BACKGROUND OF THE INVENTION

This application is a continuation-in-part of U.S. Serial No. 210,386 filed June 23, 1988, which has been allowed.

Field of the Invention

This invention is directed to a transmission line cable which allows ribbon cable segments to be formed into a round shape while maintaining a controlled relationship of signal and ground conductors so that the resulting electrical characteristics are consistent and uniform.

Description of the Prior Art

Flat transmission line cable, commonly referred to as ribbon cable, is widely used to facilitate mass terminations. Unlike ulticonductor round cable, the conductors in ribbon cable remain in the same position with respect to a reference and can be connected to a mass termination connector, without the need to trace each individual conductor to its source. In conventional round cable, the multiple conductors twist and undulate within the cable so that it is impossible to determine by inspection without the use of color codes whether the relationship of the conductors at the end of the cable is the same as at the beginning of the cable, and mass termination techniques cannot be utilized. While round cable is disadvantageous from the point of view of mass termination, it possesses other properties which provide advantages over ribbon cable. In particular, round cable is easier to shield, bends in any direction for easier handling and installation, and has a more compact profile for some applications.

In view of the distinct advantages of round cable in terms of shielding and handling, it has been proposed to configure ribbon cable into a round shape by folding the ribbon cable against itself and extruding a plastic jacket in a round configuration thereover. The ribbon cable is thereby configured into a round shape but can be re¬ configured as ribbon cable by stripping away the round jacket and unfolding the ribbon cable. The unfolded ribbon cable can then be mass terminated in the normal manner. Prior attempts to configure ribbon cable into a round shape by folding and jacketing did not address the variations that occur with electrical characteristics. In such configurations, impedance and capacitance variations can be relatively high due to the position of the conductors when the ribbon cable is folded and cannot be considered controlled from a transmission line cable perspective, as the tolerances usually associated with such cable are relatively tight. The position of the conductors caused by folding the ribbon cable can also lead to increases in crosstalk.

Accordingly, there remains a need in the art for a transmission line cable with controlled and predictable electrical characteristics, which combines the handling and shielding advantages of round cable and the advantages of mass termination of ribbon cable.

SUMMARY OF THE INVENTION

It is, therefore, a primary object of the invention to configure a ribbon transmission line cable into a round shape and still maintain consistent and uniform electrical characteristics.

The foregoing object is achieved by providing a transmission line cable comprised of a plurality of generally flat transmission line segments stacked together in an interlocking manner. At least one of the segments

comprises a generally flat insulating material having disposed therein at least one signal conductor and ground conductors on opposite sides of said signal conductor. Other segments may comprise all ground conductors, no conductors, or a plurality of different elements.

Each segment is configured so as to have alternating regions of reduced and expanded thickness which can receive corresponding regions of expanded and reduced thickness in an adjacent segment with which it is stacked. The segments are stacked together in the cable such that every signal conductor can be surrounded by ground conductors. Also, the segments can be configured so that air spaces exist between adjacent segments when stacked to enhance electrical properties. In each segment in which each signal conductor is surrounded with ground conductors, consistent and uniform electrical characteristics are maintained and crosstalk is inhibited. However, the segments may also include other conductor arrangements or components, uniquely permitting the invention to meet numerous different cable user requirements. A protective jacket surrounds the plurality of stacked transmission line segments forming a round transmission line cable.

BRIEF DESCRIPTION OF THE FIGURES OF DRAWING

Figure 1 is an elevational view of a prior art cable in which a ribbon cable is folded together into a round cable.

Figure 2 is a cross-sectional view of the ribbon cable depicted in Figure 1, taken along line 2'-2 ^/ .

Figure 3 is a cross-sectional view of the folded ribbon cable depicted in Figure 1, taken along line 3'-3'.

Figure 4 is an elevational view of individual transmission line segments used to form the transmission line cable of the invention.

Figure 5 is a cross-sectional view of a first embodiment of the invention in which a plurality of transmission line segments are stacked together.

Figure 6 is a cross-sectional view of the first embodiment of the invention with an alternative structure for wrapping the stacked transmission line segments.

Figure 7 is a cross-sectional schematic view of a second embodiment of the invention in which the plurality of transmission line segments have equal and different widths.

Figure 8 is a cross-sectional schematic view of a third embodiment of the invention in which all of the conductors in one of the plurality of transmission line segments are ground conductors for shielding purposes. Figure 9 is a cross-sectional schematic view of a fourth embodiment of the invention in which the type of conductor differs from segment to segment and within segments.

Figure 10 is a cross-sectional schematic view of a fifth embodiment of the invention in which two of the transmission line segments are spacer elements.

Figure 11 is a cross-sectional view of a sixth embodiment of the invention which combines features of the other embodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to Figure 1, a prior art cable in which ribbon cable is folded together and jacketed into a round cable is shown. Ribbon cable 1 is folded against itself and wrapped with tape 3 into a round cross-sectional configuration. A metal braid 5 is applied over the tape to provide added shielding and strength. A paper liner 7 is placed over the braid. Finally, jacket 9 is extruded over the entire structure to form a jacketed round cable. When

the jacket, liner, braid and tape are stripped away, the ribbon cable can be unfolded for mass termination.

Figure 2 shows a cross-sectional view of the ribbon cable in its unfolded state. The cable contains a plurality of individual conductors 11 disposed within insulating material 13. A web of insulating material 15 connects adjacent insulated conductors to maintain the continuous ribbon-like structure. Ribbon cable, as depicted in this figure, is typically made by aligning the individual conductors and continuously extruding insulating material, such as polyvinyl chloride, therearound.

Figure 3 shows the folded ribbon cable 1 with tape 3. As is evident from this figure, the cable extends from the first conductor 19 to the last conductor 17. At some points there are spaces 14 between the tape 3 and/or adjacent rows of insulated conductors, while at other points 15 adjacent insulated conductors contact one another. Because of this positioning of the conductors, inconsistencies in electrical characteristics occur. Moreover, the lack of shielding between adjacent conductors can cause undesirable levels of crosstalk.

Referring to Figures 4-6, the transmission line cable of the invention is seen to be comprised of a plurality of individual transmission line segments 21, 23 and 25, of indefinite length and varying widths. Each segment contains at least one signal conductor 27 surrounded on either side by ground conductors 29. Segment 21 has two signal conductors, while segments 23 and 25 have three and four signal conductors, respectively. The conductors are disposed within an insulating material 31 which may be any polymeric material that can be shaped or extruded into the trans-mission line segments, such as polyvinyl chloride, polyethylene, polypropylene and fluorinated ethylene propylene. These materials are extruded over the conductors in a conventional manner. The extrusion die is configured so that while each segment is generally flat, each contains alternating regions of reduced and expanded

thickness 33 and 35, respectively, which are adapted to receive a corresponding region of expanded and reduced thickness 35 ^/ and 33' of an adjacent segment when they are stacked together. As shown in Figures 4-6, the region of expanded thickness has an octagonal shape which is received in interlocking relation with a corresponding region of reduced thickness.

The widths of the segments are varied to accommodate additional signal conductors and to provide a round cable when the segments are properly stacked together and wound with tape 37, as shown in Figure 5. In a preferred embodiment metal braid 38 is applied over the tape followed by polymer jacket 40. Figure 6 shows an alternative structure in which the polyester tape is replaced with a metal laminate tape having an inner polyester tape 42 and an outer metal layer 44 laminated thereto. In both Figures 5 and 6, the width of the segments vary from segments 21 having two signal conductors to segments 25 having four signal conductors. However, it is to be understood that different combinations of segments of varying width are possible, so long as the final stacking has a generally round cross section when wrapped.

Furthermore, it is possible to obtain a generally round cross section by using segments 50 of equal width, as depicted in Figure 7. Reference numeral 49 denotes segments of different width similar to corresponding segments shown in Figures 4-6. However, it is understood that segments of different widths can be combined to form a single layer of the cable as shown in the middle layer of Figure 7.

It will be noted by those skilled in the art that the interlocking segments of the invention need not have the exact shape shown in Figures 4-6, but may have any shape which permits interlocking or bonding of the segments into a round cable structure. In addition, the segments can be configured to provide air space between adjacent, stacked segments Toy, for example, sizing the expanded region so

that it does not completely fill the region of reduced thickness in the adjacent stacked segment. The segments of Figures 7-11 have been depicted as rectangles for ease of illustration, but the actual shape of the segments may be identical to those shown in Figures 4-6.

A particular advantage of the transmission line cable of the invention is that every signal conductor is shielded from all adjacent signal conductors by ground planes formed by adjacent ground conductors, thereby greatly inhibiting crosstalk between the signal conductors. Thus, with reference to Figure 5, signal conductor 41 is completely surrounded by ground conductors 43. Unlike the round cable made by folding ribbon cable, there are no signal conductors which are directly adjacent to each other. When even greater shielding is desired, the signal conductors can be spaced farther apart by simply transmitting the signals through signal conductors which are spaced farther apart, such as conductors 41 and 45 as opposed to conductors 41 and 47, or by spacing the signal conductors farther apart within each segment. Greater shielding can also be produced by including more ground wires in each segment and/or by increasing the size of the ground wires, or all of the above.

Also, the signal conductors in one or more of the individual segments may be isolated from the signal conductors in each of the other segments, as illustrated in Figure 8, by providing one or more segments 51 in which all of the conductors are ground conductors. Reference numeral 49 again designates segments having the conductor and ground arrangement shown in Figures 4-6.

It is also advantageous in a variety of applications to provide segments having different gauge wires and/or different components for assembly into a single cable. For example, as shown in Figure 9, segment 53 contains ground conductors and signal carrying conductors having respective gauges of 30 AWG and 34 AWG, segment 54 contains ground conductors and signal-carrying conductors of

respective 28 AWG and 32 AWG gauges, and segment 55 includes fiber optic components. Of course, it will be recognized by those skilled in the art that numerous other signal carrying components may also be included in the individual segments of the invention, for example other types of circuit element, super-conductor components, or any combination of the above.

Another advantageous modification of the embodiment described above includes the substitution of spacer segments 52 containing no active lines for the conductor- carrying segments, as shown in Figure 10.

Finally, as shown in Figure 11, the various different types of segments described above may be assembled into numerous other different combinations or configurations. In Figure 11, for example, reference numeral 51 again designates an all-ground segment, reference numeral 50 denotes equal size segments, element 52 is a spacer, and elements 53-55 are segments including a plurality of different wire gauges and components as shown in Figure 9. The transmission line cable of the invention, therefore, provides more consistent electrical characteristics than prior constructions in which ribbon cable is folded into a round configuration. At the same time, it maintains the ability to be mass terminated since the conductors are locked into a fixed relationship within the cable. Accordingly, the cable of the invention combines the advantageous shielding and handling properties of round cable with the installation advantages of ribbon cable in a manner heretofore unknown in the art. In making the transmission line cable of the invention, the appropriate transmission line segments are continuously fed in line to a point where they are stacked together in interlocking relation to produce the desired cross-sectional configuration. A gradual twist or lay is imparted to each segment to improve flexibility of the resulting cable, as is well known in the cable making art. The stacked segments are wrapped with a tape, such as a

polyester tape or metal laminate tape, as is conventional in the cabling art. A metal braid may be applied over this structure to provide added shielding and strength properties if necessary or desirable. Finally, a polymer jacket is extruded over the structure to provide the final jacketed transmission line cable.

While the present invention has now been described in terms of certain preferred embodiments, one skilled in the art will readily appreciate that various modifications, changes, omissions and substitutions may be made without departing from the spirit thereof. It is intended, therefore, that the present invention be limited solely by the scope of the following claims.