Patent Publication Number: US-11024941-B2

Title: Window glass for vehicle and antenna

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
     The present application is based on and claims priority under 35 U.S.C. § 119 of Japanese applications No. 2018-022010 filed Feb. 9, 2018, and No. 2018-216002 filed Nov. 16, 2018. The contents of the applications are incorporated herein by reference in their entirety. 
     FIELD OF INVENTION 
     The disclosure herein generally relates to a window glass for a vehicle and an antenna. 
     BACKGROUND 
     Conventionally, an antenna, in which an antenna element and an internal electrode connected to the antenna element are arranged between two glass plates, and an external electrode opposite to the internal electrode is arranged on a surface of the glass plate, has been known (See, for example, Japanese Unexamined Patent Application Publication No. 2011-114404). In the antenna, a reception signal from the antenna element arranged between the two glass plates is extracted from the external electrode via a capacitance coupling between the internal electrode and the external electrode. 
     However, in the case of receiving electromagnetic waves in a frequency band of AM (amplitude modulation) broadcasting where the frequency is relatively low by the antenna element between the two glass plates, and extracting a signal, which is obtained by receiving, from the external electrode via the capacitance coupling, a coupling loss in the capacitance coupling is large, and a sufficient receiving sensitivity may not be obtained. 
     SUMMARY 
     The embodiments of the present application provide a window glass for a vehicle and an antenna, with which a sufficient receiving sensitivity can be obtained, in the case of extracting a signal obtained by receiving an electromagnetic wave in the frequency band of the AM broadcasting via a capacitance coupling. 
     In some embodiments, a window glass for a vehicle includes 
     a glass plate; 
     a dielectric having a first surface on a side facing the glass plate, and a second surface on a side opposite to the first surface; 
     a first electrode arranged between the glass plate and the first surface of the dielectric; 
     a second electrode arranged on a second surface side of the dielectric such that the dielectric is interposed between the first electrode and the second electrode; and 
     an antenna element arranged between the glass plate and the first surface of the dielectric, and connected to the first electrode, 
     the antenna element receiving at least an electromagnetic wave in a frequency band of amplitude modulation (AM) broadcasting, and 
     when a coupling capacitance between the first electrode and the second electrode is denoted by C c , an antenna capacitance of the antenna element is denoted by C a , an input capacitance of an amplifier connected to the second electrode is denoted by C i , a voltage value, which is lower by x decibels than a voltage value output from the second electrode when the coupling capacitance C c  is infinity is denoted by v xdB , and a reception voltage value of the antenna element is denoted by v a , 
     a value of x being 3.0 or less, and 
     the coupling capacitance C c  satisfying formula 1: 
     
       
         
           
             
               
                 
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     In some embodiments, an antenna includes 
     a dielectric having a first surface, and a second surface on a side opposite to the first surface; 
     a first electrode arranged on a first surface side of the dielectric or inside the dielectric; 
     a second electrode arranged on a second surface side of the dielectric such that at least a part of the dielectric is interposed between the first electrode and the second electrode; and 
     an antenna element arranged on the first surface side of the dielectric or inside the dielectric, and connected to the first electrode, 
     the antenna element receiving at least an electromagnetic wave in a frequency band of amplitude modulation (AM) broadcasting, and 
     when a coupling capacitance between the first electrode and the second electrode is denoted by C c , an antenna capacitance of the antenna element is denoted by C a  an input capacitance of an amplifier connected to the second electrode is denoted by C i , a voltage value, which is lower than a voltage value output from the second electrode by x decibels when the coupling capacitance C c  is infinity is denoted by v xdB , and a reception voltage value of the antenna element is denoted by v a , 
     a value of x being 3.0 or less, and 
     the coupling capacitance C c  satisfying formula 1: 
     
       
         
           
             
               
                 
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     With the antenna or the window glass for a vehicle described herein, in the case of extracting a signal obtained by receiving an electromagnetic wave in the frequency band of the AM broadcasting via a capacitance coupling, a sufficient receiving sensitivity can be obtained. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings, in which: 
         FIG. 1  is an exploded perspective view depicting an example of a configuration of a window glass for a vehicle according to a first embodiment; 
         FIG. 2  is a cross-sectional view depicting an example of a configuration of a window glass for a vehicle according to the first embodiment; 
         FIG. 3  is a cross sectional view depicting an example of a configuration of a window glass for a vehicle according to a second embodiment; 
         FIG. 4  is a cross sectional view depicting an example of a configuration of a window glass for a vehicle according to a third embodiment; 
         FIG. 5  is a cross sectional view depicting an example of a configuration of a window glass for a vehicle according to a fourth embodiment; 
         FIG. 6  is a cross sectional view depicting an example of a configuration of a window glass for a vehicle according to a fifth embodiment; 
         FIG. 7  is a cross sectional view depicting an example of a configuration of a window glass for a vehicle according to a sixth embodiment; 
         FIG. 8  is a diagram depicting an example of an equivalent circuit from an antenna to an amplifier; 
         FIG. 9  is a diagram showing an example of a result of simulation measuring a relation between an input capacitance of the amplifier and the coupling capacitance, where a coupling loss is 3.0 dB; 
         FIG. 10  is a diagram showing an example of a result of simulation measuring a relation between the input capacitance of the amplifier and the coupling capacitance, where the coupling loss is 2.0 dB; 
         FIG. 11  is a diagram showing an example of a result of simulation measuring a relation between the input capacitance of the amplifier and the coupling capacitance, where the coupling loss is 1.0 dB; 
         FIG. 12  is a diagram showing an example of a result of simulation measuring a relation between the input capacitance of the amplifier and the coupling capacitance, where the coupling loss is 0.5 dB; 
         FIG. 13  is a diagram illustrating a mode in which two electrodes of a capacitance coupling portion overlap with each other, in a planar view; and 
         FIG. 14  is a diagram depicting an example of a result of simulation for dimensions of respective parts for each shape of the electrode, where the coupling capacitance C c  is 54 pF. 
     
    
    
     DETAILED DESCRIPTION 
     In the following, with reference to drawings, embodiments for implementing the present invention will be described. Note that in each embodiment, a direction, such as parallel, a right angle, orthogonal, horizontal, vertical, up-down, right-left, or the like, allows a deviation enough to keep the effect of the present invention. Moreover, a shape of a corner portion of an antenna element is not limited to a right angle, but may be arcuate and rounded. Moreover, as a window glass for a vehicle, to which the present invention can be applied, a rear glass installed in a rear part of a vehicle is preferable. However, the window glass for a vehicle to which the present invention can be applied may be, for example, a front windshield installed in a front part of the vehicle, a side glass installed in a side part of the vehicle, or a roof glass installed in a ceiling part of the vehicle. 
     Moreover, in each mode, a direction parallel to an X-axis (X-axis direction), a direction parallel to a Y-axis (Y-axis direction), and a direction parallel to a Z-axis (Z-axis direction) indicate the right-left direction of the glass plate (horizontal direction), the up-down direction of the glass plate (vertical direction), and a direction orthogonal to a surface of the glass plate (also referred to as a normal direction), respectively. The X-axis direction, the Y-axis direction and the Z-axis direction are orthogonal to each other. 
       FIG. 1  is an exploded perspective view depicting an example of a configuration of a window glass for a vehicle according to a first embodiment. In  FIG. 1 , a positive side in the Z-axis direction represents a vehicle exterior side, and a negative side in the Z-axis direction represents a vehicle interior side. A window glass  100  has a structure of laminated glass, in which a glass plate  10  arranged on the vehicle exterior side and a glass plate  20  arranged on the vehicle interior side are bonded to each other via an intermediate film  40 .  FIG. 1  illustrates elements of the window glass  100  being separated in a normal direction to a surface of the glass plate  10  or the glass plate  20 . 
     The window glass  100  includes the glass plate  10  arranged on the vehicle exterior side; the glass plate  20  arranged on the vehicle interior side; an interior electrode  31  and an antenna element  71  arranged inside the laminated glass; and an exterior electrode  32  arranged on a vehicle interior side outer surface of the laminated glass. 
     The glass plate  10  and the glass plate  20  are transparent plate-like dielectrics. Any one of or both the glass plate  10  and the glass plate  20  may be translucent. The glass plate  10  is an example of a first glass plate, and the glass plate  20  is an example of a second glass plate. 
     The glass plate  10  has a plate face  11 , and a plate face  12  on a side opposite to the plate face  11  in the Z-axis direction. The plate face  11  represents a surface of the glass plate  10  on the vehicle interior side, and the plate face  12  represents a surface of the glass plate  10  on the vehicle exterior side. Particularly, the plate face  12  corresponds to a vehicle exterior side outer surface of the laminated glass. 
     The glass plate  20  has a plate face  21  on a side facing the plate face  11  of the glass plate  10 , and a plate face  22  on a side opposite to the plate face  21  in the Z-axis direction. The plate face  21  represents a surface of the glass plate  20  on the vehicle exterior side. The plate face  22  represents a surface of the glass plate  20  on the vehicle interior side. Particularly, the plate face  22  corresponds to a vehicle interior side outer surface of the laminated glass. 
     The intermediate film  40  is a transparent or translucent dielectric intervening between the glass plate  10  and the glass plate  20 . The glass plate  10  and the glass plate  20  are bonded to each other by the intermediate film  40 . A material configuring the intermediate film  40  includes, for example, thermoplastic polyvinylbutyral. Note that a dielectric constant of the intermediate film  40  is preferably 2.8 or more and 3.5 or less. 
     The internal electrode  31  is a conductor arranged between the plate face  11  of the glass plate  10  and the plate face  21  of the glass plate  20 . The internal electrode  31  is an example of a first electrode. The internal electrode  31  according to the embodiment has a linear portion having a predetermined width with a longitudinal direction directed in the X-axis direction, which will be a vehicle width direction, and extends from one side edge of the glass plate  20  toward the other side edge, along an upper edge in the Y-axis direction of the glass plate  20 . Moreover, in the embodiment, the internal electrode  31  is formed contacting the plate face  21  of the glass plate  20 . 
     The external electrode  32  is a conductor arranged on the plate face  22  side of the glass plate  20  such that the glass plate  20  that is a dielectric is interposed between the internal electrode  31  and the external electrode  32 . The external electrode  32  is an example of a second electrode. The external electrode  32  has a linear portion having a predetermined width with a longitudinal direction directed in the X-axis direction, which will be the vehicle width direction, and extends from one side edge of the glass plate  20  toward the other side edge, along the upper edge in the Y-axis direction of the glass plate  20 . Moreover, in the embodiment, the external electrode  32  is formed contacting the plate face  22  of the glass plate  20 . Note that a mode of “extending along an upper edge” may be a mode of contacting the upper edge, or may be a mode of separating from the upper edge. 
     The antenna element  71  is a conductor arranged between the plate face  11  of the glass plate  10  and the plate face  21  of the glass plate  20 , and connected to the internal electrode  31 . The antenna element  71  is designed, i.e. a shape and a dimension thereof are determined, so as to receive at least an electromagnetic wave in a frequency band of amplitude modulation (AM) broadcasting (e.g. within a band from 500 kHz to 1800 kHz). However, as long as the antenna element  71  is formed so as to receive at least an electromagnetic wave in the frequency band of the AM broadcasting (500 kHz to 1800 kHz), the shape and the dimension thereof are not limited to those illustrated in  FIG. 1 . 
     For example, the antenna element  71  may be formed suitable for receiving an electromagnetic wave in a medium frequency (MF) band that includes the frequency band of the AM (amplitude modulation) broadcasting. Alternatively, the antenna element  71  may be formed as a shared antenna element that receives electromagnetic waves both in the MF band and in a high frequency (HF) band. Note that the MF band means a frequency band of 300 kHz or more and 3 MHz or less. The HF band means a frequency band of 3 MHz or more and 30 MHz or less, and is also referred to as a short wave (SW) band. Moreover, the antenna element  71  may be formed as a shared antenna element that receives at least one of the electromagnetic wave in the MF band, an FM (frequency modulation) broadcasting wave, a DAB (Digital Audio Broadcast) wave, and a terrestrial digital television broadcast wave. 
       FIG. 1  is a diagram depicting an example of a mode in which the antenna element  71  is formed on a conductive film  50  arranged between the glass plate  10  and the glass plate  20 . In the embodiment illustrated in  FIG. 1 , the conductive film  50  is a transparent or translucent conductor arranged between the intermediate film  40  and the glass plate  20 , and may be, for example, a metallic film such as an Ag film, a metal oxide film such as an ITO (indium tin oxide) film, a resin film containing conductive fine particles, or a stacked film stacking a plurality of types of films. The conductive film  50  may be coated on a resin film made of polyethylene terephthalate or the like by a vapor deposition process or the like. 
     In the embodiment illustrated in  FIG. 1 , the conductive film  50  around the conductor that will become the antenna element  71  is removed. Thus, the conductor that will become the antenna element  71  is left as the conductive film  50 , and the antenna element  71  is formed of the conductive film  50 . That is, in the embodiment illustrated in  FIG. 1 , the conductive film  50  includes the antenna element  71 . A lattice part  56  is a region in which an electric resistance is increased by removing the conductive film  50  around the conductor that will become the antenna element  71 . 
     On the conductive film  50 , for example, a heater  55  is formed. The heater  55  heats the window glass  100  when a direct current voltage is applied between the pair of bus bars  51  and  52 , and snow melting, ice melting and defogging by the window glass  100  becomes possible. For example, the bus bar  51  is connected to a negative electrode of the direct current power source via a flat wire  53 , and the bus bar  52  is connected to a positive electrode of the direct current power source via a flat wire  54 . Alternatively, the conductive film  50  may be a heat-ray reflecting film that reflects a heat ray entering from outside the vehicle. However, the usage of the conductive film  50  is not limited to this. 
     On the conductive film  50 , at least one antenna element other than the antenna element  71  may be formed. For example,  FIG. 1  depicts antenna elements  72  and  73  in addition to the antenna element  71 . That is, in the embodiment, illustrated in  FIG. 1 , the conductive film  50  includes the antenna elements  72  and  73 . The antenna elements  72  and  73  are formed so as to receive an electromagnetic wave of a frequency band with a frequency higher than that of the HF band, respectively. The electromagnetic wave of the frequency band with a frequency higher than that of the HF band, includes, for example, a terrestrial digital television broadcast wave, a DAB (Digital Audio Broadcast) wave, or an FM (frequency modulation) broadcasting wave. 
     In the embodiment, illustrated in  FIG. 1 , the antenna element  71  is connected to the internal electrode  31 , and the antenna element  72  is connected to the internal electrode  34 , and the antenna element  73  is connected to the internal electrode  36 . The internal electrodes  31 ,  34  and  36  may be portions formed of the conductive film  50 . In this case, the conductive film  50  includes the internal electrodes  31 ,  34  and  36 . However, at least one of the internal electrodes  31 ,  34  and  36  may be a portion formed of a conductor that is different from the conductive film  50 . Similarly, in the embodiment, illustrated in  FIG. 1 , the antenna elements  71 ,  72 , and  73  are portions formed of the conductive film  50 , respectively. However, at least one of the antenna elements  71 ,  72  and  73 , may be a portion formed of a conductor that is different from the conductive film  50 . 
     As the aforementioned conductor that is different from the conductive film  50 , for example, at least one of the antenna elements  71 ,  72  and  73  may be formed by printing a paste including conductive metal (e.g. silver paste) on a plate surface  21  of the glass plate  20  (or a plate surface  11  of the glass plate  10 ), and baking the paste. The same applies to any of the internal electrodes  31 ,  34  and  36 . Alternatively, at least one of the antenna elements  71 ,  72  and  73  may be formed of a wire enclosed between the glass plate  20  and the glass plate  10 . 
     At least a part of the internal electrode  31 , to which the antenna element  71  is connected, faces the external electrode  32  via the glass plate  20 . To the external electrode  32 , a first input part of an amplifier  60  is connected. Then, a signal obtained by being received at the antenna element  71  is input to the first input part of the amplifier  60  via a capacitive coupling between the internal electrode  31  and the external electrode  32 . 
     Similarly, at least a part of the internal electrode  34 , to which the antenna element  72  is connected, faces the external electrode  33  via the glass plate  20 . To the external electrode  33 , a second input part of the amplifier  60  is connected. Then, a signal obtained by being received at the antenna element  72  is input to the second input part of the amplifier  60  via a capacitive coupling between the internal electrode  34  and the external electrode  33 . 
     Similarly, at least a part of the internal electrode  36 , to which the antenna element  73  is connected, faces the external electrode  35  via the glass plate  20 . To the external electrode  35 , an input part of an amplifier  61  is connected. Then, a signal obtained by being received at the antenna element  73  is input to the input part of the amplifier  61  via a capacitive coupling between the internal electrode  36  and the external electrode  35 . 
     Moreover, the glass plate  10  may be provided with a light shielding film  13  that shields visible light. The light shielding film  13  is arranged on an external peripheral portion of the glass plate  10 . The light shielding film  13  overlaps with at least one of the internal electrode  31  and the external electrode  32  in the thickness direction of the glass plate  10 . Specifically, the light shielding film  13  includes a ceramic film such as a black ceramic film. In the case where, among the internal electrode, the external electrode, the antenna element and the bus bar, there is a part overlapping with the light shielding film  13  in a planar view of the glass plate  10 , when the window glass  100  is viewed from outside the vehicle, it is difficult to visually recognize the overlapping part. Thus, the design property of the window glass  100  and the vehicle is enhanced. Particularly, as described later, because the internal electrode  31  and the external electrode  32  have relatively large areas, the light shielding film  13  only need to overlap with at least one of the internal electrode  31  and the external electrode  32 , preferably overlaps with an electrode having a large area of the internal electrode  31  and the external electrode  32 , and more preferably overlaps with both the internal electrode  31  and the external electrode  32 . The electrode having a larger area from among the internal electrode  31  and the external electrode  32  only needs to have an area of 1675 mm 2  or more, preferably 1682 mm 2  or more, more preferably 1705 mm 2  or more, and further preferably 1863 mm 2  or more. 
       FIGS. 2 to 7  depict a variation of the mode of lamination of the window glass for a vehicle on which the antenna  70  according to the embodiment is arranged.  FIG. 2  corresponds to a cross-sectional view of the configuration illustrated in  FIG. 1 . 
     In  FIGS. 2 to 4 , the antenna element  71  and the internal electrode  31  are arranged between the glass plate  10  and the glass plate  20 . The internal electrode  31  and the external electrode  32  are arranged so as to overlap with each other via the glass plate  20 , in a planar view in the thickness direction of the glass plate  20  (Z-axis direction). Moreover, the antenna element  71  and the internal electrode  31  contact an intermediate film  40  arranged between the glass plate  10  and the glass plate  20 . 
     A value of a ratio of areas where the internal electrode  31  and the external electrode  32  overlap with each other (“ratio S” which will be described later) is preferably large, because an exposure (extrusion) of electrode from the overlapping part can be made smaller, it becomes easier to cause the electrodes to overlap with the light shielding film  13 , and it becomes easier to reduce a coupling loss. According to a result of simulations, which will be described later, under a condition where the electrodes have predetermined areas, the ratio of an area of the overlapping part to a larger area from among areas of the internal electrode  31  and the external electrode  32  (“ratio S”, expressed as a percentage where said larger area=100%, which will be further described later) is preferably 1.5% or more, in order to reduce the coupling loss. Moreover, in addition to the reduction of the coupling loss between the internal electrode  31  and the external electrode  32 , in order to reduce the exposure (extrusion) of electrode, as described above, the ratio of overlap (“ratio S” which will be described later) is preferably 10% or more, more preferably 40% or more, and further preferably 70% or more. 
       FIG. 2  is a diagram depicting a configuration in which the antenna element  71  and the internal electrode  31  are formed on a plate surface  21  of the glass plate  20 . For example, the antenna element  71  and the internal electrode  31  are formed as a conductive film coated on the plate surface  21  by performing a deposition process on the plate surface  21  of the glass plate  20 . 
       FIG. 3  is a diagram depicting a configuration in which the antenna element  71  and the internal electrode  31  are formed on a plate surface  11  of the glass plate  10 . For example, the antenna element  71  and the internal electrode  31  are formed as a conductive film coated on the plate surface  11  by performing a deposition process on the plate surface  11  of the glass plate  10 . As illustrated in  FIG. 3 , between the internal electrode  31  and the external electrode  32 , in addition to the glass  20 , the intermediate film  40  may be present. 
       FIG. 4  is a diagram depicting a configuration in which the antenna element  71  and the internal electrode  31  are located between an intermediate film  41  and an intermediate film  42 . The intermediate film  41  is an example of a first layer included in the intermediate film  40 , and the intermediate film  42  is an example of a second layer included in the intermediate film  40 . For example, the antenna element  71  and the internal electrode  31  are formed in a conductive film interposed between the intermediate film  41  contacting the plate surface  11  of the glass plate  10 , and the intermediate film  42  contacting the plate surface  21  of the glass plate  20 . As illustrated in  FIG. 4 , between the internal electrode  31  and the external electrode  32 , in addition to the glass plate  20 , the intermediate film  42  may be present. 
     Moreover, as illustrated in  FIGS. 5 to 7 , the window glass for a vehicle according to the disclosure is not limited to a laminated glass. In this case, a dielectric, present between the internal electrode  31  and the external electrode  32 , may not have the same size as the glass plate  10  in a planar view in the thickness direction (Z-axis direction), and may be a dielectric substrate or a dielectric film having a size, at least, enough to form the external electrode  32 . 
     In  FIGS. 5 to 7 , the antenna element  71  and the internal electrode  31  are arranged between the glass plate  10  and a dielectric substrate  23 . The internal electrode  31  and the external electrode  32  are arranged so as to overlap with each other via the dielectric substrate  23 , in a planar view in the thickness direction (Z-axis direction) of the dielectric substrate  23 . The dielectric substrate  23  is, for example, a printed substrate made of resin (e.g. a glass epoxy substrate in which a copper foil adheres to an FR4 (Flame Retardant Type 4)). The dielectric substrate  23  may be replaced by a dielectric film. 
       FIG. 5  is a diagram depicting an example of a configuration in which the antenna element  71  and the internal electrode  31  are formed on the plate surface  11  of the glass plate  10 . For example, the antenna element  71  and the internal electrode  31  are formed as a conductive film coated on the plate surface  11  by performing a deposition process on the plate surface  11  of the glass plate  10 . The external electrode  32  is provided on the plate surface  22  of the dielectric substrate  23 . The dielectric substrate  23  is bonded to the conductive film, in which the antenna element  71  and the internal electrode  31  are formed, via a bonding layer  43 , so that the external electrode  32  faces the internal electrode  31 . 
       FIG. 6  is a diagram depicting another example of the configuration in which antenna element  71  and the internal electrode  31  are formed on the plate surface  11  of the glass plate  10 . For example, the conductive film, in which the antenna element  71  and the internal electrode  31  are formed, is bonded to the plate surface  11  via a bonding layer  43   a . The external electrode  32  is provided on the plate surface  22  of the dielectric substrate  23 . The dielectric substrate  23  is bonded to the conductive film in which the antenna element  71  and the internal electrode  31  are formed, via a bonding layer  43   b , so that the external electrode  32  faces the internal electrode  31 . 
       FIG. 7  is a diagram depicting an example of a configuration in which the dielectric substrate  23  that is a component of the antenna  70  is bonded to the plate surface  11  of the glass plate  10  via the bonding layer  43 . The antenna  70  is provided with the dielectric substrate  23  on which the antenna element  71 , the internal electrode  31  and the external electrode  32  are formed. For example, the dielectric substrate  23  includes the plate surface  22  on which the external electrode  32  is formed so that at least a part of a dielectric portion is interposed between the plate surface  21  on which the antenna element  71  and the internal electrode  31  are formed, and the internal electrode  31 . At least one of the antenna element  71  and the internal electrode  31  may be provided in a form of being embedded inside the dielectric substrate  23 . 
     In this way, in the antenna  70  and the window glass  100  according to the embodiment, at least a part of the internal electrode  31 , to which the antenna element  71  is connected, faces the external electrode  32  via a dielectric (a glass plate or a dielectric substrate). Then, a signal obtained by being received at the antenna element  71  is extracted from the external electrode  32  via a capacitive coupling between the internal electrode  31  and the external electrode  32 . The signal extracted from the external electrode  32  is transferred to a (first) inputting part of an amplifier  60  (See  FIG. 1 ) via a conductive member that is connected enabling conduction with the external electrode  32 . The conductive member includes specifically a feeder wire such as an AV wire or a coaxial cable. 
     A coaxial cable is employed as the feeder wire, a core wire of the coaxial cable (internal conductor) is connected to the external electrode  32 , and an external conductor of the coaxial cable is connected to the ground such as a vehicle body. Moreover, a connector for connecting the amplifier  60  to the external electrode  32  may be used. The connector is, for example, mounted on the external electrode  32 . Alternatively, the amplifier  60  may be implemented in the connector. 
     In this way, the signal obtained by being received at the antenna element  71  is extracted from the external electrode  32  via the capacitive coupling between the internal electrode  31  and the external electrode  32 . The (first) input part of the amplifier  60  is connected to the external electrode  32  directly or indirectly. The amplifier  60  amplifies the signal extracted from the external electrode  32 , and outputs the amplified signal to a signal processing circuit (not shown) mounted on the vehicle. 
     An equivalent circuit from the antenna element  71  to the amplifier  60  can be expressed by a circuit illustrated in  FIG. 8 . In  FIG. 8 , the coupling capacitance between the internal electrode  31  and the external electrode  32  is denoted by C c , an antenna capacitance of the antenna element  71  is denoted by C a  and an input capacitance of the amplifier  60  connected to the external electrode  32  is denoted by C i . Moreover, an electric voltage value, which is lower than a voltage value V output from the external electrode  32 , when the coupling capacitance is infinity, by x decibels, is denoted by v xdB , and a reception voltage value of the antenna element  71  is denoted by v a . Note that x is 3.0 or less. At this time, when the coupling capacitance C c  satisfies the following formula 1, a coupling loss in the coupling capacitance between the internal electrode  31  and the external electrode  32  is x decibels or less. 
     
       
         
           
             
               
                 
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     Ca represents a capacitance between the antenna element  71  and the ground such as a vehicle body. C i  represents an input capacitance between the input part of the amplifier  60  and the ground such as a vehicle body. “When the coupling capacitance C c  is infinity” means that the internal electrode  31  and the external electrode  32  are directly connected to each other via a conductor, without the capacitive coupling. That is, it represents a state where the coupling loss in the coupling capacitance between the internal electrode  31  and the external electrode  32  is zero. In the following, “the coupling loss in the coupling capacitance between the internal electrode  31  and the external electrode  32 ” will be also referred to simply as a “coupling loss”. 
     The state where the coupling capacitance C c  is infinity is an ideal state in which a coupling loss is absent in the capacitive coupling. Because the coupling loss in the coupling capacitance is smaller in accordance with the coupling capacitance C c  being larger, a divided voltage applied to the input capacitance C i  (voltage input to the amplifier  60 ) can be prevented from decreasing due to the coupling loss. Thus, when the coupling capacitance C c  is set so as to satisfy the formula 1, a voltage input to the amplifier  60  can be prevented from decreasing due to the coupling loss. Thus, in the case of extracting, via a capacitive coupling, a signal obtained by receiving an electromagnetic wave in the frequency band of the AM broadcasting, an electric voltage input to the amplifier  60  is secured, and a sufficient receiving sensitivity is obtained in the amplifier  60 . Note that regarding the coupling loss of x decibels, the value of x is preferably 2.0 or less, more preferably 1.0 or less, and further preferably 0.5 or less. 
       FIG. 9  is a diagram showing an example of a result of a simulation measuring a relation between an input capacitance C i  of the amplifier  60  and the coupling capacitance C c , where the coupling loss is 3.0 dB.  FIG. 10  is a diagram showing an example of a result of simulation measuring a relation between an input capacitance C i  of the amplifier  60  and the coupling capacitance C c , where the coupling loss is 2.0 dB.  FIG. 11  is a diagram showing an example of a result of simulation measuring a relation between an input capacitance C i  of the amplifier  60  and the coupling capacitance C c , where the coupling loss is 1.0 dB.  FIG. 12  is a diagram showing an example of a result of simulation measuring a relation between an input capacitance C i  of the amplifier  60  and the coupling capacitance C c , where the coupling loss is 0.5 dB. Curves shown in  FIGS. 9 to 12  are expressed by the following formula 2. 
     
       
         
           
             
               
                 
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     A curve shown in  FIG. 9  indicates the case where x=3.0 for v xdB , a curve shown in  FIG. 10  indicates the case where x=2.0 for v xdB , a curve shown in  FIG. 11  indicates the case where x=1.0 for v xdB , and a curve shown in  FIG. 12  indicates the case where x=0.5 for v xdB . Because typically an antenna capacitance of an antenna element for receiving AM broadcasting wave falls within a range from 20 pF to 80 pF, the antenna capacitance C a  in  FIGS. 9 to 12  is set to the minimum value of the range (i.e. 20 pF). Moreover, typically an input capacitance of an amplifier falls within a range from 10 pF to 80 pF. 
     Thus, as illustrated in  FIG. 9 , for example, in the case of using an amplifier  60  with an input capacitance C i  of 10 pF, by designing the antenna so that the coupling capacitance C c  is 16.2 pF or more, the coupling loss can be made 3.0 dB or less, and the receiving sensitivity of the amplifier  60  can be enhanced. Moreover, as illustrated in  FIG. 10 , for example, in the case of using an amplifier  60  with an input capacitance C i  of 10 pF, by designing the antenna so that the coupling capacitance C c  is 25.7 pF or more, the coupling loss can be made 2.0 dB or less, and the receiving sensitivity of the amplifier  60  can be enhanced. Moreover, as illustrated in  FIG. 11 , for example, in the case of using an amplifier  60  with an input capacitance C i  of 10 pF, by designing the antenna so that the coupling capacitance C c  is 54.6 pF or more, the coupling loss can be made 1.0 dB or less, and the receiving sensitivity of the amplifier  60  can be enhanced. Moreover, as illustrated in  FIG. 12 , for example, in the case of using an amplifier  60  with an input capacitance C i  of 10 pF, by designing the antenna so that the coupling capacitance C c  is 112.5 pF or more, the coupling loss can be made 0.5 dB or less, and the receiving sensitivity of the amplifier  60  can be enhanced. 
     In a planar view in the thickness direction of the dielectric, the coupling capacitance C c  is larger in accordance with an area where the internal electrode  31  and the external electrode  32  overlap with each other (in the following, also referred to as an “overlapping area A”) being larger. Thus, the overlapping area A is preferably larger in reducing the coupling loss. However, when an upper limit of the overlapping area A is calculated taking into account an upper limit of an area of the glass plate or the dielectric substrate, an upper limit of the coupling capacitance C c  is about 3500 pF. 
       FIG. 13  is a diagram depicting a configuration in which two electrodes of the capacitive coupling part overlap with each other in the planar view. In  FIG. 13 , an electrode among the internal electrode  31  and the external electrode  32  having a larger area is set to an electrode  1 , and an electrode having a smaller area is set to an electrode  2 .  FIG. 14  is a diagram depicting an example of a result of simulation for dimensions of respective parts for each shape of the electrode, where the coupling capacitance C c  is 54 pF. When the coupling capacitance C c  is 54 pF or more, as described above, the coupling loss can be made about 1 dB or less.  FIG. 14  shows three cases: the electrodes  1  and  2 , illustrated in  FIG. 13 , having rectangular shapes (pattern # 1  and pattern # 2 ) and having square shapes (pattern # 3 ). As assumptions of the simulation, the dielectric between the electrode  1  and the electrode  2  had a thickness of 1.6 mm and a dielectric constant of 8.0. The electrode  2  had a shape in which an outer edge of the electrode  2  was shifted inward from an outer edge of the electrode  1  by 3 mm, taking into account variation in sizes of the electrodes  1  and  2  in manufacturing. The maximum length L 1  of the electrode  1  was set to 1600 mm taking into account the maximum width of a rear glass of the vehicle in the vehicle width direction. The maximum width H 1  of the electrode  1  was set to 50 mm taking into account the maximum width of the light shielding film  13 . The area of the electrode  1  is denoted by S 1 , and the area of the electrode  2  is denoted by S 2 . 
     When the maximum area of the electrode  1  (maximum value of the area S 1 ) is 80000 mm 2 , which is a product of 1600 mm (length) and 50 mm (width), the overlapping area A where the coupling capacitance C c  is 16.2 pF or more was calculated to be 366 mm 2  or more. Thus, the ratio S of the overlapping area A is only required to be 0.46% or more for the electrode  1 . That is, in order to make the coupling loss 3.0 dB or less, the overlapping area A is preferably 366 mm 2  or more, or the ratio S of the overlapping area A is preferably 0.46% or more for the electrode  1 . Moreover, in order to make the coupling loss 2.0 dB or less, according to the simulation, the overlapping area A is preferably 582 mm 2  or more, or the ratio S of the overlapping area A is preferably 0.73% or more for the electrode  1 . In order to make the coupling loss 1.0 dB or less, according to the simulation, the overlapping area A is preferably 1220 mm 2  or more, or the ratio S of the overlapping area A is preferably 1.5% or more for the electrode  1 . Moreover, in order to make the coupling loss 0.5 dB or less, according to the simulation, the overlapping area A is preferably 2520 mm 2  or more, or the ratio S of the overlapping area A is preferably 3.1% or more for the electrode  1 . 
     When the overlapping area A is 366 mm 2  and the width H 2  of the electrode  2  is 10 mm, the length L 2  of the electrode  2  is 36.6 mm. Thus, in order to make the coupling loss 3.0 dB or less, the electrode  2  preferably has a length L 2  of 36.6 mm or more in the vehicle width direction. Moreover, when the overlapping area A is 582 mm 2  and the width H 2  of the electrode  2  is 10 mm, the length L 2  of the electrode  2  is 58.2 mm. Thus, in order to make the coupling loss 2.0 dB or less, the electrode  2  preferably has a length L 2  of 58.2 mm or more in the vehicle width direction. Moreover, when the overlapping area A is 1220 mm 2  and the width H 2  of the electrode  2  is 50 mm, the length L 2  of the electrode  2  is 24.4 mm. Thus, in order to make the coupling loss 1.0 dB or less, the electrode  2  preferably has a length L 2  of 24.4 mm or more in the vehicle width direction. 
     As described above, the window glass for a vehicle and the antenna have been described by the embodiments. The present invention is not limited to the embodiments. Various variations and enhancements, such as combination/replacement with/by a part or whole of another embodiment may be made without departing from the scope of the present invention. 
     REFERENCE SIGNS LIST 
       10  glass plate (example of first glass plate);  13  light shielding film;  20  glass plate (example of second glass plate or dielectric);  21  plate surface (example of first surface);  22  plate surface (example of second surface);  23  dielectric substrate (example of dielectric);  31  internal electrode (example of first electrode);  32  external electrode (example of second electrode);  40  intermediate film;  41  intermediate film (example of first layer);  42  intermediate film (example of second layer);  43  bonding layer;  50  conductive film;  51 , 52  bus bar;  55  heater;  56  lattice part;  60 , 61  amplifier;  70  antenna;  71 , 72 , 73  antenna element;  100  window glass