Patent Publication Number: US-6664466-B2

Title: Multiple shielded cable

Description:
This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application No. 60/205,247, filed on May 19, 2000. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to electrical cables. More particularly, the present invention relates to shielded electrical cables capable of preventing radiation from signals contained within, while also avoiding the creation of undesirable ground loops. In general, ground loop formation is an unintentional side effect of the process of cable shield connection to the terminating devices. 
     BACKGROUND OF THE INVENTION 
     The use of shielded electrical cables for establishing suitable electromagnetic compatibility (EMC) margins in commingled communications, or other electronic equipment environments, is nearly ubiquitous. In such equipment settings, isolated single purpose connections are commonly utilized to bond conductive equipment shells to supporting frames and structures, and then through these, to earth or ground potential. This is primarily done to prevent hazardous voltage differences from developing between the exposed surfaces of the various entities so interconnected, and to improve signal integrity between equipment communicating over an electrical path. Nonetheless, easily measurable, and operationally problematic, voltage differences can result from any number of a variety of factors such as, for example, local fault currents, or external influences such as lightning, power system induction or faults, or even the ramifications of ambient magnetic disturbances created by solar storms. 
     In an effort to achieve suitable EMC margins, a shield conductor of a connecting cable is frequently connected at each end to an equipment shell. This practice, however, leads to the undesirable result of creating a complete electrical loop, which in the present context, is called a ground loop. Specifically, in this example, the ground loop consists of the preexisting equipment bonding mechanisms and the interconnecting cable shield. FIG. 1 provides a schematic representation of this condition. In FIG. 1, cable shield  10  is connected at opposite ends to a first equipment shell  12  and a second equipment shell  14 , and thereby to area bonding network  16  to form a complete electrical loop or ground loop  18 . 
     Often, the effects of the group loop are benign because there is little or no potential difference between cable ends, as a result of no external currents and a relatively small loop area as defined by the enclosing ground loop path. In other cases, however, a ground loop formed incidentally by the shield connections of the cable can create serious problems. For example, even though potential differences can be controlled by bonding system design to no more than a few volts, such a voltage can produce unintended cable shield currents of many amperes. This unintended current can, in turn, induce disturbances in other proximally located cables and, due to imperfections of shield construction, disturb the signals carried within the offending cable itself. Unreliable communication between interconnected equipment can result, and in rare instances, destructive levels can occur. 
     Therefore, because it is difficult to establish the immediate and future ramifications of incidental cabling ground loops, the routine creation of ground loops is to be avoided. Present practice is to avoid the creation of cable shielding ground loops by establishing a shield connection at only one end of the subject cable. By doing so, the continuous ground loop may be broken and the incidental and unwanted current flow in the shield interrupted. 
     This solution, however, is contrary to EMC best practices. In this regard, connecting the cable shielding at only one end of the cable gives rise to a number of other problems. These, in particular, include signal leakage radiation, and susceptibility to external radio frequency and other electromagnetic ambient conditions. To elaborate, shielding is used when it is desirable to prevent conducted signal leakage and resultant radiation from cabling. In a reciprocal manner, external electromagnetic fields are intended to induce currents on the cable shield, as opposed to the signal conductors contained within. Any discontinuity in the shield, such as intentionally disconnecting one end from the equipment shell at that end, to interrupt a ground loop path, for example, allows a voltage differential to develop across the discontinuity, with attendant undesirable coupling between external fields and the intentional signal currents. 
     To this date, the devices of the prior art have not been effective in addressing these and other problems. Current cabling designs alone cannot directly satisfy the contradictory goals of providing a continuous, and thus potentially effective, radio frequency (RF) shielding, and in the same instance, provide a discontinuous ground path, thus avoiding the formation of a ground loop. A well known, but rarely practiced solution because of induced mechanical complexities, and consequent cost penalties in equipment design, is to incorporate a discrete capacitor which is in series between the conductive equipment shell and each of the corresponding cable end shield connection means, in at least one of the devices to be interconnected, taken two at a time. For this purpose, a blocking capacitor typically in the order of 0.1 microfarads is selected, which must, along with its mounting means, possess very low stray inductive and resistive effects to avoid materially affecting shield RF performance as a result of its introduction. 
     A typical prior art cable  20  used for telecommunications equipment interconnections, which employs a metallized film shielding means is shown in cross-section in FIG.  2 A. The metallized film used as the shield itself is shown in cross-section in FIG.  2 B. Referring first to FIG. 2B, shield  28  is composed of a strip of nonconductive or insulating material  44  with a metallized layer  48  formed on one side. Referring next to FIG. 2A, shield  28  is helically or longitudinally wrapped around a plurality of conductors or signal leads  24 . One edge of the metallized film shield, essentially parallel to the cable axis, is folded  40  so that when the shield material is formed around leads  24  and overlapped, the metallized surfaces so overlapped connect, forming an electrically continuous shield circumferentially. An uninsulated wire or drainwire  36 , in turn, is wound in a widely spaced helix around shield  28  along its entire length in such a manner that it is in continuous contact with metallized outer layer  48 . Drainwire  36  serves the purpose of mitigating the effects of the unavoidable shield seam, and when exposed at each cable end, provides a convenient means of connection to the cable shield. An insulating jacket  38  surrounds the shield  28  and the drainwire  36 . 
     As in the case with this and any other form of shielded cable lacking isolation, connection of the shield to equipment enclosure at both ends in an environment where the enclosures are otherwise connected, in most instances by a grounding network, undesirably creates a ground loop. 
     Thus, prior art does not provide an economical or routine way to achieve simultaneously good cable RF shielding and avoidance of ground loop creation during interconnection of electronic equipment. Consequently, a need exists for a cabling mechanism which directly and economically addresses both performance goals at one time. 
     SUMMARY OF THE INVENTION 
     To address these and other needs of the prior art, it is an object of the present invention to provide a shielded cable capable of connecting, communications equipment in a manner that avoids the formation of undesirable ground loops while also avoiding signal radiation and unwanted external radio frequency and electromagnetic interference. 
     It is another object of the present invention to provide a shielded cable that incorporates a blocking capacitor within the shield construction itself. 
     It is yet another object of the present invention to provide a shielded cable that possesses the characteristics of capacitively coupled yet electrically isolated parallel shield surfaces. 
     It is yet another object of the present invention to provide a shielded cable which may be implemented utilizing, for example, simply constructed and applied shield material 
     To meet these and other objects, the present invention provides an electrical cable which includes one or more conductors; at least one shield encircling the at least one conductor, the shield extending along a length of the cable, each shield comprising at least one conductive layer separated electrically from at least another conductive layer by at least one nonconductive layer; and a plurality of connection mechanisms to the at least one conductive layer, each of the connection mechanisms being in substantially continuous contact with the at least one conductive layer of the at least one shield and being electrically separated from other conductive layers of other shields and from other connection mechanisms of said plurality of connection mechanisms, each of the connection mechanisms and each at least one conductive layer in contact therewith comprising one electrode of a plurality of electrodes electrically connectable at an end of the cable. 
     In one embodiment of the present invention, the electrodes of the electrical cable are electrically insulated from one another. Thus, the conductive layer of each of the shields is electrically separated from the conductive layers of other shields. Furthermore, each electrode may be connected to equipment at one end, with adjacent electrodes being connectable at an opposite end. 
     In another embodiment of the present invention, the cable includes two or more shields, with each shield and connection mechanism in contact therewith being connectable at one end of the cable and being positioned adjacent only shields and connection mechanisms connectable at an opposite end thereof. 
     In yet another embodiment of the present invention, each of the one or more shields may include one shield which has one nonconductive layer and two conductive layers formed thereon, with the nonconductive layer separating the two conductive layers. A related embodiment of the present invention includes shields comprised of a first tape and a second tape, each of the first tape and the second tape including a nonconductive layer and a conductive layer, the shield being arranged with the nonconductive layer of the first tape facing the nonconductive layer of the second tape. The second tape may also be oriented with the conductive surface of the second tape facing the nonconductive surface of the first tape, to provide increased inter shield capacitance per unit length and provide for one exposed surface of the shield assembly to be nonconductive, as desired. 
     In still another embodiment of the present invention, circumferential electrical continuity is facilitated by a first fold extending along a first end edge of the shield with the conductive layer facing outwardly and a second fold extending along a second end edge of the shield with another conductive layer facing outwardly, wherein the outwardly facing portion of the first end edge is in substantially continuous contact with a portion of the conductive layer spaced apart from the first end edge at a first predetermined position, thereby facilitating circumferential electrical continuity in the conductive layer, and wherein the outwardly facing portion of the second end edge is in substantially continuous contact with a portion of the another conductive layer spaced apart from the second end edge at a second predetermined position, thereby facilitating circumferential electrical continuity in the another conductive layer. 
     In contrast to the above embodiment, in another embodiment, the shields of the electrical cable include a first fold extending along a first end edge of the shield with the nonconductive layer facing outwardly, the outwardly facing portion of the first end edge separating the conductive layer from contact with other conductive layers of other shields. 
     In still other embodiments, the one or more conductors are grouped into two or more bundles of conductors, with each bundle of conductors being encircled by at least one shield of the one or more shields. Similarly, each bundle of the two or more bundles may just as easily be encircled by two or more shields, or encircled by one shield with all of the bundles in turn being encircled by another shield. 
     In yet other embodiments of the present invention, one or more of the conductive layers of the one or more shields includes a predetermined loss sufficient to control resonant effects introduced as a function of the exact cable length utilized. In contrast, in further embodiments, each nonconductive layer of the one or more shields includes a predetermined loss sufficient to control resonant length effects. 
     There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described below and which will form the subject matter of the claims appended hereto. 
     In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract included below, are for the purpose of description and should not be regarded as limiting. 
     As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic representation of a ground loop formed between two communications equipment shells; 
     FIG. 2A is a cross sectional view of a prior art shielded electrical cable; 
     FIG. 2B is a cross sectional view of a shield utilized in the electrical cable of FIG. 2A; 
     FIG. 3 is a cross sectional view of one embodiment of a shielded electrical cable of the present invention; 
     FIG. 4 is a cross sectional view of one example of a shield for use with the present invention, with partially underlapped metallization layers applied to opposing surfaces of an insulating film; 
     FIG. 5A is a cross sectional view of one example of a shield for use with the present invention, composed of two layers of insulating film, each with one surface uniformly coated with metallization; 
     FIG. 5B is a cross sectional view of another example of a shield for use with the present invention, composed of two layers of insulating film, each with one surface uniformly coated with metallization; 
     FIG. 6 is a cross sectional fold detail of one example of the shielded electrical cable of the present invention; 
     FIG. 7 is another cross sectional fold detail of one example of the shielded electrical cable of the present invention; 
     FIG. 8 is yet another cross sectional fold detail of one example of the shielded electrical cable of the present invention; 
     FIG. 9 is a cross sectional view of an alternate embodiment of a shielded electrical cable of the present invention; and 
     FIG. 10 is a cross sectional view of an other alternate embodiment of a shielded electrical cable of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In accordance with the principles of the present invention, a shielded electrical cable capable of preventing signal radiation while also avoiding the generation of undesirable ground loops is disclosed. More particularly, the shielded electrical cable of the present invention includes one or more conductors and one or more shields encircling the conductors. Each of these shields includes a conductive layer and a nonconductive layer electrically separating each of the conductive layers from one another. In addition, the shielded electrical cable also includes a plurality of drainwires or other connection mechanisms to the plurality of conductive layers. In the case of drainwires, they are in turn, each in substantially continuous contact with one conductive layer of at least one shield, as well as electrically separated from other conductive layers of other shields and other drainwires. Each drainwire and conductive layer in contact therewith then includes an electrode which is electrically connectable at an end of the cable. With this combination, the shielded electrical cable of the present invention prevents signal radiation while also avoiding the generation of undesirable ground loops. 
     Referring to FIG. 3, a cross sectional view of one example of a shielded electrical cable  300  implemented in accordance with the principles of the present invention is depicted. As shown in FIG. 3, cable  300  includes a number of elongated signal leads or conductors  308  used for the transmission of signals from one end of cable  300  to the other. Conductors  308 , in turn, are encircled, either helically or longitudinally or via any other suitable orientation, by shield  304  substantially along an entire length of cable  300 . Surrounding both shield  304  and conductors  308  is an insulating jacket  320 , which may be formed of, for example, plastic or any of a number of other suitable materials. As will be described below, insulating layer  430  may be formed of any one of a number of materials, for example, a plastic such as polyethylene-terephthalate (mylar). 
     FIG. 4 depicts a cross sectional view of one example of shield  304 . In this example, shield  304  includes a single insulating or dielectric layer  430 . For use as conductive shields, a layer of metallization  410 ,  420  is formed on each surface of insulating layer  430 . Thus, insulating layer  430  electrically separates layer of metallization  410  from layer of metallization  420 . Insulating layer  430  may be formed of any one of a number of materials, such as for instance plastic, polyethylene-terephthalate (mylar) or any other suitable materials. The layers of metallization  410 ,  420 , on the other hand, are typically formed of aluminum, or the like, and may be formed or laminated onto insulating layer  430  through any suitable process, such as for instance, a sputtering technique or a vapor deposition technique. Furthermore, although the layers of metallization  410 ,  420  are shown as being laminated to insulating layer  430 , it is to be understood that the layers of metallization may just as easily exist as distinct elements freely moveable with respect to insulating layer  430 . Therefore, with this construction, the layers of metallization are electrically separated from one another allowing the shield structure to impede any unwanted ground currents, while at the same time maintaining a large capacitance between the layers of metallization to provide a low impedance for radio frequency (RF) currents. 
     Referring again to FIG. 3, a first or inner drainwire  316  and a second or outer drainwire  312  extend substantially helically or longitudinally (or via some other suitable orientation) along the entire length of cable  300 . In this particular embodiment, drainwires  312  and  316  are uninsulated and are in substantially continuous electrical contact with the layers of metallization  410  and  420 , respectively, of shield  304 . This combination of metallized layer and drainwire thus forms an electrode which may be connected to, for example, an equipment shield at either end of cable  300 . Advantageously, drainwires  316  and  312  mitigate any effects of the shield fold seam. 
     The drainwires also provide, for example, a convenient method of electrical connection to equipment shields at each end of cable  300 . Thus, by connecting drainwire  312  at a first end of cable  300  and drainwire  316  at the other end of cable  300  the formation of a ground loop may be avoided. Insulating layer  430 , along with layers of metallization  410  and  420 , in essence form an unrolled capacitor with the two drainwires  316 ,  312  forming the opposing plate connections. As a result, the cabling intrinsically embodies a high quality distributed RF capacitor that does not require connection at both ends of the cable  300  of either drainwire, but only a connection at one end to a first drain wire and a connection at another end of a second drainwire. In addition, the combination of elements described above results in not only a shielded cable which incorporates a blocking capacitor within the shield construction itself, but also a shielded cable which possesses the characteristics of capacitively coupled yet electrically isolated parallel shield surfaces. 
     As should be apparent from the discussion above, numerous processes and constructions may be used to implement shield  304 . As an example, one or more insulating overhangs (see FIG.  4  and further below with respect to FIG. 5A) may optionally be formed on, for example, one or more longitudinal edges of shield  304 . This construction is particularly useful for providing additional electrical clearance between distinct conductive surfaces of one or more shields. Specifically, the nonconductive overhang may be formed by cutting or etching (or any other suitable mechanical, chemical or electromechanical fabrication process or the like) the conductive portions from the underlying nonconductive layer. Similarly, the conductive layer may be selectively applied to an underlying layer in a manner that produces an overhang. In this manner, one or more overhangs of nonconductive material are formed, which in turn provide additional nonconductive clearance between the conductive layers. 
     Although in the example described above shield  304  is depicted as including a single insulating layer with metallized layers formed on each of its surfaces, cable  300  may utilize any number of shields. Indeed, the single and two piece implementations of any one shield are substantially identical so long as the dielectric properties of the insulating materials are identical, and the sum of the thicknesses of the individual insulating layers is equal to the thickness of the insulator in the single layer embodiment. For example, referring to FIG. 5A, shield  304   a  may just as easily be comprised of two distinct strips  510  and  520 . 
     In FIG. 5A, shield  304   a  is formed of a first insulating strip or tape  510  and a second insulating strip or tape  520 . Each insulating strip  510 ,  520 , in turn, has a metallized layer  410   a ,  420   a , respectively, formed on one of its surfaces. Furthermore, although the insulating layers are positioned facing one another in this example, they may just as easily be facing inwardly or outwardly so long as the metallized layers  410   a ,  420   a  are electrically separated from one another. In addition, the strips  510 ,  520  may be laminated or adhered to one another or they may be mechanically independent of one another. As an optional feature, as shown in FIG. 5A, each distinct strip  510  or  520  may be offset from the other strip  510  or  520  to form an overhang providing additional electrical clearance for the metallized layers  410   a ,  420   a.    
     As mentioned above, the particular orientations and placements of the layers of metallization can be varied without departing from the principles and scope of the present invention. Hence although FIG. 5A depicts a metallized layer  420   a  facing inwardly and separated from an outwardly facing outer metallized layer  410   a  by intermediate insulating layers  510  and  520 , other implementations are possible. For example, as depicted in FIG. 5B, shield  304   b  may just as easily have an inwardly facing insulating layer  520   b  having thereon an intermediate metallized layer  420   b , and an intermediate insulating layer  510   b  having an outwardly facing metallized layer  410   b.    
     Likewise, again referring to FIG. 5B, the assignment of inwardly and outwardly facing surfaces may be exchanged so that metallization layer  410   b  faces inwardly, and the insulating material  520   b  faces outwardly. In each of these examples the metallized layers are separated from one another by one or more insulating layers and are in substantially continuous electrical contact with a drainwire. Furthermore, each metallized layer and drainwire in contact therewith, for example, is connectable at one end of the cable and is positioned adjacent only to shields and drainwires connectable at an opposite end thereof. 
     Advantageously, more than one shield of the construction described above may be utilized. Thus, although the examples described above utilize a single shield pair, it is to be understood that two or more composite shields may be implemented with the advantage of even further reducing field leakage. For instance, any number of metallized layers may be utilized with odd numbered layers in parallel at one end and even numbered layers in parallel at an opposite end. This interdigitation of multiple shields could also be employed if a higher intershield capacitance per unit length is desired. 
     In accordance with the principles of the present invention, the end edges of the shields may optionally be folded to, for example, ensure circumferential electrical continuity and to provide nonconductive clearance between conductive layers. In this manner, complete shield coverage is achieved and as a result, leakage radiation is minimized. Specifically, referring to FIG. 6 one example of a fold detail utilizable in the cable  300  of the present invention is depicted. 
     In FIG. 6, a shield  304  has conductive or metallized layers  410 ,  420  on each side of the nonconductive layer. The metallized or conductive layer  410  is facing outwardly, and the metallized or conductive layer  420  faces inwardly. 
     A first elongated fold  601  extends along a first end edge of shield  304  having a first metallized or conductive layer  410  facing outwardly. The outer metallized or conductive layer  410  does not extend along the first end edge of the shield  304 . Similarly, a second fold  602  extends along a second elongated end edge of shield  304  having the metallized or conductive layer  410  thereon also facing outwardly. The inner metallized or conductive layer  420  does not extend to the second end edge of the shield  304 . Thus, the inner portions of the folds  601 ,  602  are not metallized. 
     The outwardly facing portion of the first end edge at the fold  601  is in substantially continuous contact with a portion of the inwardly facing conductive or metallized layer  420  which is spaced apart from the second end edge at position  603 , thereby facilitating circumferential electrical continuity in metallized or conductive layer  420 . Likewise, the outwardly facing portion of the second end edge at the fold  602  is in substantially continuous contact with a portion of the outwardly facing metallized or conductive layer  410  spaced apart from the first end edge at position  604 , thereby facilitating circumferential electrical continuity in metallized or conductive layer  410 . 
     FIG. 7 illustrates an example of the folds implemented with a two piece shield as described above. The two piece shield includes a strip  510  and a strip  520  which are layered on each other, or fixed on each other by any suitable means. Strip  510  is the outer strip, and strip  520  is the inner strip of the two piece shield. The strips  510 ,  520  are offset to produce an overhang, such that at the first end edge, inner strip  520  extends past outer strip  510 , and at the second end edge, outer strip  510  extends past inner strip  520 . 
     A first fold  701  extends along a first end edge of the overhang of strip  520  of the two piece shield  304   a , with a first metallized or conductive layer  420   a  facing inwardly. Strip  510 , is layered on an inner surface of the strip  520  of the first piece of the two piece shield, but does not extend proximate to the first fold  701  of strip  520 . Strip  510  has a metallized or conductive layer  410   a  thereon facing outwardly. 
     Similarly, a second fold  702  extends along a second end edge of strip  510 , a second piece of the two piece shield  304   a , with an opposing metallized or conductive layer  410   a  also facing outwardly. Strip  520  is layered on an inner surface of the strip  510  of the second piece of the two piece shield, but does not extend proximate to the second fold  702  of the strip  510 . Strip  520  has a metallized or conductive layer  420   a  thereon facing inwardly. 
     The outwardly facing portion of the first end edge of strip  520  of a first piece of the two piece shield  304   a , is in substantially continuous contact with a portion of the conductive or metallized layer  420   a  of the strip  520  of the first piece of the two piece shield  304   a , at a position  703 , thereby facilitating circumferential electrical continuity in metallized or conductive layer  420   a . Likewise, the outwardly facing portion of the second end edge of strip  510  of the second piece of the two piece shield  304   a  is in substantially continuous contact with a portion of metallized or conductive layer  410   a  at position  704 , thereby facilitating circumferential electrical continuity in metallized or conductive layer  410   a.    
     Alternatively, the end edges of the strips  520  and  510  of the first and second pieces of the two piece shield  304   a , may be formed with the conductive or metallized surface facing inwardly and the nonconductive or dielectric layer facing outwardly. In this manner, a metallized surface and the resultant electrode may be better insulated. For instance, FIG. 8 depicts an example of the folds implemented in the shield of FIG. 5B, so that the exposed metallized surface of the layered shield  304   b  faces inwardly. In particular, a first fold  801  extends along a first edge of strip  510   b  of a first piece (includes layered strips  510   b  and  520   b ) of a two piece shield  304   b , such that metallized layer  410   b  thereon faces outwardly. This outwardly facing portion of  410   b  is in substantially continuous contact with a portion of metallized layer  410   b  at a second edge of strip  510   b  (includes layered strips  510   b  and  520   b ) of the two piece shield  304   b , at position  805 , thereby facilitating circumferential electrical continuity in metallization or conductive layer  410   b.    
     Similarly, a second fold  802  extends along a second edge of strip  520   b  of the second piece of the two piece shield  304   b , with metallization layer  420   b  thereon facing outwardly, and with metallization layer  420   b  being in substantially continuous contact with a portion of metallization layer  420   b  on strip  520   b  of the second piece of the two piece shield  304   b , at position  806 , to facilitate circumferential electrical continuity in metallized layer  420   b.    
     In contrast, a third fold  803  extends along a third end edge of strip  510   b  of the first piece of the two piece shield  304   b  with insulating or nonconductive layer  510   b  facing inwardly. Like fold  803 , a fourth fold  804  extends along a fourth end edge of strip  520   b  of the second piece of the two piece shield  304   b , with insulating or nonconductive layer  520   b  facing inwardly. These inwardly facing portions, then, face respective portions of nonconductive layers  510   b  and  520   b  and are spaced apart from the end edges of the opposing nonconductive layers  510   b  and  520   b . Thus the conductive or metallized layers  410   b  and  420   b  are separated from contact with other conductive or metallized layers of other shields. Consequently, folds  801  and  802  ensure electrical continuity while folds  803  and  804  insulate metallized layers from one another. Furthermore, with any of the above examples, the folds and drainwires may be located in any angular position. 
     In an alternate embodiment, the above described conductors may be grouped into a number of bundles, each of which may be encircled by one or more shields according to the techniques of the present invention. Any number of these shielded bundles may, in turn, be encircled by one or more additional shields and optionally by an outer insulating jacket. By selecting the insulating surface of the shield strips for each individual bundle to be oriented outwardly, and shield isolation between individual bundles with an overall cable is advantageously achieved without the requirement for additional insulation layers. Such a cable is particularly useful for installations which require the individual bundles, at either or both ends, to fan out to divergent equipment locations for interconnection. Likewise, this cable may also be useful where, for example, at most, one end of the cable is required to have the individual bundles fan out to divergent locations. 
     As one example, FIG. 9 depicts three individual bundles  900 ,  910 , and  920  encircled by an outer insulating jacket  930 . More specifically, each of bundles  900 ,  910  and  920  is implemented utilizing, for example, two shields which are folded at the end edges in the arrangements specified above. Furthermore, in this particular example the metallized layers of the shields are facing inwardly and are separated by at least one insulating or nonconductive layer. In addition, it is important to note that different and additional shield arrangements may be utilized by each of the bundles. 
     Referring to FIG. 10, another embodiment of the present invention includes an outer shield  100  common to all bundles within. In this embodiment, each bundle  101 ,  102 ,  103  is encircled first by its own inner shield  104 ,  105 ,  106 . In this case, the inner shields  104 ,  105 ,  106  are arranged with the metallized layer facing inwardly. Then, a single outer shield  100 , also with the metallized layer facing inwardly, is used to encircle each of the bundles  101 ,  102 ,  103 . Again, like the embodiment described above, different and additional shield arrangements may be utilized by each of the bundles  101 ,  102 ,  103 . 
     In each of the embodiments of FIGS. 9 and 10, the electrodes formed by the metallized layer and drainwire combination are electrically insulated from one another. Furthermore, each of these electrodes is connectable at one end and positioned adjacent electrodes connectable at an opposite end. 
     As mentioned above, any of a number of materials may be utilized in the construction of insulating layer  930 . As discussed, one suitable example is mylar. Such material, and the like, are desirable for their exceptional mechanical properties as well as because above 1 MHz they also possess significant electrical loss. In this regard, some shield dielectric loss is needed to reduce the undesirable effects of intershield resonances, the frequencies of which are determined by specific cable lengths as the closely spaced isolated shield layers behave as extremely low impedance transmission lines. Advantageously, additional distributed loss may be added, in the form of a resistive component, such as for example, carbon black or the like, introduced into the insulating material. Alternatively, the loss per unit cable length associated with the resistivity of one or more metalized shield layers, which can be adjusted by controlling metallization thickness and composition, may be used to damped intershield resonances. 
     The many features and advantages of the invention are apparent from the detailed specification, and thus, it is intended by the appended claims to cover all such features and advantages of the invention which fall within the true spirit and scope of the invention. Further, since numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.