Patent Publication Number: US-8523583-B2

Title: Receptacle connector and an electrical connector using the same

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present disclosure relates to a receptacle connector serving as a female connector for an electrical connector configured to connect two circuit boards to each other. More specifically, the present disclosure relates to a receptacle connector having a crosstalk reduction structure, and to an electrical connector using the same. 
     2. Description of the Related Art 
     Heretofore, it is well-known to provide a receptacle connector serving as a female connector to a printed wiring board serving as a circuit board, and to electrically connect this printed wiring board to another printed wiring board serving as another circuit board through the receptacle connector. Such an electric connector at least including a receptacle connector has been disclosed in Japanese Patent Laid-Open No. 2007-149643, for example. 
     In the related-art receptacle connector, the following contact layout has been known in order to suppress crosstalk. Specifically, a coplanar structure is adopted as the contact layout, and ground contacts (G) are disposed such that the ground contacts sandwiches two signal line contacts (S) used for transmitting signals. That is, the contacts are laid out so as to form a G-S-S-G pattern. 
     However, along with speeding up of signal transmission in recent years, crosstalk between adjacent signal lines is becoming a serious problem. In particular, in high-speed transmission, it is necessary to suppress an amount of crosstalk to a very small level in a much higher frequency domain. 
     A layout structure generally used in connectors for high-speed transmission of differential signals is that the ground contacts are placed on both sides of two signal line contacts as in the G-S-S-G pattern as described above. Moreover, when a plurality of sets each consisting of two signal line contacts are adjacent to each other, the adjacent sets of two signal line contacts are separated from each other by only one common ground contact as in a G-S-S-G-S-S-G pattern. 
     In one instance of this the ground wires arranged on the printed wiring board are connected to one another by use of a ground common plane or the like inside the printed wiring board, for example, and are configured to have the same electric potential. However, in the case of a connector in which a plurality of contacts are connected to the printed wiring board through only both end sides of the plurality of contacts, the ground contacts are located at a distance from the ground common plane provided inside the print wiring board. As a result, the ground contacts of the connector have electric potentials different from each other, and have electric potentials also different from an electric potential of the ground wires on the printed wiring board. This degrades shielding effects of the ground contacts against high-frequency signals having frequency components of several gigahertz (GHz). As a consequence, there is a risk of causing a problem of increase in the crosstalk between two immediately-adjacent signal line contacts or between two adjacent signal line contacts located across a ground contact. 
     To solve this problem, the applicant has already proposed an invention in which a plurality of ground contacts arranged in a receptacle connector are coupled together by use of a common contact made of metal (see Japanese Patent Laid-Open No. 2011-159465). The present invention aims at a further improvement of this application. 
     An object of the present invention is to provide: a receptacle connector which achieves reduction in crosstalk between vertically or horizontally adjacent signal line contacts by equalizing electric potentials of ground contacts arranged across every two signal line contacts; and an electrical connector using the receptacle connector. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the invention, a receptacle connector is a receptacle connector used for an electrical connector configured to connect two circuit boards to each other. The receptacle connector comprises: a housing made of an electrically-insulating synthetic resin material, the housing including an upper wall, a lower wall, left and right sidewalls, the housing having a receiving space formed therein, the receiving space having an opening portion, through which a connection target is inserted, on a front side thereof; a plurality of contacts made of a metal material and arranged parallel to one another, the plurality of contacts including a plurality of signal line contacts and a plurality of ground contacts, and the plurality of contacts being placed with every two adjacent signal line contacts interposed between two ground contacts; a supporting member made of an electrically-insulating synthetic resin material, and configured to integrally support and fix thereto the plurality of contacts; and a common contact made of a conductive resin material and configured to electrically connect the a plurality of ground contacts together among the a plurality of contacts. The plurality of contacts are received in the receiving space of the housing, the plurality of contacts being integrated together by the supporting member, all the plurality of ground contacts among the plurality of contacts being electrically connected together by the common contact. 
     In an aspect of the present invention, it is desirable that the plurality of contacts of the receptacle connector of the present invention are formed into two contact assemblies each integrated together by the supporting member, the two contact assemblies are disposed parallel to each other inside the receiving space of the housing and the two circuit boards are electrically connected to each other by inserting the connection target between the two contact assemblies disposed parallel to each other. 
     In another aspect of the present invention, it is desirable that the two contact assemblies of the receptacle connector of the present invention are integrated together. 
     In addition, the receptacle connector of the present invention may include the plurality of contacts which are integrally supported by and fixed to the supporting member with insert molding and the common contact which is formed by injecting a conductive resin material into a cavity formed in advance inside the supporting member at the time of insert molding. 
     Furthermore, an electrical connector of the present invention comprises: the above-mentioned receptacle connector being attached to one of two circuit boards; and a plug connector attached to the other of the two circuit boards and configured to be inserted in the receptacle connector. In addition, the plug connector includes: a blade; a plurality of external contacts arranged corresponding to the plurality of contacts of the receptacle connector; and a common contact configured to electrically connect together a plurality of ground external contacts among the plurality of external contacts, the plurality of ground external contacts corresponding to the plurality of ground contacts of the receptacle connector. 
     In the present invention, all the plurality of ground contacts arranged with every two signal line contacts for transmitting signals at high speed interposed therebetween are electrically connected to one another by use of the common contact, whereby the electric potentials of all the ground contacts connecting the two circuit boards can be kept equal to one another. Accordingly, the connector of the present invention exerts a better shielding effect than a conventional connector, and can sufficiently reduce crosstalk between signals passing through the signal line contacts which are arranged vertically or horizontally adjacent to each other. Moreover, it is possible to suppress the occurrence of noises attributable to the signals passing through the signal line contacts. 
     Meanwhile, the plurality of contacts in each of the two rows included in the receptacle connector are integrated with the common contact by the supporting member. For this reason, it is easy to assemble the connector, and it is possible to ensure that: the plurality of ground contacts are coupled together by the common contact; and accordingly, the plurality of ground contacts are electrically connected together by the common contact. Moreover, it is possible to simplify the structure of the receptacle connector, and thereby to reduce manufacturing costs and a length of time needed to manufacturing the receptacle connector. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an electrical connector including a receptacle connector according to the present invention, which shows the electrical connector in a pre-connected state; 
         FIG. 2  is a schematic cross-sectional view of the electrical connector shown in  FIG. 1  in a connected state, which is taken along the II-II line; 
         FIG. 3  is a schematic cross-sectional view showing the electrical connector with a housing removed therefrom on the basis of the cross-sectional view of the electrical connector shown in  FIG. 2 ; 
         FIG. 4  is a perspective view showing an outline of connection between a plug connector and contacts of the receptacle connector in the electrical connector illustrated in  FIG. 2 ; 
         FIG. 5  is a partially enlarged perspective view showing layout relationships among a plurality of contacts in a first row and a common contact in the receptacle connector included in the electrical connector illustrated in  FIG. 1 ; 
         FIG. 6  is a partially enlarged perspective view showing connection relationships among a plurality of ground contacts, which are obtained by removing signal line contacts from the contacts in the first row, and the common contact in the receptacle connector illustrated in  FIG. 5 ; 
         FIG. 7  is a perspective view of a first common contact which is one of the common contacts included in the receptacle connector shown in  FIG. 1 , and which is configured to connect together the plurality of ground contacts in the first row; 
         FIG. 8  is a perspective view of a second common contact which is one of the common contacts included in the receptacle connector shown in  FIG. 1 , and which is configured to connect the plurality of ground contacts in a second row; 
         FIG. 9  is a graph in which cross talk reduction effects are compared between the common contacts made of a conductive resin according to the present invention and a conventional common contact made of conductive metal; and 
         FIG. 10  is a cross-sectional view of principal part of an electrical connector which is a modification of the electrical connector shown in  FIG. 1 , which represents the electrical connector in a connected state. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
       FIG. 1  shows a preferred embodiment of an electrical connector including a receptacle connector according to the present invention. In the following description of the embodiment, it is to be noted that: terms “front” and “back” respectively indicate a +x direction and a −x direction in  FIG. 1 ; terms “left” and “right” respectively indicate a +y direction and a −y direction therein; and terms “upper” and “lower” respectively indicate a +z direction and a −z direction therein. 
     An electrical connector according to the present invention includes a receptacle connector  10  and a plug connector  80 . As shown in  FIGS. 1 to 4 , the receptacle connector  10  according to the embodiment of the present invention is attached to a first printed wiring board  70  serving as a circuit board. Meanwhile, the plug connector  80  to be inserted into the receptacle connector  10  is attached to a second printed wiring board  90  serving as the other circuit board. The plug connector  80  is inserted into the receptacle connector  10 . Incidentally, the second printed wiring board  90  (or an external terminal portion thereof) as the other circuit board may be directly inserted into the receptacle connector  10  with no plug connector  80  interposed in between. 
     Specifically, a blade  81  of the plug connector  80  is inserted into a first receiving space  16  of the receptacle connector  10 . Thereby, a plurality of first pads  82   a  arranged on an upper surface of the blade  81  are brought into contact with contacts  20  of a contact assembly C 1  in a first row arranged on an upper side of the receptacle connector  10 , while a plurality of second pads  82   b  arranged on a lower surface of the blade  81  are brought into contact with contacts  40  of a contact assembly C 2  in a second row arranged on a lower side of the receptacle connector  10 , respectively. The plurality of first pads  82   a  and the plurality of second pads  82   b  serve as external contacts, and are made of conductive metal thin plates. The contacts  20  in the first row include a plurality of ground contacts (G)  20   a  and a plurality of signal line contacts (S)  20   b , which are arranged in the G-S-S-G-S-S-G pattern as described above (see  FIG. 5 ). Like the contacts in the first row, the contacts  40  in the second row include a plurality of ground contacts (G) and a plurality of signal line contacts (S), which are arranged in the G-S-S-G-S-S-G pattern as in the case of the first row. For this reason, it is understood that: the plurality of first pads  82   a  and the plurality of second pads  82   b  on the plug connector  80  include a plurality of signal line external contacts and a plurality of ground external contacts, which are arranged in the G-S-S-G pattern, as well. As a result, the first printed wiring board  70  and the second printed wiring board  90  are electrically connected to each other. Thereby, signals can reciprocate between the first printed wiring board  70  and the second printed wiring board  90  by high speed transmission. Incidentally, this embodiment is based on the assumption that the first pads  82   a  and the second pads  82   b  on the plug connector  80  are staggered when viewed from the back. Accordingly, the contacts  20  in the first row and the contacts  40  in the second row of the receptacle connector  10  are arranged in a way that contact portions  21  of the plurality of contacts  20  and contact portions  41  of the plurality of contacts  40  are staggered when viewed from the front as described later. That is, when viewed from the front, the contact portions  21  and the contact portions  41  are not arranged on the same lines in the vertical direction, but are displaced in a left-right direction. 
     The receptacle connector  10  according to this embodiment generally comprises a housing  11 , the plurality of contacts  20  in the first row, the plurality of contacts  40  in the second row, a first common contact  30 , and a second common contact  50 . The plurality of contacts  20  in the first row include the plurality of ground contacts  20   a  and the plurality of signal line contacts  20   b . The plurality of contacts  40  in the second row include the plurality of ground contacts and the plurality of signal line contacts. Moreover, the first common contact  30  electrically connects the plurality of ground contacts  20   a  in the first row to one another, while the second common contact  50  electrically connects the plurality of ground contacts in the second row to one another. 
     The housing  11  is made of an electrically-insulating synthetic resin such as an LCP (liquid crystal polymer), and a contour thereof is substantially formed in a rectangular solid. In this embodiment, the housing  11  is provided with an upper wall  11   a , a lower wall  11   b , a left sidewall  11   c , and a right sidewall  11   d . A front portion of the housing  11  is provided with: the first receiving space  16  into which the plug connector  80  is inserted; a plurality of first slits  14  in which the respective a plurality of contacts  20  in the first row are partially received; and a plurality of second slits  15  in which the respective a plurality of contacts  40  are partially received. Meanwhile, a back portion of the housing  11  is provided with a second receiving space  18  in which a first supporting member  35  and a second supporting member  55  are received. The plurality of contacts  20  in the first row are fixed to and supported by the first supporting member  35 . The plurality of contacts  40  in the second row are fixed to and supported by the second supporting member  55 . 
     The first receiving space  16  is formed in a way to be opened forward, to extend horizontally in a left-right direction of the receptacle connector  10 , and to enable the blade  81  of the plug connector  80  to be inserted thereinto. A vertical sectional shape of the first receiving space  16  is formed in a shape similar to a vertical sectional shape of the plug connector  80 , as shown in  FIG. 2 . Meanwhile, it is desirable that the gap between a front opening portion  12   b  and a front opening portion  13   b  of the first receiving space  16  should have a tapered shape which becomes wider toward the front end in order to guide smooth insertion of the plug connector  80 . 
     To be more specific, the first receiving space  16  is defined by first cutout recessed portions  12   a  provided in a plurality of first partition walls  12  and second cutout recessed portions  13   a  provided in a plurality of second partition walls  13 . The first partition walls  12  are formed so as to partition the adjacent first slits  14 . Moreover, the first cutout recessed portions  12   a  are formed by partially cutting out the front and lower portions of each of the plurality of first partition walls  12  substantially in a rectangular shape. The front portion of each first cutout recessed portion  12   a  is formed as an inclined surface which is inclined upward. In the meantime, the second partition walls  13  are formed so as to partition the adjacent second slits  15 . Moreover, the second cutout recessed portions  13   a  are formed by partially cutting out the front and upper portions of each of the plurality of second partition walls  13  substantially in a rectangular shape while opposed to the first cutout recessed portions  12   a . The front portion of each second cutout recessed portion  13   a  is formed as an inclined surface which is inclined downward. The front opening portions  13   b  of the second cutout recessed portions  13   a  and the front opening portions  12   b  of the first cutout recessed portions  12   a  collectively define a front opening portion of the first receiving space  16 . 
     Each of the plurality of first slits  14  provided in the front portion of the housing  11  extends in an anteroposterior direction. Each of the plurality of first slits  14  is opened toward: its front; the first receiving space  16  defined by the first cutout recessed portions  12   a  and the second cutout recessed portions  13   a ; and the second receiving space  18 . Thus, the plurality of first slits  14  are configured in a way that the first slits  14  are located on the upper portion of the first receiving space  16  and the first slits  14  penetrate the housing  11  via the second receiving space  18 . The plurality of first slits  14  are formed parallel to one another, at equal intervals, and at a right angle to the horizontal first receiving space  16 . Moreover, the adjacent first slits  14  are partitioned by the first partition walls  12 . The first partition walls  12  are formed in a way to extend downward from a lower surface of the upper wall  11   a  at a right angle to the upper wall  11   a.    
     Similarly, each of the plurality of second slits  15  provided in the front portion of the housing  11  extends in the anteroposterior direction, and is opened toward: its front; the first receiving space  16  defined by the first cutout recessed portions  12   a  and the second cutout recessed portions  13   a ; and the second receiving space  18 . Thus, the plurality of second slits  15  are configured in a way that the second slits  15  are located in the lower portion of the first receiving space  16  and the second slits  15  penetrate the housing  11  via the second receiving space  18 . The plurality of second slits  15  are formed in parallel with one another, at equal intervals, and at a right angle to the horizontal first receiving space  16 . Furthermore, the adjacent second slits  15  are partitioned by the second partition walls  13 . The second partition walls  13  are formed in a way to extend upward from an upper surface of the lower wall  11   b  at a right angle to the lower wall  11   b.    
     In this embodiment, as learned from the cross-sectional view in  FIG. 2 , the upper-disposed first slits  14  and the lower-disposed second slits  15 , which are opposed to one another, are displaced in the left-right direction when viewed from the front. Specifically, the first slits  14  and the second slits  15  are staggered when viewed from the front. Furthermore, the first partition walls  12  for partitioning the first slits  14  and the second partition walls  13  for partitioning the second slits  15  are staggered when viewed from the front. 
     In this embodiment, back end surfaces  12   c  of the respective first partition walls  12  are formed in a way to abut on a front surface of the first supporting member  35  that supports the plurality of contacts  20  in the first row, and define the second receiving space  18 . Back end surfaces  13   c  of the respective second partition walls  13  are formed in a way to abut on a front surface of the second supporting member  55  that supports the a plurality of contacts  40  in the second row. The back end surfaces  13   c  define the second receiving space  18  together with the back end surfaces  12   c . It is desirable that, as shown in  FIG. 2 , the back end surfaces  12   c  of the first partition walls  12  and the back end surfaces  13   c  of the second partition walls  13   c  should be formed on the same vertical planes, respectively. Moreover, it is desirable that a clearance between the upper surface of each lower wall  11   b  and the lower surface of the corresponding upper wall  11   a  should be set at a value which is equal to or slightly greater than a sum of the heights of the first supporting member  35  and the second supporting member  55 . 
     Next, as shown in  FIG. 2 , the second receiving space  18  provided in the back portion of the housing  11  is shaped substantially like the letter L in a way that a vertical section of the second receiving space  18  taken along the anteroposterior direction is similar to cross-sectional shapes of the contacts  20 ,  40  in the first and second rows. The second receiving space  18  is opened backward and partially downward, and the front portion of the second receiving space  18  also communicates with the first and second slits  14 ,  15 . Moreover, the second receiving space  18  is formed in way that: the second receiving space  18  extends horizontally in the left-right direction of the receptacle connector  10 ; and when assembling the receptacle connector  10 , the plurality of contacts  20  in the first row and the plurality of contacts  40  in the second row can be inserted into the second receiving space  18  from the back. In this embodiment, the second receiving space  18  is defined by part of the lower surface of the upper wall  11   a , part of the upper surface of the lower wall  11   b , parts of inner surfaces of the left and right sidewalls  11   c ,  11   d , the back end surfaces  12   c  of the first partition walls  12 , and the back end surfaces  13   c  of the second partition walls  13  of the housing  11 . 
     First engagement grooves  17  configured to guide the first supporting member  35 , which the contacts  20  in the first row are fixed to and supported by, are formed in the inner surfaces of the left and right sidewalls  11   c ,  11   d  defining the second receiving space  18  in a way that the first engagement grooves  17  extend horizontally in the anteroposterior direction. Meanwhile, it is desirable that the first engagement grooves  17  should be formed along the lower surface of the upper wall  11   a  of the housing  11 . Further, second engagement grooves  19  configured to guide the second supporting member  55 , which the contacts  40  in the second row are fixed to and supported by, are formed below the first engagement grooves  17  in the inner surfaces of the left and right sidewalls  11   c ,  11   d  in a way that the second engagement grooves  19  are parallel to the first engagement grooves  17 . In addition, it is desirable that the second engagement grooves  19  should be formed along the upper surface of the lower wall  11   b.    
     As described previously, the plurality of contacts  20  in the first row in this embodiment include the plurality of signal line contacts  20   b  and the plurality of ground contacts  20   a  which are arranged in the G-S-S-G pattern (see  FIG. 5 ). Each of the plurality of contacts in the first row in this embodiment is formed in the same shape by: punching a substantially elongated plate shape member out of a metal thin plate; and then bending the member into a form of the letter L. 
     As shown in  FIG. 3 , each of the plurality of contacts  20  in the first row includes a contact portion  21 , an elastically-deformable portion  22 , a fixed portion  23 , a vertical portion  24 , and a terminal portion  25 . In this embodiment, the contact portions  21  and the elastically-deformable portions  22  are respectively disposed in the first slits  14  provided in the housing  11 , as shown in  FIG. 2 , when the plurality of contacts  20  in the first row are installed in the housing  11 . Meanwhile, the vertical portions  24  and the terminal portions  25  are respectively located inside the second receiving space  18  and behind vertical portions  44  and terminal portions  45  of the plurality of contacts  40  in the second row, when the contacts  20  therein are installed in the housing  11 . 
     In this embodiment, the contact portion  21  of each contact  20  in the first row is shaped like a downward convex curve, and is formed in a way to protrude downward from the first slit  14  into the first receiving space  16 , as well as is capable of contacting the corresponding first pad  82   a  serving as one of the external contacts of the plug connector  80  at a desired contact pressure (see  FIG. 4 ). 
     In this embodiment, the elastically-deformable portion  22  is formed in a way to extend substantially horizontally forward from the fixed portion  23 , and to continue to the contact portion  21 . When elastically deformed, the elastically-deformed portion  22  gives a desired contact pressure to the contact portion  21 . 
     In this embodiment, the fixed portion  23  is formed in a way to extend continuously from the elastically-deformable portion  22  in the horizontal direction, and to have a width (a length in the left-right direction) smaller than a width of the elastically-deformable portion  22  and a width of the vertical portion  24  that continues from the fixed portion  23  (see  FIG. 5 ). As will be described later, the plurality of contacts  20  in the first row are integrated together by molding the first supporting member  35 , which is made of an electrically-insulating synthetic resin, with the fixed portions  23  inserted in the first supporting member  35  (see  FIG. 4 ), and are thereby formed as the contact assembly C 1  in the first row. The fixed portions  23  of the plurality of contacts  20  in the first row are integrated together while surrounded by the electrically-insulating synthetic resin having a specific permittivity which is greater than that of air. Accordingly, impedance of the fixed portions  23  is lower than otherwise. For this reason, in this embodiment, impedance matching can be achieved by forming the fixed portions  23  narrower than the other portions in order to suppress reduction in the impedance. Incidentally, among the plurality of contacts  20  in the first row, the plurality of contacts  20   a  used as the ground contacts are electrically connected to the first common contact  30  made of a conductive resin material via the respective fixed portions  23 , as will be described later (see  FIG. 6 ). 
     It is to be noted that a reason why a conventionally-known press-fit mechanism is not adopted for the purpose of fixation of the plurality of contacts  20  in this embodiment is that, if protrusions are provided for the press-fitting, the impedance is reduced and the impedance matching cannot be achieved. 
     The vertical portion  24  is the portion configured to connect the fixed portion  23  to the terminal portion  25 . The vertical portion  24  is bent substantially perpendicularly from the horizontal fixed portion  23 , and extends downward in the substantially perpendicular direction, continuing to the terminal portion  25 . 
     The terminal portion  25  is formed below the vertical portion  24 . The terminal portion  25  is bent substantially perpendicularly from the vertical portion  24 , and is formed in a way to extend backward, as well as is capable of being connected to an external contact (not shown) of the printed wiring board  70 . To be concretely, the terminal portion  25  is soldered to the external contact of the printed wiring board  70 , and is thereby electrically connected to an electric circuit on the printed circuit board  70 . 
     Next, as described previously, the plurality of contacts  40  in the second row in this embodiment include the plurality of signal line contacts and the plurality of ground contacts which are arranged in the G-S-S-G pattern. In addition, like each of the plurality of contacts  20  in the first row, each of the plurality of contacts in the second row in this embodiment is formed in the same shape by: punching a substantially elongated plate-shape member out of a conductive metal thin plate; and then bending the member into a form of the letter L. 
     As shown in  FIG. 3 , like each of the contacts  20  in the first row, each of the plurality of contacts  40  in the second row includes a contact portion  41 , an elastically-deformable portion  42 , a fixed portion  43 , a vertical portion  44 , and a terminal portion  45 . In this embodiment, the contact portions  41  and the elastically-deformable portions  42  are respectively disposed in the second slits  15  provided in the housing  11 , as shown in  FIG. 2 , when the plurality of contacts  40  in the second row are installed in the housing  11 . Meanwhile, the vertical portions  44  and the terminal portions  45  are respectively located inside the second receiving space  18  and in front of the vertical portions  24  and the terminal portions  25  of the plurality of contacts  20  in the first row, when the contacts  40  are installed in the housing  11 . 
     In this embodiment, the contact portion  41  of each contact  40  in the second row is shaped like an upward convex curve, and is formed in a way to protrude upward from the second slit  15  into the first receiving space  16 , as well as is capable of contacting the corresponding second pad  82   b  serving as one of the external contacts of the plug connector  80  at a desired contact pressure (see  FIG. 4 ). 
     In this embodiment, the elastically-deformable portion  42  is formed in a way to extend substantially horizontally forward from the fixed portion  43 , and to continue to the contact portion  41 . When elastically deformed, the elastically-deformed portion  42  gives a desired contact pressure to the contact portion  41  (see  FIG. 3 ). 
     In this embodiment, the fixed portion  43  extends continuously in the horizontal direction from the elastically-deformable portion  42 . As in the case of each contact  20  in the first row, the fixed portion  43  included in each contact  40  in the second row is formed in a way to have a width (a length in the left-right direction) smaller than a width of the elastically-deformable portion  42  and a width of the vertical portion  44  that continues from the fixed portion  43 . In addition, as will be described later, the plurality of contacts in the second row are integrated together by molding an electrically-insulating synthetic resin into the second supporting member  55  with the fixed portions  43  inserted in the second supporting member  55 , and are thereby formed into the contact assembly C 2  in the second row. With regard to the fixed portions  43  of the plurality of contacts  40  in the second row, too, impedance matching is achieved by forming the fixed portions  43  narrower than the other portions for the same reason as the fixed portions  23  are formed narrower than the other portions in the above-described contacts  20  in the first row. Furthermore, among the plurality of contacts  40  in the second row, the plurality of contacts used as the ground contacts are electrically connected to the second common contact  50  made of a conductive synthetic resin via the respective fixed portions  43 , as will be described later. 
     The vertical portion  44  is the portion configured to connect the fixed portion  43  to the terminal portion  45 . The vertical portion  44  is bent substantially perpendicularly from the horizontal fixed portion  43 , and extends downward in the substantially perpendicular direction, continuing to the terminal portion  45 . 
     The terminal portion  45  is formed below the vertical portion  44 . The terminal portion  45  is bent substantially perpendicularly from the vertical portion  44 , and is formed in a way to extend forward, as well as is capable of being connected to an external contact (not shown) of the printed wiring board  70 . To be concretely, the terminal portion  45  is soldered to the external contact of the printed wiring board  70 , and is thereby electrically connected to an electric circuit on the printed circuit board  70 . 
     Here, descriptions will be provided for the first supporting member for connecting together the plurality of contacts  20  in the first row and the second supporting member for connecting together the plurality of contacts  40  in the second row according to this embodiment with reference to  FIGS. 2 to 4 . 
     As described previously, the first supporting member  35  is a member to connect together the plurality of contacts  20  in the first row which are arranged parallel to one another, and is made of the electrically-insulating synthetic resin material such as an LCP (liquid crystal polymer). In this embodiment, the first supporting member  35  and the plurality of contacts  20  in the first row are integrally formed by the insert molding. Thereby, the plurality of contacts  20  in the first row are integrally supported by and fixed to the first supporting member  35  in a way to be arranged parallel to one another and in a straight line in the left-to-right direction. Incidentally, at this stage, a cavity for the first common contact  30 , which will be described later, is formed inside the first supporting member  35 . The first supporting member  35  is shaped like an elongated rectangular solid extending substantially in the left-to-right direction, and is formed in a way to surround the fixed portions  23  of each of the plurality of contacts  20  in the first row. First engagement protrusions  36 ,  37  are provided in upper portions of both left and right end portions of the first supporting member  35 , respectively, in a way that the first engagement protrusions  36 ,  37  make a pair (see  FIG. 4 ). The paired first engagement protrusions  36 ,  37  are respectively fitted in the paired first engagement grooves  17  provided in the inner surfaces of the left and right sidewalls  11   c ,  11   d  of the housing  11 , and are useful as a guide when the first supporting member  35  is installed into the second receiving space  18  of the housing  11 . Moreover, because the first engagement grooves  17  receive an upward force which is produced by elastic deformation of the contacts  20  in the first row when the contacts  20  come into contact with the first pads  82   a  on the blade  81 , the contacts  20  in the first row can obtain a stable contact force. Here, a depth (a length in the anteroposterior direction) of the first supporting member  35  is denoted by reference sign L 1 ; a width (a length in the left-to-right direction) thereof is denoted by reference sign W 1 ; and a height (a length in the vertical direction) thereof is denoted by reference sign H 1 . Moreover, a height and a protruding length (a protruding length in the left-right direction) of each of the first engagement protrusions  36 ,  37  are denoted by reference signs H 11 , W 11 , respectively. 
     As described previously, the second supporting member  55  is a member to connect together the plurality of contacts  40  in the second row which are arranged parallel to one another, and is made of the electrically-insulating synthetic resin material such as an LCP (liquid crystal polymer). In this embodiment, the second supporting member  55  and the plurality of contacts  40  in the second row are integrally formed by the insert molding. Thereby, the plurality of contacts  40  in the second row are integrally supported by and fixed to the second supporting member  55  in a way to be arranged parallel to one another and in a straight line in the left-to-right direction. Incidentally, at this stage, a cavity for the second common contact  50 , which will be described later, is formed inside the second supporting member  55 . The second supporting member  55  is shaped like an elongated rectangular solid extending substantially in the left-to-right direction, and is formed in a way to surround the fixed portions  43  of each of the plurality of contacts  40  in the second row. Second engagement protrusions (although only the protrusion  56  on the right side is shown in  FIG. 4 ) are provided in lower portions of both left and right end portions of the second supporting member  55 , respectively, in a way that the second engagement protrusions make a pair. The paired second engagement protrusions  56  are respectively fitted in the paired second engagement grooves  19  provided in the inner surfaces of the left and right sidewalls  11   c ,  11   d  of the housing  11 , and are useful as a guide when the second supporting member  55  is installed into the second receiving space  18  of the housing  11 . Moreover, because the second engagement grooves  19  receive a downward force which is produced by elastic deformation of the contacts  40  in the second row when the contacts  40  come into contact with the second pads  82   b  on the blade  81 , the contacts  40  in the second row can obtain a stable contact force. Here, a depth (a length in the anteroposterior direction) of the second supporting member  55  is denoted by reference sign L 2 ; a width (a length in the left-right direction) thereof is denoted by reference sign W 2 ; and a height (a length in the vertical direction) thereof is denoted by reference sign H 2 . Moreover, a height and a protruding length (a protruding length in the right-left direction) of each of the second engagement protrusions  56  are denoted by reference signs H 21 , W 21 , respectively. 
     In this embodiment, dimensional relationships between the first supporting member  35  and the second supporting member  55  are as follows. Specifically, the length L 1  of the first supporting member  35  is greater than the length L 2  of the second supporting member  55  (L 1 &gt;L 2 ), while the widths and the protruding lengths of these members are equal (W 1 =W 2 , W 11 =W 21 ). Meanwhile, the heights (H 1  and H 2 ) of the first and second supporting members  35 ,  55  and the heights of the first engagement protrusions  36 ,  37  as well as the heights (H 11  and H 21 ) of the second engagement protrusions  56  thereof are equal to one another (H 1 =H 2 , H 11 =H 21 ). 
     Next, the common contacts constituting the receptacle connector  10  according to this embodiment, which represent the characteristic feature of the present invention, will be described with reference to  FIGS. 6 to 8 . In this embodiment, the first common contact  30  is provided in order to equalize the electric potentials of each of the plurality of ground contacts  20   a  among the plurality of contacts  20  in the first row. Similarly, the second common contact  50  is provided in order to equalize the electric potentials of each of the plurality of ground contacts among the plurality of contacts  40  in the second row. 
     To begin with, descriptions will be provided for the first common contact  30 . The first common contact  30  is a member configured to electrically connect together the plurality of ground contacts  20   a , which are located in every third place, among the plurality of contacts  20  in the first row, in block in order to equalize the electric potentials of the respective ground contacts  20   a . The first common contact  30  is formed by molding with the conductive resin injected into the cavity provided inside the first supporting member  35  after the plurality of contacts  20  in the first row are integrated together by the first supporting member  35 . 
     To be specific, the first common contact  30  is made of a conductive resin material, which is prepared by mixing micro particulates or fibers of a conductive material such as carbon or nickel into a synthetic resin material such as an LCP (liquid crystal polymer) or PPS (polyphenylene sulfide). The first common contact  30  is integrally formed inside the first supporting member  35  by pouring this conductive resin material into the cavity formed in advance in the first supporting member  35 , which is configured to integrally support the plurality of contacts  20  in the first row. 
     As shown in  FIGS. 5 and 6 , the first common contact  30  is molded in a way to be provided with a certain gap with respect to the first common contact  30  and the fixed portions  23  of the ground contacts  20   a , which are arranged in every third place, among the plurality of contacts  20  in the first row. 
     As shown in  FIG. 7 , the first common contact  30  includes a flat and elongated connecting body  31 , protrusions  32 , and a pair of extended engagement portions  33 ,  34 . The elongated connecting body  31  extends in the left-right direction, and includes the plurality of protrusions  32  configured to be provided with a certain gap with respect to the corresponding ground contacts  20   a . The plurality of protrusions  32  are configured to protrude upward from the connecting body  31  and to extend in the anteroposterior direction, and are disposed parallel to one another. The paired extended engagement portions  33 ,  34  are provided on both ends of the connecting body  31 , respectively. 
     Since the extended engagement portions  33 ,  34  make a pair, only the extended engagement portion  34  formed on a right end side of the connecting body  31  will be explained herein while omitting description of the extended engagement portion  33  on a left end side. In this embodiment, the extended engagement portion  34  formed on the right end side of the connecting body  31  includes a horizontal lower step portion  34   a , a vertical portion  34   b , and a horizontal upper step portion  34   c , and therefore is shaped substantially like a staircase when viewed from the front. To be more specific, the horizontal lower step portion  34   a  protrudes horizontally rightward from a right end surface of the connecting body  31 . Subsequently, the vertical portion  34   b  extends upward from a right end portion of the horizontal lower step portion  34   a  at a right angle to the horizontal lower step portion  34   a . Further, the horizontal upper step portion  34   c  extends horizontally rightward from an upper end of the vertical portion  34   b  at a right angle to the vertical portion  34   b . All of the horizontal lower step portion  34   a , the vertical portion  34   b , and the horizontal upper step portion  34   c  have the same depth (the length in the anteroposterior direction). As shown in  FIG. 4 , the horizontal upper step portion  34   c , together with the first engagement protrusion  37  of the first supporting member  35 , is fitted in the first engagement groove  17  provided in the inner surface of the right sidewall  11   d  of the housing  11 , and is useful as a guide when the first supporting member  35  is installed into the second receiving space  18  of the housing  11 . 
     Here, as shown in  FIG. 7 , a depth (a length in the anteroposterior direction) of the first common contact  30  is denoted by reference sign L 3 ; a width (a length in the left-right direction) thereof is denoted by reference sign W 3 ; and a height (a length in the vertical direction) thereof is denoted by reference sign H 3 . Moreover, a length in the anteroposterior direction, a height (a length in the vertical direction), and a protruding length (a protruding length in the left-right direction) of the horizontal upper step portions  33   c ,  34   c  of the paired the extended engagement portions  33 ,  34  are denoted by reference signs L 31 , H 31 , and W 31 , respectively. 
     As described previously, in this embodiment, first of all, the plurality of contacts  20  in the first row are formed integrally with the first supporting member  35  made of the electrically-insulating synthetic resin material by insert molding in a way to that the cavity corresponding to the shape of the first common contact  30  is formed in the first supporting member  35  in advance. Next, the first common contact  30  is formed by injecting the conductive resin material from either or both of the paired extended engagement portions  33 ,  34 . That is to say, the first common contact  30  is formed by two-step molding. The contact assembly C 1  in the first row, in which the plurality of contacts  20  in the first row are integrally bonded together with the ground contacts  20   a  provided with a certain gap with respect to the first common contact  30 , is formed by this two-step molding method. At this time, the plurality of contacts  20  in the first row are arranged with every two adjacent signal line contacts  20   b ,  20   b  for transmitting high-speed signals interposed between two ground contacts  20   a , or, the G-S-S-G pattern. 
     In this embodiment, dimensional relationships between the first supporting member  35  and the first common contact  30  are as follows because of the two-step molding method. Specifically, the relation L 1 &gt;L 3 &gt;L 31  holds, because the first common contact  30  is formed inside the first supporting member  35 . Meanwhile, W 1 =W 3 , W 11 =W 31 , and H 11 =H 31 , because the first engagement protrusions  36 ,  37  of the first supporting member  35 , the horizontal upper step portions  33   c ,  34   c  of the extended engagement portions  33 ,  34  of the first common contact  30  are formed in a way to be fitted in the engagement groove  17 . 
     Because the first common contact  30  are formed such that the plurality of protrusions  32  configured to be provided with a certain gap with respect to the corresponding ground contacts  20   a , the first common contact  30  is not physically in contact with the ground contacts  20   a . If the first common contact  30  is physically in contact with the ground contacts  20   a , the ground contacts  20   a  are electrically connected to each other by direct-current. In this case, since the direct-current resistance is low, there is a disadvantage that the ground contacts  20   a  are susceptible to electronic interference by each other. Further, it is difficult to apply a bias voltage to the contacts due to a leakage of direct current. In order to eliminate such a disadvantage, in the embodiment, the first common contact  30  is configured to be not physically in contact with the ground contacts  20   a  by providing with a certain gap between the first common contact  30  and the ground contacts  20   a , to thereby interrupt the direct-current. Accordingly, in the embodiment, the ground contacts  20   a  can be electrically connected to each other only in high-frequency regions. Therefore, the first common contact  30  can electrically connect together all of the plurality of ground contacts  20   a  among the plurality of contacts  20  in the first row in the high-frequency regions, and can resultantly equalize the electric potentials of each of the plurality of ground contacts  20   a.    
     In this embodiment, because the first common contact  30  of this kind is included therein, it is possible to prevent reduction in a shielding effect attributable to ground conductive lines in two connector regions of the plug connector  80  and the receptacle connector  10  in this embodiment. Accordingly, crosstalk between the signal lines is reduced, and noise emission is prevented. 
     Next, descriptions will be provided for the second common contact  50 . The second common contact  50  is a member configured to electrically connect together the plurality of ground contacts (not shown), which are located in every third place among the plurality of contacts  40  in the second row, in block in order to equalize the electric potentials of the respective ground contacts. The second common contact  50  is formed by molding with the conductive resin injected into the cavity provided inside the second supporting member  55  after the plurality of contacts  40  in the second row are integrated together by the second supporting member  55 . 
     To be specific, like the first common contact  30 , the second common contact  50  is made of a conductive resin material, which is prepared by mixing micro particles or fibers of a conductive material such as carbon or nickel into a synthetic resin material such as an LCP or PPS. The second common contact  50  is integrally formed inside the second supporting member  55  by pouring this conductive resin material into the cavity formed in advance in the second supporting member  55 , which is configured to integrally support the plurality of contacts  40  in the second row. The second common contact  50  is molded in a way to be in contact with the fixed portions  43  of the ground contacts (not shown), which are arranged in every third place among the plurality of contacts  40  in the second row like the contacts  20  in the first row. 
       FIG. 8  shows the second common contact  50  accordingly to this embodiment. The second common contact  50  includes an upper body  51   a  and a lower body  51   b  which are arranged in higher and lower positions, respectively; contact protrusions  52   a ,  52   b  respectively provided on the two bodies  51   a ,  51   b ; and a pair of extended engagement portions  53 ,  54  configured to connect the two bodies  51   a ,  51   b  together. The lower and upper elongated bodies  51   a ,  51   b  have the same length and the same width; extend in the left-right direction; are disposed parallel to each other; and are provided with the plurality of contact protrusions  52   a ,  52   b  configured to contact the corresponding fixed portions  43  of the ground contacts in the second row. The plurality of contact protrusions  52   a  provided on the upper body  51   a  protrude downward from the upper body  51   a , extend in the anteroposterior direction, and are disposed parallel to one another. Similarly, the plurality of contact protrusions  52   b  provided on the lower body  51   b  protrude upward from the lower body  51   b , extend in the anteroposterior direction, and are disposed parallel to one another. Note that the contact protrusions  52   a  provided on the elongated upper body  51   a  or the contact protrusions  52   b  provided on the elongated lower body  51   b  may be omitted. 
     The pair of extended engagement portions  53 ,  54  in this embodiment are provided in order that both ends of the upper body  51   a  are connected to both ends of the lower body  51   b , respectively. Since the extended engagement portions  53 ,  54  make a pair, descriptions will be herein provided for only the extended engagement portion  54  configured to connect the right end sides of the respective upper and lower bodies  51   a ,  51   b  together, while omitting descriptions of the extended engagement portion  53  configured to connect the left end sides thereof together. In this embodiment, the extended engagement portion  54  configured to connect the right ends of the respective upper and lower bodies  51   a ,  51   b  includes a lower horizontal portion  54   c , a vertical portion  54   b , an upper horizontal portion  54   a , and an engagement protrusion  54   d ; and is therefore shaped substantially like the letter h which is laid down, when viewed from the front. To be specific, the lower horizontal  54   c  protrudes horizontally rightward from a right end surface of the lower body  51   b  with a length which is equal to a length in the anteroposterior direction of the lower body  51   b . Subsequently, the vertical portion  54   b  extends upward from a right end portion of the lower horizontal portion  54   c  at a right angle to the lower horizontal portion  54   c . Further, the upper horizontal portion  54   a  extends horizontally leftward from an upper end of the vertical portion  54   b  at a right angle to the vertical portion  54   b , and is connected to the upper body  51   a . Furthermore, the engagement protrusion  54   d  is formed in a way to protrude in a rightward direction, which is opposite to a direction toward the lower horizontal portion  54   c , from a lower end portion of the vertical portion  54   b . As shown in  FIG. 4 , the engagement protrusion  54   d , together with the second engagement protrusion  56  of the second supporting member  55 , is fitted in the second engagement groove  19  provided in the inner surface of the right sidewall  11   d  of the housing  11 , and is useful as a guide when the second supporting member  55  is installed into the second receiving space  18  of the housing  11 . 
     Here, as shown in  FIG. 8 , a depth (a length in the anteroposterior direction) of the second common contact  50  is denoted by reference sign L 4 ; a width (a length in the left-right direction) thereof is denoted by reference sign W 4 ; and a height (a length in the vertical direction) thereof is denoted by reference sign H 4 . Moreover, a length in the anteroposterior direction, a height (a length in the vertical direction), and a protruding length (a protruding length in the left-right direction) of the engagement protrusions  53   c ,  54   d  of the paired extended engagement portions  53 ,  54  are denoted by reference signs L 41 , H 41 , and W 41 , respectively. 
     As described previously, in this embodiment, first of all, the plurality of contacts  40  in the second row are formed integrally with the second supporting member  55  made of the electrically-insulating synthetic resin material by insert molding in a way that the cavity corresponding to the shape of the second common contact  50  is formed in the second supporting member  55  in advance. Next, the second common contact  50  is formed by injecting the conductive resin material from either or both of the paired extended engagement portions  53 ,  54 . The contact assembly C 2  in the second row, in which the plurality of contacts  40  in the second row are integrally bonded together with the ground contacts connected to the second common contact  50 , is formed by this two-step molding method. At this time, the plurality of contacts  40  in the second row are arranged with every two adjacent signal line contacts for transmitting high-speed signals interposed between two ground contacts, or in the G-S-S-G pattern. 
     In this embodiment, dimensional relationships between the second supporting member  55  and the second common contact  50  are as follows because of the two-step molding method. Specifically, L 2 &gt;L 4 =L 41  because the second common contact  50  is formed inside the second supporting member  55 . Meanwhile, W 2 =W 4 , W 21 =W 41 , and H 21 =H 41 , because the engagement protrusions  56  of the second supporting member  55  and the engagement protrusions  53   d ,  54   d  of the extended engagement portions  53 ,  54  of the second common contact  50  are formed in a way to be fitted in the second engagement grooves  19 . 
     Because the second common contact  50  are formed in this manner, the second common contact  50  can electrically connect together all of the plurality of ground contacts among the plurality of contacts  40  in the second row, and can resultantly equalize the electric potentials of each of the plurality of ground contacts. In addition, because the second common contact  50  of this kind is included therein, it is possible like the first common contact  30  to prevent reduction in a shielding effect attributable to the ground conductive lines in the two connector regions of the plug connector  80  and the receptacle connector  10  in this embodiment. Accordingly, crosstalk between the signal lines is reduced, and noise emission is prevented. 
     In this embodiment, the contact assembly C 1  in the first row and the contact assembly C 2  in the second row are formed as separate assemblies. However, these assemblies may be formed into a single assembly instead. For example, the contact assembly C 1  in the first row and the contact assembly C 2  in the second row may be formed into a unified assembly by attaching the two contact assemblies together vertically by use of an adhesive or the like. Alternatively, as shown as a modified example of this embodiment in  FIG. 10 , the plurality of contacts  20  in the first row and the plurality of contacts  40  in the second row are integrally formed together with the first supporting member  35  and the second supporting member  55  by insert molding in a way that the cavity corresponding to the shape of a single common contact  65  is formed inside the first supporting member  35  and the second supporting member  55  in advance. Next, the common contact  65  is formed by injecting the conductive resin material into the cavity formed in advance in the first supporting member  35  and the second supporting member  55 , thereby collectively forming the contact assembly C 1  in the first row and the contact assembly C 2  as the single assembly. Accordingly, the single common contact is configured to electrically connect together the plurality of ground contacts among the plurality of contacts  20  in the first row and the plurality of ground contacts among the plurality of contacts  40  in the second row. In this modified example shown in  FIG. 10 , the common contact  65  is provided with a certain gap from the ground contacts among the contacts  20  in the first row to electrically connect the ground contacts to each other in high-frequency regions. Incidentally, the single common contact  65  receives upward and downward forces produced which are produced by elastic deformation of the contacts  20  in the first row and the contacts  40  in the second row when the contacts  20  come into contact with the first pads  82   a  on the blade  81  and the contacts  40  come into contact with the second pads  82   b  on the blade  81 . Hence, the contacts  20  and the contacts  40  can obtain the stable contact force. Furthermore, this enables simple and easy management of the dimensions concerning the heights (H 1 , H 2 ) of the first engagement protrusions  36 ,  37  and the second engagement protrusions  56 , and thereby makes it easier to assembly the receptacle connector  10 . 
     Further, this embodiment uses the common contacts only for the receptacle connector  10 . However, the present invention is not limited to this. The plug connector  80  may be provided with a common contact  85 , a shown in  FIG. 4 . As with the first common contact  30 , the common contact  85  may be provided with a certain gap with respect to the plug connector  80 . By employing such a configuration, in the high-frequency regions, the common contact  85  can electrically connects together all of the plurality of ground external contacts corresponding to the plurality of ground contacts  20   a  among the plurality of contacts  20  in the first row and the plurality of ground contacts among the plurality of contacts  40  in the second row. This configuration further enhances the operation and effect of crosstalk reduction produced by the providing of the first and second common contacts  30 ,  50  to the receptacle  10 . 
     Next, brief descriptions will be provided how the contact assembly C 1  in the first row and the contact assembly C 2  in the second row are installed into the receptacle connector  10  according to this embodiment by using  FIG. 2 . 
     First of all, the second row contact assembly C 2  is inserted from the back into the second receiving space  18  with the paired second engagement protrusions  56  of the second supporting member  55  fitted in the paired second engagement grooves  19  which are formed in the inner surfaces of the left and right sidewalls  11   c ,  11   d  of the housing  11 . At this time, the contact portions  41  and the elastically-deformable portions  42  of the plurality of contacts  40  in the second row are placed inside the corresponding second slits  15 . The contact assembly C 2  in the second row is supported by and fixed to the receptacle connector  10 , because the front surface and the lower surface of the second supporting member  55  abut on the back end surfaces  13   c  of the second partition walls  13  and the upper surface of the lower wall  11   b.    
     Subsequently, the contact assembly C 1  in the first row is inserted from the back into the second receiving space  18  with the paired first engagement protrusions  36 ,  37  of the first supporting member  35  fitted in the paired first engagement grooves  17  which are formed in the inner surfaces of the left and right sidewalls  11   c ,  11   d  of the housing  11 . At this time, the contact portions  21  and the elastically-deformable portions  22  of the plurality of contacts  20  in the first row are placed inside the corresponding first slits  14 . The contact assembly C 1  in the first row is supported by and fixed to the receptacle connector  10 , because the upper surface, the front surface and the lower surface of the first supporting member  35  abut on the lower surface of the upper wall  11   a , the back end surfaces  12   c  of the first partition walls  12  and the upper surface of the second supporting member  55 . 
     As a result, as shown in  FIGS. 2 and 4 , the contact assembly C 1  in the first row and the contact assembly C 2  in a second row are disposed parallel to each other inside the housing  11 , whereby the assemblage of the receptacle connector  10  according to this embodiment is completed. Incidentally, as described previously, the further integration of the contact assembly C 1  in the first row and the contact assembly C 2  in the second row makes the assemblage easier and more secure, and makes it possible to reduce manufacturing (assembling) steps in number. 
     The receptacle connector  10  according to the present invention brings about excellent operation and effect of crosstalk reduction, because the plurality of contacts  20  in the first row and the plurality of contacts  40  in the second row are provided with the first common contact  30  and the second common contact  50 , respectively.  FIG. 9  shows a graph comparing the present invention and a conventional example in terms of crosstalk reduction. In  FIG. 9 , a solid line indicates the amount of crosstalk which occurs when signals are transmitted at high speed through the receptacle connector  10  including the first and second common contacts  30 ,  50  which are made of the conductive resin material according to the present invention. A dotted line therein indicates the amount of crosstalk which occurs when signals are similarly transmitted at high speed through a receptacle connector including the first and second common contacts which are made of a conventional conductive metal material. As shown in  FIG. 9 , in the case the common contacts are made of the conventional metal material, ripples occur when the frequency of signals to be transmitted at high speed reaches about 9, 18, 21, and 27 GHz and their vicinities, and insertion loss peaks around these frequencies. From this, it is apparent that the amount of crosstalk accordingly reaches peaks of over −30 dB around these frequencies as well. Considering that it is desirable to reduce the amount of crosstalk to −40 dB or less, it is understood that the conventional receptacle connector is unsatisfactory when the frequency is higher. On the other hand, it is clear that, in the case where the common contacts are made of the conductive resin material whose electric conductivity is far smaller than the electric conductivity of the metal material as in the present invention, the amount of crosstalk gently increases until the frequency reaches 30 GHz, and even the largest amount of crosstalk is reduced to −30 dB or less. 
     The including of the above-described configuration in the receptacle connector of the present invention makes the structure of the receptacle connector simpler and the production of the receptacle connector easier, and makes it possible to reduce the amount of crosstalk sufficiently. Further, since the common contact is provided with a certain gap from the ground contacts, the common contact can electrically contact the ground contacts to each other in high-frequency regions. Accordingly, the present invention makes it possible to reduce the amount of crosstalk sufficiently with eliminating interference between the ground contacts. 
     The embodiment has been described on the basis of the concept that the common connectors are provided only to the contacts  20 ,  40  of the receptacle connector  10 . However, the present invention is not limited to this configuration. As described previously, the common contacts may be provided to the plug connector included in the electrical connector as well. Thereby, it is possible to prevent reduction in the shielding effect attributable to the ground conductive lines in the two connector regions of the plug connector and the receptacle connector, and also to reduce the amount of crosstalk at the same time. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded with the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.