Patent Publication Number: US-11656582-B2

Title: Radio wave watch

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a National Stage of International Application No. PCT/JP2018/034461 filed Sep. 18, 2018, claiming priority based on Japanese Patent Application No. 2017-194336 filed Oct. 4, 2017. 
     FIELD 
     The present invention relates to a radio wave watch. 
     BACKGROUND 
     Conventional watches have an antenna. Patent Literature 1 discloses the technology of a watch device that has a housing configured with a metal concave container and where, in addition to a watch operating part, an inverted F antenna for receiving a radio wave from a GPS satellite is disposed in the concave part of the housing. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Patent Application Laid-Open. No. 2012-75090 
     SUMMARY 
     Technical Problem 
     There is room for improving the reception sensitivity of an antenna. 
     An object of the present invention is to provide a radio wave watch that can improve the reception sensitivity of an antenna. 
     Solution to Problem 
     A radio wave watch according to the present invention includes an exterior case; a dial plate disposed within the exterior case; a substrate disposed on a rear side of the dial plate within the exterior case; a first ground layer disposed on the substrate; an antenna that has a planar emitting electrode disposed between a center of the exterior case and an inner wall surface of the exterior case and opposed to the first ground layer, a planar short-circuit part electrically connecting an end part of the emitting electrode to the first ground layer, and a connecting part connecting the emitting electrode to a receiving circuit of the substrate; and a second ground layer disposed on an opposite side to the emitting electrode side across the short-circuit part on the substrate and having a width equal to or greater than a width of the short-circuit part. 
     Advantageous Effects of Invention 
     A radio wave watch according to the present invention has a second ground layer disposed on an opposite side to an emitting electrode side across a short-circuit part on a substrate and having a width equal to or greater than a width of the short-circuit part. The second ground layer improves the symmetricity of an antenna and an image antenna and improves the reception sensitivity of the antenna. The radio wave watch according to the present invention thus exhibits its effect of enabling the reception sensitivity of the antenna and improve the reception sensitivity. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a plan view illustrating a radio wave watch according to an embodiment. 
         FIG.  2    is a sectional view of the radio wave watch according to the embodiment. 
         FIG.  3    is a sectional view of a main part of the radio wave watch according to the embodiment. 
         FIG.  4    is a perspective view of an antenna according to the embodiment. 
         FIG.  5    is an illustrative view of an image antenna. 
         FIG.  6    is a perspective view illustrating a first placement of the antenna. 
         FIG.  7    is a perspective view illustrating a second placement of the antenna. 
         FIG.  8    is a view illustrating the sensitivity of the antenna in the first placement and the second placement. 
         FIG.  9    is a perspective view illustrating a configuration where a ground layer is extended in the first placement. 
         FIG.  10    is a perspective view illustrating a configuration where a ground layer is extended in the second placement. 
         FIG.  11    is a view illustrating a measurement result of the reception sensitivity in the first placement. 
         FIG.  12    is a view illustrating a measurement result of the reception sensitivity in the second placement. 
         FIG.  13    is a perspective view illustrating a configuration having a surrounding metal cover in the first placement. 
         FIG.  14    is a perspective view illustrating a configuration having the surrounding metal cover in the second placement. 
         FIG.  15    is a view illustrating a measurement result of the reception sensitivity in the first placement. 
         FIG.  16    is a view illustrating a measurement result of the reception sensitivity in the second placement. 
         FIG.  17    is a plan view illustrating a placement example of a solar cell. 
         FIG.  18    is a plan view illustrating a placement example of a date plate. 
         FIG.  19    is a plan view illustrating another placement, example of the antenna. 
         FIG.  20    is a perspective view illustrating one example of the shape of the antenna. 
         FIG.  21    is a sectional view illustrating the solar cell disposed to overlap with a second region. 
         FIG.  22    is a plan view illustrating a radio wave watch according to a first variation of the embodiment. 
         FIG.  23    is a perspective view of an antenna according to the first variation of the embodiment. 
         FIG.  24    is a front view of the antenna according to the first variation of the embodiment. 
         FIG.  25    is a side view describing the directivity of the antenna. 
         FIG.  26    is a perspective view illustrating one example of the shape of the antenna. 
         FIG.  27    is a perspective view illustrating another example of the antenna. 
         FIG.  28    is a plan view of a radio wave watch according to a second variation of the embodiment. 
         FIG.  29    is a plan view of a radio wave watch according to a third variation of the embodiment. 
         FIG.  30    is a plan view of a radio wave watch according to a fourth variation of the embodiment. 
         FIG.  31    is a sectional view of a radio wave watch according to a fifth variation of the embodiment. 
         FIG.  32    is a sectional view of a main part of a radio wave watch according to a sixth variation of the embodiment. 
         FIG.  33    is a plan view of an antenna according to a seventh variation of the embodiment. 
         FIG.  34    is a plan view of an antenna according to an eighth variation of the embodiment. 
         FIG.  35    is a perspective view of the antenna according to the eighth variation of the embodiment. 
         FIG.  36    is a front view of the antenna according to the eighth variation of the embodiment. 
         FIG.  37    is a plan view illustrating a placement example of the antenna according to the eighth variation of the embodiment. 
         FIG.  38    is a plan view illustrating one example of a shape of the solar cell. 
         FIG.  39    is a plan view illustrating another placement example of the antenna. 
         FIG.  40    is a plan view illustrating a placement of a motor according to a ninth variation of the embodiment. 
         FIG.  41    is a plan view illustrating a placement of a ground layer according to a tenth variation of the embodiment. 
         FIG.  42    is a plan view illustrating a condition where a device is disposed on a substrate according to the tenth variation of the embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A radio wave watch according to an embodiment of the present invention will now be described in detail with reference to the drawings. Note that this invention is not limited by this embodiment. Components in the following embodiment include components that those skilled in the art can conceive of easily or substantially the same as those. 
     Embodiment 
     An embodiment will be described with reference to  FIGS.  1  to  21   . The present embodiment relates to a radio wave watch.  FIG.  1    is a plan view illustrating a radio wave watch according to the embodiment;  FIG.  2    is a sectional view of the radio wave watch according to the embodiment;  FIG.  3    is a sectional view of a main part of the radio wave watch according to the embodiment;  FIG.  4    is a perspective view of an antenna according to the embodiment; and  FIG.  5    is an illustrative view of an image antenna. A section II-II in  FIG.  1    is illustrated in  FIG.  2   . 
     As illustrated in  FIGS.  1  and  2   , a radio wave watch  1  of the embodiment has an exterior case  2 , a windshield  3 , a dial plate  4 , a hand  5 , a solar cell  6 , a substrate  7 , a battery  8 , an antenna  9 , and a rear cover  10 . Note that the illustration of the windshield  3 , the dial plate  4 , the hand  5 , and the solar cell  6  is omitted in  FIG.  1   . The radio wave watch  1  receives a radio wave from a satellite. The radio wave watch  1  has a function to correct its internal time based on information acquired from the radio wave. The radio wave watch  1  of the present embodiment receives a global positioning system (GPS) radio wave output from a GPS satellite. Note that the GPS radio wave is a radio wave including GPS time information and uses, for example, two types of a 1.5 GHz band (1575.42 MHz) and a 1.2 GHz band (1227.60 MHz). 
     The exterior case  2  is a member constituting the shell of the rad to wave watch  1 . For example, the exterior case  2  is formed of a conductive material, such as titanium and titanium alloys. The exterior case  2  has an approximately cylindrical body part  21  and a lug  22 . The body part  21  is a cylindrical constituent part where both ends in an axial direction are opened. The lug  22  is formed integrally with the body part  21  and projects from the circumferential surface of the body part  21  toward the outside in a radial direction. A belt is coupled to the lug  22 . 
     In the present specification, the direction of a center axis line X 1  of the body part  21  is referred to as an “axial direction”. The axial direction corresponds to a vertical direction of the radio wave watch  1 . Furthermore, a direction perpendicular to the center axis line X 1  is referred to as a “radial direction”, and a circumferential direction centered at the center axis line X 1  is referred to as a “circumferential direction”. In the radial direction, a side near the center axis line X 1  is referred to as the “inside”, and a side far from the center axis line X 1  is referred to as the “outside”. 
     The windshield  3  blocks an opening on the front side of the body part  21 . The windshield  3  is formed of a transparent material, such as glass. The windshield  3  covers the dial plate  4  and the hand  5  on the front side. The rear cover  10  blocks an opening on the back side of the body part  21 . The rear cover  10  is a plate-shaped member and, for example, is formed of metal. The rear cover  10  covers the substrate  7  on the hack side. 
     The exterior case  2  has an accommodating space  23 , the sectional shape of which is generally circular. The accommodating space  23  is an inner space of the body part  21 . The accommodating space  23  is a closed space surrounded by the body part  21 , the windshield  3 , and the rear cover  10 . The accommodating space  23  accommodates the dial plate  4 , the hand  5 , the solar cell  6 , the substrate  7 , the battery  8 , and the antenna  9 . 
     The dial plate  4  is a disk-shaped member and fixed to the body part  21 . The dial plate  4  is configured so that the dial plate  4  can pass light from the front side to the back side. For example, the dial plate  4  is formed of an optically transparent material. For example, the dial plate  4  may be formed of a non-conductive material, such as a synthetic resin. 
     The hand  5  has a second hand  51 , a minute hand  52 , and an hour hand  53 . The hand  5  is disposed coaxially with the center axis line X 1  of the exterior case  2 . A rotation shaft  55  of the hand  5  is passed through a through hole of the dial plate  4 . Each of the second hand  51 , the minute hand  52 , and the hour hand  53  is coupled to a drive source, such as a motor, through a wheel train  54 . The wheel train  54  is disposed on the back side relative to the dial plate  4  and decelerates the rotation of a drive source  56  to convey it to the hand  5 . The drive source  56  of the present embodiment is a step motor. The drive source  56  rotationally drives the hand  5  with power supplied from the battery  8 . 
     The solar cell  6  is disposed on the back surface of the dial plate  4 . The solar cell  6  is formed into a plane shape. The solar cell  6  converts received light into electric energy. The solar cell  6  is an aggregate of photovoltaic elements, and its front side is a light-receiving surface. The solar cell  6  generates electricity with light penetrating the dial plate  4 . The solar cell  6  is electrically connected with the substrate  7 . The power generated by the solar cell  6  may be supplied to devices of the radio wave watch  1 , or may be charged into the battery  8 . 
     The substrate  7  is disposed in the vicinity of the rear cover  10  in the accommodating space  23 . The substrate  7  is fixed to a main plate, which is not shown, and the main plate is fixed to the body part  21 . The substrate  7  is disposed separately on the back side from the dial plate  4  in the axial direction and is opposed to the dial plate  4 . The substrate  7  is a component of a controller controlling the radio wave watch  1 . The substrate  7  has a control circuit  14  and a receiving circuit  15 . The control circuit  14  controls driving of the drive source  56  and corrects the internal time. The receiving circuit  15  is connected with the antenna  9 . The receiving circuit  15  decodes a satellite signal received by the antenna  9  to generate a digital signal. The digital signal generated by the receiving circuit  15  is sent to the control circuit  14 . The control circuit  14  corrects the internal time based on the signal acquired from the receiving circuit  15 . The control circuit  14  can correct display time of the hand  5  based on the internal time. Furthermore, the control circuit  14  has, in a storage region, geographic data where location information is associated with time zones and, from a result of the satellite reception, can determine a time zone to which a current location belongs to reflect it on the watch. 
     A ground layer  70  is disposed on the substrate  7 . For example, the ground layer  70  may be formed of a ground plate formed of a conductive material, a ground electrode film formed on the substrate  7 , or other components. The position and shape of the ground layer  70  is determined depending on the position and shape of the antenna  9 . As discussed below, the ground layer  70  of the present embodiment is disposed to be opposed to the antenna  9  and an image antenna  9   i  (see  FIG.  5   ). The ground layer  70  of the present embodiment is formed on a front surface  7   a  of the substrate  7 . The ground layer  70  is electrically connected with the exterior case  2 . The electrical connection may be either direct-current connection or alternate-current connection. The ground layer  70  may be connected with the exterior case  2  via an inner layer of the substrate  7 . Note that the ground layer  70  may be electrically connected with the rear cover  10  instead of the exterior case  2 . 
     The shape of the ground layer  70  of the present embodiment is rectangular. The ground layer  70  has a first side  70   a , a second side  70   b , a third side  70   c , and a fourth side  70   d . The first side  70   a  is a side facing an inner wall surface  21   a  of the exterior case  2 . The first side  70   a  and the fourth side  70   d  are opposed to each other in the radial direction. The second side  70   b  and the third side  70   c  are opposed to each other in the circumferential direction. 
     For example, the ground layer  70  is disposed so that a foot of a perpendicular line  70   p  drawn from the center axis line X 1  to the first side  70   a  is the center of the first side  70   a  or a position in the vicinity of the center. In this case, each of the second side % and the third side  70   c  of the ground layer  70  is parallel to the perpendicular line. In the ground layer  70  of the present embodiment, the first side  70   a  is a short side, and the second side  70   b  and the third side  70   c  are long sides. The first side  70   a  is slightly shorter than the second side  70   b  and the third side  70   c . Note that the length of the first side  70   a  may be equal to the length of the second side  70   b  and the third side  70   c.    
     As illustrated in  FIG.  1   , a width WG of the ground layer  70  is greater than a width WE of an emitting electrode  91  described below. In the present embodiment, the width WG of the ground layer  70  is greater than the width WE of the emitting electrode  91  and is smaller than the width WB of a base part  94 . Note that, in the present embodiment, a width WS of a short-circuit part  92  (see  FIG.  4   ) is equal to the width WE of the emitting electrode  91 . The width WG of the ground layer  70  is thus greater than the width WS of the short-circuit part  92 . However, the width WG of the ground layer  70  may be equal to the width WS of the short-circuit part  92 . 
     As illustrated in  FIG.  3   , the fourth side  70   d  of the ground layer  70  is located at an inside end part in the radial direction of the antenna  9 . More specifically, the fourth side  70   d  is located inside in the radial direction relative to the inside end part in the radial direction of the emitting electrode  91 . Thus, the short-circuit part  92  is disposed between the first side  70   a  and the fourth side  70   d  of the ground layer  70 . The emitting electrode  91  is disposed between the short-circuit part  92  and the fourth side  70   d  on the ground layer  70 . As illustrated in  FIG.  1   , the emitting electrode  91  is disposed between the second side  70   b  and the third side  70   c  of the ground layer  70 . Note that the fourth side  70   d  may be located inside relative to the inside end part in the radial direction of the antenna  9 . 
     The antenna  9  is disposed on the substrate  7 . More specifically, the antenna  9  is disposed on the front surface  7   a  of the substrate  7 . The antenna  9  is disposed between the center axis line X 1  and the inner wall surface  21   a  of the exterior case  2 . The antenna  9  has the emitting electrode  91 , the short-circuit part  92 , a connecting part  93 , and the base part  94 . 
     The base part  94  is formed, of a dielectric, into a cubic shape. For example, the base part  94  is formed of a non-conductive dielectric, such as a ceramic. The base part  94  is configured with a material having a high dielectric constant, such as zirconia or titanium oxide, and exhibits a wavelength-shortening effect. The shape of the base part  94  of the present embodiment is a rectangular parallelepiped. The base part  94  enables a substantial wavelength λ′ of a radio wave that the emitting electrode  91  receives to be smaller than a wavelength λ corresponding to the frequency of the GPS radio wave. 
     As illustrated in  FIG.  4   , the base part  94  is disposed so that a front surface  94   a  faces the front side, or the front surface  94   a  is opposed to the windshield  3 . The base part  94  is disposed so that a first side surface  94   c  is opposed to the inner wall surface  21   a  of the exterior case  2  and a second side surface  94   d  faces the center axis line X 1  side. The first side surface  94   c  and the second side surface  94   d  are side surfaces located across the front surface  94   a  and face in mutually opposite directions. The base part  94  of the present embodiment is disposed so that the position of a foot of a perpendicular line  94   e  drawn from the center axis line X 1  to the second side surface  94   d  is the center position in a width direction of the second side surface  94   d . The shape of the antenna  9  is symmetric with reference to the perpendicular line drawn from the center axis line X 1  to the foot of the perpendicular line  94   e . Note that the first side surface  94   c  and the second side surface  94   d  of the present embodiment are side surfaces along the long side of the front surface  94   a.    
     The ground layer  70  is formed so that the fourth side  70   d  (see  FIG.  3   ) is parallel to the second side surface  94   d  of the base part  94  and the first side  70   a  is parallel to the first side surface  94   c  of the base part  94 . The base part  94  is disposed in an inside region in the radial direction of the ground layer  70 . 
     The emitting electrode  91  is disposed on the front surface  94   a  of the base part  94 . The emitting electrode  91  is a planar constituent part formed of a material having conductivity, such as metal. The emitting electrode  91 , as well as the short-circuit part  92  and the connecting part  93  described below may be configured with a conductive-material thin film formed on the dielectric, which is the base part  94 , or may be configured with a plate-shaped member. Note that the antenna  9  illustrated in the present embodiment is the one where a thin film is formed on the dielectric, but, instead of this, the antenna  9  may be configured only with a conductive plate-shaped member, or may be configured by combining the base part  94  with the conductive plate-shaped member. Examples of the planar emitting electrode  91  include both the one configured with a thin film and the one formed into a plate shape. Also, examples of the planar short-circuit part  92  and the connecting part  93  include both the ones configured with a thin film and the ones formed into a plate shape. Furthermore, the planar emitting electrode  91 , the short-circuit part  92 , and the connect-ng part  93  also includes a configuration where they have an uneven part on the whole or part of their surfaces. 
     The shape of the emitting electrode  91  of the present embodiment is rectangular. The emitting electrode  91  is disposed, on the front surface  94   a , to cover a most region of the front surface  94   a . The emitting electrode  91  is disposed to expose an edge part of the front surface  94   a  in a U shape. More specifically, a partial region inside in the radial direction of the front surface  94   a  and regions at both ends in the width direction thereof are exposed. Each side of the emitting electrode  91  is parallel to the corresponding side of the front surface  94   a . Note that the emitting electrode  91  may be provided to prevent the exposure of the front surface  94   a , in other words, cover the whole of the front surface  94   a.    
     Note that, in the description of the antenna  9  and the ground layer  70  in the present specification, the “width direction” is a direction perpendicular to an extension direction of the emitting electrode  91 . For example, the emitting electrode  91  of the present embodiment extends from the short-circuit part  92  along the radial direction. The “extension direction” in this case is a direction of the perpendicular line that links the center axis line X 1  to the line of the perpendicular line  70   p . The width direction is a direction perpendicular to this perpendicular line, and, for example, a direction parallel to the first side  70   a  of the ground layer  70 . 
     The emitting electrode  91  has first emitting sides  91   a  and  91   a , and a second emitting side  91   b . The first emitting sides  91   a  are sides along the radial direction of the emitting electrode  91 . One of the first emitting sides  91   a  and the other of the first emitting sides  91   a  are generally parallel or substantially parallel. The second emitting side  91   b  is a side substantially perpendicular to the first emitting sides  91   a  of the emitting electrode  91 , in other words, a side along the width direction. The substantial antenna length of the emitting electrode  91  is the length of a side from a point  91   c , to which the short-circuit part  92  is connected, to the second emitting side  91   b , i.e., the length of the first emitting sides  91   a  and  91   a . The emitting electrode  91  is formed so that, for example, the antenna length is a length of ¼ of the substantial wavelength λ′ after shortening. The antenna  9  of the present embodiment has characteristics of a planar monopole antenna. More specifically, in the antenna  9  of the present embodiment, each of the first emitting sides  91   a  and  91   a  exhibits antenna characteristics similar to a monopole antenna. The first emitting sides  91   a  and  91   a  have directivity along the direction of the center axis line X 1 . That is to say, the first emitting sides  91   a  and  91   a  have high sensitivity to a radio wave along the direction of the center axis line X 1 . 
     The short-circuit part  92  is disposed on the first side surface  94   c  of the base part  94 . The first side surface  94   c  a surface facing outside in the radial direction of the base part  94 . The short-circuit part  92  is a planar constituent part formed of a material having conductivity, such as metal. For example, the shape of the short-circuit part  92  is rectangular. The short-circuit part  92  extends from the upper end of the first side surface  94   c  to the lower end thereof. The short-circuit part  92  is disposed to expose both end parts in the width direction of the first side surface  94   c . The upper end of the short-circuit part  92  leads to the emitting electrode  91  and is electrically connected with the emitting electrode  91 . The lower end of the short-circuit part  92  is electrically connected with the ground layer  70 . In the present embodiment, the width WE of the short-circuit part  92  is equal to the width. WE of the emitting electrode  91 . 
     The connecting part  93  is disposed on the second side surface  94   d  of the base part  94 . The second side surface  94   d  is a surface facing inside in the radial direction of the base part  94 . The connecting part  93  is a planar constituent part formed of a material having conductivity, such as metal. For example, the shape of the connecting part  93  is rectangular. The connecting part  93  extends from an end part on a back surface  94   b  side of the second side surface  94   d  to a position relatively on the front side as compared with the center. The connecting part  93  is an RF connecting part and connected to the receiving circuit  15 . In the antenna  9  of the present embodiment, the connecting part  93  is capacitively coupled to the emitting electrode  91 . The connecting part  93  and the emitting electrode  91  are separated without physical contact. The capacitive coupling of the connecting part  93  and the emitting electrode  91  achieves non-contact-type signal transmission. Impedance matching is achieved based on the distance between an end part on the front side of the connecting part  93  and the second emitting side  91   b . Note that power may be supplied by directly connecting the connecting part  93  with the emitting electrode  91 . 
     The base part  94  is supported by the substrate  7  so that its back surface  94   b  contacts with the ground layer  70 . The hack surface  94   b  is opposed to an inside region in the radial direction of the ground layer  70 . The first side surface  94   c  of the base part  94  is parallel to the first side  70   a  of the ground layer  70 , and the second side surface  94   d  of the base part  94  is parallel to the fourth side  70   d  of the ground layer  70 . To prevent the ground layer  70  from being electrically connected with the connecting part  93 , the connecting part  93  and a connected electrode  75  (see  FIG.  3   ) are disposed at a predetermined distance to the ground layer  70 . The connecting part  93  is connected to the receiving circuit  15  via the electrode  75 . It is preferable for the electrode  75  to be made as small as possible in terms of reducing influence on the impedance of the antenna  9 . Furthermore, it is preferable for the distance between the electrode  75  and the ground layer  70  to be separated as far as possible. Furthermore, it is preferable for the electrode  75  and the ground layer  70  not to overlap in a planar manner. 
     As illustrated in  FIG.  3    and other figures, the ground layer  70  of the present embodiment has a first region  71  and a second region  72 . The first region  71  is an inside region in the radial direction relative to the short-circuit part  92 . The second region  72  is an outside region in the radial direction relative to the short-circuit part  92 . The first region  71  and the second region  72  are continuous and constitute the single ground layer  70 . In the ground layer  70  of the present embodiment, the shape of the first region  71  and the shape of the second region  72  are the same. That is to say, the ground layer  70  has a symmetric shape with reference to the short-circuit part  92 . More specifically, a length LG 1  of the first region  71  in the radial direction is equal to a length LG 2  of the second region  72  in the radial direction. Also, the width of the first region  71  and the width of the second region  72  are the same. Thus, the area of the first region  71  is equal to the area of the second region  72 . 
     As described with reference to  FIG.  5   , the radio wave watch  1  of the present embodiment enables the reception sensitivity of the antenna  9  to be improved with the image antenna  9   i . The image antenna  9   i  is a virtual antenna and paired with the antenna  9 . It is thought that the image antenna  9   i  is generated on the opposite side to the emitting electrode  91  side across the short-circuit part  92 . The image antenna  9   i  is generated in a shape symmetric to the antenna  9  and at a position symmetric to it with reference to the short-circuit part  92 . 
     The image antenna  9   i  includes a virtual electrode  91   i . The virtual electrode  91   i  is a virtual constituent part formed, by an image effect, at the position symmetric to the emitting electrode  91  with reference to the short-circuit part  92 . The virtual electrode  91   i  extends from the short-circuit part  92  toward the outside in the radial direction and is opposed to the second region  72  of the ground layer  70 . 
     In the present embodiment, no components are disposed in the space part where the image antenna  9   i  is generated. In other words, the exclusive space for generating the image antenna  9   i  secured. Furthermore, the ground layer  70  is symmetrically formed with reference to the short-circuit part  92 . That is, the electrical symmetricity between the inside region in the radial direction and the outside region in the radial direction is secured with reference to the short-circuit part  92 . This generates the image antenna  9   i  having high symmetricity to the antenna  9 . As a result, the radio wave watch  1  of the present embodiment enables the reception sensitivity of the antenna  9  to be improved to the maximum. However, a mounted object may be disposed in the region where the image antenna  9   i  is generated. Disposing the mounted object in the region for generating the image antenna  9   i  enables a power-supplying line to the mounted object to be shortened, and can decrease the influence of wiring capacity and reducing propagation loss. 
     Referring to  FIGS.  6  to  16   , the reception sensitivity of the antenna  9  of the radio wave watch  1  of the present embodiment will be described. 
     One example of a placement of the antenna  9  on the ground layer  70  is illustrated in  FIGS.  6  and  7   . Each antenna  9  in  FIGS.  6  and  7    is disposed at an end part of the ground layer  70 , and the positions of their short-circuit part  92  are different. In the antenna  9  illustrated in  FIG.  6   , the short-circuit part  92  faces the central side of the ground layer  70 , similarly to the placement of the radio wave watch  1  of the present embodiment. In other words, the ground layer  70  extends frontward from the short-circuit part  92 , in the placement of the antenna  9  in  FIG.  6   . A length LGX of the ground layer  70  extending forward from the short-circuit part  92  is twice or more than a length LB of the base part  94 . 
     In contrast, the short-circuit part  92  of the antenna  9  illustrated in  FIG.  7    faces the opposite side to the central side of the ground layer  70 . In this case, no ground layer  70  substantially exists forward from the short-circuit part  92 . That is,  FIGS.  6    and  FIG.  7    have the difference of whether the ground layer  70  is provided forward from the short-circuit part  92 . In the following description, the placement of the antenna  9  in  FIG.  6    is referred to as a “first placement”, and the placement of the antenna  9  in  FIG.  7    is referred to as a “second placement”. 
       FIG.  8    illustrates the sensitivity of the antenna  9  in the first placement and the second placement. In  FIG.  8   , the vertical axis represents the reception sensitivity C/N [dB] of the antenna  9 .  FIG.  8    illustrates the sensitivity to a radio wave received from four GPS satellites. As is apparent from  FIG.  8   , the reception sensitivity in the first placement is better than the reception sensitivity in the second placement. That is, it is found that the reception sensitivity of the antenna  9  in the case where the ground layer  70  exists forward from the short-circuit part  92  is improved as compared with the case where no ground layer  70  exists. It is considered that this is because the ground layer  70  forward from the short-circuit part  92  results in forming the image antenna  9   i  having high symmetricity to the antenna  9 . 
     Next, a change in the sensitivity in the case where the ground layer  70  is added in the first placement and the second placement will be described.  FIG.  9    is a view illustrating a configuration where the ground layer is extended in the first placement, and  FIG.  10    is a perspective view illustrating a configuration where the ground layer is extended in the second placement. The ground layer  70  illustrated in  FIGS.  9  and  10    has an extension part  70 X. The extension part  70 X is a part where the end part of the ground layer  70 , on the side where the antenna  9  is disposed, is extended. As illustrated in  FIG.  9   , the extension part  70 X in the first placement extends frontward from the connecting part  93 . In other words, the part, of the ground layer  70 , disposed forward from the short-circuit part  92  has no change from that in  FIG.  6   . 
     In contrast, the extension part  70 X in the second placement extends forward from the short-circuit part  92 , as illustrated in  FIG.  10   . That is, the ground layer  70  is added forward from the short-circuit part  92  as compared with the configuration in  FIG.  7   . The length LX of the extension part  70 X is similar to the length LB of the base part  94 . 
       FIG.  11    illustrates a measurement result of the reception sensitivity in the first placement.  FIG.  12    illustrates a measurement result of the reception sensitivity in the second placement.  FIG.  11    illustrates, in the first placement, the reception sensitivity in the case where no extension part  70 X is provided ( FIG.  6   ) and the reception sensitivity in the case where the extension part  70 X is provided ( FIG.  9   ).  FIG.  12    illustrates, in the second placement, the reception sensitivity in the case where no extension part  70 X is provided ( FIG.  7   ) and the reception sensitivity in the case where the extension part  70 X is provided ( FIG.  10   ). 
     As illustrated in  FIG.  11   , the presence or absence of the extension part  70 X in the first placement has no large influence on the reception sensitivity of the antenna  9 . In contrast, as illustrated in  FIG.  12   , the presence or absence of the extension part  70 X in the second placement have significant influence on the reception sensitivity of the antenna  9 . In the case where the extension part  70 X is provided, the reception sensitivity is significantly improved as compared with the case where no extension part  70 X is provided. 
     As is apparent from the above result, disposing the ground layer  70  on the opposite side to the emitting electrode  91  side across the short-circuit part  92  improves the sensitivity of the antenna  9 . It is considered that this improvement in the reception sensitivity arises from that the ground layer  70  disposed forward from the short-circuit part  92  secures the symmetricity between the antenna  9  and the image antenna  9   i . That is to say, in the ground layer  70 , it is considered that the enhanced symmetricity of both sides across the short-circuit part  92  enables the reception sensitivity of the antenna  9  to be improved. 
     Next, the influence of a surrounding metal member on the reception sensitivity of the antenna  9  will be described.  FIG.  13    illustrates a configuration where a metal cover  12  is put on in the first placement.  FIG.  14    illustrates a configuration where the metal cover  12  is put on in the second placement. The cover  12  is a box-shaped member configured with metal having conductivity. The cover  12  covers the surroundings of the ground layer  70  and the antenna  9 . The cover  12  is electrically connected with the ground layer  70 . A height HC of the cover  12  is approximately twice the length LB of the base part  94 . 
       FIG.  15    illustrates a measurement result of the reception sensitivity in the first placement.  FIG.  16    illustrates a measurement result of the reception sensitivity in the second placement.  FIG.  15    illustrates, in the first placement, the reception sensitivity in the case where no cover  12  is provided ( FIG.  6   ) and the reception sensitivity in the case where the cover  12  is provided ( FIG.  13   ).  FIG.  16    illustrates, in the second placement, the reception sensitivity in the case where no cover  12  is provided ( FIG.  7   ) and the reception sensitivity in the case where the cover  12  is provided ( FIG.  14   ). 
     As illustrated in  FIG.  15   , the presence or absence of the cover  12  in the first placement have significant influence on the reception sensitivity of the antenna  9 . In the case where the cover  12  is provided in the first placement, the reception sensitivity significantly drops as compared with the case where no cover  12  is provided. In contrast, the presence or absence of the cover  12  in the second placement has influence on the reception sensitivity to some extent. In the case where the cover  12  is provided in the second placement, the reception sensitivity also drops as compared with the case where no cover  12  is provided. However, the degree of drop in the reception sensitivity in the second placement is smaller than the degree of drop in the reception sensitivity in the first placement. That is, it is said that the second placement has high tolerance to the metal enclosure as compared with the first placement. 
     In the first placement, it is considered that the connecting part  93 , which is capacitively coupled to the emitting electrode  91 , is disposed near the cover  12 , which is the metal member, and thus the reception sensitivity drops under the influence of the metal of the cover  12 . 
     In the radio wave watch  1  of the present embodiment, each component is disposed so that the metal member does not cover the antenna  9  and the image antenna  9   i  from above. For example, as illustrated in  FIGS.  3  and  5   , the solar cell  6  is disposed not to cover the second region  72  of the ground layer  70  and the antenna  9  from above. More specifically, an end surface  6   a  of the solar cell  6  is located inside in the radial direction relative to the emitting electrode  91 . That is, the solar cell  6  is disposed not to overlap with at least, the emitting electrode  91  when viewed in the axial direction. The radio wave watch  1  of the present embodiment thus enables the reception sensitivity of the antenna  9  to be improved. 
     The solar cell  6  may be configured as illustrated in  FIG.  17   .  FIG.  17    is a plan view illustrating a placement example of the solar cell. The shape of the solar cell  6  illustrated in  FIG.  17    is a shape where a part of its disk is notched. The solar cell  6  has a sector-shaped notch part  6   b . The width of the notch part  6   b  becomes wider as it goes outside in the radial direction from the center axis line X 1 . The shape and placement of the notch part  6   b  are determined so that the solar cell  6  does not overlap with the antenna  9  and the ground layer  70  when viewed in the axial direction. That is, the notch part  6   b  is formed so that the solar cell  6  does not shield the front side of the antenna  9  and the ground layer  70 . 
     Note that a non-conductive member may be disposed on the front side of the ground layer  70 .  FIG.  18    is a plan view illustrating a placement example of a date plate. In the case where a date plate  13  disposed in the radio wave watch  1  is a non-conductive member, the date plate  13  may overlap with the ground layer  70  when viewed in the axial direction. For example, the date plate  13  is disposed coaxially with the center axis line X 1 . For example, the date plate  13  is disposed to overlap with the second region  72  of the ground layer  70  and not to overlap with the antenna  9 . In other words, the date plate  13  is disposed outside in the radial direction relative to the antenna  9 . It is considered that the non-conductive member is unlikely to affect the symmetricity between the antenna  9  and the image antenna  9   i  even when it is disposed at a position opposed to the ground layer  70 . However, in view of the thickness of the whole watch, it, is preferable for it to be disposed not to overlap with the antenna  9 . 
     Another placement example of the antenna  9  will be described.  FIG.  19    is a plan view illustrating another placement example of the antenna. In the placement illustrated in  FIG.  19   , the short-circuit part  92  of the antenna  9  is disposed to face in the circumferential direction. In other words, the emitting electrode  91  extends from the short-circuit part  92  along the circumferential direction, in the placement illustrated in  FIG.  19   . The second region  72  of the ground layer  70  extends from the antenna  9  toward the opposite side to the emitting electrode  91  side along the circumferential direction. 
     For example, the antenna  9  is disposed so that the short-circuit part  92  is located on a virtual plane S 1 . The virtual plane S 1  is a plane including the center axis line X 1 . In other words, the antenna  9  is disposed so that the short-circuit part  92  extends along the virtual plane S 1  in the radial direction. In this case, the ground layer  70  is disposed to be symmetric with reference to the virtual plane S 1 . That is, in the ground layer  70 , the first region  71  and the second region  72  are located on the different sides across the virtual plane S 1 . 
     The placement as illustrated in  FIG.  19    also enables the reception sensitivity of the antenna  9  to be improved by the effect of the image antenna  9   i.    
     Another shape of the antenna  9  will be described.  FIG.  20    is a perspective view illustrating one example of the shape of the antenna. In the antenna  9  illustrated in  FIG.  20   , the first side surface  94   c  of the base part  94  is an inclined surface. The first side surface  94   c  is inclined to approach the second side surface  94   d  as it goes from the back surface  94   b  side to the front surface  94   a  side. The short-circuit part  92  is inclined similarly to the first side surface  94   c . Various shapes other than the illustrated one can be adopted as the shape of the antenna  9 . 
     As discussed above, the radio wave watch  1  according to the present embodiment has the exterior case  2 , the dial plate  4 , the substrate  7 , the first region  71  of the ground layer  70 , the antenna  9 , and the second region  72  of the ground layer  70 . The dial plate  4  is disposed within the exterior case  2 . The first region  71  of the ground layer  70  corresponds to a first ground layer disposed on the substrate  7 . The antenna  9  is disposed between the center axis line X 1 , which is the center of the exterior case  2 , and the inner wall surface  21   a  of the exterior case  2 . The antenna  9  has the planar emitting electrode  91 , the planar short-circuit part  92 , and the connecting part  93 . The emitting electrode  91  is opposed to the first region  71  of the ground layer  70 . The short-circuit part  92  electrically connects the end part of the emitting electrode  91  with the first region  71  of the ground layer  70 . The connecting part  93  connects the emitting electrode  91  with the receiving circuit  15  of the substrate  7 . 
     The second region  72  of the ground layer  70  corresponds to a second ground layer disposed on the substrate  7 . The second region  72  is disposed on the opposite side to the emitting electrode  91  side across the short-circuit part  92  on the substrate  7 . The width WG of the second region  72  is equal to or greater than the width WS of the short-circuit part  92 . The antenna  9  of the present embodiment improves, with the second region  72  of the ground layer  70 , the symmetricity between the image antenna  9   i  and the antenna  9 . Thus, the antenna  9  of the present embodiment can achieve improving its reception sensitivity. 
     In the antenna  9  of the present embodiment, the first region  71  as the first ground layer and the second region  72  as the second ground layer are integrated with each other. The integration of the first region  71  and the second region  72  facilitates improving the symmetricity between the image antenna  9   i  and the antenna  9 . Furthermore, the configuration of the ground layer  70  is simplified. 
     In the antenna  9  of the present embodiment, the emitting electrode  91  extends from the short-circuit part  92  toward the radial direction, which is a direction perpendicular to the center axis line X 1  of the exterior case  2 . Such a placement easily secures the symmetricity of the emitting electrode  91  in positional relationship with the inner wall surface  21   a  of the exterior case  2 . 
     In the antenna  9  of the present embodiment, the second region  72  of the ground layer  70  extends from the short-circuit part  92  toward the opposite side to the emitting electrode  91  side. The length LG 2  of the second region  72  in this extension direction is equal to or greater than a length LE of the emitting electrode  91 . Thus, the second region  72  of the present embodiment can improve the symmetricity between the image antenna  9   i  and the antenna  9 . 
     Note that the length LG 2  of the second region  72  may be less than the length LE of the emitting electrode  91 . For example, the length LG 2  of the second region  72  is determined depending on the size of a region to be secured. In the ground layer  70 , the shape of the first side  70   a  may be an arc shape corresponding to the shape of the inner wall surface  21   a  of the exterior case  2 , instead of the straight shape. This enables a limited space to be effectively utilized to enhance the symmetricity between the first region  71  and the second region  72 . 
     In the antenna  9  of the present embodiment, the metal member is disposed in a region not overlapping with the emitting electrode  91  in the direction of the center axis line X 1  of the exterior case  2 , in the space between the dial plate  4  and the substrate  7 . For example, the solar cell  6  is disposed in the region not overlapping with the emitting electrode  91  when viewed in the axial direction, as illustrated in  FIG.  17   . The drive source  56  and the wheel train  54  are also disposed in the region not overlapping with the emitting electrode  91  when viewed in the axial direction. Disposing the metal member in the region not overlapping with the emitting electrode  91  enables the reception sensitivity of the antenna  9  to be improved. 
     In the antenna  9 , the metal member may be disposed in a region overlapping with the second region  72 . The metal member disposed in the region overlapping with the second region  72  is, for example, the solar cell  6 , the drive source  56 , a magnetic shield, and the wheel train  54 .  FIG.  21    illustrates the solar cell  6  disposed to overlap with the second region  72 . The solar cell  6  is opposed to the second region  72  of the ground layer  70  in the axial direction. The solar cell  6  has an opening part  6   c  at a position opposed to the emitting electrode  91 . For example, the shape of the opening part  6   c  is rectangular. The opening part  6   c  is provided in a range overlapping with the emitting electrode  91  when viewed in the axial direction. The opening width and the opening length of the opening part  6   c  may be greater than the width WE and the length LE of the emitting electrode  91 , respectively. Disposing the solar cell  6  also in the region overlapping with the second region  72  can achieve maximizing the light-receiving area of the solar cell  6  while achieving improvement in the reception sensitivity of the antenna  9 . 
     Note that, in  FIG.  21   , the solar cell  6  overlaps with the whole region of the second region  72 , but it is not limited to this. The solar cell  6  may overlap with a partial region of the second region  72 . In the solar cell  6 , the region overlapping with the second region  72  may have an opening, a slit, or other empty spaces. For example, a part of the opening part  6   c  may be formed to overlap with the second region  72  when viewed in the axial direction. 
     The solar cell  6  above the antenna  9  may have the notch part  6   b  as illustrated in  FIG.  17   . In the case where the solar cell  6  is disposed between the dial plate  4  and the substrate  7 , it is preferable for the solar cell  6  to be disposed without causing the drop in the reception sensitivity of the antenna  9 . The solar cell  6  illustrated in  FIG.  17    has the notch part  6   b  at a position opposed to the emitting electrode  91  and the second region  72 . The notch part  6   b  includes a range overlapping with the emitting electrode  91  and the second region  72  when viewed in the axial direction. The solar cell  6  does not shield the front side of the emitting electrode  91  and the second region  72 , so that the drop in the reception sensitivity of the antenna  9  is reduced. 
     In the space between the dial plate  4  and the substrate  7 , a non-conductive member may be disposed to be opposed to the second region  72 . For example, in the case where the wheel train  54  is a non-conductive member, the wheel train  54  may be disposed to be opposed to the second region  72 . The non-conductive member is disposed to be opposed to the second region  72  in this way, so that the space between the second region  72  and the dial plate  4  is effectively utilized. Furthermore, the non-conductive member unlikely affects the characteristics of the image antenna  9   i . This enables the limited space within the exterior case  2  to be effectively utilized while achieving improvement in the reception sensitivity of the antenna  9 . 
     The radio wave watch  1  may have a planar, non-conductive rotating member opposed to the substrate  7 , for example, the date plate and a day plate. In this case, it is preferable for this rotating member to be disposed not to overlap with the emitting electrode  91  and disposed to overlap with the second region  72 , in the direction of the center axis line X 1  of the exterior case  2 . For example, the date plate  13  illustrated in  FIG.  18    is disposed in the outermost periphery in the inner space of the exterior case  2 . The inner periphery of the date plate  13  is located, at least, outside in the radial direction relative to the emitting electrode  91 . Furthermore, a part of the date plate  13  overlaps with the second region  72  of the ground layer  70  when viewed in the axial direction. Such a placement can achieve enlarging the date plate  13  in diameter while reducing the influence on the reception sensitivity of the antenna  9 . 
     The connecting part  93  of the present embodiment connects the emitting electrode  91  with the receiving circuit  15  by capacitive coupling. The connecting part  93  is disposed at a position that is closer to the center of the exterior case  2  than the short-circuit part  92  is. The connecting part  93  is far from the inner wall surface  21   a  of the exterior case  2 , so that the capacitive coupling between the connecting part  93  and the emitting electrode  91  is unlike to be affected by the exterior case  2 . 
     Note that, in the present embodiment, the antenna center of the antenna  9  is disposed on the straight line that links the center of the battery  8  to the center axis line X 1 , but this placement is one example. In the example of the present embodiment, the center of the antenna  9  is disposed at the position of approximately 12 o&#39;clock, and the center of the battery  8  is disposed at the position of approximately 6 o&#39;clock. Instead of this, the center of the antenna  9  may be disposed at a position between 9 o&#39;clock and 11 o&#39;clock, and the center of the battery  8  may be disposed at a position between 4 o&#39;clock and 6 o&#39;clock. 
     Note that, in the ground layer  70 , the shape of the first region  71  may be different from the shape of the second region  72 . The length LG 1  of the first region  71  may be different from the length LG 2  of the second region  72 . For example, the length LG 1  of the first region  71  may be greater than the length LG 2  of the second region  72 . 
     Not only the antenna  9  receives the radio wave, but also it may be used for transmitting the radio wave. For example, the antenna  9  may be used to perform transmission to and reception from peripheral equipment. In this case, the radio wave watch  1  may communicate with other equipment via short-distance wireless communication by, for example, Bluetooth (registered trademark) or Wi-Fi. In the case where the antenna  9  transmits the radio wave, power is supplied to the emitting electrode  91  through the connecting part  93 . The radio wave watch  1  may have a radio communication circuit including the receiving circuit  15  and a transmitting circuit. In this case, the connecting part  93  connects the radio communication circuit with the emitting electrode  91 . 
     First Variation of Embodiment 
     With referring to  FIGS.  22  to  27   , a first variation of the embodiment will be described.  FIG.  22    is a plan view illustrating a radio wave watch according to the first variation of the embodiment;  FIG.  23    is a perspective view of an antenna according to the first variation of the embodiment;  FIG.  24    is a front view of the antenna according to the first variation of the embodiment; and  FIG.  25    is a side view describing the directivity of the antenna. The antenna  9  of the first variation has a connecting part  96  instead of the connecting part  93  of the above embodiment. In the radio wave watch  1  of the first variation, the configuration other than the antenna  9  is similar to that of the above embodiment. The connecting part  96  connects the receiving circuit  15  to the emitting electrode  91  physically and electrically. The connecting part  96  is a planar constituent part and disposed on the first side surface  94   c . The connecting part  93  of the above embodiment indirectly connects the emitting electrode  91  to the receiving circuit  15  by capacitive coupling. In contrast, the connecting part  96  of the first variation directly connects the emitting electrode  91  to the receiving circuit  15 . In the first variation, the first side surface  94   c  faces inside in the radial direction. 
     The antenna  9  of the first variation has a paired short-circuit parts  95  and  95 . Each of the paired short-circuit parts  95  and  95  is a planar constituent part and disposed on the first side surface  94   c . The paired short-circuit parts  95  and  95  are disposed in line with the connecting part  96  on both sides of the connecting part  96 . The paired short-circuit parts  95  and  95  each extend along the axial direction and are disposed apart from each other in the width direction. The connecting part  96  is disposed between the paired short-circuit parts  95  and  95  and extends along in the axial direction. The connecting part  96  and the paired short-circuit parts  95  and  95  extend along a virtual plane S 2 . The virtual plane S 2  is a plane parallel to the center axis line X 1  of the exterior case  2 . That is, the connecting part  96  and the paired short-circuit parts  95  and  95  extend to be perpendicular to a perpendicular line drawn from the center axis line X 1  to the virtual plane S 2 . 
     The connecting part  96 , and the paired short-circuit parts  95  and  95  are connected mutually at an end part of the emitting electrode  91  side. That is, the connecting part  96 , and the paired short-circuit parts  95  and  95  constitute one conductive member. 
     In the antenna  9  of the first variation, as illustrated in  FIG.  24   , the direction of a current Ia flowing through the connecting part  96  and the direction of a current Ib flowing through the short-circuit part  95  are opposite to each other. Thus, in the case where power is supplied to the emitting electrode  91 , a substantial power-supplying point is a power-supplying part  97  illustrated in  FIG.  24   . The direction of the current Ia and the direction of the current Ib are opposite to each other and cancelled mutually, so that the connecting part  96  fails to contribute to substantial emission. That is, the connecting part  96  functions as a transmission path that fails to contribute to emission. Thus, as illustrated in  FIG.  25   , the emitting electrode  91  of the antenna  9  mainly contributes to emission. The antenna  9  has its directivity along the axial direction as illustrated in  FIG.  25   . That is, the antenna  9  can receive a radio wave traveling along the axial direction with high sensitivity. 
     As illustrated in  FIG.  23   , each of the paired short-circuit parts  95  and  95  has a width WS 1 . The paired short-circuit parts  95  and  95  are formed into the same shape. For example, the width WS 1  of the short-circuit part  95  is greater than a width WP of the connecting part  96 . 
     As illustrated in  FIG.  22   , the antenna  9  is disposed so that the short-circuit part  95  and the connecting part  96  face inside in the radial direction. The emitting electrode  91  extends from the connecting part  96  toward the outside in the radial direction. In other words, the emitting electrode  91  extends from the connecting part  96  toward the inner wall surface  21   a  of the exterior case  2  along the radial direction. 
     The second region  72  of the ground layer  70  is disposed inside in the radial direction relative to the antenna  9 . Also in the first variation, the position of the second region  72  is the opposite position to the emitting electrode  91  side across the short-circuit part  95  on the substrate  7 . The width WG of the second region  72  is equal to or greater than the width WS 1  of the short-circuit part  95 . Similarly to the above embodiment, the ground layer  70  has the first region  71  corresponding to the antenna  9 . The shape of the first region  71  may be the same as that of the second region  72 . It is preferable for the length LG 2  of the second region  72  to be equal to or greater than the length LE of the emitting electrode  91 . 
     In the radio wave watch  1  of the first variation, the inside in the radial direction relative to the antenna  9  is the region of the image antenna  9   i . The second region  72  of the ground layer  70  enhances the symmetricity between the antenna  9  and the image antenna  9   i . This improves the reception sensitivity of the antenna  9  also in the radio wave watch  1  of the first variation. 
     Note that the shape of the antenna  9  may be a shape as illustrated in  FIG.  26    in the antenna  9  illustrated in  FIG.  26   , the first side surface  94   c  of the base part  94  is an inclined face. The first side surface  94   c  is inclined to approach the second side surface  94   d  as it goes from the back surface  94   b  side to the front surface  94   a  side. The short-circuit parts  95  and  95  and the connecting part  96  are inclined similarly to the first side surface  94   c.    
     The emitting electrode  91  may extend to a surface other than the front surface  94   a  of the base part  94 . For example, as illustrated in  FIG.  27   , the emitting electrode  91  may extend from the front surface  94   a  to the second side surface  94   d . The extension of the emitting electrode  91  over a plurality of surfaces can achieves downsizing the antenna  9 . Various shapes other than the illustrated one can be adopted as the shape of the antenna  9 . 
     In the radio wave watch  1  of the first variation, it is preferable for the metal member to be disposed in the region not overlapping with the emitting electrode  91  in the direction of the center axis line X 1 . The metal member may be disposed in the region overlapping with the second region  72  of the ground layer  70 . The solar cell  6  may have a notch part at the position opposed to the emitting electrode  91  and the second region  72 . 
     The non-conductive member may be disposed to be opposed to the second region  72  of the ground layer  70 . In the case where the radio wave watch  1  has a non-conductive rotating member, this rotating member may be disposed not to overlap with the emitting electrode  91  and disposed to overlap with the second region  72 , in the direction of the center axis line X 1 . 
     Second Variation of Embodiment 
     With referring to  FIG.  28   , a second variation of the embodiment will be described.  FIG.  28    is a plan view of a radio wave watch according to the second variation of the embodiment. In the radio wave watch  1  of the second variation, the battery  8  functions as the second ground layer. The battery  8  is disposed so that its negative electrode faces the front side. The antenna  9  is disposed adjacently to the battery  8  so that the short-circuit part  92  faces the battery  8 . The battery  8  is thus located on the opposite side to the emitting electrode  91  across the short-circuit part  92 . The negative electrode of the battery  8  functions as the second ground layer and enables the symmetricity between the antenna  9  and the image antenna  9   i  to be improved. 
     Note that the antenna  9  of the above first variation may be disposed adjacently to the battery  8 . In this case, the antenna  9  is disposed adjacently to the battery  8  so that the paired short-circuit parts  95  and  95  face the battery  8 . Such a placement is advantageous in the case where it is difficult to secure a region of the substrate  7  for the second region  72 . Note that, in the case where the antenna  9  is a direct-connection type, the connecting part  96  of the antenna  9  may be disposed close to the exterior case  2  side, with the exterior case  2  set to the ground potential. In such a placement, the exterior case  2  also functions as the second region  72 . For example, such a placement is effective in the case where it is difficult to secure a space on the substrate  7  for the second region  72 . 
     Third Variation of Embodiment 
     With referring to  FIG.  29   , a third variation of the embodiment will be described.  FIG.  29    is a plan view of a radio wave watch according to the third variation of the embodiment. The antenna  9  of the third variation is disposed similarly to the antenna  9  of the above embodiment. The solar cell  6  of the third variation has a projecting part  6   d , which overlaps with the antenna  9  when viewed in the axial-direction. 
     The solar cell  6  is provided with the notch part  6   b  and has the projecting part  6   d  at the center in the circumferential direction of the notch part  6   b . The projecting part  6   d  extends from the center axis line X 1  toward the outside in the radial direction. The projecting part  6   d  is a rectangular constituent part having a constant width. The projecting part  6   d  is disposed to overlap with a central part in the width direction of the emitting electrode  91  and the ground layer  70 . The width of the projecting part  6   d  is less than both the width WE of the emitting electrode  91  and the width WG of the ground layer  70 . Thus, the projecting part  6   d  does not overlap with the first emitting sides  91   a  and  91   a  of the emitting electrode  91 . The projecting part  6   d  overlaps with the central part of the second emitting side  91   b  when viewed in the axial-direction. The central part of the second emitting side  91   b  is a part where its potential fluctuation is smaller than that in the first emitting side  91   a . Thus, even when the central part of the second emitting side  91   b  is shielded, this has no large influence on the reception sensitivity of the emitting electrode  91 . Thus, the projecting part  6   d  can increase the light-receiving area of the solar cell  6  while reducing the influence on the reception sensitivity of the emitting electrode  91 . 
     Fourth Variation of Embodiment 
     With referring to  FIG.  30   , a fourth variation of the embodiment will be described.  FIG.  30    is a plan view of a radio wave watch according to the fourth variation of the embodiment. The antenna  9  of the fourth variation is curved along the shape of the inner wall surface  21   a  of the exterior case  2 . 
     As illustrated in  FIG.  30   , each of the first side surface  94   c  and the second side surface  94   d  of the base part  94  is a curved surface having an arc shape. Each shape of the first side surface  94   c  and the second side surface  94   d  is an arc shape concentric with the inner wall surface  21   a  of the exterior case  2 . The paired short-circuit parts  95  and  95  and the connecting part  96  are disposed along the first side surface  94   c . That is, the paired short-circuit parts  95  and  95  and the connecting part  96  extend along a curved surface parallel to the center axis line X 1 . 
     The shape of the emitting electrode  91  is a curved shape similar to the base part  94 . The shape of the second emitting side  91   b  is an arc shape concentric with the inner wall surface  21   a  of the exterior case  2 . The first emitting sides  91   a  are inclined to approach mutually as they go inside in the radial direction. 
     The shape of the ground layer  70  is a curved shape similar to the base part  94 . Each shape of the first side  70   a  and the fourth side  70   d  is an arc shape concentric with the inner wall surface  21   a  of the exterior case  2 . The second side  70   b  and the third side  70   c  are inclined to approach mutually as they go inside in the radial direction. It is desirable that the curvature of the curved shape of the ground layer  70  be a curvature where a distance from the center axis line X 1  is assumed as a radius. Furthermore, in the case where a rotating member (e.g., a date plate) overlaps with the second region  72  of the ground layer  70 , it is preferable to match the curvature of the curved shape of the ground layer  70  with the curvature of the rotating member. 
     The antenna  9  is disposed in the outside region in the radial direction of the ground layer  70 . That is, the outside region in the radial direction of the ground layer  70  is the first region  71 , and the inside region in the radial direction is the second region  72 . 
     Note that the first emitting sides  91   a  of the emitting electrode  91  may be parallel to each other. In this case, the second side  70   b  and the third side  70   c  of the ground layer  70  may be parallel. Instead of a direct power-supplying type of the antenna  9 , the antenna  9  of the above embodiment, i.e., the antenna  9  where power is supplied to the emitting electrode  91  by capacitive coupling may have a curved shape. In this case, the antenna  9  may be disposed in the inside region in the radial direction of the ground layer  70 . It is preferable for the connecting part  93  to be disposed toward the in the radial direction. 
     Fifth Variation of Embodiment 
     With referring to  FIG.  31   , a fifth variation of the embodiment will be described.  FIG.  31    is a sectional view of a radio wave watch according to the fifth variation of the embodiment. In the radio wave watch  1  of the fifth variation, a first ground layer  73  and a second ground layer  74  are separated. 
     The ground layer  70  has the first ground layer  73  and the second ground layer  74 . The first ground layer  73  is disposed on the front surface  7   a  of the substrate  7 . In contrast, the second ground layer  74  is disposed within the substrate  7 . The ground layer  70  is configured so that the potential of the first ground layer  73  is the same as that of the second ground layer  74 . For example, the first ground layer  73  and the second ground layer  74  may be electrically connected via a through hole formed in the substrate  7 . 
     The second ground layer  74  is disposed on the opposite side to the first ground layer  73  across the short-circuit part  92 . In the fifth variation, the first ground layer  73  is disposed inside in the radial direction relative to the second ground layer  74 . In this way, the first ground layer  73  and the second ground layer  74  may be disposed in different layers in the substrate  7 . This can contribute to downsizing and thinning because a mounted object  16  having a physical height and the antenna  9  can be disposed on the same plane. Note that the first ground layer  73  and the second ground layer  74  may be disposed independently in the same layer of the substrate  7 . The second ground layer  74  may be disposed on the back side (the rear cover  10  side) of the substrate  7 . 
     Sixth Variation of Embodiment 
     A sixth variation of the embodiment will be described.  FIG.  32    is a sectional view of a main part of a radio wave watch according to the sixth variation of the embodiment. As illustrated in  FIG.  32   , the antenna  9  is disposed to be embedded in the substrate  7 . 
     The ground layer  70  according to the sixth variation has a first ground layer  76  and a second ground layer  77 . The substrate  7  according to the sixth variation is a stacked substrate. For example, the first ground layer  76  is formed in the bottom layer. Here, the bottom layer is the most back-side layer in a stacked direction of the substrate  7 . The substrate  7  has a concave part  7   b  to expose the first ground layer  76 . The antenna  9  is accommodated in the concave part  7   b.    
     The second ground layer  77  is formed on the front surface  7   a  of the substrate  7 . The second ground layer  77  is disposed on the opposite side to the first ground layer  76  across the short-circuit part  92 . In other words, the second ground layer  77  is disposed on the opposite side to the emitting electrode  91  across the short-circuit part  92 . The first ground layer  76  and the second ground layer  77  are electrically connected. The configuration of this variation contributes to thinning of the watch, for example. Note that the second ground layer  77  may be disposed in a middle layer or the bottom layer of the substrate  7 , instead of the front surface  7   a.    
     Seventh Variation of Embodiment 
     A seventh variation of the embodiment will be described.  FIG.  33    is a plan view of an antenna according to the seventh variation of the embodiment. In the emitting electrode  91  according to the seventh variation, the first emitting side  91   a  is formed into a meander shape. The first emitting side  91   a  has continuously formed unevenness. Making the first emitting side  91   a  into the meander shape enables the antenna  9  to be downsized while securing a required antenna length. Note that, in addition to the first emitting side  91   a  or instead of the first emitting side  91   a , the second emitting side  91   b  may be formed into a meander shape. 
     Eighth Variation of Embodiment 
     An eighth variation of the embodiment will be described.  FIG.  34    is a plan view of an antenna according to the eighth variation of the embodiment;  FIG.  35    is a perspective view of the antenna according to the eighth variation of the embodiment;  FIG.  36    is a front view of the antenna according to the eighth variation of the embodiment;  FIG.  37    is a plan view illustrating a placement example of the antenna according to the eighth variation of the embodiment;  FIG.  38    is a plan view illustrating one example of the shape of the solar cell; and  FIG.  39    is a plan view illustrating another placement example of the antenna. In the antenna  9  according to the eighth variation, an intersection angle of the second emitting side  91   b  and the first emitting side  91   a  is different from a right angle. More specifically, the first emitting side  91   a  extends so that an intersection angle θ with the second emitting side  91   b  is an obtuse angle. Such an extension of the first emitting side  91   a  in a slanting direction can lengthen the length of the first emitting side  91   a  as compared with the case where the intersection angle θ is the right angle. As a result, the antenna  9  can be downsized while a required antenna length is secured. The shape of the emitting electrode  91  of the eighth variation is a tapering shape in which its width becomes narrower as it goes from the base end to the tip. Here, the base end side of the emitting electrode  91  is a side where the short-circuit part  95  and the connecting part  96  are connected, i.e., the first side surface  94   c  side, and the tip side of the emitting electrode  91  is the second side surface  94   d  side. 
     To improve the sensitivity of the antenna  9 , it is preferable for the area of the emitting electrode  91  to be increased, for example. In this case, it is conceivable that the base part  94  as a foundation is extended. On the other hand, the substantial wavelength λ is shortened by the wavelength-shortening effect as the frame of the base part  91  becomes larger. As a result, the most suitable length of the first emitting side  91   a  is shortened, and the extension of the area of the emitting electrode  91  is limited. The antenna  9  of the eighth variation can maximize the area of the emitting electrode  91  and the length of the first emitting side  91   a  without excessively increasing the frame of the base part  94 . Note that the first emitting side  91   a  and the second emitting side  91   b  may be formed into a meander shape. In terms of obtaining stable characteristics of the antenna  9 , it is desirable to secure the symmetricity between the inclined, paired first emitting sides  91   a  and  91   a.    
     It is preferable for the width WS 1  (see  FIG.  36   ) of the short-circuit part  95  to be increased in a feasible range, and it is preferable for the width WP of the connecting part  96  to be decreased in a feasible range. As an example, the width WS 1  of the short-circuit part  95  may be greater than the width WP of the connecting part  96 . Increasing the width WS 1  of the short-circuit part  95  enhances, for example, the effect of the sensitivity improvement by the image antenna  9   i . Decreasing the width WP of the connecting part  96  can decrease a width. WN of the electrode  75  of the substrate  7 . Decreasing the width WN of the electrode  75  reduces capacitive coupling of the electrode  75  with another electrode of a circuit of the substrate  7  and other surrounding metal members. As a result, the impedance matching about the antenna  9  is facilitated. 
     For example, the antenna  9  of the eighth variation is disposed as illustrated in  FIG.  37   . The antenna  9  in  FIG.  37    is disposed so that the short-circuit part  95  and the connecting part  96  face inside in the radial direction. That is, the connecting part  96  is opposed to the center axis line X 1  in the radial direction. The base part  94  may be disposed so that the second side surface  94   d  is close to the inner wall surface  21   a . The base part  94  is disposed near the inner wall surface  21   a , so that a space for placing other parts is easily secured in the vicinity of the center axis line X 1 . Furthermore, a space for the image antenna  9   i  is easily secured inside in the radial direction relative to the antenna  9 . 
     In the case where the shape of the emitting electrode  91  is the tapering shape as in the eighth variation, the solar cell  6  may have a shape as illustrated in  FIG.  38   . In the radio wave watch  1  in  FIG.  38   , the solar cell  6  has a notch part  60  at a position opposed to the antenna  9 . The notch part  60  is formed not to overlap with at least the emitting electrode  91  in the axial direction. The notch part  60  has a first side  60   a , second sides  60   b  and  60   c , and inclined sides  60   d  and  60   e.    
     The first side  60   a  is a side parallel to the first side surface  94   c  of the base part  94 . The first side  60   a  is located inside in the radial direction relative to the first side surface  94   c , The second sides  60   b  and  60   c  are sides extending along end surfaces  94   f  and  94   g  of the base part  94 . The second sides  60   b  and  60   c  are substantially parallel to the end surfaces  94   f  and  94   g . The inclined sides  60   d  and  60   e  link the first side  60   a  to the second sides  60   b  and  60   c , The inclined sides  60   d  and  60   e  extend in a direction inclined relative to the first side  60   a  and the second sides  60   b  and  60   c . For example, the inclined sides  60   d  and  60   e  extend along the radial direction from the center axis line X 1 . 
     In planar view, the second sides  60   b  and  60   c  are opposed to the first emitting side  91   a  of the emitting electrode  91 . The second sides  60   b  and  60   c  extend in a direction intersecting with the first emitting side  91   a . More specifically, in planar view, the second sides  60   b  and  60   c  are separated from the first emitting side  91   a  as they go outside in the radial direction. The second sides  60   b  and  60   c  extend in the direction intersecting with the first emitting side  91   a , so that currents flowing the second sides  60   b  and  60   c  are unlikely to cause the drop in the sensitivity of the emitting electrode  91 . Thus, the solar cell  6  of the eighth variation can achieve maximizing the solar cell  6  while reducing the drop in the sensitivity of the antenna  9 . 
     Note that the antenna  9  may be disposed as illustrated in  FIG.  39   . The antenna  9  illustrated in FIG.  39  is disposed so that the short-circuit part  95  and the connecting part  96  face outside in the radial direction. That is, the connecting part  96  is opposed to the inner wall surface  21   a  of the exterior case  2  in the radial direction. This placement can increase the distance between the first emitting side  91   a  of the emitting electrode  91  and the inner wall surface  21   a.    
     Ninth Variation of Embodiment 
     A ninth variation of the embodiment will be described.  FIG.  40    is a plan view illustrating a placement of a motor according to the ninth variation of the embodiment. In the radio wave watch  1  according to the ninth variation, a part of a motor  11  is disposed at a position opposed to the short-circuit part  95  in the radial direction. The motor  11  is an electromagnetic motor, and has a housing  11   a , a coil  11   b , and a rotor  11   c . The motor  11  rotates the rotor  11   c  with an induced electromotive force that is generated by powering the coil  11   b . For example, the motor  11  is installed in the radio wave watch  1  as a drive source rotating the hand. The motor  11  is disposed so that the rotor  11   c  is located on the opposite side to the antenna  9  side relative to the coil  11   b.    
     More specifically, the antenna  9  of the ninth variation is disposed so that the short-circuit part  95  faces inside in the radial direction. The motor  11  is disposed inside in the radial direction relative to the antenna  9 . The motor  11  is disposed so that the rotor  11   c  is located inside in the radial direction relative to the coil  11   b . The coil  11   b  thus extends between the rotor  11   c  and the antenna  9 . The radio wave watch  1  has a magnetic shield  17 . In planar view, the magnetic shield  17  covers the rotor  11   c . That is, the magnetic shield  17  shields the rotor  11   c  in the axial direction. The magnetic shield  17  of this variation is disposed to cover the rotor  11   c  and not to cover the antenna  9 . 
     As in the ninth variation, the rotor  11   c  of the motor  11  is disposed apart from the antenna  9 , so that the magnetic shield  17  can be disposed at a position with few influence on the emitting electrode  91 . As a result, the magnetic shield  17  is unlikely to cause the drop in the sensitivity of the antenna  9 . Thus, the placement of the ninth variation achieves downsizing by disposing the motor  11  in the vicinity of the antenna  9  while reducing the drop in the sensitivity of the antenna  9  as far as possible. 
     Tenth Variation of Embodiment 
     A tenth variation of the embodiment will be described.  FIG.  41    is a plan view of a ground layer according to the tenth variation of the embodiment, and  FIG.  42    is a plan view illustrating a condition where devices are disposed on the substrate according to the tenth variation of the embodiment. The ground layer  70  is only required to be disposed in the region where the image antenna  9   i  is formed, and the shape and placement of the ground layer  70  are not limited to the shape and placement illustrated in the embodiment and other variations. The ground layer  70  according to the tenth variation is formed over the almost whole of the substrate  7  except a region required for wiring. 
     As illustrated in  FIG.  41   , the substrate  7  has wirings  78 ,  79 , and  80 . The wirings  78 ,  79 , and  80  are conductive films formed on the substrate  7 . The wiring  78  connects the connecting part  93  and the connecting part  96  of the antenna  9  to the receiving circuit  15 . The wiring  79  connects the control circuit  14  to the drive source  56 . Note that, in  FIG.  42   , the illustration of the wirings  79  and  80  is omitted. The wiring  80  connects between other various circuits  57  (see  FIG.  42   ) disposed on the substrate  7 . The various circuits  57  include, for example, an oscillator circuit. The ground layer  70  is formed over the almost whole of the substrate  7  to surround these wirings  78 ,  79 , and  80 . The ground layer  70  may be individually disposed on a plurality of layers of the substrate  7 . For example, the ground layer  70  is stacked and disposed on the layers including the front surface  7   a  of the substrate  7 . Disposing the ground layer  70  having a large area in this way enables the reception sensitivity of the antenna  9  to be further improved. 
     Eleventh Variation of Embodiment 
     An eleventh variation of the embodiment will be described. The data included in a radio wave that the radio wave watch  1  transmits and receives is not limited to data including time information for correcting time. The data included in the radio wave to be transmitted and received may be a data signal, such as control program data and measurement data. 
     The contents disclosed in the embodiment and variations described above can be performed in combination as necessary. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  radio wave watch 
               2  exterior case 
               3  windshield 
               4  dial plate 
               5  hand 
               6  solar cell 
               6   a  end surface 
               6   b  notch part 
               6   c  opening part 
               6   d  projecting part 
               7  substrate 
               7   a  front surface 
               8  battery 
               9  antenna 
               10  rear cover 
               11  motor 
               12  cover 
               13  date plate 
               14  control circuit 
               15  receiving circuit 
               16  mounted object 
               17  magnetic shield 
               21  body part 
               21   a  inner wall surface 
               22  lug 
               23  accommodating space 
               51  second hand. 
               52  minute hand. 
               53  hour hand 
               54  wheel train 
               55  rotation shaft 
               56  drive source 
               60  notch part 
               70  ground layer 
               70   a  first side 
               70   b  second side 
               70   c  third side 
               70   d  fourth side 
               70   p  foot of perpendicular line 
               70 X extension part 
               71  first region (first ground layer) 
               72  second region (second ground layer) 
               73 ,  76  first ground layer 
               74 ,  77  second ground layer 
               75  electrode 
               78 ,  79 ,  80  wiring 
               91  emitting electrode 
               91   a  first emitting side 
               91   b  second emitting side 
               92 ,  95  short-circuit part 
               93 ,  96  connecting part 
               94  base part 
               94   a  front surface 
               94   b  back surface 
               94   c  first side surface 
               94   d  second side surface 
               94   e  foot of perpendicular line 
             LE length of emitting electrode 
             LG 1  length of first region 
             LG 2  length of second region 
             S 1 , S 2  virtual plane 
             WG width of ground layer 
             WE width of emitting electrode 
             WB width of base part 
             WP width of connecting part 
             WS, WS 1  width of short-circuit part 
             X 1  center axis line