Modular electrical plug and plug-cable assembly including the same

[0002] This invention relates generally to electrical connectors and, more particularly, to multi-position modular plugs offering improved and consistent near end crosstalk (“NEXT”) performance, i.e., NEXT values between wire pairs for plugs having the same design are substantially the same. The modular plugs in accordance with the invention may be used, depending on the construction, as Category 5, Category 5E or Category 6 plugs.

[0003] The present invention also relates to assemblies of the modular plug and a multi-wire cable terminated at one end by the plug and at the other end by another plug or another electrical connector.

[0004] Data communication networks are being developed which enable the flow of information to ever greater numbers of users at ever higher transmission rates. However, data transmitted at high rates in multi-pair data communication cables have an increased susceptibility to crosstalk, which often adversely affects the processing of the transmitted data. Crosstalk occurs when signal energy inadvertently “crosses” from one signal pair to another. The point at which the signal crosses or couples from one set of wires to another may be 1) within the connector or internal circuitry of the transmitting station, referred to as “near-end” crosstalk, 2) within the connector or internal circuitry of the receiving station, referred to as “far-end crosstalk”, or 3) within the interconnecting cable.

[0005] Near-end crosstalk (“NEXT”) is especially troublesome in the case of telecommunication connectors of the type specified in sub-part F of FCC part 68.500, commonly referred to as modular connectors. The EIA/TIA (Electronic/Telecommunication Industry Association) of ANSI has promulgated electrical specifications for near-end crosstalk isolation in network connectors to ensure that the connectors themselves do not compromise the overall performance of the unshielded twisted pair (UTP) interconnect hardware typically used in LAN systems. The EIA/TIA Category 5 electrical specifications specify the minimum near-end crosstalk isolation for connectors used in 100 ohm unshielded twisted pair Ethernet type interconnects at speeds of up to 100 MHz.

[0006] A typical modular jack includes a housing having a cavity therein of a size for receiving a modular plug, where the cavity is provided with a plurality of cantilevered spring contacts which correspond to a like plurality of contact terminals in the mating modular plug. The modular plug receives discrete, insulated, stranded or solid conductors in conductor-receiving channels or slots formed in a dielectric housing. Flat, blade-like metallic terminals are then inserted into individual vertically oriented slots in the housing in a generally side-by-side arrangement with contact portions thereof extending into engagement with the conductors. When the plug is inserted into a modular jack, the cantilevered portions of the terminals in the jack engage portions of associated terminals in the plug.

[0007] The characteristics of Category 5 plugs must be verified to conform with FCC standard ANSI/TIA/EIA-568-A by measuring near-end crosstalk loss between the unshielded twisted pair conductor combinations when the plug is in an unmated state, i.e., when there is no current flow through the plug. This measurement is sometimes referred to as a “terminated open circuit” or TOC test.

[0008] In an eight-position modular plug, the contacts and twisted wires are numbered from 1 to 8, from left to right with the contacts facing upward. Wires 4 and 5 form signal pair number 1, i.e., they are operatively electrically coupled in an electrical circuit, wires 1 and 2 form signal pair number 2, wires 3 and 6 form signal pair number 3 and wires 7 and 8 form signal pair number 4. In this case, the TOC test is performed on the six different twisted pair conductor/wire combinations, namely the combinations of signal pair numbers 1 and 2, 1 and 3, 1 and 4, 2 and 3, 2 and 4, and 3 and 4.

[0009] To conduct the TOC test, the apparatus shown in FIG. 1 is used. A 100 Ω resistor 10 is connected in parallel with the 100 Ω test leads 12 (where they connect to the wideband baluns 14) and NEXT is measured by the network analyzer 16. The measured NEXT loss at 100 MHz must be in the range shown in Table 1.

[0010] In addition, for wire pair combination 1 and 3, the difference between the NEXT loss measured at 100 MHz and the NEXT loss measured at 10 MHz must be 20±0.5 dB. Additional TOC requirements for wire pair combination 1 and 3 of the test plugs include: at least one of the test plugs must exhibit NEXT loss in the range of ≧40.0 dB to <40.5 dB at 100 MHz; at least one of the test plugs must exhibit NEXT loss in the range of ≧40.5 dB to <41.5 dB at 100 MHz; and at least one of the test plugs must exhibit NEXT loss in the range of ≧41.5 dB at 100 MHz;

[0011] Conventional modular plugs include one or more load bars for receiving the conductors in separate conductor-receiving passages. The use of load bars contributes to control of the inter-conductor capacitance in the plug. FIG. 2 shows typical TOC values measured for ten eight-position modular plugs of the same design between the pair combination 2 and 4, specifically, an RJ 45 plug having two load bars terminating a 24 AWG Tinned Stranded UTP cable made by Lucent Technologies. As shown in FIG. 2, for eight-position modular plugs having the same design, TOC values can vary by as much as 40 dB between plugs (compare test plugs 1 and 10). This variation is partially due to the relatively random arrangement of the unshielded twisted pairs (UTP) of conductors in the body of the plug, i.e., in the wire-receiving channels in the plug body, which causes small changes in the capacitance between the conductors.

[0012] One way to reduce inter-conductor capacitance in a plug is by offsetting adjacent conductors. Examples of this type of plug are disclosed in U.S. Pat. No. 5,628,647 (Rohrbaugh et al.) wherein the conductors are arranged in two planar arrays spaced one above the other. The offset conductors helps lower the plug's internal capacitance but does not result in stable TOC values for plugs having the same design.

[0013] In another attempt to stabilize the capacitance in an RJ 45 plug in order to obtain consistent TOC values for plugs having the same design, three plugs 20 were assembled with four load bars 22 each (FIG. 3). The plugs initially were a standard RJ 45 plug manufactured by Stewart Connector Systems but modified to include four load bars, and as tested, terminate a Berk-Tek Lan-Mark-350 cable (the same cable is used in all of the TOC tests described herein unless stated to the contrary). The use of four load bars fixed the inter-conductor capacitance within the length of the body of the plug. TOC measurements were then made on each pair combination to determine the degree of TOC stability. As shown in FIG. 4, the TOC values measured on the three plugs using four load bars each had less than a 4 dB variation from plug to plug.

[0014] Although the measured TOC values for a four-load bar plug as shown in FIG. 4 exhibits less variation from plug to plug than a standard Category 5, eight-position modular plug using two load bars, the wire pair combination 1 and 3 does not always yield a TOC value that complies with the requirements of TIA/EIA-568A. Indeed, the lowest TOC value obtained in the three plugs tested is 39.8 dB between the wire pair combination 1 and 3. However, the minimum requirement for pair combination 1 and 3 is 40 dB (See Table 1) and thus these modified plugs would not pass the TOC test according to ANSI standard EIA/TIA-568-A.

[0015] With respect to NEXT values (a measure of both capacitive and inductive crosstalk) between wire pairs of plugs, it has been found that variations in NEXT values between plugs of the same design are caused at least in part by the random arrangement of the UTP conductors underneath the plug's strain relief element. That is, the strain relief element in typical plugs engages with a shielded cable at a location prior to unsheathing of the cable and thus prior to insertion of the conductors in positioning channels in the plug (e.g., in a load bar of the plug) and therefore, the UTP conductors are arranged in the cable underneath the strain relief element in an arbitrary, random manner. It has also been found that TOC values between wire pairs also vary in view of the random nature of the arrangement of the conductors in the cable below the strain relief element. In this regard, FIG. 15 shows a table of the results of tests performed on ten (10) different plugs of a model of an RJ45 Category 5 plug manufactured by the assignee hereof for

[0016] both NEXT values and TOC values for all of the combinations of wire pairs (e.g., wire pair 1 to wire pair 2 is represented by 45-12). The measurement of NEXT is “de-embedded” NEXT, i.e., the crosstalk of a mating plug and jack is measured and the crosstalk of the jack is subtracted therefrom so that the resultant value is only the crosstalk caused by the construction of the plug. FIG. 16 is a table of maximum, minimum and variation in de-embedded NEXT values based on the data in the table of FIG. 15. As seen in FIG. 16, the variation in de-embedded NEXT values (delta) ranges from 7.1 dB to 27.6 dB. FIG. 17 is a table of maximum, minimum and variation in TOC values based on the data in the table of FIG. 15. As seen in FIG. 17, the variation in TOC values (delta) ranges from 5.9 dB to 20.9 dB. It would be beneficial to reduce the extent of these variations in de-embedded NEXT values and TOC values since variations in NEXT and TOC values could result in adverse operational performance of the plug.

[0017] It is an object of the present invention to provide new and improved modular plugs and modular plug-cable assemblies including the same.

[0018] It is another object of the present invention to provide new and improved multi-position modular Category 5, Category 5E and Category 6 plugs offering consistent NEXT values between plugs of the same design.

[0019] It is another object of the present invention to provide new and improved multi-position modular Category 5 plugs satisfying ANSI standard TIA/EIA-568A and offering consistent NEXT values between plugs of the same design.

[0020] It is another object of the present invention to provide new and improved multi-position modular Category 5 plugs satisfying ANSI standard TIA/EIA-568A and offering consistent NEXT values wherein the deviation in NEXT values between plugs of the same design is typically of an order of ±1.5 dB.

[0021] Yet another object of the invention is to provide a new and improved load bar for use in modular plugs which provide improved NEXT performance.

[0022] Briefly, in accordance with the present invention, some of these objects are achieved by providing including a housing defining a plurality of terminal-receiving slots, conductor-receiving channels each situated in communication with a slot and a longitudinal cavity extending from a rear surface of housing to the channels and which is in communication with the channels. The plug also includes contact terminals situated in the slots and a load bar arranged in the cavity. The load bar defines wire-receiving channels for receiving the wires of the cable. At least first and second wire-receiving channels are arranged in a first plane parallel to the upper and lower faces of the load bar and at least third and fourth channels are arranged in a second plane parallel to the first plane. The first and second channels are adapted to receive two of the wires of the cable which operatively form part of a first circuit during use.

[0023] In one particular embodiment, the wire-receiving channels are situated at successively arranged positions designated 1-8 whereby the channels at positions 1 and 2 are adapted to receive two wires forming part of a second circuit during use, the channels at positions 4 and 5 are adapted to receive two wires forming part of a third circuit during use and the channels at positions 7 and 8 are adapted to receive two wires forming part of a fourth circuit during use. Accordingly, the first and second channels are those at positions 3 and 6. As discussed herein, crosstalk is particularly a problem between wire pair 1 (formed by the wires at positions 4 and 5) and wire pair 3 (formed by the wires at positions 3 and 6) and thus, the separation between the wires at positions 3 and 6 from the wires at positions 4 and 5 in the load bar contributes to the reduction in crosstalk between these wire pairs and the improvement in NEXT performance.

[0024] A cable-plug assembly in accordance with the invention includes a multi-wire cable having first and second ends and a respective plug terminating one or both ends of the cable. Each plug may be as described above.

[0025] A more complete appreciation of the present invention and many of the attendant advantages thereof will be readily understood by reference to the following detailed description when considered in connection with the accompanying drawings in which:

[0026] FIG. 1 is a schematic illustration of an apparatus for conducting TOC tests on multi-position modular plugs;

[0027] FIG. 2 shows TOC values measured between the pair combination 2 and 4 for ten eight-position RJ45 modular plugs of the same design manufactured by Stewart Connector Systems, Inc. and including two load bars;

[0028] FIG. 3 shows a plug manufactured by Stewart Connector Systems modified to include four load bars;

[0029] FIG. 4 shows TOC values measured for three plugs of the type shown in FIG. 3;

[0030] FIG. 5 is a schematic view of a plug in accordance with the invention in an open position;

[0031] FIG. 6 is a top view of the lower frame part of the plug shown in FIG. 5 prior to insertion of wires into wire-receiving channels thereof;

[0032] FIG. 7 is a cross-sectional view of the plug in accordance with the invention shown in FIG. 5 but in a closed position;

[0033] FIG. 8 shows a load bar for use in another embodiment of a plug in accordance with the invention;

[0034] FIG. 9 shows the deviation in measured TOC values between all of the pair combinations for the plug including the load bar shown in FIG. 8;

[0035] FIG. 10 is a cross-sectional view of a prior art plug;

[0036] FIG. 11 is a cross-sectional view of another embodiment of a plug in accordance with the invention including lead frames;

[0037] FIG. 12A is a cross-sectional view taken along the line 12A—12A of FIG. 11;

[0038] FIG. 12B is a cross-sectional view taken along the line 12B—12B of FIG. 11;

[0039] FIG. 12C is a cross-sectional view taken along the line 12C—12C of FIG. 11;

[0040] FIG. 13 is a cross-sectional view of another embodiment of a plug in accordance with the invention including lead frames;

[0041] FIG. 14A is a cross-sectional view taken along the line 14A—14A of FIG. 13;

[0042] FIG. 14B is a cross-sectional view taken along the line 14B—14B of FIG. 13;

[0043] FIG. 14C is a cross-sectional view taken along the line 14C—14C of FIG. 13;

[0044] FIG. 15 is a table of measured de-embedded NEXT values and TOC values between all of the pair combinations for ten different samples of a model of an RJ45 Category 5 plug;

[0045] FIG. 16 is a table of maximum, minimum and variation in NEXT values based on the table of FIG. 15;

[0046] FIG. 17 is a table of maximum, minimum and variation in TOC values based on the table of FIG. 15;

[0047] FIG. 18 is an exploded perspective view of a plug in accordance with another embodiment of the invention which provides reduced variations in NEXT and TOC values;

[0048] FIG. 19 is an exploded perspective view of the plug of FIG. 18 showing the conductors inserted into the load bar of the plug;

[0049] FIG. 20 is another exploded perspective view of the plug of FIG. 18;

[0050] FIG. 21 is a rear view of the housing of the plug of FIG. 18;

[0051] FIG. 22 is a perspective view of the load bar of the plug of FIG. 18;

[0052] FIG. 23 is another exploded perspective view of the plug of FIG. 18;

[0053] FIG. 24 is a schematic view of the plug of FIG. 18 terminating a multi-conductor cable;

[0054] FIG. 25 is a schematic view of the terminated cable prior to insertion into the plug of FIG. 18;

[0055] FIG. 26 is a longitudinal cross-sectional view of the assembled plug shown in FIG. 18;

[0056] FIG. 27 is a table of measured de-embedded NEXT values and TOC values between all of the pair combinations for twelve different samples of a Cat 5E plug having a similar construction to the plug shown in FIG. 18;

[0057] FIG. 28 is a table of maximum, minimum and variation in NEXT values based on the table of FIG. 27;

[0058] FIG. 29 is a table of maximum, minimum and variation in TOC values based on the table of FIG.27;

[0059] FIG. 30 is a cross-sectional view of a plug including a load bar in accordance with another embodiment of the invention;

[0060] FIG. 30A is another cross-sectional view of the plug shown in FIG. 30.

[0061] FIG. 31 is an view of the rear end of the plug of FIG. 30 in a condition where it terminates wires;

[0062] FIG. 32 is a first cross-sectional view of the load bar shown in FIG. 31; and

[0063] FIG. 33 is a second cross-sectional view of the load bar shown in FIG. 31.

[0064] Referring now to the drawings wherein like reference characters designate identical or corresponding parts throughout the several views, and more particularly to FIGS. 5-7, a multi-position modular plug in accordance with the present invention is designated generally as 28 and comprises a plug housing 30 having an upper frame part 32, a lower frame part 34 and a hinge 36 pivotally connecting the upper frame part 32 to the lower frame part 34 so that the upper frame part 32 is pivotable about the hinge 36 into connection with the lower frame part 34. Connector latches 38 are provided in the upper frame part 32 and adapted to engage with corresponding recesses 40 in the lower frame part 34 when the upper frame 32 is pivoted about hinge 36 to secure the upper frame part 32 and lower frame part 34 together.

[0065] The upper frame part 32 includes a plurality of parallel, spaced-apart, longitudinally extending terminal receiving slots 41 formed through the lower surface 42 of the upper frame part 32 (when in the open position shown in FIG. 5), each of which receives a respective contact terminal or contact blade 44. Each contact blade 44 is made of an electrically conductive material and includes a flat conductive portion 46 having a pair of insulation-piercing tines 48.

[0066] The lower frame part 34 includes a plurality of wire-receiving channels 50, each arranged to receive an unshielded wire portion 52 of one of the wires of a multi-wire cable 54 terminated by the plug 30. As shown in FIG. 7, each wire-receiving channel 50 has a flat, horizontal bottom surface 50a, opposed vertical side surfaces 50band inclined surfaces 50cextending between the bottom surface 50aand the side surfaces 50b. Other surface formations of the channels 50 may be used in accordance with the invention without deviating from the scope and spirit thereof. The terminal-receiving slots 41 in the upper frame part 32 are arranged relative to the wire-receiving channels 50 in the lower frame part 34 so that when the upper frame part 32 is pivoted about hinge 36, the tines 48 of the contact blades 44 penetrate through the insulation sheath 52aof a wire 52 in a respective wire-receiving channel 50 into contact with the core 52btherein. Also, at this time, the latches 38 engage with the recesses 40 to connect the upper and lower frame parts 32, 34.

[0067] The plug described above is but one application of the invention and the invention may be used in conjunction with other plugs. Also, a plug in accordance with the invention may terminate each end of a cable having any number of wires, although the description herein relates generally to an eight-position modular plug. Although the channels 50 are shown in a single planar array, it is possible to form the channels 50 in two or more planar arrays, in which case, the size of the contact blades 44 is adjusted to ensure penetration of the tines 48 of the contact blades 44 through the insulation sheath of all of the wires. Also, although the channels are shown formed in the lower frame part 34, it is possible to provide the lower frame part with a recess and form the channels in a member such as load bar separate from the lower frame part and insertable into the recess of the lower frame part.

[0068] In accordance with the invention, the plug 28 includes means 56 for developing a capacitance between a wire forming part of one signal pair which is received in one wire-receiving channel 50 and a wire forming part of another signal pair which is received in another wire-receiving channel 50. This development or increase in capacitance between the wires in the wire-receiving channels improves the TOC performance between the associated signal pairs, i.e., those formed in part by the wires received in these wire-receiving channels, and specifically makes it more consistent when measured for plugs having the same design. In one embodiment, the capacitance developing means 56 comprise an electrically conductive material, such as a trace of copper foil 58 as shown in FIGS. 6 and 7, arranged in the wire-receiving channels 50 at each of positions P3 and P5, designated 503 and 505, respectively, and a electrical lead 60 connecting the foil traces 58 and situated within the lower frame part 34. The copper foil traces 58 overlie the bottom surface 50a, side surfaces 50band inclined surfaces 50cof the wire-receiving channels 50₃and 50₅and directly engage the insulation sheath 52abut do not contact the core 52band therefore do not affect the data transmission. Although, to obtain advantages of the invention, the foil traces 58 may overlie only one of the surfaces 50a, 50b,50c. The capacitance operatively developed between the wires in the wire-receiving channels 50₃and 50₅would be in the order of about 0.2-0.6 picofarads and would improve the TOC values, vis-a-vis the consistency thereof from plug to plug, for the wire combination 1 and 3 (the wire in channel 50₃being in wire pair 3 whereas the wire in channels 50₅is in wire pair 1). The magnitude of the capacitance depends on the dimensions, e.g., length, of the foil trace 58 in each wire-receiving channel 50₃and 50₅.

[0069] Although wire-receiving channels 50₃and 50₅are electrically connected together in the embodiment illustrated in FIGS. 5-7 to improve the TOC values for the wire combination 1 and 3, an improvement in TOC values for other wire combinations can be obtained by electrically connecting any two wire-receiving channels in the plug which receive wires belonging to different signal pairs. Moreover, an improvement in multiple wire combinations can be obtained by electrically connecting more than one pair of wire-receiving channels together.

[0070] Instead of the foil traces 58, it is possible to provide the electrically conductive material in the wire-receiving channels by selectively plating an area of each wire-receiving channel 50₃and 50₅and connecting the plated areas to each other through an electrical lead extending through the lower frame part. In the alternative, it is possible to incorporate into the lower frame part 34, metallized plastic to form at least a portion of each wire-receiving channel 50₃and 50₅and electrically couple the metallized plastic portions together.

[0071] In another embodiment of a plug in accordance with the invention, the plug includes a housing defining a longitudinal cavity, terminal-receiving slots at a front end into which contact terminals are arranged, channels for receiving wires of a multi-wire cable, each channel in communication with a respective one of the slots, a latch and a strain relief element. In accordance with the invention, the plug includes a load bar 62 as shown in FIG. 8 arranged in the longitudinal cavity and having wire-receiving channels 60 arranged in two planar arrays, such as in U.S. Pat. No. 5,628,647 discussed above, and capacitance developing means 64 for developing a capacitance between the wires in the wire-receiving channels at positions P3 and P5, designated 60₃and 60₅. The capacitance developing means 64 comprise a foil trace 66 arranged on a surface of the load bars 62 over substantially all of wire-receiving channels 60₃and 60₅and a foil trace 68 spanning the gap between the foil traces 66 to thereby form an H-shaped foil trace pattern on the load bar 62. It is also possible to provide metallized plastic portions in the load bar 62 as discussed above.

[0072] The wire-receiving channels 60 are in alignment with the channels in the plug housing so that the wires pass through the load bar and enter into the channels in the plug housing whereby the portion in the channels in the plug housing is pierced by the respective contact terminal. In the alternative, it is possible to extend the longitudinal cavity up to below the slots so that the load bar extends up to below the slots, and provide openings in the load bar to enable penetration by the contact terminals in the slots of the wires retained by the load bar.

[0073] FIG. 9 shows TOC values between all the pair combination 1 and 2 for a plug as described above with reference to FIG. 8 (except that instead of a unitary load bar, four smaller identical load bars were used) in which the plug terminates a Berk-Tek Lan-Mark-350 UTP cable. Six plugs were tested and TOC values measured for each plug. The deviations are also shown in FIG. 9.

[0074] To compare TOC values for a plug in accordance with the invention as shown in FIG. 6 and a standard prior art plug without capacitance developing means (shown in FIG. 10), a computer-generated electrical analysis simulation was performed for each plug. It was found that the TOC value for the wire combination 1 and 3 was 37.9 dB for the prior art plug, which is below the required minimum according to ANSI standard EIA/TIA-568-A, whereas the TOC value for the same wire combination was 44.3 dB for the plug in accordance with the invention, above the minimum requirement.

[0075] FIGS. 11-12C show a cross-section of a plug housing 100 having eight lead frames 104 at positions designated P1-P8, each lead frame 104 includes an integral plug interface blade 102. An insulation displacing contact (IDC) 106 is coupled to each lead frame 104 and a respective wire is connected to each IDC 106, e.g., by staking the wire to a bottom of the IDC 106. An electrically conductive material 108 is connected to lead frame 104 at position P3 and extends over a length portion of and at a distance from the lead frame 104 at position P5 to thus form an L-shape (FIG. 13). The electrically conductive material 108 also extends over a portion of the lead frame 104 at position P4 and is spaced therefrom. A substrate of insulating material 110 is arranged between the electrically conductive material 108 and the lead frames 104 at least at position P5 (also position P4 in the illustrated embodiment) so that the electrically conductive material 108 is not electrically connected to the lead frame 104 at position P5. By means of this construction, compensation capacitance is developed between the lead frames 104 at positions P3 and P5 thereby improving TOC performance measured between the pair combination 1 and 3.

[0076] FIGS. 13-14C show a cross-section of a plug housing 120 having eight lead frames 124 at positions designated P1-P8 arranged in two planar arrays, each lead frame 124 includes an integral plug interface blade 122. An IDC 126 is coupled to each lead frame 124 and a respective wire is connected to each IDC 126. In this embodiment, an electrically conductive material 128 is connected to lead frame 124 at position P3 in the lower plane and extends obliquely through the body of the plug 120 over a length portion of and at a distance from the lead frame 124 at position P5 in the upper plane. A substrate of insulating material 130 is arranged between the electrically conductive material 128 and the lead frame 124 at position P5 so that the electrically conductive material 128 is not electrically connected to the lead frame 124 at position P5. By means of this construction, compensation capacitance is developed between the lead frames 124 at positions P3 and P5 thereby improving TOC performance measured between the pair combination 1 and 3.

[0077] The plugs described with respect to FIGS. 11-14C may be used to terminate an end of a multi-wire cable whereby the other end of the cable is terminated by a similar plug or another modular connector. A plug-cable assembly is thus formed.

[0078] The embodiment of a plug in accordance with the invention described above provides consistent TOC performance. However, as telecommunications develop, it is also beneficial to have consistent overall NEXT performance in plugs, whether Category 5, Category 5E or Category 6 plugs.

[0079] A second embodiment of a plug in accordance with the invention is shown in FIGS. 18-26 and provides consistent TOC performance and NEXT performance. In this embodiment, plug 140 includes a housing 142 made of dielectrical material and a load bar 144. Housing 142 has the dimensions of a standard RJ45 plug and includes a latch 146 projecting from a lower surface 148. Housing 142 also includes parallel, spaced, longitudinal extending terminal-receiving slots 150 formed in an upper surface 152 at a front end of the housing 142 and a longitudinal cavity 154 extending from a rear face 156 of the housing 142 inward to a location below the terminal-receiving slots 150. A rearward portion 158 of the cavity 154 has a substantially rectangular cross-section while a forward portion 160 of the cavity 154 is constructed so that it is adapted to receive the forward end 162 of the load bar 144 having the conductors or wires of a cable terminated by the plug inserted thereon. The load bar 144 is preferably substantially longitudinally coextensive with the cavity 154. The rearward portion 158 of the cavity 154 tapers inward from the rear face 156. A strain relief element 164 extends from an upper surface 152 of housing 142 and has a lower surface extending close to or in the rearward portion 158 of the cavity 154.

[0080] Load bar 144 is made of a dielectric material and includes wire-receiving channels 166, four channels in each of two rows in the illustrated embodiment. The channels 166 are staggered in relation to one another and are dimensioned to receive different-sized wires. The channels 166 are open in order to facilitate easy insertion of the wires 168 and constructed to facilitate secure retention of the wires 168 in the channels 166. More specifically, each channel 166 is formed by a longitudinally extending, arcuate surface 170 which forms a cradle receivable of a wire 168 (FIG. 22). Projections 171 are thereby formed between adjacent channels 166. The projections 171 formed between the channels 166 in the lower row are truncated before the forward edge of the load bar 144 to thereby form a sort of step in a forward end 172 of the load bar 144 in which the channels 166 in the lower row are defined by an underlying surface and the channels 166 in the upper row are defined by opposed side surfaces.

[0081] The forward end 172 of the load bar 144 is dimensioned to allow for complete insertion into the forward portion 160 of the cavity 154 and the rear end 173 of the load bar 152 is dimensioned to allow for complete insertion into the rearward portion 158 of the cavity 154. The forward portion 160 of the cavity 154 thus provides opposed upper and lower surfaces 174,176 along which the wires 168 in the lower row slide during insertion of the load bar 144 into the plug housing 142 until they abut against the front end of the cavity 154, and opposed side surfaces 178 and an upper surface 180 along which the wires 168 in the upper row slide during insertion of the load bar 144 into the plug housing 142 until they abut against the front end of the cavity 154 (FIG. 26). The upper surfaces 176,180 include a slit therein through which the contact terminals 182 pass in order to pierce the wires 168 (see FIG. 26).

[0082] An important feature of the load bar 144 is that it includes a “hinge” to enable rotational movement of a rearward portion of the load bar 144 relative to a forward portion. This movement may be realized once the load bar 144 is inserted into the cavity 154 and the forward portion thereof fixed within the cavity 154. More specifically, the load bar 144 includes aligned transverse slits 184 in the projections 171 and in the edge portions 145 on both sides. The presence of slits 184 allows the rear portion 186 of the rear end 173 of the load bar 144 to flex with respect to the front portion 188 of the rear end 173 and the front end 172 of the load bar 144. The flex is necessary for reasons discussed below.

[0083] By means of the load bar 144, the entire portion of each of the wires 168 within the plug housing 142 is positioned in a precise, pre-determined position, including at the location below the strain relief element 164. In this manner, a random arrangement of any portion of the wires 168 within the plug 140 is avoided. The position of the portion of each of the wires 168 which is to be engaged by the terminals 182 is also in a pre-determined position. At a minimum, in a plug in accordance with the invention, it is desirable that the portion of the wires between the location below the strain relief element 164 and the terminals 182 is fixed in position.

[0084] To enable fastening of a cable 190 in connection with the plug 140 vis-a-vis the strain relief, as shown in FIGS. 24-26, a portion of the cable jacket or sheath 192 of the cable 190 overlies the rear portion 186 of the rear end 173 of the load bar 144. This is enabled by slitting the cable jacket 192 a distance at least as large as the length of the wires 168 required to terminate the cable 190 by the plug 140 and then cutting the slit portion of the cable jacket 192 leaving a sufficient amount of the cable jacket 192 to extend above and below the rear portion 186 of the rear end 173 of the load bar 144 about up to the slits 184. The slits 184 are formed on the load bar 144 at a location so that the strain relief element 164 is situated between the rear end of the load bar 144 and the slits 184.

[0085] To terminate the cable 190 by means of the plug 140, two opposed longitudinal slits are made in the cable jacket 192 to expose a length of the wires 168 at least as large as the length of the load bar 144. The wires 168, which are usually in twisted pairs in the cable, are untwisted and pressed into the channels 166 in the load bar 144 in correspondence with the designation of the wires 168, as in the conventional manner. The ends of the wires 168 extending beyond the load bar 144 are then cut flush with the front end of the load bar 144. The slit portions of the cable jacket 192 are cut to extend only up to the slits 184 as shown in FIG. 25. The load bar 144 having the slit portions of the cable jacket 192 alongside it is then inserted into the cavity 154 in the housing 142 until the front end of the load bar 144 abuts against the front end of the cavity 154 (FIG. 26). Since the cavity 154 is dimensioned to receive the load bar 144 without clearance below the load bar 144, and with some clearance above the load bar 144, upon insertion of the load bar 144 into the cavity 154, the slit portion of the cable jacket 192 below the load bar 144 causes an upward flex of the rear portion 186 of the rear end 173 of the load bar 144, which flexure is enabled by the slits 184 (FIG. 26). The terminals 182 in the terminal-receiving slots 150 in the housing 142 (see FIGS. 24 and 26) are then pressed into the wires 168 to pierce the insulation of the wires 168 and engage the metal cores therein. The terminals 182 may be pre-positioned in the slots 168 so that it is only necessary to press them into the wires 168.

[0086] Thereafter, the strain relief element 164 is pressed inward or set to engage the slit portion of the cable jacket 192 overlying the rear portion of the load bar 144 to thereby secure the cable 190 in connection with the plug 140 (see FIG. 24). The pressing of the strain relief element 164 inward causes the rear portion 186 of the rear end 173 of the load bar 144 to be pressed downward against the lower surface of the cavity 154 thereby reducing the angle between the rear portion 186 of the rear end 173 and the front portion 188 of the rear end 173 and front end 172 (compare FIG. 26 to FIG. 24). The rear portion 186 is not planar with the front portion 188 in view of the presence of the cable jacket between the rear portion 186 ad the lower surface of the cavity 154.

[0087] The positioning of the wires 168 in pre-determined positions below the strain relief element 164 reduces variations in NEXT and TOC values between plugs having the same construction. In conventional plugs in which the wires are randomly arranged at the location below the strain relief element, when the strain relief element is pressed inward into the cable, the wires in the cable remain in this random arrangement and even more so, the wires are susceptible to additional random movement. This random arrangement of wires results in inconsistent NEXT and TOC values for plugs having the same design.

[0088] A particular advantage of the construction of the plug housing 142 and load bar 144 in accordance with the invention is that cables having different thicknesses of jackets and different diameter wires can be terminated by the plug 140. For the wires, the channels 166 are provided with a size equal to or larger than a relatively large diameter wire so that smaller diameter wires could also be positioned therein. For the different thicknesses of jackets, the height of the rearward portion 158 of the cavity 154 is provided with a size greater than the height of the load bar 144 and twice the thickness of the jacket of a relatively large cable. As such, cables with smaller cable jackets and insulation sheaths can be used to surround the load bar whereby the strain relief element 164 would engage with the upper portion of the cable jacket and thereby fix the cable in connection withe plug 140.

[0089] The plug described above in FIGS. 18-26 may be used to terminate an end of a multi-wire cable whereby the other end of the cable is terminated by a similar plug or another modular connector. A plug-cable assembly is thus formed.

[0090] With reference to FIGS. 27-29, FIG. 27 shows a chart of de-embedded NEXT values and TOC values for samples of a plug having a similar construction to that shown in FIGS. 18-26. The plug as tested included two load bars of the same type as used in the tests of an RJ45 plug, the results of which are set forth in FIGS. 15-17 (only one load bar was used in those tests whereby the cable was engaged by the strain relief element). In the plug having two load bars, the second load bar was placed adjacent the first load bar, which in a conventional manner was positioned at the front of the cavity below the terminal-receiving slots, and so that the strain relief element would engage a slit cable jacket above this second load bar. It is believed that this construction, although different than the construction of a plug described above with respect to FIGS. 18-26, has NEXT and TOC performance substantially the same as a plug in accordance with the invention.

[0091] The plugs as tested terminate a Berk-Tek Hyper-Grade Cat 5 UTP Patch Cable. FIG. 28 is a table of the maximum, minimum and variation in de-embedded NEXT values for tests performed on the twelve different plugs. It can be seen that the variation in NEXT values (delta) ranges between any two wire pairs is from 1.36 dB to 4.94 dB. FIG. 29 is a table of maximum, minimum and variation in TOC values for the same plugs. As shown in FIG. 29, the variation in TOC values (delta) ranges between any two wire pairs is from 2.07 dB to 6.21 dB. These variations are significantly less than the variations in the RJ45 plug, the test results for NEXT and TOC values of which are set forth in FIGS. 15-17 (discussed above).

[0092] Another embodiment of a modular plug having a load bar and exhibiting improved NEXT performance will be described with reference to FIGS. 30-33. In this embodiment, the plug 200 includes a housing 202 made of dielectric material and a load bar 204 (FIG. 30). Housing 202 includes a latch 206 projecting from a lower surface, parallel, spaced-apart, longitudinally extending terminal-receiving slots 208 formed in an upper surface at a front end, wire-receiving channels 210 formed at the front end and a longitudinal cavity 212 extending from a rear face inward up to the channels 210. Each channel 210 communicates with a respective slot 208 and the cavity 212 communicates with all of the channels 210. Cavity 212 is constructed to receive the load bar 204. Channels 210 are arranged in a specific pattern, as discussed below.

[0093] The load bar 200 is formed with eight conductor-receiving channels 214 arranged in a specific manner to provide improved NEXT performance. Specifically, two channels are arranged in an upper, substantially planar row designated R1 and six channels are arranged in a lower, substantially planar row designated R2 whereby the channels 214 in the upper row are those at positions 3 and 6 and thus the channels 214 in the lower row are those at positions 1, 2, 4, 5, 7 and 8 (FIG. 32). The rows R1 and R2 are substantially parallel to one another and preferably parallel to the planar, parallel upper and lower faces of the load bar 214. As shown in FIGS. 30 and 30A, channels 214 are also preferably substantially coaxial with channels 210 in the housing 202.

[0094] To terminate a cable 218, an end of the cable 218 is unsheathed, the twisted wire pairs are separated and inserted into a rear of the corresponding channels 214 in the load bar 204. The wires are pushed forward in the load bar 204 until a portion thereof extends from the front end of the load bar 204. The wires are then cut off flush with the front face of the load bar 204 and then the load bar 204 is inserted into the cavity 212 in the housing 202. The wires are then urged forward such that a portion thereof enters into the channels 210 in the housing 202. Contact terminals 216, which may be pre-loaded in the slots 208 of the housing 202, are then pushed downward into the wires lying in the channels 210 and pierce the insulation thereof to engage with the conductive core and thereby form an electrical connection. A strain relief element 220 on the housing 202 is then pressed into a portion of the cable 218 within the cavity 212 to secure the same to the housing 202.

[0095] Once the wires of the cable 218 are threaded onto the load bar 204, the separation between the wires at positions 3 and 6 and those at the remaining positions results in a reduction in crosstalk.

[0096] It has been found that the NEXT value for the wire pairs 45 and 36 (1 and 3) in the plug 200 having a load bar 204 with channels 214 arranged as shown in FIG. 32 is 33.69 dB which is better than the NEXT value for the same wire pairs in plugs with conventional load bars.

[0097] FIG. 33 shows a second cross-sectional view of a load bar for use in plug 200 and which is designated 204′. The main difference between load bar 204′ and load bar 204 is that the channels 214 at positions 3 and 6 are spaced at a larger distance from the row R2 in which the channels 214 at positions 1, 2, 4, 5, 7 and 8 are situated such that the wires at positions 3 and 6 are further separated from the wires at positions 1, 2, 4, 5, 7 and 8 (D2>D1).

[0098] Although two rows of channels are shown in the load bar, it is possible to arranged the channels in more than two rows, so long as the channels which receive wires operatively forming one circuit pair are situated in the same row which is different than the row(s) in which other wires are situated.

[0099] It has been found that the NEXT value for the wire pairs 45 and 36 (1 and 3) in the plug 200 having the load bar 204′ with channels 214 arranged as shown in FIG. 33 is 36.21 dB which is better than the NEXT value for the same wire pairs in plugs with conventional load bars. Also, it has been found that the separation distance between the planes in which the wires are situated affects the NEXT performance.

[0100] This positioning of wire-receiving channels in a load bar and the corresponding position of channels in a plug as shown in FIGS. 32 and 33 may be used in conjunction with the any of the load bars and plugs described herein as well in numerous other load bars and plugs. For example, the wire-receiving channels of the load bar shown in FIGS. 5-7 may be arranged as shown in FIGS. 32 and 33.

[0101] Although the load bar shown in FIGS. 32 and 33 includes eight channels, other load bars having a different number of channels could also be used applying the principles of the invention as described above.

[0102] Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. Accordingly, it is understood that other embodiments of the invention are possible in the light of the above teachings. For example, with respect to the embodiment in FIGS. 18-26, it is pointed out that the disclosed unitary load bar is only one way to ensure a pre-determined positioning for the conductors below the strain relief element. Other ways for maintaining the conductors in predetermined positions in the area below the strain relief element are also contemplated to be within the scope and spirit of the invention. Also, the load bar which is substantially coextensive with the cavity in the plug housing is a preferred embodiment. To obtain some of the advantages of the invention, the load bar should extend at least opposite the strain relief element so that the conductors positioned on the load bar are in set positions below the strain relief element thereby avoiding randomness in the organization of the conductors in the plug. As such, the load bar need not necessarily be coextensive with the cavity in the plug.