Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 12/399,331 filed Mar. 6, 2009, which claims the benefit of provisional U.S. Patent Application No. 61/034,312, filed Mar. 6, 2008, which is incorporated herein in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to communication cables, and more particularly to methods and apparatus to enhance the attenuation of crosstalk associated with such cables. 
     BACKGROUND OF THE INVENTION 
     As networks become more complex and have a need for higher bandwidth cabling, attenuation of cable-to-cable crosstalk (or “alien crosstalk”) becomes increasingly important to provide a robust and reliable communication system. Alien crosstalk is primarily coupled electromagnetic noise that can occur in a disturbed cable arising from signal-carrying cables that run near the disturbed cable. Additionally, crosstalk can occur between twisted pairs within a particular cable, which can additionally degrade a communication system&#39;s reliability. 
     SUMMARY OF THE INVENTION 
     In some embodiments, the present invention relates to the use of multiple layers of material having conductive segments as a method of enhancing the attenuation of alien crosstalk. In one embodiment, the present invention comprises a double-layered metal patterned film (or barrier tape) that is wrapped around the wire pairs of a high performance 10 Gb/s (gigabit/second) unshielded twisted pair (UTP) cable. In general, the present invention can be used in communication cable of higher or lower frequencies, such as (TIA/EIA standards) Category 5e, Category 6, Category 6A, Category 7, and copper cabling used for even higher frequency or bit rate applications, such as, 40 Gb/s and 100 Gb/s. The conductive segments in the layers are positioned so that gaps in one layer are substantially overlain by conductive segments of a neighboring layer. The multiple layers reduce crosstalk while gaps between the conductive segments reduce the emission of electromagnetic energy from the conductive material and also reduce the susceptibility of the conductive material to radiated electromagnetic energy. The present invention solves deficiencies in the prior art of UTP cable to reduce cable-to-cable crosstalk, or other types of crosstalk. Embodiments of the present invention may be applied to other types of cable in addition to UTP cable. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For the purpose of facilitating an understanding of the inventions, the accompanying drawings and description illustrate embodiments thereof, from which the inventions, structure, construction and operation, and many related advantages may be readily understood and appreciated. 
         FIG. 1  is a schematic view of an embodiment of a communication system including multiple communication cables according to the present invention; 
         FIG. 2  is a cross-sectional view of one of the communication cables of  FIG. 1 ; 
         FIG. 3  is a fragmentary plan view of an embodiment of a barrier tape according to the present invention and used in the cables of  FIGS. 1 and 2 ; 
         FIG. 4  is a cross-sectional view of the barrier tape of  FIG. 3 , taken along section  4 - 4  in  FIG. 3 ; 
         FIG. 5  is a longitudinal cross-sectional view of the parasitic capacitive modeling of two prior art cables; 
         FIG. 6  is a longitudinal cross-sectional view of the parasitic capacitive modeling of two cables according to an embodiment of the present invention; 
         FIG. 7  is a longitudinal cross-sectional view of a parasitic inductive modeling of two prior art cables; 
         FIG. 8  is a longitudinal cross-sectional view of a parasitic inductive modeling of two cables according to an embodiment of the present invention 
         FIG. 9  is a perspective view of an embodiment of the cable of  FIG. 1 , illustrating the spiral nature of the barrier tape installed within the cable; 
         FIG. 10  is a fragmentary plan view of an embodiment of a barrier tape according to the present invention in the form of a triple layer patterned discontinuous conductive material on an insulative substrate material; 
         FIG. 11  is a fragmentary plan view of another embodiment of a barrier tape according to the present invention; 
         FIG. 12  is a cross-sectional view of the barrier tape of  FIG. 11  taken along the line  12 - 12  of  FIG. 11 ; 
         FIG. 13  is a cross-sectional view of a cable according to one embodiment of the present invention having an alternative twisted-pair divider; 
         FIG. 14  is a cross-sectional view of a cable according to another embodiment of the present invention having an alternative twisted-pair divider; 
         FIG. 15  is a cross-sectional view of a cable incorporating an embossed film as an insulating layer; 
         FIG. 16  is a cross-sectional view of a cable incorporating a embossed films as twisted pair separators and as an insulating layer; and 
         FIG. 17  is a plan view of an embossed film. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Referring now to the drawings, and more particularly to  FIG. 1 , there is shown a communication system  20 , which includes at least one communication cable  22 , connected to equipment  24 . Equipment  24  is illustrated as a patch panel in  FIG. 1 , but the equipment can be passive equipment or active equipment. Examples of passive equipment can be, but are not limited to, modular patch panels, punch-down patch panels, coupler patch panels, wall jacks, etc. Examples of active equipment can be, but are not limited to, Ethernet switches, routers, servers, physical layer management systems, and power-over-Ethernet equipment as can be found in data centers/telecommunications rooms; security devices (cameras and other sensors, etc.) and door access equipment; and telephones, computers, fax machines, printers and other peripherals as can be found in workstation areas. Communication system  20  can further include cabinets, racks, cable management and overhead routing systems, for example. 
     Communication cable  22  can be in the form of an unshielded twisted pair (UTP) cable, and more particularly a Category 6A cable which can operate at 10 Gb/s, as is shown more particularly in  FIG. 2 , and which is described in more detail below. However, the present invention can be applied to and/or implemented in a variety of communications cables, as have already been described, as well as other types of cables. Cables  22  can be terminated directly into equipment  24 , or alternatively, can be terminated in a variety of plugs  25  or jack modules  27  such as RJ45 type, jack module cassettes, Infiniband connectors, RJ21, and many other connector types, or combinations thereof. Further, cables  22  can be processed into looms, or bundles, of cables, and additionally can be processed into preterminated looms. 
     Communication cable  22  can be used in a variety of structured cabling applications including patch cords, backbone cabling, and horizontal cabling, although the present invention is not limited to such applications. In general, the present invention can be used in military, industrial, telecommunications, computer, data communications, and other cabling applications. 
     Referring more particularly to  FIG. 2 , there is shown a transverse cross-section of cable  22 . Cable  22  includes an inner core  23  of four twisted conductive wire pairs  26  that are typically separated with a crossweb  28 . An inner insulating layer  30  (e.g., a plastic insulating tape or an extruded insulating layer, for example a 10 mil thick inner insulating jacket material) surrounds the conductive wire pairs  26  and cross web  28 . A wrapping of barrier tape  32  surrounds the inner insulating layer  30 . Barrier tape  32  can be helically wound around the insulating layer  30 . Cable  22  also can include an outer insulating jacket  33 . The barrier tape  32  is shown in a condensed version for simplicity in  FIG. 2 , illustrating only an insulating substrate  42  and conductive segments  34  and  38 . Referring also to  FIGS. 3 and 4 , and as is discussed in more detail below, barrier tape  32  includes a first barrier layer  35  (shown in  FIG. 2  as a inner barrier layer) comprising conductive segments  34  separated by gaps  36 ; a second barrier layer  37  (shown in  FIG. 2  as an outer barrier layer) comprising conductive segments  38  separated by gaps  40  in the conductive material of segments  38 ; and an insulating substrate  42  separating conductive segments  34  and gaps  36  of the first conductive layer from conductive segments  38  and gaps  40  of the second conductive layer. The first and second barrier layers, and more particularly conductive segments  34  and conductive segments  38 , are staggered within the cable so that gaps  40  of the outer barrier layer align with the conductive segments  34  of the inner conductive layer. Barrier tape  32  can be helically or spirally wound around the inner insulating layer  30 . Alternatively, the barrier tape can be applied around the insulative layer in a non-helical way (e.g., cigarette or longitudinal style). 
     Outer insulating jacket  33 , can be 15 mil thick (however, other thicknesses are possible). The overall diameter of cable  22  can be under 300 mils, for example; however, other thicknesses are possible. 
       FIG. 3  is a plan view of barrier tape  32  illustrating the patterned conductive segments on an insulative substrate where two barrier layers  35  and  37  of discontinuous conductive material are used. The conductive segments  34  and  38  are arranged as a mosaic in a series of plane figures along both the longitudinal and transverse direction of an underlying substrate  42 . As described, the use of multiple barrier layers of patterned conductive segments facilitates enhanced attenuation of alien crosstalk, by effectively reducing coupling by a cable  22  to an adjacent cable, and by providing a barrier to coupling from other cables. The discontinuous nature of the conductive segments  34  and  38  reduces or eliminates radiation from the barrier layers  35  and  37 . In the embodiment shown, a double-layered gridlike metal pattern is incorporated in barrier tape  32 , which spirally wraps around the twisted wire pairs  26  of the exemplary high performance 10 Gb/s cable. The pattern may be chosen such that conductive segments of a barrier layer overlap gaps  36 ,  40  from the neighboring barrier layer. In  FIGS. 3 and 4 , for example, both the top  35  and bottom  37  barrier layers have conductive segments that are arranged in a series of squares (with rounded corners) approximately 330 mil×330 mil with a 60 mil gap size  44  between squares. According to one embodiment, the rounded corners are provided with a radius of approximately 1/32″. 
     Referring to the upper barrier layer  35 , the performance of any single layer of conductive material is dependent on the gap size  44  of the discontinuous pattern and the longitudinal length  46  of the discontinuous segments and can also be at least somewhat dependent on the transverse widths  48  of the conductive segments. In general, the smaller the gap size  44  and longer the longitudinal length  46 , the better the cable-to-cable crosstalk attenuation will be. However, if the longitudinal pattern length  46  is too long, the layers of discontinuous conductive material will radiate and be susceptible to electromagnetic energy in the frequency range of relevance. One solution is to design the longitudinal pattern length  46  so it is slightly greater than the average pair lay of the twisted conductive wire pairs within the surrounded cable but smaller than one quarter of the wavelength of the highest frequency signal transmitted over the wire pairs. The pair lay is equal to the length of one complete twist of a twisted wire pair. 
     Typical twist lengths (i.e., pair lays) for high-performance cable (e.g., 10 Gb/s) are in the range of 0.8 cm to 1.3 cm. Hence the conductive segment lengths are typically within the range of from approximately 1.3 cm to approximately 10 cm for cables adapted for use at a frequency of 500 MHz. At higher or lower frequencies, the lengths will vary lower or higher, respectively. 
     Further, for a signal having a frequency of 500 MHz, the wavelength will be approximately 40 cm when the velocity of propagation is 20 cm/ns. At this wavelength, the lengths of the conductive segments of the barrier layers should be less than 10 cm (i.e., one quarter of a wavelength) to prevent the conductive segments from radiating electromagnetic energy. 
     It is also desirable that the transverse widths  48  of the conductive segments “cover” the twisted wire pairs as they twist in the cable core. In other words, it is desirable for the transverse widths  48  of the conductive segments to be wide enough to overlie a twisted pair in a radial direction outwardly from the center of the cable. Generally, the wider the transverse widths  48 , the better the cable-to-cable crosstalk attenuation is. It is further desirable for the barrier tape  32  to be helically wrapped around the cable core at approximately the same rate as the twist rate of the cable&#39;s core. For high-performance cable (e.g., 10 Gb/s), typical cable strand lays (i.e., the twist rate of the cable&#39;s core) are in the range of from approximately 6 cm to approximately 12 cm. It is preferred that barrier tapes according to the present invention are wrapped at the same rate as the cable strand lay (that is, one complete wrap in the range of from approximately 6 cm to approximately 12 cm). However, the present invention is not limited to this range of wrap lengths, and longer or shorter wrap lengths may be used. 
     A high-performing application of a barrier tape of discontinuous conductive segments is to use one or more conductive barrier layers to increase the cable-to-cable crosstalk attenuation. For barriers of multiple layers, barrier layers are separated by a substrate so that the layers are not in direct electrical contact with one another. Although two barrier layers  35  and  37  are illustrated, the present invention can include a single barrier layer, or three or more barrier layers. (See  FIG. 10  for example.) 
       FIG. 4  illustrates a cross-sectional view of barrier tape  32  in more detail as employed with two barrier layers  35  and  37 . Each barrier layer includes a substrate  50  and conductive segments  34  or  38 . The substrate  50  is an insulative material and can be approximately 0.7 mils thick, for example. The layer of conductive segments contains plane figures, for example squares with rounded corners, of aluminum having a thickness of approximately 0.35 mils. According to other embodiments of the present invention, the conductive segments may be made of different shapes such as regular or irregular polygons, other irregular shapes, curved closed shapes, isolated regions formed by conductive material cracks, and/or combinations of the above. Other conductive materials, such as copper, gold, or nickel may be used for the conductive segments. Semiconductive materials may be used in those areas as well. Examples of the material of the insulative substrate include polyester, polypropylene, polyethylene, polyimide, and other materials. 
     The conductive segments  34  and  38  are attached to a common insulative substrate  42  via layers of spray glue  52 . The layers of spray glue  52  can be 0.5 mils thick and the common layer of insulative substrate  42  can be 1.5 mil thick, for example. Given the illustrated example thicknesses for the layers, the overall thickness of the barrier tape  32  of  FIG. 4  is approximately 4.6 mils. It is to be understood that different material thicknesses may be employed for the different layers. According to some embodiments, it is desirable to keep the distance between the two layers of conductive segments  34  and  38  small so as to reduce capacitance between those layers. 
     When using multiple layers of discontinuous conductive material as barrier material the gap coverage between layers assists in decreasing cable-to-cable crosstalk. This may be best understood by examining the capacitive and conductive coupling between cables. 
       FIG. 5  illustrates a model of parasitic capacitive coupling of two prior art cables  401  and  402 . Here, the two cables  401  and  402  employ insulating jackets  404  as a method of attenuating cable-to-cable crosstalk between the two twisted pairs of wire  403  of standard 10 G b/s Ethernet twist length  54  (pair lay). The resultant parasitic capacitive coupling, as illustrated by modeled capacitors  405 - 408 , creates significant cable-to-cable crosstalk. Although capacitors  405 - 408  are shown as lumped capacitive elements for the purpose of the  FIG. 5  model, they are in fact a distributed capacitance. 
     In contrast,  FIG. 6  illustrates the parasitic capacitive coupling of two cables  22   a  and  22   b  using the barrier technique of the present invention. Though the overall effect results from a distributed capacitance, lumped element capacitor models are shown for the purpose of illustrating the distributed parasitic capacitive coupling. First and second twisted wires  101  and  102  of the twisted pair  26   a  carry a differential signal, and can be modeled as having opposite polarities. The “positive” polarity signal carried by the first wire  101  and the “negative” polarity signal carried by the second wire  102  couple approximately equally to the conductive segment  34   a.  This coupling is modeled by the capacitors  504  and  505 . As a result, very little net charge is capacitively coupled from the twisted pair  26  onto the conductive segment  34   a,  resulting in a negligible potential. What little charge is coupled onto the conductive segment  34   a  is further distributed by coupling onto the conductive segments  38   a  and  38   b  in the outer barrier layer of the cable  22   a  via modeled capacitors  506  and  507 . Because the conductive segments  38   a  and  38   b  are also capacitively coupled with additional inner conductive segments  34   b  and  34   c,  the amount of capacitive coupling is further mitigated due to cancellation effects resulting from the opposite polarities of the twisted wires  101  and  102 . Similar cancellation effects carry through the additional modeled capacitors  508 - 513 , so that the overall capacitive coupling between the twisted pair  26   a  of the first cable  22   a  and the twisted pair  26   b  of the second cable  22   b  is substantially decreased as compared to a prior art system. The spacing of the gaps  36  and  40  in the two barrier layers of a barrier tape greatly reduces the opportunity for direct cable-to-cable capacitive coupling. 
     Turning to inductive modeling,  FIG. 7  illustrates the parasitic distributed inductive modeling of two prior art cables. In  FIGS. 7 and 8 , currents in the conductors produce magnetic fields and the distributed inductance of the conductors results in inductive coupling shown by the arrows. For purposes of illustration, specific regions of the magnetic fields are indicated by arrows, but the magnetic fields are actually distributed throughout the illustrated areas. Here, both cables  601  and  602  employ only insulating jackets  604  as a method of attenuating cable-to-cable crosstalk between the two twisted pairs of wire  605  of standard 10 Gb/s Ethernet twist length  54  (pair lay). The resultant parasitic inductive coupling modeled at  606 - 609  creates significant cable-to-cable crosstalk. 
       FIG. 8  illustrates inductive modeling of two cables using the barrier techniques as proposed by the present invention. The two twisted wires of cables  22   a  and  22   b  respectively contain twisted pairs  26   a  and  26   b  and same standard 10 Gb/s Ethernet twist length  56  (pair lay), as the prior art model. However, the two cables  22   a  and  22   b  are protected with barrier tape  32 . The barrier layers  35  and  37  contain respective gaps  36  and  40  in the conductive material to prevent the conductive material segments  34  and  38  from radiating. The conductive segments are staggered within the cable so that most gaps in the conductive material are aligned conductive segments of the adjacent layer. 
     Magnetic fields are induced in the first cable  22   a  by the twisted wire pair  26   a.  However, as the magnetic fields pass through the inner barrier layer of the barrier tape  32 , they create eddy currents in the conductive segments, reducing the extent of magnetic coupling  710  and  711 , and reducing cable-to-cable crosstalk. However, the need for gaps  36  and  40  in the barrier layers  35  and  37  results in some portions of the magnetic fields passing near a boundary or gap. Eddy currents are not as strongly induced near a boundary or gap, resulting in less reduction of the passing magnetic field in these regions. 
     One solution again is to use multiple barrier layers  35  and  37  so that a gap from one layer is covered by conductive material from the adjacent layer. The second cable  22   b  illustrates an outer barrier layer (particularly conductive segment  38 ) covering a gap  36  in the inner conductive layer  35 . As discussed above, the magnetic fields passing through the conductive layer  35  and  37  do not lose much energy because eddy currents are not as strongly induced near boundaries or gaps  36  and  40 . However, by ensuring that a gap  36  in the inner conductive layer  35  is covered by a conductive segment from the outer barrier layer, the magnetic fields passing through the inner barrier layer create stronger eddy currents while passing through the outer barrier layer, therefore reducing their energy and reducing cable-to-cable crosstalk. Therefore, it is desirable to arrange the gaps  36  and  40  of the barrier layers to be aligned with conductive segments from an adjacent barrier layer; however, some gaps in the barrier layers may remain uncovered without significantly affecting the cable-to-cable crosstalk attenuation of the present invention. 
       FIG. 9  illustrates how the barrier tape  32  is spirally wound between the insulating layer  30  and the outer jacket  33  of the cable  22 . Alternatively, the barrier tape can be applied around the insulative layer in a non-helical way (e.g., cigarette or longitudinal style). It is desirable for the helical wrapping of the barrier tape  32  to have a wrap rate approximately equal to the core lay length of the cable  22  (i.e., the rate at which the twisted pairs  26  of the cable wrap around each other). However, in some embodiments the helical wrapping of the barrier tape  32  may have a wrap rate greater or less than the core lay length of the cable  22 . 
       FIG. 10  illustrates another embodiment of a barrier tape  60  according to the present invention that includes a third conductive layer with conductive segments  62  to specifically cover gaps  64 . Barrier tape  60  can have a structure similar to that shown in  FIG. 4 , but with an additional barrier layer, and intervening substrate and glue layer, where the conductive segments  62  overlap gaps  64  as shown. The present invention is not limited to the embodiments shown, but can also include embodiments with a single barrier layer, or four or more barrier layers, in the barrier tape. 
       FIG. 11  illustrates another embodiment of a barrier tape  80  according to the present invention. The barrier tape  80  is similar to the barrier tape  32  shown and described above, except that the barrier tape  80  is provided with upper and lower rectangular conductive segments  82  and  83 . The rectangular segments on each layer are separated by gaps  84 . The rectangular conductive segments  82  and  83  have a longitudinal length  86  and a transverse width  88 . According to one embodiment, the longitudinal length  86  of each rectangular conductive segment  82  is approximately 822 mils, and the transverse width  88  is approximately 332 mils. In this embodiment, the gaps  84  are approximately 60 mils wide. As the conductive segment shape and size can be varied, so can the gap width. For example, the gap can be 55 mils or other widths. In general, the higher the ratio of the longitudinal lengths of the conductive segments to the gap widths, the better the crosstalk attenuation. Different dimensions may be provided, however, depending on the desired performance characteristics of the cable. The rectangular conductive segments  82  are provided with rounded corners  90 , and in the illustrated embodiment the rounded corners  90  have a radius of approximately 1/32″. 
     It is desirable for conductive segments according to the present invention to be provided with curved corners in order to reduce the chances of undesirable field effects that could arise if sharper corners are used. According to some embodiments of the present invention, curved corners having radii in the range of 10 mils to about 500 mils are preferable, though larger or smaller radii may be beneficial in certain embodiments. 
       FIG. 12  is a cross-sectional view of the barrier tape  80  taken along the line  12 - 12  of  FIG. 11 . The barrier tape  80  comprises an insulative substrate  92  and upper and lower barrier layers  91  and  93  having rectangular conductive segments  82  and  83 . The rectangular conductive segments  82  and  83  are attached to the substrate  92  by a layer of spray glue  94  and are bordered by outer substrate layers  96 . According to one embodiment, the insulative substrate  92  has a thickness of about 1.5 mils, the spray glue layers  94  have thicknesses of approximately 0.5 mils, the conductive segments  82  and  83  have thicknesses of about 1 mil, and the outer substrate layers  96  have thicknesses of about 1 mil. Other thicknesses may be used for the layers depending on the desired physical and performance qualities of the barrier tape  80 . 
       FIG. 13  is a cross-sectional view of a cable  110  having an alternative twisted-pair divider  112 . The twisted-pair divider  112  has radial crossweb members  114  that extend outwardly from a center  116  of the divider  112  to circumferential crossweb members  118 . Twisted pairs  120  of the cable  110  are contained within open regions  122  bordered by the radial and circumferential crossweb members  114  and  118 . The circumferential crossweb members  118  serve as an inner insulating layer similar to the layer  30  of  FIG. 2 . The twisted-pair divider  112  may incorporate a barrier layer comprising conductive segments, similar to the barrier tapes  32 ,  60 , and  80  discussed above. 
       FIG. 14  is a cross-sectional view of another cable  124  having an alternative twisted-pair divider  126 . The twisted-pair divider  126  has radial crossweb members  128  that extend from a center  130  of the divider  126  and terminate at shortened circumferential crossweb members  132 . Twisted pairs  134  of the cable  124  are contained within open regions  136  partially bounded by the radial and shortened circumferential crossweb members  126  and  132 . The twisted-pair divider  126  may incorporate a barrier layer comprising conductive segments, similar to the barrier tapes  32 ,  60 , and  80  discussed above. 
       FIG. 15  is a cross-sectional view of another cable  130  having an embossed film  132  as the insulating layer between the twisted wire pairs  26  and the barrier tape  32 . According to some embodiments, the embossed film  132  is in the form of an embossed tape made of a polymer such as polyethylene, polypropylene, or fluorinated ethylene propylene (FEP). In some embodiments, the embossed film  132  is made of an embossed layer of foamed polyethylene or polypropylene. Unfoamed fire-retardant polyethylene may be used as the base material. Embossing the film  132  provides for an insulating layer having a greater thickness than the thickness of the base material of the film. This produces a greater layer thickness per unit mass than non-embossed solid or foamed films. The incorporation of more air into the layer, via embossing, lowers the dielectric constant of the resulting layer, allowing for an overall lower cable diameter because the lower overall dielectric constant of the layer allows for a similar level of performance as a thicker layer of a material having a higher dielectric constant. The use of an embossed film reduces the overall cost of the cable by reducing the amount of solid material in the cable, and also improves the burn performance of the cable because a smaller amount of flammable material is provided within the cable than if a solid insulating layer is used. The use of an embossed film as the insulting layer has also been found to improve the insertion loss performance of the cable. Insulating layers according to the present invention may be spirally or otherwise wrapped around a cable core. 
       FIG. 16  is a cross-sectional view of a cable  134  having an embossed film  132  as the insulating layer between the twisted pairs  26  and the barrier tape  32 , and also having embossed films as separators between the individual twisted pairs  26 . The separators shown in  FIG. 16  include a central straight separator  136  and a pair of bent separators  138 . Using embossed films as separators between the twisted wire pairs has many of the same advantages as using an embossed film as the insulating layer, as discussed above. 
       FIG. 17  is a plan view of one embodiment of an embossed film  132 . Side detail views S are also shown in  FIG. 17 . In the embodiment shown in  FIG. 17 , the embossed film  132  takes the form of a repeating pattern of embossed squares  140  in a base material such as polyethylene or polypropylene, either foamed or unfoamed. In a preferred embodiment, a foamed polymer film material is used. The aspect ratio of the embossed film  132  is the ratio between the effective thickness of the embossed film, t e , and the thickness of the base material, t b . Aspect ratios of up to 5, for example with a base material thickness of 3 mils and an effective thickness of 15 mils for the embossed film, are used according to some embodiments. Other useful ratios include a base material thickness of 3 mils and an effective thickness of 14 mils; a base material thickness of 5 mils and an effective thickness of 15 mils. According to some embodiments, base materials in the range of from 1.5 to 7 mils are embossed to effective thicknesses of from 8 mils to 20 mils. While embossed squares  140  are shown in  FIG. 17 , other shapes may be used, as may a combination of different shapes over the length of the film  132 , including the use of patterned embossing. 
     Barrier tapes according to the present invention can be spirally, or otherwise, wrapped around individual twisted pairs within the cable to improve crosstalk attenuation between the twisted pairs. Further, barrier layers according to the present invention may be incorporated into different structures within a cable, including an insulating layer, an outer insulating jacket, or a twisted-pair divider structure. 
     From the foregoing, it can be seen that there have been provided features for improved performance of cables to increase attenuation of cable-to-cable crosstalk. While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects. Therefore, the aim is to cover all such changes and modifications as fall within the true spirit and scope of the invention. The matter set forth in the foregoing description and accompanying drawings is offered by way of illustration only and not as a limitation.

Technology Category: y