phase of the power fed by the power feeding portion, and to generate an electric field rotating about an axis along a direction orthogonal to both the first direction and the second direction parallel to the surface of the substrate as a rotation axis based on the difference in the charge distribution. Therefore, it is possible to implement a small antenna device that can be used for transmission and reception of circularly polarized radio waves. 
     It is preferable that the ground portion includes a protruding portion protruding from a second point side of the linear portion toward the other side in the second direction with a predetermined width, and the second element portion extends from the first element portion toward the protruding portion. 
     According to this configuration, when there is a difference between the charge distribution in the ground portion including the linear portion and provided on the one side in the second direction, and the charge distribution in the element portion, according to the phase of the power fed by the power feeding portion, it is possible to generate the electric field between the ground portion including the linear portion and provided on the one side in the second direction, and the element portion. When there is a difference between charge distribution in the protruding portion and charge distribution in the element portion according to a phase of the power fed by the power feeding portion, it is possible to generate an electric field between the protruding portion and the element portion. Therefore, the circularly polarized radio waves can be more easily transmitted and received with the direction orthogonal to both the first direction and the second direction as an axis. 
     It is preferable that a length of the ground portion along the second direction is greater than a length of the ground portion along the first direction. 
     According to such a configuration, it is possible to easily generate a difference between charge distribution in the ground portion including the linear portion and provided on the one side in the second direction, and charge distribution in the protruding portion, according to a phase of the power fed by the power feeding portion. Therefore, it is possible to generate an electric field between the ground portion and the element portion and between the protruding portion and the element portion, the ground portion including the linear portion and being provided on the one side in the second direction, according to the phase of the power fed by the power feeding portion, and the circularly polarized radio waves can be more easily transmitted and received with the direction orthogonal to both the first direction and the second direction as the axis. 
     Alternatively, a length of the ground portion along the second direction may be equal to or smaller than half of a length of the ground portion along the first direction. 
     Even in such a configuration, it is possible to generate the difference between the charge distribution in the ground portion including the linear portion and provided on the one side in the second direction, and the charge distribution in the element portion, based on the power fed by the power feeding portion, and to generate the electric field between the ground portion including the linear portion and provided on the one side in the second direction, and the element portion. Therefore, the size of the antenna device capable of transmitting and receiving the circularly polarized radio waves can be further reduced. 
     It is preferable that the second element portion is formed to be gradually spaced apart from the linear portion as the second element portion approaches the second point from the first element portion. 
     With such a configuration, it is possible to reduce influence of the charge distribution in the ground portion including the linear portion and provided on the one side in the second direction on the charge distribution in the element portion. Therefore, it is possible to easily generate the electric field between the ground portion including the linear portion and provided on the one side in the second direction, and the element portion. 
     It is preferable that the second element portion includes a reduced width portion in which a width along an orthogonal direction orthogonal to an extending direction of the second element portion extending from the first element portion gradually decreases as the second element portion approaches the second point from the first element portion. 
     With such a configuration, it is possible to more easily reduce the influence of the charge distribution in the ground portion including the linear portion and provided on the one side in the second direction on the charge distribution in the element portion. It is possible to vary, in the element portion, an antenna length formed between a power feeding point at which the power is fed by the power feeding portion and a distal end portion of the second element portion closest to the second point. Therefore, it is possible to widen a band of radio waves that can be transmitted and received. 
     It is preferable that the second element portion further includes a constant width portion electrically connected to the reduced width portion on the second point side of the reduced width portion and having a constant width. 
     Even with such a configuration, it is possible to vary, in the element portion, the antenna length formed between the power feeding point at which the power is fed by the power feeding portion and the distal end portion of the second element portion closest to the second point. 
     It is preferable that the first element portion has a rectangular shape in a plan view, and the second element portion has a triangular shape in the plan view. 
     With such a configuration, the element portion can be easily processed. 
     The principles, preferred embodiment and mode of operation of the present invention have been described in the foregoing specification. However, the invention which is intended to be protected is not to be construed as limited to the particular embodiments disclosed. Further, the embodiments described herein are to be regarded as illustrative rather than restrictive. Variations and changes may be made by others, and equivalents employed, without departing from the spirit of the present invention. Accordingly, it is expressly intended that all such variations, changes and equivalents which fall within the spirit and scope of the present invention as defined in the claims, be embraced thereby.