Patent Publication Number: US-2022239003-A1

Title: Antenna

Description:
TECHNICAL FIELD 
     This invention relates to an antenna configured to be mounted on a board, in particular, relates to an antenna having a split-ring resonator structure. 
     BACKGROUND ART 
     For example, an antenna having a split-ring resonator structure is disclosed in Patent Document 1. 
     As shown in  FIG. 9 , Patent Document 1 discloses an antenna 90 which has a dielectric layer 910, a conductive layer 920 and a feeding line 930. The conductive layer 920 is formed on one of paired principal surfaces of the dielectric layer 910. The feeding line 930 is formed on a remaining one of the paired principal surfaces of the dielectric layer 910. The conductive layer 920 is formed in a C-like shape. The conductive layer 920 has opposite ends which are apart from each other and face each other to form a capacitor 94. The conductive layer 920 and the feeding line 930 are connected to each other by using a via 950 which passes through the dielectric layer 910. In detail, the via 950 connects an end of the feeding line 930 to the vicinity of one of the ends of the conductive layer 920. 
     PRIOR ART DOCUMENTS 
     Patent Document(s) 
     Patent Document 1: JP A 2016-225956 
     SUMMARY OF INVENTION 
     Technical Problem 
     The antenna of Patent Document 1 is formed by using a printed circuit board (board). When an antenna formed by using a board does not have expected characteristics because of manufacturing variations, etc., a matching circuit such as inductors and capacitors should be additionally formed, or the board itself should be made again. Therefore, the antenna of Patent Document 1 tends to be high in cost. 
     It is therefore an object of the present invention to provide an antenna which is low in cost and has stable characteristics. 
     Solution to Problem 
     An aspect of the present invention provides an antenna comprising a conductive member. The conductive member has a body, facing portions, a first feeding terminal and a second feeding terminal. The body extends along a horizontal plane so as to have an open ring-like shape. The body has a first end and a second end which are apart from each other. The facing portions include a first facing portion provided on the first end and a second facing portion provided on the second end. The first facing portion and the second facing portion are apart from each other and face each other. The body has a thin portion which is thinner than any of the first facing portion and the second facing portion. 
     Advantageous Effects of Invention 
     According to an aspect of the present invention, the conductive member of the antenna can be formed as a discrete component separated from the board, and thereby the overall cost of the antenna can be reduced. Moreover, according to the antenna of an aspect of the present invention, each of the first facing portion and the second facing portion, which relatively easily get out of alignment, can be formed as a part of the conductive member. By forming the first facing portion and the second facing portion as described above, degradation of antenna characteristics, which might be caused because of the misalignment between the first facing portion and the second facing portion, can be reduced. Thus, an aspect of the present invention provides the antenna which is low in cost and has stable characteristics. 
     In addition, according to an aspect of the present invention, the inductance of the antenna can be made large by providing the thin portion on the body of the conductive member. As a result, the size of the whole antenna can be reduced without changing its antenna characteristics. 
     An appreciation of the objectives of the present invention and a more complete understanding of its structure may be had by studying the following description of the preferred embodiment and by referring to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view showing an antenna according to an embodiment of the present invention, wherein boundary positions between a body and facing portions of a conductive member are illustrated with dashed line. 
         FIG. 2  is a partially cut-away, perspective view showing a board of the antenna of  FIG. 1 , wherein a part of the board enclosed by chain dotted lines is enlarged and illustrated, and in the enlarged view, connected positions of a first feeding terminal, second feeding terminals and fixed portions of the conductive member are illustrated with dashed line. 
         FIG. 3  is a perspective view showing the conductive member of the antenna of  FIG. 1 , wherein boundary positions between the body and the facing portions of the conductive member are illustrated with dashed line. 
         FIG. 4  is a bottom view showing the conductive member of  FIG. 3 . 
         FIG. 5  is a cross-sectional view showing the conductive member of  FIG. 4 , taken along line V-V. 
         FIG. 6  is a cross-sectional view showing a part of the conductive member enclosed by dashed line A of  FIG. 5 . 
         FIG. 7  is a perspective view showing a modification of the conductive member of  FIG. 3 . 
         FIG. 8  is a perspective view showing a part of the conductive member enclosed by dashed line B of  FIG. 7 . 
         FIG. 9  is a plan view showing an antenna of Patent Document 1. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims. 
     Referring to  FIG. 1 , an antenna  10  according to an embodiment of the present invention comprises a conductive member  20  made of conductor and a board  70 . The conductive member  20  has a body  30 , two facing portions  50 , a first feeding terminal  62  and three second feeding terminals  64 . The body  30  extends along a horizontal plane (XY-plane) so as to have an open ring-like shape. In other words, the body  30  is a ring having opposite ends which are apart from each other. In detail, the body  30  has a first end  32  and a second end  34 . The first end  32  and the second end  34  are located at opposite ends of the body  30 , respectively, and are apart from each other with the facing portions  50  located therebetween. Each of the first feeding terminal  62  and the second feeding terminals  64  extends downward, or in the negative Z-direction, from the body  30  in a perpendicular direction (Z-direction: upper-lower direction) perpendicular to the XY-plane. Referring to  FIGS. 1 and 2 , the board  70  extends along the XY-plane. The board  70  is a printed circuit board and is formed with a signal line  72  and a ground plane  78 . 
     The conductive member  20  of the present embodiment is configured to be mounted on the board  70  to form the antenna  10  together with the board  70 . In the antenna  10 , the first feeding terminal  62  of the conductive member  20  is fixed on and connected to the signal line  72  of the board  70  via soldering, etc. In the antenna  10 , each of the second feeding terminals  64  of the conductive member  20  is fixed on and connected to the ground plane  78  of the board  70  via soldering, etc. The conductive member  20  has an inductance component and a capacitance component as described later and works as an LC resonator of the antenna  10 . Thus, the antenna  10  is a resonant antenna, and the conductive member  20  works as the antenna  10  together with the signal line  72  and the ground plane  78  of the board  70 . 
     According to the present embodiment, the conductive member  20 , i.e. the LC resonator, of the antenna  10  can be formed as a discrete component separated from the board  70 . According to this structure, inductance and capacitance of the antenna  10  can be adjusted only by the conductive member  20 , and thereby the overall cost of the antenna  10  can be reduced. 
     In the present embodiment, the board  70  is connected to a connector  80 . In detail, the signal line  72  of the board  70  is connected to a signal terminal (not shown) of the connector  80 , and the ground plane  78  of the board  70  is connected to a ground terminal  84  of the connector  80 . According to this structure, the antenna  10  can send out signals transmitted from the connector  80  and can transmit received signals to the connector  80 . However, the present invention is not limited thereto, but the connector  80  may be provided as necessary. 
     Referring to  FIG. 3 , the conductive member  20  of the present embodiment is formed by bending a single metal plate which has a flat-plate shape of a thickness TC. In other words, the conductive member  20  is a single metal plate with bends. However, the present invention is not limited thereto. For example, the conductive member  20  may be formed by welding a plurality of metal members to each other. Moreover, as described later, the structure of the conductive member  20  can be variously modified as necessary. 
     As shown in  FIGS. 3 and 4 , the body  30  of the conductive member  20  has an angular C-like shape in the XY-plane. In detail, the body  30  has two front portions  402 , one rear portion  404  and two side portions  406  which correspond to the front portions  402 , respectively. Each of the front portions  402  is located at a front side (positive X-side) of the body  30  in a front-rear direction (X-direction) perpendicular to the Z-direction and extends along a lateral direction (Y-direction) perpendicular to both the X-direction and the Z-direction. The rear portion  404  is located at a rear side (negative X-side) of the body  30  and extends along the Y-direction. The side portions  406  are located at opposite sides of the body  30  in the Y-direction, respectively. Each of the side portions  406  extends along the X-direction and couples one of opposite ends of the rear portion  404  in the Y-direction and an outer end of the corresponding front portion  402  in the Y-direction to each other. The first end  32  is an inner end of one of the front portions  402  in the Y-direction. The second end  34  an inner end of a remaining one of the front portions  402  in the Y-direction. 
     The body  30  of the present embodiment has the aforementioned structure and has a rectangular ring shape when seen along the Z-direction. Each of the rear portion  404  and the side portions  406  of the present embodiment has a parallel part, or a part which extends in parallel to the XY-plane, and another part which is bent so as to extend downward from the parallel part. The body  30 , which has the rear portion  404  and the side portions  406  formed as described above, is hardly deformed. However, the present invention is not limited thereto. For example, the body  30  may have a circular ring shape or may have a polygonal ring shape when seen along the Z-direction. Moreover, each of the rear portion  404  and the side portions  406  may have only the part which extends in parallel to the XY-plane. 
     In the present embodiment, the first feeding terminal  62  is located at the first end  32 . One of the second feeding terminals  64  is located at the middle of the rear portion  404  of the body  30  in the Y-direction. The other two of the second feeding terminals  64  are located at front ends (positive X-side ends) of the two side portions  406  of the body  30 , respectively. According to this arrangement, the body  30  of the conductive member  20  works as an inductor. However, the present invention is not limited thereto, but the arrangement of the first feeding terminal  62  and the second feeding terminals  64  can be variously modified, provided that the conductive member  20  has an inductance component. 
     The facing portions  50  of the conductive member  20  include a first facing portion  52  and a second facing portion  54 . The first facing portion  52  is connected to the first end  32  and is located inward of the first end  32  in the Y-direction. The second facing portion  54  is connected to the second end  34  and is located inward of the second end  34  in the Y-direction. Thus, the facing portions  50  include the first facing portion  52  provided on the first end  32  and the second facing portion  54  provided on the second end  34 . 
     The first facing portion  52  of the present embodiment has a first upper portion  522 , a first lower portion  524  and a first coupling portion  528 . The first upper portion  522  is located at an upper side (positive Z-side) of the first facing portion  52  and extends along the XY-plane. The first lower portion  524  is located at a lower side (negative Z-side) of the first facing portion  52  and extends along the XY-plane. The first coupling portion  528  couples a front end of the first upper portion  522  and a front end of the first lower portion  524  to each other. 
     The second facing portion  54  of the present embodiment has a second upper portion  542 , a second lower portion  544  and a second coupling portion  548 . The second upper portion  542  is located at an upper side of the second facing portion  54  and extends along the XY-plane. The second lower portion  544  is located at a lower side of the second facing portion  54  and extends along the XY-plane. The second coupling portion  548  couples a front end of the second upper portion  542  and a front end of the second lower portion  544  to each other. 
     The first facing portion  52  and the second facing portion  54  of the present embodiment are formed in the shapes described above and have the shapes corresponding to each other. However, the present invention is not limited thereto, but the shape of each of the first facing portion  52  and the second facing portion  54  can be variously modified as necessary. 
     Referring to  FIGS. 3 to 5 , a split  58  is formed between the first facing portion  52  and the second facing portion  54 . The first upper portion  522  of the first facing portion  52  and the second upper portion  542  of the second facing portion  54  are located at positions same as each other in the Z-direction, and are apart from each other and face each other in the XY-plane with the split  58  located therebetween. The first lower portion  524  of the first facing portion  52  and the second lower portion  544  of the second facing portion  54  are located at positions same as each other the Z-direction, and are apart from each other and face each other in the XY-plane with the split  58  located therebetween. 
     Referring to  FIGS. 4 and 5 , the first facing portion  52  has a first edge surface  532  which is located at an edge thereof in the XY-plane. The first edge surface  532  is provided on the first upper portion  522  and the first lower portion  524  of the first facing portion  52 . The second facing portion  54  has a second edge surface  552  which is located at an edge thereof in the XY-plane. The second edge surface  552  is provided on the second upper portion  542  and the second lower portion  544  of the second facing portion  54 . 
     The first edge surface  532  of the first upper portion  522  and the second edge surface  552  of the second upper portion  542  are apart from each other and face each other in the XY-plane. The first edge surface  532  of the first lower portion  524  and the second edge surface  552  of the second lower portion  544  are apart from each other and face each other in the XY-plane. As can be seen from this arrangement, the first edge surface  532  and the second edge surface  552  work as a capacitor of the conductive member  20 . In other words, the capacitor of the conductive member  20  of the present embodiment includes the first edge surface  532  provided on the first facing portion  52  and the second edge surface  552  provided on the second facing portion  54 . 
     As described above, the first facing portion  52  and the second facing portion  54  are apart from each other and face each other and thereby work as a capacitor. According to the present embodiment, the first facing portion  52  and the second facing portion  54  face, at least in part, each other in the XY-plane. However, the present invention is not limited thereto, but a facing direction of the first facing portion  52  and the second facing portion  54  can be variously modified. 
     Referring to  FIG. 3 , the conductive member  20  has a split-ring resonator structure. The first facing portion  52  and the second facing portion  54  are arranged on opposite ends of a split-ring, respectively. The existing first facing portion and the existing second facing portion, which are arranged as described above, tend to be misaligned with each other in a manufacturing process of an antenna. In contrast, according to the antenna  10  of the present embodiment, each of the first facing portion  52  and the second facing portion  54 , which relatively easily get out of alignment in the existing structure, can be formed as a part of the conductive member  20  which is a unitary member. By forming the first facing portion  52  and the second facing portion  54  as described above, degradation of antenna characteristics, which might be caused because of the misalignment between the first facing portion  52  and the second facing portion  54 , can be reduced. Thus, the present embodiment provides the antenna  10  which is low in cost and has stable characteristics. 
     As shown in  FIGS. 3 and 4 , the conductive member  20  of the present embodiment has three fixed portions  66  and  68  in addition to the body  30 , the facing portions  50 , the first feeding terminal  62  and the second feeding terminals  64 . Each of the fixed portions  66  and  68  extends downward from the body  30 . As previously described, the first feeding terminal  62  is provided to the first end  32 . In contrast, the fixed portion  66  is provided to the second end  34 . One of the fixed portions  68  is provided to the first upper portion  522  of the first facing portion  52 . A remaining one of the fixed portions  68  is provided to the second lower portion  544  of the second facing portion  54 . 
     Referring to  FIG. 3  together with  FIGS. 1 and 2 , in the antenna  10 , each of the fixed portions  66  and  68  is fixed on the board  70  via soldering, etc. In addition, as previously described, the first feeding terminal  62  is fixed on the board  70  via soldering, etc. When the first feeding terminal  62  and the fixed portions  66  and  68  are fixed on the board  70 , a movement of each of the first facing portion  52  and the second facing portion  54  is reduced in the Z-direction. Thus, the misalignment between the first edge surface  532  of the first facing portion  52  and the second edge surface  552  of the second facing portion  54  is reduced, and thereby degradation of antenna characteristics can be reduced. However, the present invention is not limited thereto, but the fixed portions  66  and  68  may be provided as necessary. Moreover, the number and the arrangement of the fixed portions  66  and  68  can be variously modified as necessary. 
     Referring to  FIG. 5 , a thickness of the first facing portion  52  (thickness TC) and a thickness of the second facing portion  54  (thickness TC) are same as each other. More specifically, each of the first facing portion  52  and the second facing portion  54  is a part of a metal plate having thickness TC. By making the thickness TC sufficiently large, degradation of antenna characteristics can be reduced even if the first edge surface  532  of the first facing portion  52  and the second edge surface  552  of the second facing portion  54  get out of alignment to some extent in the Z-direction. However, the present invention is not limited thereto. For example, the thickness of the first facing portion  52  and the thickness of the second facing portion  54  may be different from each other. 
     Referring to  FIGS. 4 to 6 , the body  30  of the conductive member  20  of the present embodiment has an inner edge  42 , a thick portion  44  and a thin portion  46 . Referring to  FIGS. 3 to 5 , the inner edge  42  is an inside edge of the body  30  in the XY-plane. Referring to  FIG. 5 , a thickness of the thick portion  44  (thickness TC) is same as the thickness of the first facing portion  52  (thickness TC) and the thickness of the second facing portion  54  (thickness TC). More specifically, the thick portion  44  is a part of a metal plate having the thickness TC. In contrast, referring to  FIGS. 3 and 5 , a thickness of the thin portion  46  (thickness TL) is thinner than the thickness of the thick portion  44 . More specifically, the thin portion  46  is a part of the metal plate having the thickness TC but is partially made thin by a process such as coining. 
     The thickness of the thin portion  46  which is formed as described above is thinner than any of the thickness of the first facing portion  52 , the thickness of the second facing portion  54  and the thickness of the thick portion  44 . In other words, the body  30  of the conductive member  20  of the present embodiment has the thin portion  46  which is thinner than any of the first facing portion  52 , the second facing portion  54  and the thick portion  44 . By providing the thin portion  46  on the body  30 , cross-section of electric current which flows through the body  30  is made small, and thereby inductance of the conductive member  20  can be made large. Thus, inductance of the antenna  10  (see  FIG. 1 ) can be made large by providing the thin portion  46  on the body  30 . As a result, the size of the whole antenna  10  can be reduced without changing its antenna characteristics. 
     Referring to  FIGS. 4 and 5 , according to the present embodiment, a part of the thin portion  46  is located on the inner edge  42  of the body  30  in the XY-plane. The inner edge  42  is a part which tends to contribute to inductance of the antenna  10  (see  FIG. 1 ). Therefore, according to this arrangement, inductance of the antenna  10  can be easily made large. However, the present invention is not limited thereto. For example, the thin portion  46  may be located to be outward of the inner edge  42  in the XY-plane. 
     According to the present embodiment, the body  30  has the thick portion  44  which is thicker than the thin portion  46 . The thin portion  46  is located over an area between the thick portion  44  and the inner edge  42  in the XY-plane. According to this arrangement, inductance of the antenna  10  (see  FIG. 1 ) can be easily made large. However, the present invention is not limited thereto. For example, the body  30  may have no thick portion  44 , and the whole body  30  may be the thin portion  46 . According to this structure, inductance can be further made large. However, the present embodiment is preferable from a viewpoint of maintaining the strength of the body  30 . 
     As previously described, the first facing portion  52 , the second facing portion  54  and the thick portion  44  of the present embodiment have thicknesses same as each other. However, the present invention is not limited thereto. For example, the thick portion  44  may be thinner than any of the first facing portion  52  and the second facing portion  54 , provided that the thick portion  44  is thicker than the thin portion  46 . However, the present embodiment is preferable from a viewpoint of easy fabrication of the conductive member  20 . 
     Referring to  FIG. 6 , in the present embodiment, the thin portion  46  is a part which is recessed upward from the thick portion  44 . A boundary surface  484  is formed between the thin portion  46  and the thick portion  44 . The thin portion  46  has a lower surface which is a planar surface in parallel to the XY-plane. A part of the thick portion  44  which is located in the vicinity of the boundary surface  484  has a lower surface which is a planar surface in parallel to the XY-plane. On the other hand, the boundary surface  484  is a sloping surface oblique to the XY-plane. In other words, a distinct step is formed between the thin portion  46  and the thick portion  44 . However, the present invention is not limited thereto. For example, the thin portion  46  may be a part which is recessed downward from the thick portion  44 . The thin portion  46  may gradually become thicker toward the thick portion  44 . 
     Referring to  FIG. 6 , in the present embodiment, the thickness of the thin portion  46  (thickness TL) is about half of the thickness of the thick portion  44  (thickness TC). However, the present invention is not limited thereto. For example, the thickness of the thin portion  46  may be not more than half of the thickness of the thick portion  44  or may be more than half of the thickness of the thick portion  44 . 
     Referring to  FIG. 4 , the thin portion  46  of the present embodiment continuously extends between the first end  32  and the second end  34  along the inner edge  42  of the body  30 . In particular, the thin portion  46  is formed only in the vicinity of the inner edge  42 . According to this arrangement, the inductance component of the conductive member  20  can be sufficiently made high while degradation of the strength of the body  30 , which might be caused because of the formation of the thin portion  46 , can be prevented. However, the present invention is not limited thereto. For example, the thin portion  46  may be formed only on the rear portion  404  of the body  30 . 
     The conductive member  20  of the present embodiment can be further variously modified in addition to the already described modifications. 
     For example, comparing  FIG. 7  with  FIG. 3 , a conductive member  20 A according to a modification has a structure same as that of the conductive member  20 , except that it has a body  30 A of a shape different from that of the body  30  of the conductive member  20 . Comparing  FIG. 7  with  FIG. 4 , the body  30 A of the conductive member  20 A has a structure same as that of the body  30 , except that it has a thick portion  44 A and a thin portion  46 A which are different from the thick portion  44  and the thin portion  46  of the body  30 , respectively. 
     Referring to  FIG. 7 , the thin portion  46 A according to the modification is formed of a plurality of recesses  48 A which are arranged along the inner edge  42  of the body  30 A. The recesses  48 A are alternately recessed in the Z-direction. In detail, the recess  48 A, which is adjacent to the recess  48 A recessed downward, is recessed upward, and the recess  48 A, which is adjacent to the recess  48 A recessed upward, is recessed downward. Moreover, the first facing portion  52 , the second facing portion  54  and the thick portion  44 A have thicknesses (thickness TC) same as each other. The thin portion  46 A is thinner than any of the first facing portion  52 , the second facing portion  54  and the thick portion  44 A. A part of the thin portion  46 A is located on the inner edge  42  of the body  30 A in the XY-plane. 
     Referring to  FIG. 8 , the recesses  48 A are formed via coining. Each of the recess  48 A has a bottom surface  482 A, a boundary surface  484 A and two side surfaces  486 A. The bottom surface  482 A is a planar surface in parallel to the XY-plane. A part of the thick portion  44 A which is located in the vicinity of the boundary surface  484 A has an upper surface and a lower surface which are planar surfaces in parallel to the XY-plane. On the other hand, the boundary surface  484 A is a sloping surface oblique to the XY-plane. In other words, a distinct step is formed between the thin portion  46 A and the thick portion  44 A. 
     According to the thin portion  46 A of the modification, inductance of the antenna  10  (see  FIG. 1 ) can be made large. As a result, the size of the whole antenna  10  can be reduced without changing its antenna characteristics. 
     The present application is based on a Japanese patent application of JP2019-118248 filed on Jun. 26, 2019 before the Japan Patent Office, the content of which is incorporated herein by reference. 
     While there has been described what is believed to be the preferred embodiment of the invention, those skilled in the art will recognize that other and further modifications may be made thereto without departing from the spirit of the invention, and it is intended to claim all such embodiments that fall within the true scope of the invention. 
     REFERENCE SIGNS LIST 
       10  antenna 
       20 ,  20 A conductive member 
       30 ,  30 A body 
       32  first end 
       34  second end 
       402  front portion 
       404  rear portion 
       406  side portion 
       42  inner edge 
       44 ,  44 A thick portion 
       46 ,  46 A thin portion 
       48 A recess 
       482 A bottom surface 
       484 ,  484 A boundary surface 
       486 A side surface 
       50  facing portion 
       52  first facing portion 
       522  first upper portion 
       524  first lower portion 
       528  first coupling portion 
       532  first edge surface 
       54  second facing portion 
       542  second upper portion 
       544  second lower portion 
       548  second coupling portion 
       552  second edge surface 
       58  split 
       62  first feeding terminal 
       64  second feeding terminal 
       66 ,  68  fixed portion 
       70  board 
       72  signal line 
       78  ground plane 
       80  connector 
       84  ground terminal