Patent Publication Number: US-11031735-B2

Title: Electrical connector assembly

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Japanese Patent Application No. 2018-168012, filed Sep. 7, 2018, the contents of which are incorporated herein by reference. 
     BACKGROUND 
     Technical Field 
     The present invention relates to an electrical connector assembly. 
     Related Art 
     A variety of shapes are considered for the terminal contact portions placed in mutual contact when a pair of electrical connectors are mated. For example, a connector assembly in which mutual contact is established using rectilinear plug terminals that are not subject to resilient displacement and in which receptacle terminals are brought into contact with said plug terminals as a result of undergoing resilient displacement has been disclosed in the connector of Patent Document 1. The electrical connector assembly of this Patent Document 1 has a plug connector used as a connector for circuit boards and a receptacle connector used as another connector for circuit boards. The multiple terminals retained in place in array form in the plug connector are rectilinear plug terminals extending in the direction of connector plugging and unplugging, and the multiple terminals retained in place in array form in the receptacle connector are resiliently displaceable receptacle terminals. After undergoing resilient displacement and sliding under contact pressure from the above-mentioned plug terminals in the process of connector mating, said receptacle terminals come into contact with the above-mentioned plug terminals while maintaining the state of resilient displacement. 
     In the above-mentioned plug terminals, the sections that extend from the distal ends (free ends) on the connector mating side to an intermediate location are formed as contact arm portions that are capable of contacting the above-mentioned receptacle terminals. The specific shape of said contact arm portions is unknown, as no detailed description is provided. On the other hand, the above-mentioned receptacle terminals have protruding contact portions (convex contact point portions) formed in their distal end portions on the connector mating side, with said convex contact point portions adapted to come into contact with said contact arm portions at an intermediate location in the longitudinal direction of the above-mentioned contact arm portions. Configuring a longer effective mating length, i.e., a greater distance from the location of contact with the convex contact point portions of the receptacle terminals to the distal ends (free ends) of the plug terminals, ensures a reliable state of contact independently of the mating depth of the two connectors. 
     PATENT DOCUMENTS 
     Patent Document 1 
     Japanese Patent No. 6,198,712. 
     SUMMARY OF THE INVENTION 
     Technical Problem to be Solved 
     However, the section of a plug terminal representing the above-mentioned effective mating length, i.e., the distance from a location of contact with a convex contact point portion of a receptacle terminal to the distal end (free end) of the plug terminal, is referred to as a “stub.” When high-speed signals are transmitted by connecting pairs of terminals, the transmitted signals may sometimes be reflected by said stubs and thus create resonance. As a result, there is a risk of degradation in the quality of high-speed signal transmission, e.g., the transmitted signals may be weakened. 
     The above-described signal reflection and, therefore, the degree of degradation in high-speed signal transmission quality reaches a maximum point when the frequency of the transmitted high-speed signals is a particular frequency (resonance frequency). Signal reflection occurs not only at the resonance frequency, but also within a predetermined range of frequencies in the vicinity of said resonance frequency. As the resonance frequency is approached, the degree of reflection increases and the high-speed signal transmission quality is simultaneously degraded. 
     In view of such circumstances, it is an object of the present invention to provide an electrical connector assembly capable of minimizing signal reflection and, therefore, degradation in signal transmission quality within a range of frequencies in the vicinity of the resonance frequency. 
     Technical Solution 
     It is an object to provide an electrical connector assembly capable of minimizing signal reflection and, therefore, degradation in signal transmission quality within a range of frequencies in the vicinity of a resonance frequency. 
     When signals are transmitted by contacting terminals having a contact arm portion extending in the direction of connector plugging and unplugging (referred to as “first terminals” for ease of discussion) and terminals having a convex contact portion (referred to as “second terminals” for ease of discussion), the section of the contact arm portion of the first terminals that extends in the above-mentioned direction of plugging and unplugging from the location of contact with the above-mentioned convex contact point portion to the free end portion of said contact arm portion forms a “stub” portion, and the main transmission path is formed by the second terminals and the section of the first terminals other than the stub portion. The inventors have found that when the impedance of a section corresponding to a predetermined range including the above-mentioned location of contact in the above-mentioned main transmission path is smaller than the impedance of the above-mentioned stub portion, signal reflection and, therefore, degradation in signal transmission quality is minimized within a range of frequencies in the vicinity of the resonance frequency. By taking this into account, the present invention attempts to determine the dimensions and shape of the terminals and the plastic terminal holder that retains said terminals in place. 
     &lt;First Invention&gt; 
     The electrical connector assembly according to the first invention has a first electrical connector and a second electrical connector that are mated in a manner permitting plugging into and unplugging from each other. 
     Such an electrical connector assembly according to the present invention is characterized in that the above-mentioned first electrical connector has multiple first terminals used for signal transmission arranged such that a direction perpendicular to the direction of plugging into and unplugging from the above-mentioned second electrical connector is the terminal array direction; said first terminals, in their free end portions located on the connector mating side, have contact arm portions extending in the above-mentioned direction of plugging and unplugging; the above-mentioned second electrical connector has multiple second terminals used for signal transmission arranged in the same direction as the above-mentioned terminal array direction; said second terminals, in their free end portions located on the connector mating side, have convex contact point portions contactable with the intermediate portions of the above-mentioned contact arm portions of the above-mentioned first terminals in the above-mentioned direction of plugging and unplugging; a section of the contact arm portions of the above-mentioned first terminals that extends from the location of contact with the convex contact point portions of the above-mentioned second terminals to the free end portion of said contact arm portions in the above-mentioned direction of plugging and unplugging forms a stub portion; the section of the first terminals other than the stub portion and the second terminals constitute a main transmission path; and, within a predetermined range including the above-mentioned location of contact in the above-mentioned main transmission path, the impedance of at least a partial range of said predetermined range is made smaller than the impedance of the above-mentioned stub portion. 
     In the present invention, within a predetermined range including the above-mentioned location of contact in the above-mentioned main transmission path, the impedance of at least a partial range of said predetermined range is made smaller than the impedance of the above-mentioned stub portion, as a result of which signal reflection and, therefore, degradation in signal transmission quality due to the presence of the stub portions is minimized even if the frequency of the signals transmitted over the above-mentioned main signal path is within the range of frequencies in the vicinity of the resonance frequency. 
     In the present invention, if the electrical length of the above-mentioned stub portion is L 0 ), then the electrical length of the section corresponding to the above-mentioned predetermined range in the above-mentioned main transmission path may be set to 4L 0 . The inventors have found that suppression of signal reflection is highly effective when the electrical length of the section corresponding to the above-mentioned predetermined range is set to about four times the electrical length of the above-mentioned stub portion. Therefore, if the electrical length of the above-mentioned stub portion is L 0 , then setting the electrical length of the section corresponding to the above-mentioned predetermined range to 4L 0  can more effectively minimize degradation in signal transmission quality. 
     In the present invention, the section corresponding to the above-mentioned predetermined range in the above-mentioned main transmission path may be adapted such that the electrical length of the section formed in a first terminal and the electrical length of the section formed in a second terminal are equal. The inventors have found that suppression of signal reflection becomes even more effective if, in the section corresponding to the above-mentioned predetermined range, the electrical length of the section formed in a first terminal is made equal to the electrical length of the section formed in a second terminal. Therefore, making the electrical length of the sections formed in the above-mentioned first terminals equal to the electrical length of the sections formed in the above-mentioned second terminals can more effectively minimize degradation in signal transmission quality. 
     The magnitude of a terminal&#39;s impedance is affected by the distance between said terminal and metallic members located around the periphery of said terminal (for example, other terminals, a ground plate, etc.) and by the surface area opposed thereto. Specifically, the smaller the above-mentioned opposed surface area, the smaller the capacitance of the terminal and, as a result, the larger the impedance. On the other hand, the larger the above-mentioned opposed surface area, the larger the capacitance of the terminal and, as a result, the smaller the impedance. In addition, the longer the above-mentioned distance, the smaller the capacitance of the terminal and, as a result, the larger the impedance. On the other hand, the shorter the above-mentioned distance, the larger the capacitance of the terminal and, as a result, the smaller the impedance. 
     In addition, the magnitude of a terminal&#39;s impedance is affected by the relative magnitude of electric permittivity around the periphery of said terminal. Specifically, the higher the permittivity around the periphery of the terminal, the larger the capacitance of the terminal and, as a result, the smaller the impedance. On the other hand, the lower the permittivity around the periphery of the terminal, the smaller the capacitance of the terminal and, as a result, the larger the impedance. 
     In the present invention, in the terminal array direction, the dimensions of the section corresponding to the above-mentioned predetermined range in the above-mentioned main transmission path may be made larger than the dimensions of the above-mentioned stub portion in the same direction. As a result of setting the dimensions of the section corresponding to the above-mentioned predetermined range in this manner, the inter-terminal distance in the section corresponding to the above-mentioned predetermined range becomes smaller than the inter-terminal distance in the stub portion. In addition, if a ground plate is in juxtaposition with the terminals, the surface area opposed to the above-mentioned ground plate in the section corresponding to the above-mentioned predetermined range becomes larger than the surface area opposed to the above-mentioned ground plate in the stub portion. As a result, the impedance of the section corresponding to the above-mentioned predetermined range can be made smaller than the impedance of the stub portion. 
     The present invention may be adapted such that dimensions in a direction perpendicular to both the terminal array direction and the direction of plugging and unplugging in the section corresponding to the above-mentioned predetermined range in the above-mentioned main transmission path are larger than dimensions in the same direction in the above-mentioned stub portion. As a result of setting the dimensions of the section corresponding to the above-mentioned predetermined range in this manner, for every two terminals adjacent in the terminal array direction, the opposed surface area of the two sections corresponding to the above-mentioned predetermined range becomes larger than the opposed surface area of the two stub portions. In addition, if a ground plate is in juxtaposition with the terminals, the distance to the above-mentioned ground plate in the section corresponding to the above-mentioned predetermined range becomes smaller than the distance to the above-mentioned ground plate in the stub portion. As a result, the impedance of the section corresponding to the above-mentioned predetermined range can be made smaller than the impedance of the stub portion. 
     The present invention may be adapted such that the first and second terminals are retained in place by a plastic terminal holder and at least a portion of the section corresponding to the above-mentioned predetermined range in the above-mentioned main transmission path is covered by a portion of the above-mentioned terminal holder in the above-mentioned direction of plugging and unplugging. Covering the section corresponding to the above-mentioned predetermined range with the above-mentioned terminal holder can make the impedance of the section corresponding to the above-mentioned predetermined range smaller than the impedance of the stub portion due to the fact that a plastic member of higher electric permittivity than air is present around the periphery of the section corresponding to said predetermined range. 
     The present invention may be adapted such that the convex contact point portions of the above-mentioned second terminals are shaped to protrude toward the contact arm portions of the above-mentioned first terminals, a guiding portion used for guiding the above-mentioned contact arm portions of the above-mentioned first terminals toward the above-mentioned locations of contact is formed within the range of the free ends of the above-mentioned second terminals, and the above-mentioned terminal holder of the above-mentioned first connector covers the above-mentioned first terminals at the location corresponding to the above-mentioned guiding portion in the above-mentioned direction of plugging and unplugging when the connectors are in a mated state. 
     The inventors have found that the smaller the impedance in the section corresponding to the above-mentioned predetermined range, particularly at locations in close proximity to the location of contact between the above-mentioned first terminal and the above-mentioned second terminal, the more pronounced the effect of minimizing the reflection of transmitted signals. In the present invention, as described above, when the connectors are in a mated state, the above-mentioned terminal holder covering the above-mentioned first terminals is caused to assume a position corresponding to the above-mentioned guiding portions of the second terminals, as a result of which said terminal holder becomes positioned in close proximity to the above-mentioned locations of contact in the above-mentioned direction of plugging and unplugging. As a result, impedance at locations in close proximity to the location of contact in the section corresponding to the above-mentioned predetermined range can be reduced. 
     Effects of the Invention 
     In the present invention, as described above, in a predetermined range including a location of contact between two terminals within the main transmission path through the first and second terminals, the impedance of at least a partial range of said predetermined range is made smaller than the impedance of the stub portion of the first terminals and, as a result, even if the frequency of the signals transmitted through the above-mentioned main transmission path is within the range of frequencies in the vicinity of the resonance frequency, signal reflection and, therefore, degradation in signal transmission quality due to the presence of the stub portions can be minimized. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  illustrates a perspective view illustrating an intermediate electrical connector and counterpart connectors according to a first embodiment of the present invention, in which the connectors are shown in an unmated state. 
         FIG. 2  illustrates a perspective view illustrating the intermediate electrical connector and counterpart connectors of  FIG. 1  in a mated state. 
         FIGS. 3  (A) and  3  (B) illustrate perspective views illustrating a blade used in the intermediate electrical connector of  FIG. 1 , wherein  FIG. 3  (A) shows a view from the side of the ground plate, and  FIG. 3  (B) shows a view from the side of the terminal array face. 
         FIGS. 4  (A) and  4  (B) illustrate perspective views from the side of the terminals, in which the terminals and the ground plate are shown removed from the blade of  FIG. 3  (B) and, at the same time, the counterpart signal terminals and the counterpart ground members are shown removed from the counterpart connectors, wherein  FIG. 4  (A) illustrates a state prior to connector mating, and  FIG. 4  (B) illustrates the connectors in a mated state. 
         FIGS. 5  (A) and  5  (B) illustrate partial cross-sectional views taken at the location of the signal terminals of the intermediate electrical connector and a counterpart connector in the connector width direction, wherein  FIG. 5  (A) illustrates a state prior to connector mating, and  FIG. 5  (B) illustrates the connectors in a mated state. 
         FIGS. 6  (A) and  6  (B) illustrate partial views of the intermediate electrical connector and a counterpart connector as seen in the blade array direction, wherein  FIG. 6  (A) illustrates a state prior to connector mating, and  FIG. 6  (B) illustrates the connectors in a mated state. 
         FIG. 7  illustrates a partial cross-sectional view taken at the location of the signal terminals of the intermediate electrical connector and a counterpart connector in the connector width direction in a variation of the first embodiment, in which the connectors are shown in mated state. 
         FIGS. 8  (A) to  8  (C) illustrate diagrams explaining the principles of the present invention, wherein  FIG. 8  (A) is a schematic diagram showing a main transmission path and a stub portion, and  FIGS. 8  (B) and  8  (C) are graphs showing relationships between the frequency of transmitted signals and the attenuation of the signals. 
         FIG. 9  illustrates a perspective view illustrating an electrical connector and a counterpart connector according to a second embodiment of the present invention, in which the connectors are in an unmated state. 
         FIG. 10  illustrates a perspective view illustrating the electrical connector and counterpart connector of  FIG. 9  in a mated state. 
         FIGS. 11  (A) and  11  (B) illustrate perspective views showing single terminals removed, respectively, from the electrical connector and a counterpart connector, wherein  FIG. 11  (A) illustrates a state prior to connector mating, and  FIG. 11  (B) illustrates the connectors in a mated state. 
         FIGS. 12  (A) and  12  (B) illustrate partial cross-sectional views taken at the location of the signal terminals of the electrical connector and a counterpart connector in the connector width direction, wherein  FIG. 12  (A) illustrates a state prior to connector mating, and  FIG. 12  (B) illustrates the connectors in a mated state. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention will be described below with reference to the accompanying drawings. 
     First Embodiment 
       FIG. 1  is a perspective view illustrating an intermediate electrical connector and counterpart connectors according to a first embodiment in an unmated state. In addition,  FIG. 2  is a perspective view illustrating the intermediate electrical connector and counterpart connectors of  FIG. 1  in a mated state. 
     The electrical connector assembly according to the present embodiment is a connector assembly used for the transmission of high-speed signals and has an intermediate electrical connector  1 , which is used as a first electrical connector (hereinafter referred to as “intermediate connector  1 ”), and counterpart connectors  2 ,  3 , which are used as second electrical connectors. The intermediate connector  1  and the counterpart connectors  2 ,  3  are connectors used for the transmission of high-speed signals. The counterpart connectors  2 ,  3  are electrical connectors for circuit boards disposed on respectively different circuit boards (not shown), which are mated with the intermediate connector  1  while being oriented such that the surface of the respective circuit boards is perpendicular to the up-down direction (Z-axis direction). In this manner, the counterpart connector  2  is mated to the intermediate connector  1  from above (side Z 1 ) and the counterpart connector  3  is mated thereto from below (side Z 2 ), as a result of which, as can be seen in  FIG. 2 , the two counterpart connectors  2 ,  3  are connected through the medium of the intermediate connector  1  (counterpart connector  3  not shown). In the present embodiment, the counterpart connectors  2 ,  3  are formed as connectors of exactly the same shape. 
     As can be seen in  FIG. 1 , the intermediate connector  1  has multiple plate-like blades  20  to be described hereinafter (see also  FIGS. 3  (A) and  3  (B)) and a support  10  made of an electrically insulating material used to arrange and support the above-mentioned multiple blades  20  at predetermined intervals in the through-thickness direction thereof. Said support  10 , which has a substantially rectangular parallelepiped-like external configuration whose longitudinal direction is the array direction (X-axis direction) of the blades  20 , also serves as a housing. The support  10  is formed by combining an upper support member  11  and a lower support member  12  in the up-down direction. 
     The upper support member  11  has perimeter walls  11 A of a square frame configuration when viewed from above, which enclose the multiple blades  20 , and multiple restricting portions (not shown), which are used to position the respective blades  20  within a predetermined location range in the array direction of said blades  20 . The perimeter walls  11 A have two lateral walls  11 B, which extend in the array direction (X-axis direction) of the blades  20 , and two end walls  11 C, which extend in the connector width direction (Y-axis direction) perpendicular to said longitudinal direction and couple the two ends of the above-mentioned two lateral walls  11 B. Within the space enclosed by the perimeter walls  11 A, the above-mentioned restricting portions, which are shaped as plates whose major faces are perpendicular to the array direction of the blades  20  and which couple the two interior wall surfaces of the two lateral walls  11 B, are formed in array form at predetermined intervals in the above-mentioned array direction. 
     Slit-like spaces formed extending in the up-down direction between two mutually adjacent restricting portions or between said restricting portions and the end walls  11 C constitute blade holding spaces (not shown) used to hold the blades  20 . In the present embodiment, the above-mentioned restricting portions are positioned in a manner that permits abutment against the major faces of the blades  20  contained within the above-mentioned blade holding spaces, as a result of which said blades  20  can be positioned within a predetermined location range in the array direction (X-axis direction). In addition, upper stepped support portions (not shown) used to support the hereinafter-described supported protrusions  21 A of the blades  20  (see  FIGS. 3  (A) and  3  (B)) from above are formed on the interior wall surface of the lateral walls  11 B in the above-mentioned longitudinal direction (X-axis direction) at locations that correspond to the respective blade holding spaces and, at the same time, are proximal to the lower ends in the up-down direction (Z-axis direction). 
     As can be seen in  FIG. 1 , the perimeter walls  11 A extend upwardly past the upper ends of the restricting portions. The space enclosed by this upwardly extending section, which is upwardly open and, at the same time, is in communication with the above-mentioned blade holding spaces, is formed as an upper receiving portion  11 D used to receive the counterpart connector  2  from above. As can be seen in  FIG. 1 , when the blades  20  are held within the blade holding spaces, the upper end sections of the blades  20  protrude from the upper end openings of the blade holding spaces and are located within the upper receiving portion  11 D. 
     The lower support member  12  of the support  10  has perimeter walls  12 A which, when viewed in the up-down direction, have a square frame configuration of the same dimensions as the perimeter walls  11 A of the previously discussed upper support member  11 . Said perimeter walls  12 A have two lateral walls  12 B, which extend in the array direction of the above-mentioned blades  20 , and two end walls  12 C, which extend in a transverse direction perpendicular to said longitudinal direction and couple the two ends of the above-mentioned two lateral walls  12 B. Lower stepped support portions (not shown) used to support the hereinafter-described supported protrusions  21 A of the blades  20  from below are formed on the interior wall surface of the lateral walls  12 B in the above-mentioned array direction at locations that correspond to the respective blade holding spaces and, at the same time, are proximal to the upper ends in the up-down direction. 
     In addition, the space enclosed by the lower support member  12 , which is downwardly open at a location below the lower ends of the restricting portions of the support  10  and, at the same time, is in communication with the blade holding spaces, is formed as a lower receiving portion used to receive the counterpart connector  3  from below. When the blades  20  are held within the blade holding spaces, the lower end sections of the blades  20  protrude from the lower end openings of the blade holding spaces and are located within the above-mentioned lower receiving portion. 
     The support  10  is assembled by fitting the lower support member  12  to the upper support member  11  from below. As can be seen in  FIG. 1 , when the upper support member  11  and the lower support member  12  are combined, the lateral walls of the support  10  are formed by the lateral walls  11 B of the upper support member  11  and the lateral walls  12 B of the lower support member  12 , while the end walls of the support  10  are formed by the end walls  11 C of the upper support member  11  and the end walls  12 C of the lower support member  12 . 
       FIGS. 3  (A) and  3  (B) provide perspective views of a single blade  20 , wherein  FIG. 3  (A) shows a view from the side of the ground plate, and  FIG. 3  (B) shows a view from the side of the terminal array face.  FIGS. 4  (A) and  4  (B) illustrate a view from the side of the terminals  22 , in which the terminals  22  and the ground plate  23  are shown removed from the blade  20  of  FIG. 3  (B) and, at the same time, the counterpart signal terminals  40  and ground members  50  are shown removed from the counterpart connectors  2 ,  3 , wherein  FIG. 4  (A) illustrates a state prior to connector mating, and  FIG. 4  (B) shows the connectors in a mated state. 
     As shown in  FIGS. 3  (A) and  3  (B), the blade  20  has a substrate  21  used as a plate-like plastic terminal holder, vertically extending strip-shaped signal terminals  22  used as multiple first terminals, which are retained in place in array form via unitary co-molding on one major face of the substrate  21  (surface extending in the Y-Z direction), and a single metal ground plate  23  attached to the other major face of the substrate  21 . Below, the above-mentioned first major face is referred to as a “terminal array face,” and the above-mentioned other major face is referred to as a “ground plate mounting face.” 
     As can be seen in  FIGS. 3  (A) and  3  (B), the substrate  21  has supported protrusions  21 A formed as projections at locations proximal to the lower ends of its vertically extending two lateral edges and, as described below, said supported protrusions  21 A are adapted to be supported by the upper stepped support portions and lower stepped support portions of the support  10  from above and below. As can be seen in  FIG. 3  (A), the substrate  21  has multiple retaining studs  21 B used to retain the ground plate  23  in place formed as projections on its ground plate mounting face. 
     In addition, as can be seen in  FIG. 3  (B), an upper cover portion  21 C, a lower cover portion  21 D, and a central cover portion  21 E, which partially cover the signal terminals  2 , are formed on the terminal array face of the substrate  21  at locations respectively proximal to the upper end, lower end, and center of said substrate  21 . The upper cover portion  21 C, which extends over the terminal array range, covers the upper end sections of the hereinafter-described intermediate line portions  22 C of said signal terminals  22  with sections extending in the up-down direction at the locations of said signal terminals  22  in the terminal array direction (Y-axis direction). The lower cover portion  21 D, whose shape is an inverse of the upper cover portion  21 C in the up-down direction, covers the lower end sections of the hereinafter-described intermediate line portions  22 C of said signal terminals  22  with sections extending in the up-down direction at the locations of the signal terminals  22  in the terminal array direction (Y-axis direction). The central cover portion  21 E, which extends over the terminal array range, covers a curved section formed in the central area of the hereinafter-described intermediate line portions  22 C of the signal terminals  22  in the up-down direction. 
     The multiple signal terminals  22 , which are fabricated by stamping and partially bending a metal sheet in the through-thickness direction, have a strip-like general configuration extending in the up-down direction (Z-axis direction). Said signal terminals  22 , whose major faces are oriented at right angles to the array direction (X-axis direction) of the blades  20 , are arranged at equal intervals in a terminal array direction coinciding with the width direction (Y-axis direction) of the blades  20  and are retained in place on the substrate  21  via unitary co-molding. 
     In the present embodiment, pairs of mutually adjacent signal terminals  22  are formed as paired terminals intended for the transmission of high-speed differential signals. An example in which 5 pairs of paired terminals are provided in a single blade  20  is illustrated in  FIG. 3  (B) and  FIGS. 4  (A) and  4  (B). Among the 5 pairs of paired terminals, the two pairs located at both ends in the connector width direction (Y-axis direction) and the single pair of paired terminals located in the center do not cross, but form pseudo cross-pairs which, as a result of being bent so as to approach each other at an intermediate location in the up-down direction, appear to intersect when viewed in the array direction (X-axis direction) of the blades  20 . In addition, the rest of the paired terminals form cross-pairs crossing each other at an intermediate location in the up-down direction. In the present embodiment, the transmission of high-speed differential signals is made possible by forming pseudo cross-pairs or cross-pairs made up of two mutually adjacent signal terminals  22  in this manner. 
     As can be seen in  FIGS. 4  (A) and  4  (B), at their upper end, a pair of signal terminals  22  forming a pseudo cross-pair has formed therein upper contact arm portions  22 A used for contacting the hereinafter-described counterpart signal terminals  40  provided in the counterpart connector  2  and, at their lower end, has formed therein lower contact arm portions  22 B used for contacting the counterpart signal terminals  40  provided in the counterpart connector  3 , with said upper contact arm portions  22 A and said lower contact arm portions  22 B coupled by vertically extending intermediate line portions  22 C. Said upper contact arm portions  22 A and said lower contact arm portions  22 B are shaped to be vertically symmetrical. Below, the upper contact arm portions  22 A and lower contact arm portions  22 B are referred to as “contact arm portions  22 A,  22 B” for ease of discussion when there is no need to distinguish between the two. 
     The upper end portions (free end portions) of the upper contact arm portions  22 A and the lower end portions (free end portions) of the lower contact arm portions  22 B are bent in a crank-like configuration to one side (side X 1  in  FIGS. 4  (A) and  4  (B)) in the through-thickness direction thereof (X-axis direction). A major portion of the free ends of said contact arm portions  22 A,  22 B bent in a crank-like configuration is embedded in the substrate  21  (see  FIG. 4  (B),  FIGS. 5  (A) and  5  (B), and  FIG. 6  (A)). On the other hand, the rectilinear sections of the contact arm portions  22 A,  22 B not including the above-mentioned free end portions have their two vertically extending lateral end faces (through-thickness faces) and their major faces located on side X 1  (rolled faces) retained in place on the substrate  21 , with their faces on side X 2  exposed on said substrate  21 . 
     The width dimensions (dimensions in the Y-axis direction) of the contact arm portions  22 A,  22 B are made smaller and narrower than those of the intermediate line portions  22 C. In addition, the contact arm portions  22 A,  22 B are narrower than the hereinafter-described resilient signal arm portions  41  of the counterpart signal terminals  40  provided in the counterpart connectors  2 ,  3  (see  FIGS. 6  (A) and  6  (B)). Therefore, the spacing between two upper contact arm portions  22 A and two lower contact arm portions  22 B mutually adjacent in the Y-axis direction is wider than the spacing between two rectilinear sections of mutually adjacent intermediate line portions  22 C of the signal terminals  22  and the spacing between two resilient signal arm portions  41  of the counterpart signal terminals  40 . 
     In addition, the exposed faces (faces on side X 2 ) of the above-mentioned rectilinear sections of the contact arm portions  22 A,  22 B form inclined surfaces inclined toward side X 1  as one moves from the central area in the terminal width direction (Y-axis direction) toward the two lateral ends in the terminal width direction (see  FIG. 4  (A) and  FIG. 6  (A)). In other words, as a result of forming the above-mentioned inclined surfaces, the through-thickness dimensions (dimensions in the X-axis direction) of said contact arm portions  22 A,  22 B are made smaller than those of the intermediate line portions  22 C. 
     As can be seen in  FIG. 5  (B), in a state of contact with the convex signal contact point portions  41 A of the hereinafter-described counterpart signal terminals  40 , a section corresponding to a range S (hereinafter, “stub range S”) extending in the up-down direction from the location of contact P with said convex signal contact point portions  41 A to the free end (upper end) of said upper contact arm portions  22 A constitutes a stub portion  22 A- 1 . The length of said stub portion  22 A- 1  will be longer or shorter depending on the location of contact P of the upper contact arm portions  22 A with the convex signal contact point portions  41 A in the up-down direction. Namely, the closer said location of contact P is to the proximal end (lower end in  FIG. 5  (B)) of the upper contact arm portions  22 A, the larger the stub range S becomes and, correspondingly, the longer the stub portion  22 A- 1  will be; and, the closer said location of contact P is to the upper end (upper end in  FIG. 5  (B)) of the upper contact arm portions  22 A, the smaller the stub range S becomes and, correspondingly, the shorter the stub portion  22 A- 1  will be. 
     It should be noted that while in the present embodiment the contact arm portions  22 A,  22 B of the signal terminals  22  are designed to be unitarily molded and retained in place on the substrate  21  without resilient displacement, absence of resilient displacement is not of the essence. For example, by extending the contact arm portions from the ends of the substrate  21  in the up-down direction, the contact arm portions may be formed in a manner permitting resilient displacement in the through-thickness direction of said contact arm portions. 
     As can be seen in  FIGS. 4  (A) and  4  (B), after extending so as to approach each other in the central area in the up-down direction, the intermediate line portions  22 C of the signal terminals  22  that form pseudo cross-pairs then extend in a curved shape so as go back to the intermediate line portions  22 C. Although two portions forming part of one intermediate line portion  22 C and another intermediate line portion  22 C overlap in the above-mentioned central area in said pseudo cross-pairs when viewed in the X-axis direction, these intermediate line portions  22 C are not in contact as a result of being bent in a direction that keeps them spaced apart in the through-thickness direction (X-axis direction). Further, as can be seen in  FIGS. 4  (A) and  4  (B), the intermediate line portions  22 C of the signal terminals  22  forming the cross-pairs intersect without coming into contact with each other because one intermediate line portion  22 C and the other intermediate line portion  22 C are bent in a direction that keeps them spaced apart in the through-thickness direction in the central area in the up-down direction. 
     The upper end sections of the intermediate line portions  22 C coupled to the upper contact arm portions  22 A, the lower end sections coupled to the lower contact arm portions  22 B, and parts of the curved sections formed in the above-mentioned central area are embedded in the substrate  21  (see  FIG. 3  (B)). As far as other sections of said intermediate line portions  22 C are concerned, as can be seen in  FIG. 3  (B), the two lateral end faces (through-thickness faces) and major faces located on side X 1  (rolled faces) are retained in place on the substrate  21 , and the faces on side X 2  are exposed on said substrate  21 . 
     The ground plate  23  is fabricated by stamping sheet metal. As can be seen in  FIG. 3  (A), multiple retained aperture portions  23 A used to receive the retaining studs  21 B of the substrate  21  are formed through the ground plate  23  at locations corresponding to each retaining stud  21 B. Said retained aperture portions  23 A form long holes larger than the retaining studs  21 B in the up-down direction, with the dimensions of said long holes being slightly larger than those of the retaining studs  21 B in the top halves, and slightly smaller than those of the retaining studs  21 B in the bottom halves. 
     The upper end portion of the ground plate  23  has formed therein multiple upper notched portions  23 B cut out at equal intervals in the terminal array direction (Y-axis direction), and upper ground contact portions  23 C, which are contactable with the hereinafter-described convex ground contact point portions  51 A of the ground members  50  provided in the counterpart connector  2 , are formed on both sides of said upper notched portions  23 B. The upper ground contact portions  23 C are provided at locations between two upper contact arm portions  22 A of the signal terminals  22  in the terminal array direction (Y-axis direction) as well as at the same location as the upper end portions of the above-mentioned upper contact arm portions  22 A in the up-down direction (Z-axis direction). In addition, the lower end portion of the ground plate  23  is shaped as a vertical inversion of the upper end portion and has formed therein lower notched portions  23 D and lower ground contact portions  23 E. 
     When the ground plate  23  is mounted to the substrate  21 , the retaining studs  21 B of the substrate  21  are introduced into the top halves of the respectively corresponding retained aperture portions  23 A and the ground plate  23  is brought into surface contact with the ground plate mounting face of the substrate  21 . While in this surface contact state, the ground plate  23  is slid in the upward direction, thereby causing the retaining studs  21 B to be press-fitted into the bottom halves of the retained aperture portions  23 A. As a result, as can be seen in  FIG. 3  (A), the ground plate  23  is retained in place while covering substantially the entire extent of the above-mentioned ground plate mounting face of the substrate  21 , thereby finishing the blades  20 . 
     The intermediate connector  1  according to the present embodiment is assembled in accordance with the following procedure. First, the blades  20  are inserted into the respective multiple blade holding spaces of the upper support member  11  from below said upper support member  11 . At such time, all the blades  20  are oriented such that their terminal array faces face toward the same side (side X 2 ) (see  FIGS. 5  (A) and  5  (B)). Next, the lower support member  12  is fitted to the upper support member  11  from below, thereby completing the assembly of the intermediate connector  1 . Here, the supported protrusions  21 A of the blades  20  are supported from above and below between the upper stepped support portions of the upper support member  11  and the lower stepped support portions of the lower support member  12 , thereby preventing extraction of the blades  20  from the above-mentioned blade holding spaces. 
     The configuration of the counterpart connectors  2 ,  3  will be described below. Since the counterpart connectors  2 ,  3  have exactly the same configuration, here, the discussion will focus primarily on the counterpart connector  3  while appropriately referencing the configuration of the counterpart connector  2  illustrated in  FIG. 5  and  FIG. 6 . As can be seen in  FIG. 1 , the counterpart connector  3  has a plastic housing  30 , which is formed in a rectangular parallelepiped-like external configuration adapted to the lower receiving portion of the intermediate connector  1 , counterpart signal terminals  40 , which serve as multiple second terminals and are retained in said housing  30  in array form (see  FIG. 5  and  FIG. 6 ), and ground members  50 , which extend in the connector width direction (Y-axis direction) over the terminal array range and are retained in the housing  30  (see  FIG. 5  and  FIG. 6 ). 
     As can be seen in  FIG. 1 , the housing  30  has a plastic holder  31  serving as a terminal holder, which extends parallel to the mounting face of a circuit board (not shown) and retains the counterpart signal terminals  40  and ground members  50  in place, and a plastic container  32 , which is fitted to said holder  31  from above and accommodates the counterpart signal terminals  40  and ground members  50 . The holder  31  has formed therein signal-type retaining aperture portions  31 A in which the hereinafter-described signal-side retained portions  42  of the counterpart signal terminals  40  are secured via press-fitting, and grounding-type retaining aperture portions  31 B in which the hereinafter-described ground-side retained portions  52  of the ground members  50  are secured via press-fitting (see  FIGS. 5  (A) and  5  (B)). The above-mentioned signal-type retaining aperture portions  31 A and grounding-type retaining aperture portions  31 B are formed through the holder  31  in the up-down direction. 
     The container  32  has perimeter walls  32 A, which have a square frame configuration when viewed in the up-down direction, and multiple containing walls  32 B, which extend in the connector width direction (Y-axis direction) in the space enclosed by said perimeter walls  32 A. The perimeter walls  32 A have two lateral walls  32 A- 1 , which extend in the longitudinal direction (X-axis direction) of the housing  30 , and two end walls  32 A- 2 , which extend in the connector width direction (Y-axis direction), i.e., in a transverse direction perpendicular to said longitudinal direction, and couple the two ends of the above-mentioned two lateral walls  32 A- 1 . The multiple containing walls  32 B extend in the connector width direction (Y-axis direction) and couple the two lateral walls  32 A- 1 . Signal-type holding grooves  32 B- 1 , which are used to hold the hereinafter-described resilient signal arm portions  41  of the counterpart signal terminals  40 , are formed extending in the up-down direction on the major face that is located on side X 2  of the two major faces (faces extending in the Y-Z direction) of said containing walls  32 B. Meanwhile, grounding-type holding grooves  32 B- 2 , which are used to hold the hereinafter-described grounding resilient arm portions  51  of the ground members  50 , are formed extending in the up-down direction on the major face of the containing walls  32 B located on side X 1 . 
     As can be seen in  FIGS. 4  (A) and  4  (B), the multiple counterpart signal terminals  40 , which are made of strip-shaped sheet metal members extending in the up-down direction and have their major faces oriented perpendicular to the longitudinal direction (X-axis direction) of the counterpart connector  2 , are arranged in alignment with the terminals  22  of the intermediate connector  1  in the connector width direction (Y-axis direction). Said counterpart signal terminals  40 , which are provided along the major faces of the containing walls  32 B located on side X 1 , are secured within the signal-type holding grooves  32 B- 1  via press-fitting. In the present embodiment, the through-thickness dimensions (dimensions in the X-axis direction) of the counterpart signal terminals  40  are made larger than the through-thickness dimensions of the lower contact arm portions  22 B of the signal terminals  22  provided in the intermediate connector  1 . In addition, as far as the resilient signal arm portions  41  are concerned, the terminal width dimensions (dimensions in the Y-axis direction) of the hereinafter-described resilient signal arm portions  41  and signal-side retained portions  42  are made larger than the terminal width dimensions of the lower contact arm portions  22 B of the signal terminals  22  provided in the intermediate connector  1 . 
     As can be seen in  FIG. 4  (A), the counterpart signal terminals  40  have resilient signal arm portions  41 , which extend in the up-down direction and are resiliently displaceable in their through-thickness direction (X-axis direction), signal-side retained portions  42 , which extend downwardly from the lower ends of said resilient signal arm portions  41 , and signal connecting portions  43 , which extend downwardly from the lower ends of said signal-side retained portions  42 . The resilient signal arm portions  41  extend upwardly from the top face of the holder  31  of the housing  30  through the signal-type holding grooves  32 B- 1  of the container  32  (see  FIG. 1 ). Convex signal contact point portions  41 A protruding in a convex curved configuration toward side X 1 , in other words, toward the terminals  22  of the intermediate connector  1  when the connectors are in a mated state, are formed by bending in the upper end portions (free end portions) of said resilient signal arm portions  41 . The sections protruding outside the signal-type holding grooves  32 B- 1  (protruding apex portions) of said convex signal contact point portions  41 A are resiliently contactable with the lower contact arm portions  22 B of the signal terminals  22  of the intermediate connector  1 . In addition, guiding portions  41 B used for guiding the signal terminals  22  of the intermediate connector  1  in the X-axis direction toward the regular locations of contact are formed within the range that is located closer to the free ends, i.e., to the upper ends, than the protruding apex portions of the convex signal contact point portions  41 A (see  FIGS. 5  (A) and  5  (B)). 
     It should be noted that while in the present embodiment the sections of the counterpart signal terminals  40 , in which the convex signal contact point portions  41 A are formed, are resiliently displaceable resilient signal arm portions  41 , being capable of resilient displacement is not essential for said sections. For example, vertically extending contact arm portions not capable of resilient displacement may be provided in the counterpart signal terminals  40  instead of the above-mentioned resilient signal arm portions  41 , and convex signal contact point portions may be formed in said contact arm portions. 
     The signal-side retained portions  42  are press-fitted into the signal-type retaining aperture portions  31 A of the holder  31  of the housing  30  from above and are retained in place within said signal-type retaining aperture portions  31 A because press-fit projections formed on the lateral edges of said signal-side retained portions  42  bite into the interior wall surface of the signal-type retaining aperture portions  31 A. As can be seen in  FIG. 1 , the signal connecting portions  43 , which project in a rectilinear manner downwardly from the bottom face of the holder  31  of the housing  30 , have solder balls B provided at the lower ends thereof for solder connection to a circuit board (see also the solder balls B of the counterpart connector  2 ). 
     The ground members  50 , which are fabricated by partially bending a single sheet metal member in the through-thickness direction, have multiple grounding resilient arm portions  51 , which extend in the up-down direction and are resiliently displaceable in the through-thickness direction (X-axis direction) thereof, ground-side retained portions  52 , which extend downwardly from the lower ends of said grounding resilient arm portions  51 , ground connecting portions  53 , which extend downwardly from the lower ends of said ground-side retained portions  52 , and coupling portions  54 , which couple the two lower ends of adjacent grounding resilient arm portions  51 . 
     The grounding resilient arm portions  51  extend upwardly from the top face of the holder  31  of the housing  30  through the grounding-type holding grooves  32 B- 2  of the container  32 . The upper end portions (free end portions) of said grounding resilient arm portions  51  are bent so as to protrude toward side X 2 , and the protruding sections located outside the grounding holding grooves  32 B- 2  form convex ground contact point portions  51 A resiliently contactable with the upper ground contact portions  23 C of the ground plate  23  of the intermediate connector  1 . Said grounding resilient arm portions  51  are provided at locations offset with respect to the resilient signal arm portions  41  of the counterpart signal terminals  40  in the connector width direction (Y-axis direction). 
     The ground-side retained portions  52  are press-fitted into the signal-type retaining aperture portions  31 A of the holder  31  of the housing  30  from above and are retained in place within said signal-type retaining aperture portions  31 A because press-fit projections formed on the lateral edges of said ground-side retained portions  42  bite into the interior wall surface of the signal-type retaining aperture portions  31 A. As can be seen in  FIG. 1 , the ground connecting portions  53 , which project in a rectilinear manner downwardly from the bottom face of the holder  31  of the housing  30 , have solder balls B provided at the lower ends thereof for solder connection to a circuit board (see also the solder balls B of the counterpart connector  2 ). The coupling portions  54  extend in the connector width direction between the lower end portions of adjacent grounding resilient arm portions  51  and couple said two lower ends. 
     Since the counterpart connector  2  has the same configuration as the previously discussed counterpart connector  3 , the respective components of the counterpart connector  2  are assigned the same reference numerals as the corresponding sections of the counterpart connector  3  and not further discussed herein. 
     Next, the operation of connector mating will be described with reference to  FIG. 1 ,  FIG. 2 ,  FIG. 5 , and in  FIG. 6 .  FIG. 5  provides cross-sectional views taken at the location of the signal terminals  22  and counterpart signal terminals  40  of the intermediate connector  1  and counterpart connector  2  in the connector width direction, wherein  FIG. 5  (A) illustrates a state prior to connector mating, and  FIG. 5  (B) illustrates the connectors in a mated state. In addition,  FIG. 6  provides partial views of the intermediate connector  1  and the counterpart connector as seen in the array direction of the blades  20 , wherein  FIG. 6  (A) illustrates a state prior to connector mating, and  FIG. 6  (B) illustrates the connectors in a mated state.  FIG. 5  and  FIG. 6  provide enlarged partial cross-sectional views of the state in which in which support  10  of the intermediate connector  1  and the container  32  of the counterpart connector  2  have been removed. 
     First, the counterpart connectors  2 ,  3  are solder-connected to the corresponding circuits of the respectively corresponding circuit boards and, as shown in  FIG. 1 , the intermediate connector  1  is positioned above the counterpart connector  3 . The intermediate connector  1  and the counterpart connector  3  are then mated by lowering the intermediate connector  1  (see  FIG. 2 ). At such time, the entire counterpart connector  3  is accommodated within the lower receiving portion of the intermediate connector  1 . 
     In the process of connector mating, the lower end portions of the blades  20  resiliently displace the grounding resilient arm portions  51  of the ground members  50  and the resilient signal arm portions  41  of the counterpart signal terminals  40  of the counterpart connector  3  so as to spread them apart and enter between the two from above. Then, in the mated state, when the resilient signal arm portions  41  are in a state of resilient displacement, the convex signal contact point portions  41 A of the counterpart signal terminals  40  provided in the counterpart connector  3  are brought into contact with, and electrically connected to, the intermediate portions in the up-down direction of the lower contact arm portions  22 B of the signal terminals  22  provided in the blades  20  of the intermediate connector  1 . 
     In addition, in the mated state, when said grounding resilient arm portions  51  of the ground members  50  are in a state of resilient displacement, the convex ground contact point portions  51 A of the ground members  50  provided in the counterpart connector  3  are brought into contact with, and electrically connected to, the lower ground contact portions  23 E of the ground plate  23  provided in the blades  20  of the intermediate connector  1  (see also  FIG. 5  (B), which illustrates the upper ground contact portions  23 C of the counterpart connector  2 ). The state of contact of the signal terminals  22  and the counterpart signal terminals  40  as well as the state of contact of the ground plate  23  and the ground members  50  between the intermediate connector  1  and the counterpart connector  3  are identical to the state of contact between the intermediate connector  1  and the counterpart connector  2  described hereinafter with reference to  FIGS. 5  (A) and  5  (B). 
     Next, as can be seen in  FIG. 1 ,  FIG. 5  (A), and  FIG. 6  (A), the counterpart connector  2  is positioned above the intermediate connector  1  in an orientation obtained by flipping that of the counterpart connector  3 . The intermediate connector  1  and the counterpart connector  2  are then mated by lowering the counterpart connector  2 . At such time, as can be seen in  FIG. 2 , the entire counterpart connector  2  is accommodated within the upper receiving portion  11 D of the intermediate connector  1 . 
     In the process of connector mating, the upper end portions of the blades  20  resiliently displace the grounding resilient arm portions  51  of the ground members  50  and the resilient signal arm portions  41  of the counterpart signal terminals  40  of the counterpart connector  2  so as to spread them apart and enter between the two from below. Then, in the mated state, as can be seen in  FIG. 5  (B), when the resilient signal arm portions  41  are in a state of resilient displacement, the convex signal contact point portions  41 A of the counterpart signal terminals  40  provided in the counterpart connector  2  are brought into contact with, and electrically connected to, the intermediate portions in the up-down direction of the upper contact arm portions  22 A of the signal terminals  22  provided in the blades  20  of the intermediate connector  1 . As can be seen in  FIG. 5  (B), at such time, when the connectors are in a mated state, a stub portion  22 A- 1  is formed by a section of the upper contact arm portion  22 A extending from the location of contact P with the convex signal contact point portion  41 A of the counterpart signal terminal  40  to the upper end portion of the upper contact arm portion  22 A. In  FIG. 5  (B), the vertical range of the stub portion  22 A- 1  is designated as “S”. 
     In addition, as can be seen in  FIG. 5  (B), after mating the connectors, when the grounding resilient arm portions  51  of the ground members  50  are in a state of resilient displacement, the convex ground contact point portions  51 A of the ground members  50  provided in the counterpart connector  2  are brought into contact with, and electrically connected to, the upper ground contact portions  23 C of the ground plate  23  provided in the blades  20  of the intermediate connector  1 . 
     As can be seen in  FIG. 5  (B), in the present embodiment, once the connectors are mated, a main transmission path used to transmit high-speed signals is formed by sections other than the stub portions  22 A- 1  in the signal terminals  22  of the intermediate connector  1  and sections other than the guiding portions  41 B in the counterpart signal terminals  40  of the counterpart connector  2 . 
     In the present embodiment, as shown in  FIG. 5  (B), a predetermined range within the above-mentioned main transmission path that includes the location of contact P between the upper contact arm portion  22 A of the signal terminals  22  and the convex signal contact point portion  41 A of the counterpart signal terminals  40  is designated as “R”. Specifically, the predetermined range R is a vertical range extending between the upper end (at the same level as the top face of the holder  31  in the up-down direction) of the signal-side retained portion  42  of the counterpart signal terminals  40  provided in the counterpart connector  2  and the lower end of the upper cover portion  21 C of the substrate  21  of the blades  20  provided in the intermediate connector  1 . In addition, in  FIG. 5  (B), this predetermined range R is split into a first range R 1  located below the location of contact P and a second range R 2  located above the location of contact P such that said location of contact P forms a boundary therebetween in the up-down direction. Further, the above-mentioned first range R 1  is split in the up-down direction into a first upper range R 1 A, which extends from the location of contact P to the upper end of the upper cover portion  21 C, and a first lower range R 1 B, which extends from the upper end of said upper cover portion  21 C to the lower end of said upper cover portion  21 C. 
     The bottom portion of the upper contact arm portions  22 A of the signal terminals  22  is located in the first upper range R 1 A within the first range R 1 , and the impedance of the first upper range R 1 A is substantially equal to the impedance of the range (stub range) S of the stub portion  22 A- 1 . 
     The upper end sections of the intermediate line portions  22 C of the signal terminals  22  are located in the first lower range R 1 B within the first range R 1 . In comparison with the stub portion  22 A- 1 , which forms part of the upper contact arm portion  22 A, the upper end sections of said intermediate line portions  22 C are larger both in the terminal width direction (Y-axis direction) and in the through-thickness direction (X-axis direction). In addition, since the upper cover portion  21 C of the substrate  21  is present in said first lower range R 1 B, the upper end sections of the intermediate line portions  22 C are covered by the substrate  21  around their entire periphery. Therefore, the impedance of the first lower range R 1 B is smaller than the impedance of the range (stub range) S of the stub portion  22 A- 1 . 
     In addition, the resilient signal arm portions  41  and signal-side retained portions  42  of the counterpart signal terminals  40  are located in the second range R 2 . In comparison with the stub portions  22 A- 1 , which form part of the upper contact arm portion  22 A of the signal terminals  22 , said resilient signal arm portions  41  and signal-side retained portions  42  are larger both in the terminal width direction (Y-axis direction) and in the through-thickness direction (X-axis direction). In addition, the retained portions  42  are covered by the holder  31  of the plastic housing  110  around the entire periphery of said retained portions  42 . Therefore, the impedance of the second range R 2  is smaller than the impedance of the range (stub range) S of the stub portion  22 A- 1 . 
     As discussed above, in the present embodiment, the impedance of the first lower range R 1 B located below the above-mentioned location of contact P within the above-mentioned predetermined range R and the second range R 2  located above the above-mentioned location of contact P is smaller than the impedance of the stub range S. Making impedance in a majority of the above-mentioned predetermined range R smaller than impedance in said stub range S in this manner makes is possible to minimize signal reflection and, therefore, degradation in signal transmission quality due to the presence of the stub portions  22 A- 1  even if the frequency of the signals transmitted over the above-mentioned main transmission path is within the range of frequencies in the vicinity of the resonance frequency. 
     Although in the present embodiment, as discussed above, the impedance of the first upper range R 1 A is equal to the impedance of the range (stub range) S of the stub portion  22 A- 1 , for example, as described below with reference to  FIG. 7 , if a mating depth position is set, as the regular location of contact, such that the above-mentioned location of contact P in the upper contact arm portions  22 A of the signal terminals  22  is closer to the intermediate line portion  22 C and the first upper range R 1 A is made smaller in the up-down direction, the range within the above-mentioned predetermined range R, in which impedance is smaller than that in the stub range S, can be increased and, as a result, signal reflection and, therefore, degradation in signal transmission quality can be effectively minimized. 
       FIG. 7  is a partial cross-sectional view taken at the location of the signal terminals  22  of the intermediate connector  1  and a counterpart connector  2  in the connector width direction in a variation of the present embodiment in which the connectors are shown in a mated state. In the variation of  FIG. 7 , the shape of the upper cover portion  21 C of the substrate  21  of the blade  20  is more upwardly extended in comparison with the upper cover portion  21 C shown in  FIG. 5  (B), with its upper end section located in alignment with the guiding portion  41 B of the counterpart signal terminals  40  in the up-down direction. Shaping the upper cover portion  21 C in this manner positions the upper end of said upper cover portion  21 C in close proximity to the location of contact P between the two terminals in the up-down direction and, at the same time, expands the range in which the signal terminals  22  are covered by the upper cover portion  21 C. As a result, impedance can be reduced over a wider range within the first range R 1  and, consequently, within the above-mentioned predetermined range R. 
     In addition, if the electrical length of the above-mentioned stub portion  22 A- 1  is L 0 , then, as described below, the electrical length of the section including the above-mentioned predetermined range R is preferably about 3L 0  to 4L 0 . Configuring the electrical length of the section including said predetermined range R in this manner makes it possible to minimize signal reflection and, therefore, degradation in signal transmission quality in a more efficient manner. 
     In addition, the electrical length of the first range R 1  in the signal terminals  22  of the intermediate connector  1  and the electrical length of the second range R 2  in the counterpart signal terminals  40  of the counterpart connector  2  are preferably equal. Making the electrical length of the first range R 1  and second range R 2  equal in this manner makes it possible to minimize signal reflection and, therefore, degradation in signal transmission quality in an even more efficient manner. 
     While the relationship of impedance magnitudes has been described for the connection between the intermediate electrical connector  1  and the counterpart connector  2  with reference to  FIGS. 5  (A) and  5  (B),  FIG. 7 , etc., it goes without saying that the previously described effects of the present invention will be obtained as a result of the same connection between the intermediate electrical connector  1  and the counterpart connector  3 . 
     Next, the principles of the present invention will be described with reference to  FIG. 8  (A-C) and, in addition, reasons will be explained as to why, as described below, it is preferable that the electrical length of the section including the above-mentioned predetermined range R should be approximately 3L 0  to 4L 0  if the electrical length of the above-mentioned stub portion  22 A- 1  is L 0 .  FIG. 8  (A) is a schematic diagram illustrating the main transmission path and the stub portion. In  FIG. 8  (A), the main transmission path is divided into four blocks, i.e., block a 1 , block a 2 , block b 1 , and block b 2 . At the same time, the stub portion is shown as block a 3 . Blocks a 1  to a 3  are part of the signal terminals  22  of the intermediate connector  1 , and blocks b 1  and b 2  are part of the counterpart signal terminals  40  of the counterpart connector  2 . 
     Blocks a 1  and a 2  are sections formed in the signal terminals  22  within the main transmission path and blocks b 1  and b 2  are sections formed in the counterpart signal terminals  40  within the main transmission path. In addition, block a 1  is a section located in the signal terminals  22  outside the predetermined range R in the main transmission path, and block a 2  is a section located in the signal terminals  22  within the predetermined range R in the main transmission path, i.e., a section corresponding to the previously discussed first range R 1 . Block b 1  is a section located in the counterpart signal terminals  40  outside the predetermined range R in the main transmission path, and block b 2  is a section located in the counterpart signal terminals  40  within the predetermined range R in the main transmission path, i.e., a section corresponding to the previously discussed second range R 2 . In other words, the section consisting of block a 2  and block b 1  corresponds to the predetermined range R. In addition, as mentioned before, block a 3  is the stub portion  22 A- 1  of the signal terminals  22  and corresponds to the stub range S. 
     An example of signal transmission via connectors in which the present invention is applied to a connector transmitting high-speed signals with a frequency of about 10-20 GHz over a signal transmission path formed with a typical impedance of 50Ω is explained below. In the example of  FIG. 8  (A), the impedance of blocks a 1 , b 2  located outside the predetermined range R in the main transmission path and that of block a 3  corresponding to the stub portion is 50Ω. In addition, it is understood that, as shown in  FIG. 8  (A), the electrical length of blocks a 1 , b 2 , and a 3  is set, respectively, to 20 ps, 20 ps, and 10 ps. In the present invention, adjusting the electrical length X of blocks a 2  and b 1  located within the predetermined range R in the main transmission path and adjusting the impedance Y to a range of less than 50Ω minimizes degradation in high-speed signal transmission quality. As discussed before with reference to  FIGS. 1-7 , said electrical length and impedance may be adjusted using the shape and dimensions of the terminals as well as the size of the range in which the terminals are covered by the resin section, etc. In addition, they may be adjusted by the positional relationship of the signal terminals, the ground plate, and the ground terminals. 
       FIGS. 8  (B) and  8  (C), in which the frequency of the transmitted signal (GHz) is plotted on the horizontal axis and the attenuation of the signal (dB) is plotted on the vertical axis, are graphs illustrating relationships between the two in various insertion loss-related simulations. In  FIG. 8  (B, C) shows curves representing the relationship between the frequency of the signal and the attenuation of the signal obtained by setting the electrical length and impedance of the above-mentioned predetermined range R, i.e., blocks a 2  and b 1  of  FIG. 8  (A), to various values. In addition, in  FIGS. 8  (B) and  8  (C), ideal signal attenuation in a signal transmission path formed with an impedance of 50Ω is illustrated by the downward-sloping straight line M (shown with a dashed line), according to which attenuation gently increases as the frequency becomes higher. In addition to simply reducing loss, system designers also emphasize the importance of linearity for the frequency dependence. This means that the closer the trajectory of the curve obtained in a simulation is to said straight line M, the easier it is to compensate for the loss generated in the signal transmission path using an equalizer. 
     The graphs of  FIGS. 8  (B) and  8  (C) show curves representing the relationships between the frequency of the signal and the attenuation of the signal obtained when the electrical length X of the first range R 1  and the second range R 2  is set to various values if the impedance Y of blocks a 2  and b 1  of  FIG. 8  (A), i.e., said first range R 1  and said second range R 2 , is set to 40Ω ( FIG. 8  (B)) or 45Ω ( FIG. 8  (C)). The above-mentioned electrical length X is set to various values including 0 ps, 5 ps, 10 ps, 15 ps, 20 ps, and 100 ps. Here, setting the electrical length X to 0 means that no sections with an impedance of less than 50Ω are formed and impedance throughout the entire range of the stub portion and the main transmission path is set to 50Ω. Therefore, as a result of comparing the curve obtained when the electrical length X is set to 0 (the former) with the curves obtained when the electrical length X is set to other values (the latter), it can be said that the wider the frequency range in which the signal attenuation of the latter is smaller than the signal attenuation of the former, in other words, in which degradation in signal transmission quality can be improved in comparison with the former (the range designated by “N” in  FIGS. 8  (B) and  8  (C), hereinafter referred to as “improvement frequency range”), the more preferable the electrical length will be. 
     As can be seen in  FIG. 8  (B), when the impedance of the first range R 1  and second range R 2  is 40Ω, the curves obtained when the electrical length X is 15 ps and 20 ps are close to the shape of the straight line M. In  FIG. 8  (B), the improvement frequency range N 15  obtained when the electrical length X is 15 ps is about 12.5-25 GHz, overlapping with most of the frequency range of the transmitted high-speed signals (about 10-20 GHz). In addition, the improvement frequency range N 20  obtained when the electrical length X is 20 ps is about 10-25 GHz, comprising the frequency range of the transmitted high-speed signals (about 10-20 GHz) in its entirety. Therefore, in the first range R 1  and second range R 2 , degradation in signal transmission quality is adequately minimized by setting the impedance to 40Ω and the electrical length to 15-20 ps. 
     As can be seen in  FIG. 8  (C), when the impedance of the first range R 1  and second range R 2  is 45Ω, the curve obtained when the electrical length X is 20 ps is closest to the shape of the straight line M. In  FIG. 8  (C), the improvement frequency range N is approximately 10-25 GHz. Therefore, the improvement frequency range N includes the frequency range of the transmitted high-speed signals (about 10-20 GHz) in its entirety. Consequently, in the first range R 1  and second range R 2 , degradation in signal transmission quality is adequately minimized by setting the impedance to 45Ω and the electrical length to 20 ps. 
     Thus, based on the simulation results illustrated in  FIGS. 8  (B) and  8  (C), it was found that setting the electrical length of the first range R 1  and second range R 2  to 15-20 ps makes it possible to more effectively minimize degradation in signal transmission quality. In other words, the sum total of the electrical length of the first range R 1  and the electrical length of the second range R 2  is 30-40 ps, and this total electrical length corresponds to 3 to 4 times the electrical length of the stub range S, which is 10 ps. Therefore, if the electrical length of the above-mentioned stub portion is L 0 , then it can be said that the electrical length of the section including the above-mentioned predetermined range R is preferably about 3L 0  to 4L 0 . 
     The frequency band, electrical length, impedance, improvement frequency range, and other numerical values described above with reference to  FIGS. 8  (A) to  8  (C) are merely an example, and it goes without saying that the invention is not limited to these numerical values. To obtain the effect of minimizing degradation in signal transmission quality, the impedance of at least a partial range of the above-mentioned predetermined range R within the above-mentioned main transmission path should be smaller than the impedance of the range of the stub portion (stub range). In addition, at such time, impedance in sections outside the above-mentioned predetermined range R in the main transmission path may also be smaller than that of the stub portion. Therefore, for example, the impedance of a range extending over the entire main transmission path may be adjusted to be smaller than the impedance of the stub portion. 
     Second Embodiment 
     While in the first embodiment explanations were provided regarding an embodiment obtained by applying the present invention to a so-called three-piece electrical connector assembly composed of a single intermediate connector  1  and two counterpart connectors  2 ,  3 , the second embodiment differs from the first embodiment in that the present invention is applied to a so-called two-piece electrical connector assembly composed of a connector and a counterpart connector. 
       FIG. 9  is a perspective view illustrating an electrical connector and a counterpart connector according to the second embodiment, in which the connectors are in an unmated state.  FIG. 10  is a perspective view illustrating the electrical connector and counterpart connector of  FIG. 9  in a mated state. 
     The electrical connector assembly according to the present embodiment, which is used for the transmission of high-speed signals, has an electrical connector  101  (hereinafter referred to as “connector  101 ”) used as the first electrical connector, and a counterpart connector  102  used as a second electrical connector mated to said electrical connector  101  from above. The connector  101  and counterpart connector  102  are electrical connectors for circuit boards disposed on respectively different circuit boards (not shown), which are mated to each other while being oriented such that the surfaces of the respective circuit boards are perpendicular to the up-down direction (Z-axis direction). 
     The connector  101 , which is formed as a plug connector, has a plastic housing  110  serving as a terminal holder, multiple metal signal terminals  120  serving as first terminals arranged in a terminal array direction coinciding with the X-axis direction and retained in place in said housing  110 , and inner fittings  130  along with outer fittings  140  retained in place in the housing  110  on both sides of the terminal array range in the terminal array direction. 
     The housing  110  has a base portion  111 , which extends parallel to the mounting face of the circuit board, and mating portions  112  rising from said base portion  111  and extending in the terminal array direction (X-axis direction). The base portion  111 , which is of a substantially rectangular parallelepiped-like external configuration whose longitudinal direction is the terminal array direction (X-axis direction) when viewed in the up-down direction (Z-axis direction), has two lateral base portions  111 A, which extend in the terminal array direction, two end base portions  111 B, which extend in the connector width direction (Y-axis direction), i.e., in the transverse direction of the base portion  111 , and which couple the two ends of the two lateral base portions  111 A, and coupling base portions  111 C, which extend between the two lateral base portions  111 A in the terminal array direction (X-axis direction) and couple the two interior wall surfaces of the two end base portions  111 B (see  FIG. 12  (A)). In addition, an aperture portion  111 D passing in the up-down direction is formed between the lateral base portions  111 A and coupling base portions  111 C. 
     The mating portions  112  rise from the top face of the base portion  111  and have a square frame configuration, whose longitudinal direction is the terminal array direction (X-axis direction) when viewed in the up-down direction (Z-axis direction). Said mating portions  112  have two lateral walls  112 A, which extend in the terminal array direction, and two end walls  112 B, which extend in the connector width direction and couple the two ends of the two lateral walls  112 A. The space enclosed by the lateral walls  112 A and end walls  112 B of said mating portions  112 , which passes in the up-down direction and is in communication with the aperture portion  111 D of the base portion  111 , forms a receiving portion  112 C receiving the protruding wall  153  of the counterpart connector  102  from above when the connectors are in a mated state. 
     As can be seen in  FIGS. 12  (A) and  12  (B), in the housing  110 , vertically extending terminal holding groove portions  113  are formed in the up-down direction along inner lateral faces of the lateral walls  112 A and the inner lateral faces of the lateral base portions  111 A (faces perpendicular to the Y-axis direction). In addition, as can be seen in  FIG. 9 , inner fitting holding portions  114  used to secure the inner fittings  130  in place via press-fitting and outer fitting holding portions  115  used to secure the outer fittings  140  in place via press-fitting are formed on both sides of the terminal array range in the terminal array direction. The outer fitting holding portions  115  are formed outwardly of the inner fitting holding portions  114  in the terminal array direction. The inner fitting holding portions  114  and outer fitting holding portions  115  extend in the connector width direction (Y-axis direction) and in the up-down direction (Z-axis direction) while being formed through the end base portions  111 B and end walls  112 B of the housing  110  in the up-down direction. As can be seen in  FIG. 9 , the top portions of the inner fitting holding portions  114  form recesses in the inner lateral faces of the end walls  112 B, and the top portions of the outer fitting holding portions  115  form recesses in the outer lateral faces of the end walls  112 B. 
     As can be seen in  FIG. 9 , in the present embodiment, two rows of signal terminals  120  arranged in the terminal array direction are retained in the housing  110  symmetrically in the connector width direction (see also  FIGS. 12  (A) and  12  (B)).  FIG. 11  provides perspective views of a single signal terminal  120  contained in the terminal row on side Y 2  and a counterpart signal terminal  160  removed, respectively, from the connector  101  and the counterpart connector  102 , wherein (A) illustrates a state prior to connector mating and (B) illustrates the connectors in a mated state. As can be seen in  FIGS. 11  (A) and  11  (B), the signal terminal  120 , which is fabricated by bending a strip-shaped sheet metal member in the through-thickness direction, has a vertically extending contact arm portion  121 , a retained portion  122  extending downwardly from the lower end of said contact arm portion  121 , and a connecting portion  123 , which is obtained by bending the lower end of said retained portion  122  in the connector width direction (Y-axis direction) and extends toward side Y 2 . Said signal terminal  120  is attached to said housing  110  by press-fitting into a terminal holding groove portion  113  from underneath the housing  110  (see  FIG. 12  (A)). 
     As can be seen in  FIGS. 11  (A) and  11  (B), the contact arm portion  121 , which is oriented such that its major faces (rolled faces) are at right angles to the connector width direction (Y-axis direction), extends in the up-down direction through the terminal holding groove portion  113  (see  FIG. 12  (A)) along the lateral wall  112 A. Said contact arm portion  121 , whose through-thickness dimensions (dimensions in the Y-axis direction) in the top half are smaller than its through-thickness dimensions in the bottom half, can be brought into contact with a counterpart signal terminal  160  via its major face on side Y 1  in the top half thereof, i.e., its major face exposed in the receiving portion  112 C of the housing  110 . 
     It is to be noted that despite the fact that in the present embodiment the contact arm portions  121  of the signal terminals  120  are not intended to be resiliently displaced, it is not essential for these portions to be incapable of resilient displacement and they may be formed in a manner permitting resilient displacement in their through-thickness direction. 
     The retained portion  122 , which is oriented such that its major faces (rolled faces) are at right angles to the connector width direction (Y-axis direction), extends in the up-down direction through the terminal holding groove portion  113  (see  FIG. 12  (A)) along the lateral base portion  111 A. Two press-fitting protrusions  122 A protruding in the terminal array direction are formed on each of the two lateral edges of said retained portion  122 . The press-fitting protrusions  122 A of the retained portion  122  bite into the interior wall surface of the terminal holding groove portion  113 , thereby retaining it in place within said terminal holding groove portion  113 . 
     As can be seen in  FIGS. 11  (A) and  11  (B), the connecting portion  123  extends outwardly in the connector width direction and, as can be seen in  FIG. 9  and  FIG. 12  (A), its distal end section projects outside the housing  110  from the bottom of the lateral base portion  111 A of the housing  110 . Said connecting portions  123  are adapted to have their bottom faces solder-connected to corresponding circuits on the mounting face of the circuit board (not shown). 
     The inner fittings  130 , which are fabricated by bending a sheet metal member in the through-thickness direction and are oriented such that their major faces (rolled faces) are at right angles to the terminal array direction (X-axis direction), are retained in the housing  110  on both sides of the terminal array range. Said inner fittings  130  have a retained portion (not shown), which is retained in place by the end base portions  111 B of the housing  110 , an inner end plate portion  131 , which extends upwardly from said retained portion, and an inner securing portion  132 , which extends downwardly from said retained portion. 
     The above-mentioned retained portions are secured in place via press-fitting in inner fitting holding portions  114  formed in the end base portions  111 B of the housing  110 . The major faces (rolled faces) of the sections of the inner end plate portions  131 , which extend along the inner lateral faces of the end walls  112 B of the housing  110  in the up-down direction and are contained within the inner fitting holding portions  114 , are exposed on said end walls  112 B (see  FIG. 12  (A)). The inner securing portions  132 , which project downwardly from the bottom faces of the end base portions  111 B, are inserted into corresponding aperture portions formed in the circuit board (not shown) and, in this state, secured to said circuit board by solder connection. 
     The outer fittings  140 , which are fabricated by bending a sheet metal member in the through-thickness direction and are oriented such that their major faces (rolled faces) are at right angles to the terminal array direction (X-axis direction), are retained in the housing  110  at more outwardly positions in the terminal array direction than the inner fittings  130 . Said outer fittings  140  have a retained portion (not shown), which is retained in place by the end base portions  111 B of the housing  110 , an outer end plate portion  141 , which extends upwardly from said retained portion, and an outer securing portion  142 , which extends downwardly from said retained portion. 
     The above-mentioned retained portions are secured in place via press-fitting in outer fitting holding portions  115  formed in the end base portions  111 B of the housing  110 . The major faces (rolled faces) of the sections of the outer end plate portions  141 , which extend along the outer lateral faces of the end walls  112 B of the housing  110  in the up-down direction and are contained within the outer fitting holding portions  115 , are exposed on said end walls  112 B. The outer securing portions  142 , which project downwardly from the bottom faces of the end base portions  111 B, are inserted into corresponding aperture portions formed in the circuit board (not shown) and, in this state, secured to said circuit board by solder connection. 
     As can be seen in  FIG. 9 ,  FIG. 10  and  FIGS. 12  (A) and  12  (B), the counterpart connector  102 , which is formed as a receptacle connector, has a plastic housing  150  serving as a terminal holder, multiple metal counterpart signal terminals  160  serving as second terminals arranged in a terminal array direction coinciding with the X-axis direction and retained in place in said housing  150 , and inner fittings  170  along with outer fittings  180  retained in the housing  150  on both sides of the terminal array range in the terminal array direction. 
     As can be seen in  FIG. 9 ,  FIG. 10  and  FIGS. 12  (A) and  12  (B), the housing  150  has a bottom wall  151 , which extends parallel to the mounting face of the circuit board, as well as a protruding wall  153  and perimeter walls  152 , which extend downwardly from the perimeter edge portion of said bottom wall  151 . The perimeter walls  152 , which serve as a corresponding mating portion mated with the mating portion  112  of the connector  101  and have a square frame configuration whose longitudinal direction coincides with the terminal array direction (X-axis direction) when viewed from below, include two lateral walls  152 A, which extend in the terminal array direction, and two end walls  152 B, which extend in the connector width direction, i.e., in a direction transverse of said perimeter walls  152 , and which couple the two ends of the two lateral walls  152 A. The protruding wall  153  extends in the terminal array direction within the space enclosed by the above-mentioned perimeter walls  152  (see  FIG. 12  (A)). The downwardly open annular space formed between the perimeter walls  152  and the protruding wall  153  forms a receiving portion  154 , which is intended to receive the mating portion  112  of the connector  101  (see  FIG. 12  (A)). 
     As can be seen in  FIGS. 12  (A) and  12  (B), the housing  150  has formed therein terminal holding portions  155 , which extend in the up-down direction along both lateral faces (faces perpendicular to the Y-axis direction) of the protruding wall  153  and pass through the bottom wall  151  in the up-down direction. In addition, as can be seen in  FIG. 9 , inner fitting retaining portions  156  used to secure the inner fittings  170  in place via press-fitting and outer fitting retaining portions  157  used to secure the outer fittings  180  in place via press-fitting are formed on both sides of the terminal array range in the terminal array direction. The outer fitting retaining portions  157  are formed outwardly of the inner fitting retaining portions  156  in the terminal array direction. The inner fitting retaining portions  156  and outer fitting retaining portions  157  extend in the connector width direction (Y-axis direction) and in the up-down direction (Z-axis direction) while being formed through the end walls  152 B and bottom walls  151  of the housing  150  in the up-down direction. 
     As can be seen in  FIGS. 12  (A) and  12  (B), in the present embodiment, two rows of counterpart signal terminals  160  arranged in the terminal array direction are retained in the housing  150  symmetrically in the connector width direction. As can be seen in  FIGS. 11  (A) and  11  (B), the counterpart signal terminals  160 , which are fabricated by bending a strip-shaped sheet metal member in the through-thickness direction, have a resilient arm portion  161 , which extends in the up-down direction and is resiliently displaceable in the connector width direction (Y-axis direction), a transitional portion  162 , which is bent at the upper end of said resilient arm portion  161  in a crank-like configuration, a retained portion  163 , which extends upwardly from said transitional portion  162 , and a connecting portion  164 , which is bent at the upper end of said retained portion  163  and extends in the connector width direction (Y-axis direction) toward side Y 2 . As can be seen in  FIG. 12  (A), the counterpart signal terminals  160  are attached to the housing  150  by press-fitting from above said housing  150  into the terminal holding portions  155 . 
     As can be seen in  FIGS. 11  (A) and  11  (B), the resilient arm portion  161 , which is oriented such that its major faces (rolled faces) are at right angles to the connector width direction (Y-axis direction), extends in the up-down direction through the terminal holding portion  155  (see  FIG. 12  (A)). As can be seen in  FIGS. 11  (A) and  11  (B), said resilient arm portion  161  has formed therein a convex contact point portion  161 A protruding outwardly in the connector width direction (side Y 2  in  FIGS. 11  (A) and  11  (B)) at a location proximal to its lower end and, when the resilient arm portion  161  is in a state of resilient displacement, is adapted to contact a contact arm portion  121  of a signal terminal  120  of the connector  101  with the above-mentioned convex contact point portion  161 A (see  FIG. 12  (B)). In addition, a guiding portion  161 B used to guide the signal terminal  120  of the connector  101  in the connector width direction toward the regular location of contact is formed within the range located closer to the free end, i.e., to the lower end thereof in the up-down direction, than the protruding apex portion of the convex contact point portion  161 A. 
     It should be noted that, similar to the first embodiment, being capable of resilient displacement is not an essential feature of the section of the counterpart signal terminals  160  in which the convex contact point portion  161 A is formed. Therefore, for example, vertically extending contact arm portions not capable of resilient displacement may be provided in the counterpart signal terminals  160  instead of the above-mentioned resilient arm portions  161 , and convex contact point portions may be formed in said contact arm portions. 
     The retained portion  163 , which is located outwardly of the resilient arm portion  161  in the connector width direction and is oriented such that the major faces (rolled faces) of said retained portion  163  are at right angles to the connector width direction, extends in the up-down direction through the terminal holding portion  155  (see  FIG. 12  (A)). As can be seen in  FIG. 11  (A, B), two press-fitting protrusions  163 A protruding in the terminal array direction are formed on each of the two lateral edges of said retained portion  163 . The press-fitting protrusions  163 A of the retained portion  163  bite into the interior wall surface of the terminal holding portion  155 , thereby retaining it in place within said terminal holding portion  155 . 
     As can be seen in  FIG. 9  and  FIG. 12  (A), the connecting portions  164  extend outwardly in the connector width direction and their distal end sections project outside the housing  150  from the top of the bottom wall  151  of the housing  150 . Said connecting portions  164  are adapted to have their top faces solder-connected to corresponding circuits on the mounting face of the circuit board (not shown). 
     The inner fittings  170 , which are made from sheet metal members and are oriented such that their major faces (rolled faces) are at right angles to the terminal array direction, are retained in place in the housing  150 . As can be seen in  FIG. 9 , said inner fittings  170 , which have a retained portion (not shown) retained in place in the housing  150  and a single inner securing portion  171  extending upwardly from said retained portion, are attached to the inner fitting retaining portions  156  of the housing  150  from above by press-fitting. The inner securing portions  171  of said inner fittings  170 , which project upwardly from the bottom face (top face in  FIG. 9 ) of the bottom wall  151  of the housing  150 , are inserted into the corresponding aperture portions formed in the circuit board (not shown) and, in this state, are secured to said circuit board by solder connection. 
     The outer fittings  180 , which are made from sheet metal members and are oriented such that their major faces (rolled faces) are at right angles to the terminal array direction, in other words, parallel to the major faces of the inner fittings, are retained in place in the housing  150 . As can be seen in  FIG. 9 , said outer fittings  180 , which have a retained portion (not shown) retained in place in the housing  150  and two outer securing portions  181  extending upwardly from said retained portion, are attached to the outer fitting retaining portions  157  of the housing  150  from above by press-fitting. The outer securing portions  181  of said outer fittings  180 , which project upwardly from the bottom face (top face in  FIG. 9 ) of the bottom wall  151  of the housing  150 , are inserted into corresponding aperture portions formed in the circuit board (not shown) and, in this state, are secured to said circuit board by solder connection. 
     Next, the operation of connector mating will be described with reference to  FIG. 9  and  FIG. 12 .  FIG. 12  provides partial cross-sectional views taken at the location of the signal terminals  120  and counterpart signal terminals  160  of the connector  101  and counterpart connector  102  in the connector width direction, wherein  FIG. 12  (A) illustrates a state prior to connector mating, and  FIG. 12  (B) illustrates the connectors in a mated state. 
     First, the connector  101  and counterpart connector  102  are solder-connected to the respectively corresponding circuits of the circuit boards and, as shown in  FIG. 9  and  FIG. 12  (A), the counterpart connector  102  is positioned above the connector  101  with the receiving portion  154  of said counterpart connector  102  oriented in the downward direction. The connector  101  and counterpart connector  102  are then mated by lowering the counterpart connector  102  (see  FIG. 10  and  FIG. 12  (B)). 
     In the process of connector mating, as the mating portion  112  of the connector  101  enters the receiving portion  154  of the counterpart connector  102  from below, the protruding wall  153  of the counterpart connector  102  enters the receiving portion  112 C of the mating portion  112  of the connector  101  from above (see  FIG. 12  (B)). In this process of connector mating, the convex contact point portion  161 A of the counterpart signal terminals  160  abuts the contact arm portion  121  of the signal terminals  120 , thereby resiliently displacing the resilient arm portion  161  of the counterpart signal terminals  160  inwardly in the connector width direction. As can be seen in  FIG. 12  (B), once the connectors are mated and the resilient arm portions  161  are in a state of resilient displacement, convex contact point portions  161 A of the counterpart signal terminals  160  are brought into contact with and electrically connected to the intermediate portions in the up-down direction of the contact arm portions  121  of the signal terminals  120 . As can be seen in  FIG. 12  (B), when the connectors are in a mated state, the section extending from the location of contact with the convex contact point portions  161 A of the counterpart signal terminals  160  in the contact arm portions  121  of the signal terminals  120  to the upper end portion of the contact arm portions  121  is formed as a stub portion  121 A. In  FIG. 12  (B), the vertical range of the stub portion  121 A is designated as “S”. 
     As can be seen in  FIG. 12  (B), in the present embodiment, once the connectors are mated, a main transmission path used to transmit high-speed signals is formed by the sections other than the stub portion  121 A of the signal terminals  120  of the connector  101  and the sections other than the guiding portion  161 B of the counterpart signal terminals  160  of the counterpart connector  102 . 
     In  FIG. 12  (B), a predetermined range within the above-mentioned main transmission path that includes the location of contact P between the contact arm portion  121  of the signal terminals  120  and the convex contact point portion  161 A of the counterpart signal terminals  160  is designated as “R”. Specifically, the predetermined range R is a vertical range extending between the upper end of the retained portions  163  of the counterpart signal terminals  160  provided in the counterpart connector  102  and the lower end of the retained portions  122  of the signal terminals  120  provided in the connector  101 . In addition, in  FIG. 12  (B), this predetermined range R is split into a first range R 1  located below the location of contact P and a second range R 2  located above the location of contact P such that said location of contact P forms a boundary therebetween in the up-down direction. Further, the above-mentioned first range R 1  is split in the up-down direction into a first upper range R 1 A, which extends from the location of contact P to the lower end of the contact arm portion  121  of the signal terminals  120 , and a first lower range R 1 B, which extends from the lower end of said contact arm portion  121  to the lower end of the retained portion  122 . 
     The bottom portion of the contact arm portion  121  of the signal terminals  120  is located in the first upper range R 1 A within the first range R 1 , and the impedance of the first upper range R 1 A is substantially equal to the impedance of the range (stub range) S of the stub portion  121 A. 
     The retained portions  122  of the signal terminals  120  are located in the first lower range R 1 B within the first range R 1 . In comparison with the stub portions  121 A, which form part of the contact arm portions  121 , said retained portions  122  are formed to be larger in the through-thickness direction (X-axis direction). In addition, most of the retained portion  122  is covered by the base portion  111  of the plastic housing  110  around the entire circumference of said retained portion  122 . Therefore, the impedance of the first lower range R 1 B is smaller than the impedance of the range (stub range) S of the stub portion  121 A. 
     In addition, the resilient arm portions  161 , transitional portions  162 , and retained portions  163  of the counterpart signal terminals  160  are located in the second range R 2 . In comparison with the stub portions  121 A, which form part of the contact arm portions  121  of the signal terminals  120 , said resilient arm portions  161 , transitional portions  162 , and retained portions  163  are formed to be larger in the through-thickness direction (X-axis direction). In addition, the retained portions  163  are covered by the bottom wall  151  of the plastic housing  150  around the entire periphery of said retained portions  163 . Therefore, the impedance of the second range R 2  is smaller than the impedance of the range (stub range) S of the stub portion  121 A. 
     As discussed above, in the present embodiment, the impedance of the first lower range R 1 B located below the above-mentioned location of contact P and the second range R 2  located above the above-mentioned location of contact P within the above-mentioned predetermined range R is smaller than the impedance of the stub range S. Making the impedance of most of the above-mentioned predetermined range R smaller than impedance of the stub range S in this manner makes is possible to minimize signal reflection and, therefore, degradation in signal transmission quality due to the presence of the stub portions  121 A and even if the frequency of the signals transmitted over the above-mentioned main transmission path is within the range of frequencies in the vicinity of the resonance frequency. 
     Although in the present embodiment, as discussed above, the impedance of the first upper range R 1 A is equal to the impedance of the range (stub range) S of the stub portion  121 A, for example, if a mating depth position is set, as the regular location of contact, such that the above-mentioned location of contact P in the contact arm portions  121  of the signal terminals  120  is closer to the retained portion  122  and the first upper range R 1 A is made smaller in the up-down direction, the range within the above-mentioned predetermined range R, in which impedance in the stub range S is smaller can be increased and, as a result, signal reflection and, therefore, degradation in signal transmission quality can be more effectively minimized. 
     In addition, in order to more effectively minimize degradation in signal transmission quality, just like in the first embodiment, it is preferable that the electrical length of the section corresponding to the above-mentioned predetermined range R be approximately 3 to 4L 0  if the electrical length of the above-mentioned stub portion  121 A is L 0  and, in addition, that the electrical length of the first range R 1  in the signal terminals  120  of the connector  101  be equal to the electrical length of the second range R 2  in the counterpart signal terminals  160  of the counterpart connector  102 . 
     DESCRIPTION OF THE REFERENCE NUMERALS 
     
         
           1  Intermediate connector (first connector) 
           2  Counterpart connector (second connector) 
           3  Counterpart connector (second connector) 
           21  Substrate (terminal holder) 
           22  Signal terminals (first terminals) 
           22 A Upper contact arm portion (contact arm portion) 
           22 A- 1  Stub portion 
           22 B Lower contact arm portion (contact arm portion) 
           31  Holder (terminal holder) 
           40  Counterpart signal terminals (second terminals) 
           41 A Convex signal contact point portion (convex contact point portion) 
           41 B Guiding portion 
           101  Connector (first connector) 
           102  Counterpart connector (second connector) 
           110  Housing (terminal holder) 
           120  Signal terminals (first terminals) 
           121  Contact arm portion 
           121 A Stub portion 
           150  Housing (terminal holder) 
           160  Counterpart signal terminals (second terminals) 
           161 A Convex contact point portion 
           161 B Guiding portion 
         P Location of contact 
         R Predetermined range