Communication cable with improved crosstalk attenuation

A barrier tape used as part of a communication cable is described. The barrier tape is provided with 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.

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'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.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring now to the drawings, and more particularly toFIG. 1, there is shown a communication system20, which includes at least one communication cable22, connected to equipment24. Equipment24is illustrated as a patch panel inFIG. 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 system20can further include cabinets, racks, cable management and overhead routing systems, for example.

Communication cable22is 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 inFIG. 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. Cables22can be terminated directly into equipment24, or alternatively, can be terminated in a variety of plugs25or jack modules27such as RJ45 type, jack module cassettes, Infiniband connectors, RJ21, and many other connector types, or combinations thereof. Further, cables22can be processed into looms, or bundles, of cables, and additionally can be processed into preterminated looms.

Communication cable22can 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 toFIG. 2, there is shown a transverse cross-section of cable22, taken along section line2-2inFIG. 1. Cable22includes an inner core23of four twisted conductive wire pairs26that are separated with a crossweb28. A wrapping of barrier tape32surrounds crossweb28. Barrier tape32can be helically wound around crossweb28. Cable22also can include an outer insulating jacket33. The barrier tape32is shown in a condensed version for illustration inFIG. 2, showing only an insulating substrate42and conductive segments34and38. Crossweb28includes a central “x” section which segregates the twisted pairs26from each other, and perimeter sections extending from the periphery of the “x” section which segregate the twisted pairs26from barrier tape32. Referring also toFIGS. 3 and 4, barrier tape32includes a first barrier layer35(shown inFIG. 2as an inner barrier layer) comprising conductive segments34separated by gaps36; a second barrier layer37(shown inFIG. 2as an outer barrier layer) comprising conductive segments38separated by gaps40in the conductive material of segments38; and an insulating substrate42separating conductive segments34and gaps36of the first conductive layer from conductive segments38and gaps40of the second conductive layer. The first and second barrier layers, and more particularly conductive segments34and conductive segments38, are staggered within the cable so that gaps40of the outer barrier layer align with the conductive segments34of the inner conductive layer. Barrier tape32can be helically or spirally wound around the inner insulating layer30. Alternatively, the barrier tape can be applied around the insulative layer in a non-helical way (e.g., “cigarette” or longitudinal style).

Outer insulating jacket33can be 15 mil thick (however, other thicknesses are possible). The overall diameter of cable22can be approximately 300 mils, for example; however, other thicknesses are possible.

FIG. 3is a plan view of barrier tape32illustrating the patterned conductive segments on an insulative substrate where two barrier layers35and37of discontinuous conductive material are used. The conductive segments34and38are arranged in a series of plane figures along both the longitudinal and transverse direction of an underlying substrate42. As described, the use of multiple barrier layers of patterned conductive segments facilitates enhanced attenuation of alien crosstalk, by effectively reducing coupling by a cable22to an adjacent cable, and by providing a barrier to coupling from other cables. The discontinuous nature of the conductive segments34and38reduces or eliminates radiation from the barrier layers35and37. In the embodiment shown, a double-layered gridlike metal pattern is incorporated in barrier tape32, which spirally wraps around the twisted wire pairs26of the exemplary high performance 10 Gb/s cable. The pattern may be chosen such that conductive segments of a barrier layer overlap gaps36,40from the neighboring barrier layer. InFIGS. 3 and 4, for example, both the top35and bottom37barrier 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 size44between segments in both the horizontal and vertical directions as shown inFIG. 3. According to one embodiment, the rounded corners are provided with a radius of approximately 1/16″.

Referring to the upper barrier layer35, the performance of any single layer of conductive material is at least partially dependent on the gap size44of the discontinuous pattern and the longitudinal length46of the discontinuous segments and can also be at least somewhat dependent on the transverse widths48of the conductive segments. In general, the smaller the gap size44and longer the longitudinal length46, the better is the cable-to-cable crosstalk attenuation. However, if the longitudinal pattern length46is 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 length46so 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 widths48of the conductive segments “cover” the twisted wire pairs as they twist in the cable core. In other words, it is desirable for the transverse widths48of 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 widths48, the better the cable-to-cable crosstalk attenuation is. It is further desirable for the barrier tape32to be helically wrapped around the cable core at approximately the same rate as the twist rate of the cable'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'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 layers35and37are illustrated, the present invention can include a single barrier layer, or three or more barrier layers.

FIG. 4illustrates a cross-sectional view, taken along section line4-4inFIG. 3, of barrier tape32in more detail as employed with two barrier layers35and37. Each barrier layer includes a substrate50and conductive segments34or38. The substrate50is 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 substrate50include polyester, polypropylene, polyethylene, polyimide, and other materials.

The conductive segments34and38are attached to a common insulative substrate42via layers of spray glue52. The layers of spray glue52can be 0.5 mils thick and the common layer of insulative substrate42can be 1.5 mil thick, for example. Given the illustrated example thicknesses for the layers, the overall thickness of the barrier tape32ofFIG. 4is 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 segments34and38small so as to reduce capacitance between those layers.

FIG. 5is a fragmentary, perspective and partially exploded view of an embodiment of cable22, illustrating the spiral nature of barrier tape32installed within cable22.FIG. 5illustrates how barrier tape32is spirally wound between crossweb28and outer jacket33of cable22. Alternatively, the barrier tape can be applied around the crossweb28in a non-helical way (e.g., cigarette or longitudinal style). It is desirable for the helical wrapping of the barrier tape32to have a wrap rate approximately equal to the core lay length of the cable22(i.e., the rate at which the twisted pairs26of the cable wrap around each other, equivalent to the crossweb28wrap rate). However, in some embodiments the helical wrapping of the barrier tape32may have a wrap rate greater or less than the core lay length of the cable22.

One of the design considerations of the present invention is constructing the barrier tape structure (such as conductive segments' 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 inFIGS. 1-5is 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.