Abstract:
A barrier tape used as part of a communication cable has one or more barrier layers of discontinuous conductive segments. Conductive segments of one barrier layer are preferably sized and shaped to overlie gaps between conductive segments of another barrier layer.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 12/467,855, filed May 18, 2009, which claims the benefit of U.S. patent application Ser. No. 61/054,330, filed May 19, 2008. The subject matter of which is hereby incorporated by reference 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 perspective 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 ; and 
         FIG. 5  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. 
     
    
    
     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  is shown 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 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 , taken along section line  2 - 2  in  FIG. 1 . Cable  22  includes an inner core  23  of four twisted conductive wire pairs  26  that are separated with a crossweb  28 . A wrapping of barrier tape  32  surrounds crossweb  28 . Barrier tape  32  can be helically wound around crossweb  28 . Cable  22  also can include an outer insulating jacket  33 . The barrier tape  32  is shown in a condensed version for illustration in  FIG. 2 , showing only an insulating substrate  42  and conductive segments  34  and  38 . Crossweb  28  includes a central “x” section which segregates the twisted pairs  26  from each other, and perimeter sections extending from the periphery of the “x” section which segregate the twisted pairs  26  from barrier tape  32 . Referring also to  FIGS. 3 and 4 , barrier tape  32  includes a first barrier layer  35  (shown in  FIG. 2  as an 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 approximately 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 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 15° parallelograms (with rounded corners) approximately 1071 mil×203 mil with a 60 mil gap size  44  between segments in both the horizontal and vertical directions as shown in  FIG. 3 . According to one embodiment, the rounded corners are provided with a radius of approximately 1/16″. 
     Referring to the upper barrier layer  35 , the performance of any single layer of conductive material is at least partially 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 is the cable-to-cable crosstalk attenuation. However, if the longitudinal pattern length  46  is too long, the layers of discontinuous conductive material can radiate and can 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. 
     Twisted pairs in a communication cable may be colored blue, orange, green, and brown. In the embodiment shown the twist lengths (i.e., pair lays) for four twisted conductive wire pairs are 0.828 cm for the blue pair, 1.204 cm for the orange pair, 0.897 cm for the green pair and 1.074 cm for the brown pair. Typical 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. In the embodiment shown the cable strand lay is 7.62 cm. 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. 
       FIG. 4  illustrates a cross-sectional view, taken along section line  4 - 4  in  FIG. 3 , 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 0.75 mils thick, for example. The layer of conductive segments contains plane figures, for example parallelograms 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. The present invention can combine different shapes in multiple rows of conductive segments. Other conductive materials, such as copper, gold, or nickel may be used for the conductive segments. Other conductive segment thicknesses could range from approximately 0.3 mils to approximately 1.5 mils. Semiconductive materials may be used in those areas as well. Examples of the material of the insulative substrate  50  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 4.7 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. 
       FIG. 5  is a fragmentary, perspective and partially exploded view of an embodiment of cable  22 , illustrating the spiral nature of barrier tape  32  installed within cable  22 .  FIG. 5  illustrates how barrier tape  32  is spirally wound between crossweb  28  and outer jacket  33  of cable  22 . Alternatively, the barrier tape can be applied around the crossweb  28  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, equivalent to the crossweb  28  wrap rate). 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 . 
     One of the design considerations of the present invention is constructing the barrier tape structure (such as conductive segments&#39; dimensions, shape, spacing, quantity, number of rows and orientation) with respect to the effective twist rate (combined twist lay with cable lay) of each of the twisted pairs, to provide enhanced cable-to-cable coupling attenuation. If the relationship between the barrier tape structure and effective twist rate is not correct, the interval of the repeating pattern of the barrier tape in relation to the effective twist rate of each of the twisted pairs can create a strong coupling mechanism to adjacent cable(s) in various segments of the operating frequency spectrum of the channels, which is undesirable. The embodiment shown in  FIGS. 1-5  is one combination, according to the present invention, which provides effective ANEXT and AFEXT attenuation up to 500 MHz. The present invention also provides high longitudinal impedance in the barrier tape which reduces or eliminates EMI susceptibility in comparison to the performance of known UTP cable. 
     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.