Cable having a corrugated septum

A cable structure in round or flat form is characterized by a corrugated septum disposed intermediate an inner and an outer sheath. The septum contacts the sheaths to define tubular envelopes extending axially along the length of the cable. Each of the envelopes is able to receive a predetermined number of conductors. The sheaths and the septum are electrically connectable to a ground potential so as to totally electromagnetically isolate the conductors entirely along their axial lengths.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an electrical cable for a transmission 
line in either round or flat form and, in particular, to an electrical 
cable having a plurality of conductors therein wherein each conductor or 
set of conductors is physically separated and electromagnetically isolated 
along their entire axial length by a corrugated septum. 
2. Description of the Prior Art 
Round cables are presently used for relatively high speed data transmission 
between various system components in data processing networks. Such cables 
utilize twisted pairs of conductors to achieve the necessary electrical 
characteristics, particularly characteristic impedance and cross-talk 
control. 
One such cable arrangement is that sold by Hewlett-Packard as the HPIB 
cable. This cable includes concentrically spaced inner and outer 
conducting members disposed about a central, axially extending core. The 
inner member is typically a metallized film sheath while the outer member 
is a metallized film sheath surrounded by a metallic braid. A first layer 
of twisted pairs of conductors is disposed in the annular space defined 
between the core and the inner surface of the inner conducting member 
while a second layer of twisted pairs of conductors is disposed in the 
annular space between the outer surface of the inner member and the inner 
surface of the outer conducting member. The conductors in the inner layer 
are used as data transmission lines while the conductors in the outer 
layer serve as control lines. One conductor in each twisted pair carries 
the appropriate data or control signal while the other of the conductors 
in that pair serves as the signal return for that signal. In typical usage 
the inner conducting member is electrically grounded and acts to isolate 
the data pairs from the control pairs. 
A round cable assembly as described above is bulky and generally expensive 
to manufacture due to its complexity. Twisted conductor pairs result in an 
overall diameter of the twisted pair cable that is significantly larger 
than that of standard cables. Such a twisted pair cable can range from 
twenty to fifty percent larger than a standard cable depending upon 
conductor size and the number of conductors. These factors also result in 
a relatively stiffer cable construction which must be carefully fabricated 
in order to prevent failure due to cable flexing. Twisted pair cables 
often do not exhibit a uniform cross-section and can thus present problems 
when using automatic stripping apparatus. Furthermore, providing the 
appropriate terminations at each end of each cable is a relatively labor 
intensive endeavor since before the ends of the conductors can be 
terminated in a suitable connector the conductors comprising each twisted 
pair must be untwisted. 
Despite their problems twisted pair cables are utilized because they 
provide electrical characteristics that are closely comparable to the 
electrical characteristics of coaxial cable. Of course, the cost of 
coaxial cable prevents its widespread use in the environment here 
discussed. 
The cable disclosed and claimed in U.S. patent application Ser. No. 
06/769,725, filed Aug. 27, 1985, a continuation-in-part Ser. No. 670,948, 
filed Nov. 13, 1984 both now abandoned, assigned to the present assignee 
provides a cable assembly using ordinary individual jacketed conductors 
arranged in a form that is less expensive to manufacture, less bulky and 
more flexible when manufactured and yet provides substantially equivalent 
or better electrical characteristics than are available in a cable using 
twisted pairs. Moreover, the relatively less expensive material cost 
associated with individual jacketed conductor as compared to twisted pairs 
leads one to form a cable from such conductors. 
This cable, also known as the HPIB-II cable, uses insulated jacketed 
conductors arranged in an annular array in the annular space defined 
between an inner and an outer metallic sheath. Alternate ones of the 
insulated jacketed conductors in the array are designated as signal 
carrying conductors. The remaining conductors are electrically connected 
to the metallic sheaths. When the sheaths and the conductors associated 
with the sheaths are connected to a predetermined ground potential a cable 
is defined which permits each signal carrying conductor to be electrically 
isolated along its entire axial length. However, the grounding of 
alternate ones of the individual conductors eliminates their use as signal 
carrying conductors, thus limiting the density of the cable. 
The above-mentioned application also discloses and claims a cable which 
overcomes this limitation by having the remaining conductors used as 
signal return lines. The metallic sheaths assist in partially shielding 
the signal carrying conductors, but a sacrifice of some electrical 
performance over the totally isolated case occurs. 
In view of the foregoing it is believed advantageous to provide a cable 
structure that utilizes ordinary insulated jacketed conductors, makes 
maximum use of such conductors for signal carrying purposes, and yet 
electromagnetically isolates each signal carrying conductor along its 
entire axial length. In addition, it is believed advantageous to use 
ordinary jacketed conductors in both round and flat cable forms which 
maintains total electromagnetic isolation of the conductors along their 
entire axial length, thus approximating closely the electrical performance 
of a coaxial cable. 
SUMMARY OF THE INVENTION 
The present invention relates to a cable structure, in either round or flat 
form, which utilizes ordinary insulated jacketed conductors and which 
includes a corrugated separating member, or septum, to electromagnetically 
isolate each conductor along its entire length. In its broadest aspect, 
the septum has opposed surfaces each having a groove formed therein with a 
conductive layer disposed in each groove. The conducting layers are in 
electrical contact. An ordinary insulated jacketed conductor is disposed 
in each groove, with the axes of the conductors lying on a common locus. 
The conductive layers are, in use, maintained at a predetermined 
electrical potential such that each conductor is electromagnetically 
isolated along its entire axial length. 
In one aspect, the septum is used in a round cable configuration that 
includes an inner and an outer conducting member, or sheath, 
concentrically arranged to define an annular axially extending volume on 
the interior of the cable. The corrugated septum has a plurality of 
alternating ridges and grooves and is disposed in the annular volume, with 
each of the ridges contacting against the surface of the sheath to which 
it is radially proximal. As a result a plurality of axially extending 
substantially tubular envelopes are defined. At least one conductor is 
disposed in each of the envelopes with the axes of the conductors lying on 
a circular locus. In use, the sheaths as well as the corrugated septum are 
electrically connected to a predetermined electrical potential, typically 
ground potential, such that each of the conductors is totally 
electromagnetically isolated along its entire length. Such a cable 
structure utilizes each of the conductors as a signal carrying conductor, 
while at the same time provides electrical characteristics that closely 
approximate the characteristics of coaxial cable. 
In another aspect the invention relates to a preferred method for 
manufacturing a round electrical cable as described comprising the steps 
of providing an elongated inner metallic sheath, and surrounding the inner 
sheath with an inner array of conductors. Each conductor is separated from 
the circumferentially adjacent conductor by a predetermined clearance 
distance. A flexible tape having upper and lower conducting surfaces 
thereon is loosely spirally wrapped about the inner conductor array with 
each wrap of the tape edgewise overlapping the previously laid wrap. An 
outer array of conductors is spirally wrapped about the flexible tape so 
that the conductors in the second array radially register with the 
circumferential spaces in the inner array. The resulting structure is then 
radially compressed such that the axes of each of the conductors in the 
inner and outer arrays lie on substantially the same radius as measured 
from the axis of the cable. An outer metallic sheath is wrapped about the 
exterior of the second array of conductors. In the resultant structure the 
corrugated septum is defined by the flexible tape that is caused to 
sinuously surround the conductors in the inner and outer arrays. 
Overlapping the edges of the flexible tape and the subsequent compressing 
of the assembled structure insures the electrical interconnection of the 
septum and the inner and outer sheaths. 
In yet another aspect the corrugated septum is substantially planar in 
configuration with the axes of the conductors lying on a linear locus. The 
conductors are thus at least partially isolated over their entire axial 
lengths. To totally electromagnetically isolate the conductors the 
conductive members are disposed adjacent to each surface and in contact 
with the conductive layers in the grooves on the surface to which the 
conductive member is adjacent. Such a structure results in the definition 
of totally enclosed envelopes in which each conductor is disposed and in 
which it is totally electromagnetically isolated. In one embodiment the 
septum has a single flap integrally formed along one edge thereof. Both 
conductive members are disposed on this flap. When the flap is folded 
along a first and a second fold line each conductive member is placed into 
contact with the conductive layers on one surface of the septum. In an 
alternate embodiment the septum has a pair of flaps, one of which is 
integrally formed along each longitudinal edge of the septum. A conductive 
member is disposed on each flap. When folded along a fold line each flap 
overlies a surface of the septum so that the conductive member on that 
flap is placed into contact with the conductive layers on that surface of 
the septum which it overlies. 
In still another aspect the present invention relates to a method of 
manufacture of a flat cable as above described.

DETAILED DESCRIPTION OF THE INVENTION 
Throughout the following detailed description similar reference characters 
refer to similar elements in all Figures of the drawings. 
Referring to FIGS. 1 and 2 respectively shown in side elevation and in 
section is a round cable generally indicated by reference character 10 in 
accordance with the present invention. The cable 10 includes a central 
axially extending elastomeric filler, or core, 12 (FIG. 1) having a 
central axis 14 of the cable extending therethrough. The core 12 may be 
omitted, if desired. It should be noted that in FIGS. 2 through 5 the core 
12 is omitted from the drawings for clarity of illustration. 
An inner conducting member, or sheath, 22 surrounds the core 12. Spaced a 
predetermined radial distance outward from the inner sheath 22 is a 
second, radially outer, conducting member, or sheath 24. The inner and 
outer sheaths 22 and 24 cooperate to define an axially extending annular 
volume 26 (FIG. 2) on the interior of the cable. Each sheath 22, 24 may be 
provided in any suitable form, such as a spiral winding of a metal foil, a 
metallized plastic film, a metallic braid or a metallic served shield. 
Disposed in the volume 26 defined between the inner and outer sheaths 22, 
24 is a corrugated septum 30 having an array of corresponding ridges 32 
and grooves 34 formed therein. The septum 30 is positioned in the volume 
26 such that the peaks of the ridges 32 on the inner surface 30I of the 
septum 30 contact against the inner sheath 22, as indicated at contact 
points 36. The contact points 36 between the sheath 22 and the septum 30 
extend throughout the axial length of the cable 10. Similarly, the peaks 
of the ridges 32 on the outer surface 30E of the septum 30 contact against 
the inner surface of the outer sheath 24 throughout the axial length of 
the cable 10, as indicated by the contact points 38. The septum 30 may be 
formed from a suitable plastic material so long as at least the inner 
surface 30I and the outer surface 30E of the septum 30 are provided with a 
coating or layer of a conducting material. Alternately, the septum 30 may 
be formed entirely from a conducting material, such as a metallic foil. 
The cooperative interaction of the corrugated septum 30 and the inner and 
outer sheaths 22, 24, respectively, defines a plurality of enclosed, 
substantially tubular regions, or envelopes, 44A through 44L extending 
axially along the interior of the cable. A conductor 48A through 48L is 
disposed respectively in each of the tubular envelopes 44A through 44L. 
Each conductor 48A through 48L includes a central current carrying wire 50 
surrounded by an insulating jacket 52 as illustrated in connection with 
the conductor 48K. Preferably the wires 50 for the individual conductors 
48 are each 30 AWG annealed tinned copper. Polyolefin or fluorocarbon 
material may be used as the insulating jacket 52 for the individual 
conductors. It should, however, be understood that any suitable conductors 
may be used in the cable of the present invention including bare wire 
conductors, assuming proper precautions are taken to insure that the 
individual conductors do not contact the septum 30 or the sheath 22, 24, 
as the case may be, forming the envelope 44 in which the conductor is 
disposed. 
The conductors 48 are arranged in the envelopes 44 such that the axis of 
each of the conductors 48 lies on a substantially circular locus with each 
conductor axis being a predetermined distance 56 from the axis 14 of the 
cable 10. It should be understood, however, that such an arrangement is 
not necessarily required. 
As may be seen from FIG. 2, the conductors 48A through 48F are received in 
the envelopes 44A through 44F that are defined by the radially outer 
surface 30E of the septum 30 and the outer sheath 24. These conductors may 
be construed to comprise one conductor array. Similarly, a second 
conductor array is comprised of the conductors 48G through 48L. These 
conductors are received in the corresponding envelopes 44G through 44L 
defined by the radially inner surface 30I of the septum 30 and the inner 
sheath 22. The number of conductors in each of the conductor arrays is 
equal. 
Surrounding the exterior of the outer sheath 24 is an insulated jacket 58 
preferably formed of thirty-five mil PVC per UL 2464. 
As shown in the alternate embodiment of the cable 10 shown in FIG. 3, more 
than one conductor 48 may be disposed in each of the envelopes 44. Thus, 
for example, the envelope 44A contains the conductors 48A, 48B. In such an 
arrangement a balanced pair of conductors may be defined within each of 
the envelopes, with one of the conductors serving as a signal carrying 
conductor while the second of the conductors serves as the signal return. 
It should also be understood that different envelopes may contain differing 
numbers of conductors and remain within the contemplation of this 
invention. For example, alternate envelopes may contain two conductors 
while the intermediate envelopes may carry only a single conductor. It is 
also possible in a cable having more than one conductor in a given 
envelope to stack the conductors radially with respect to the axis of the 
cable. In such an instance, of course, the axis of all the conductors 
would not lie the same predetermined radial distance from the axis of the 
cable. 
In accordance with the present invention the inner sheath 22, the outer 
sheath 24, the inner surface 30I and the outer surface 30E of the septum 
30 are electrically interconnected. Any suitable arrangement to effect 
this interconnection may be used and lie within the contemplation of the 
present invention. 
In addition, as seen from FIGS. 4 and 5, an additional annular volume 66 
may be defined by the provision of an additional sheath 68 disposed 
radially outwardly of the sheath 24, thus placing that sheath 24 
intermediate or medially between the outermost sheath 68 and the innermost 
sheath 22. Into the annular volume 66 so defined an additional septum 30' 
is positioned so as to define another array of tubular envelopes 44'. 
Additional arrays of individual conductors 48' are arranged in the 
envelopes 44'. These additional conductors 48' may be identical to or 
different from the conductors 48. In the FIGS. 4 and 5, the conductors 48 
and 48' shown as slightly different in size to illustrate the possibility 
that a difference in conductors lies within the contemplation of this 
invention. Such arrangements are shown in FIGS. 4 and 5, which are, 
respectively, similar to the arrangements of conductors in each envelope 
as described in FIGS. 2 and 3. It should also be appreciated that the 
conductors in the inner array may be arranged in their respective 
envelopes in a manner that differs from the arrangement in the outer 
envelopes. The extension to more than two annular volumes should be 
readily apparent to those skilled in the art. Similarly, the 
interconnection of the sheaths and corrugated septum in each volume is 
also an extension of the teachings above presented. 
Referring to FIGS. 6A through 6G shown in schematic diagram form are the 
steps useful to form the round cable 10 in accordance with the present 
invention. The steps may be manually effected, or an automated apparatus, 
such as a planetary cable winder, may be used. 
As seen in FIG. 6A, as a first step the inner metallic sheath 22 is 
provided over the core 12. This is effected, for example, by spirally 
wrapping a metallized foil about the core 12. The inner array of 
conductors 48G through 48L is next laid onto the central portion defined 
by the core 12 and inner sheath 22. The conductors are spirally wrapped 
about the inner sheath 22 such that a predetermined circumferential 
spacing 72 is defined between adjacent ones of the conductors 48G through 
48L of the inner conductor array. 
The septum 30 is then loosely spirally wrapped (FIG. 6B) about the inner 
array of conductors. In the preferred case the septum 30 is provided using 
a flexible metallized foil or tape having metallic inner and outer 
surfaces. The requisite contact between the inner surface 30I and outer 
surface 30E of the septum 30 is insured by having each succeeding spiral 
wrapping of the flexible metallized tape edgewise overlap the previously 
laid wraps. 
The second, outer, array of conductors 48A through 48F is next laid (FIG. 
6C) about the assembly such that the conductors of the outer array 
register with the spaces 72 between the circumferentially adjacent 
adjacent conductors of the inner array. 
A radially inwardly compressive force is then applied to the structure of 
FIG. 6C to deform the outer array of conductors 48A through 48F as well as 
the flexible septum 30 into the structure shown in FIG. 6D. As a result, 
the axes of each of the conductors 48A through 48F in the outer array and 
the conductors 48F through 48L in the inner array lie on substantially the 
same radial distance from the axis of the cable. The compression imparts 
the corrugated shape to the septum 30. In addition, compressing the outer 
array of conductors brings the peaks of the ridges on the inner surface 
30I of the septum 30 into contact with the inner sheath 22, as indicated 
by the contact points 36. 
As seen from FIG. 6E, the outer metallic sheath 24 is provided about the 
outer array of conductors. This causes the peaks of the ridges on the 
outer surface 30E of the septum to contact against the outer sheath 24 at 
the contact points 38 and thus produces a structure wherein the inner 
sheath 22, the outer sheath 24 and the inner and outer surfaces 30I and 
30E, respectively, of the flexible septum 30 into electrical contact with 
each other. Thus, each of the conductors 48A through 48L lies enclosed in 
a substantially tubular envelope throughout its entire axial length. 
At any appropriate step the medium whereby the sheaths 22, 24 and the 
septum 30 are interconnected is introduced into the cable. For example, in 
FIG. 6E, the spiral drain wire 59 may be provided on the outer sheath 24 
so as to lie within one of the envelopes. If the sheath 24 is realized by 
a metallic foil (without an intermediate insulating layer) then the drain 
wire 59 may be wrapped about the exterior of the sheath 24. For example, a 
bare drain wire 59 may be disposed within a selected envelope to effect 
the desired electrical interconnection. Other exemplary expedients whereby 
the sheaths and the septum may be interconnected include a contact foil, a 
braid, a spiral drain wire or a served shield. Thereafter, as shown in 
FIG. 6F, the insulated jacket 58 is provided over the cable assembly. If a 
cable as shown in FIGS. 4 and 5 is to be fabricated, the steps shown in 
FIGS. 6A through 6F repeated, using a structure shown in FIG. 6E (with the 
sheath 24 as the outside layer) as the central portion about which 
additional conductors are placed. 
In operation, a predetermined electrical potential, typically ground 
potential, is applied to the interconnected sheaths 22, 24 and the surface 
of the septum 30 (and to the sheath 68 and septum 30', if provided, FIGS. 
4 and 5). By applying the potential to these conducting members each of 
the conductors 48 enclosed within the individual envelopes is 
electromagnetically isolated and shielded. If a balanced pair of 
conductors are disposed in each of the envelopes (as, for example, in 
FIGS. 4 and 5), even higher levels of performance may be achieved. 
It has been found that the structure of the cable 10 in accordance with the 
present invention provides electrical characteristics comparable to those 
produced by a coaxial cable. 
FIG. 7 illustrates a perspective view of a flat cable 10' also in 
accordance with the present invention. The cable 10' includes a corrugated 
septum 30' formed into a generally planar configuration. The septum 30' 
has extending ridges 32' and grooves 34' provided on opposed surfaces 30'I 
and 30'E thereof. The septum 30' may be formed from a suitable plastic 
material so long as conductive layers 78 are provided in each of the 
grooves 34' provided on the opposed surfaces 30'E and 30'I of the septum 
30'. The conductive layers 78 may be arranged in the form of separated 
stripes on each surface, or the layers 78 may be continuous over each 
surface. Alternately the septum 30' may be formed entirely from a 
metallized plastic film or from a conductive material, such as a metallic 
foil. In the FIGS. 7 through 10 the conductive layers 78 are shown as 
being continuous over the surface of the septum 30'. In whatever manner 
provided, the conductive layers 78 lying in the grooves 34' on each 
surface of the septum 30' are in electrical contact with each other so as 
to be connectible to a common potential. The electrical interconnection 
between the layers 78 may be effected in any convenient fashion. For 
example, the layers 78 from opposed surfaces of the septum 30' may be 
contacted with each other, as by folding, at the axial ends or lateral 
edges of the cable. Alternatively bare drain wires (e.g., the wires 59' in 
FIGS. 8 and 9) could be provided, with each drain wire being connected to 
a layer 78 by mechanical contact. The drains themselves are interconnected 
or connected to a common potential. 
Disposed in each of the grooves 78 is an insulated jacketed conductor 48. 
The conductors 48 disposed in the grooves 34' formed in one side 30'E of 
the septum 30' define a first array of conductors, while the conductors 48 
disposed in the opposed surface 30'I of the septum 30' define a second 
conductor array. In any event, the axes of the conductors 48 in both 
arrays thereof lie on a common locus that takes a linear form. 
In such a flat cable arrangement 10' as heretofore described, with the 
conducting layers 78 connected to a common (typically ground) potential, 
the individual conductors 48 are afforded some degree of electromagnetic 
isolation one from the other when the layers 78 are connected to the 
common potential. If desired sheath members formed of a nonconducting 
material, similar in form to the sheaths 22', 24' to be discussed, may be 
laid over the septum 30' to cover the grooves and the conductors 48 
received therein. As will be developed, to provide structural integrity to 
the flat cable an adhesive layer is provided between these nonconducting 
sheath members and the septum 30'. Such nonconducting sheaths may also be 
used in place of the sheaths 22', 24' shown in the round cable of FIGS. 1 
to 6. 
However, in accordance with the more preferred embodiment of the invention 
a first and a second conductive member or sheath 22', 24' is respectively 
disposed adjacent one of the surfaces 30'E, 30'I of the septum 30'. The 
sheaths 22', 24' are shown in the drawing as formed of a metallized 
plastic film material, although it should be understood that a metal foil 
may also be used. The conductive sheaths 22', 24' are arranged to contact 
the ridges 34' on the respective surface of the septum 30' to which the 
sheath is adjacent to define the axially extending envelopes 44'. The 
sheaths 22', 24' are electrically interconnected to the layers 78 by 
mechanical contact therebetween. Any convenient alternate expedient may be 
used to connect the sheaths to the layers 78. For example, suitable single 
or multi-strand bare drain wires 59' (not shown in FIG. 7 but seen in 
FIGS. 8 and 9) may be provided into an envelope on one side or on each 
side of the septum. The drains 59' may be inserted into any one of the 
grooves. The drain wires 59' are thus interconnected with the sheaths 22', 
24' and the layers 78. The sheaths 22', 24' may, in such an arrangement, 
be themselves interconnected by connecting the drains together or to a 
common potential. Conductors 48, whether used with the round cable or with 
the flat cable, may be single or multi-strands of wire and may be jacketed 
with a foamed polyolefin or fluorocarbon material. 
To provide structural integrity to the cable 10' shown in FIG. 7 in order 
to hold the same together a layer of adhesive 79 is disposed on the inner 
surfaces 22'I and 24'I of the sheaths 22' and 24', respectively. Any 
pressure sensitive adhesive, such as the acrylic adhesive transfer tape 
sold by 3M Corporation, Minneapolis, Minn. as tape No. 924 may be used. 
Alternatively any elastomeric, silicone, rubber, or plastic adhesive may 
be used. The adhesive 79 is disposed, as a minimum, along the ridges 32' 
on each side of the septum 30' at the points of mechanical contact between 
the sheaths 22', 24' and the septum 30'. In practice the adhesive 79 is 
disposed as a continuous layer on the inner surfaces of the sheaths 22', 
24'. The presence of the adhesive layer does not significantly impair the 
requisite electrical contact between the sheaths 22', 24' and the septum 
30'. Moreover, if the conductors 48 are jacketed with a polyolefin or 
fluorocarbon material, these jackets would not readily bond to the 
adhesive. Thus such jacketed conductors may move relatively to the septum 
and to the sheaths during bending, resulting in greater cable flexibility. 
The adhesive 79 causes the sheaths 22', 24' to adhere to the septum 30' 
and thereby imparts an integrity to the structure of the cable 10' so 
produced. 
In cables where foamed insulating jackets are used for the conductors, the 
foams can be readily damaged, both during the manufacturing process, and 
during subsequent use since the foams are relatively fragile. Adhesively 
bonding the corrugated septum to the outer sheaths provides a semi-rigid 
structure which protects the fragile jackets of the conductors from 
stresses which are both compressive and tensile in mode. If the adhesive 
were not present, the tensile stresses would tend to pull the cable apart, 
the conductors would become disarrayed, and the electrical characteristics 
of the cable would be significantly changed. 
If the adhesive were not used and compressive stresses were imparted to the 
cable, the corrugated septum could easily slide relative to the sheath and 
the conductors would be easily damaged. The adhesive bond prevents the 
septum from sliding relative to the sheath, and consequently the structure 
resists compression, thus protecting the relatively fragile conductors. 
FIGS. 8 and 9 illustrate alternate embodiments of a flat cable 10' in 
accordance with the present invention. In the embodiment of FIG. 8 the 
septum 30' has a single flap 82 integrally formed therewith and extending 
along one longitudinal edge of the septum 30'. The conducting sheaths 22', 
24' are defined as separate layers of conductive material on the surface 
of the flap 82. The flap 82, when folded along fold lines 84A and 84B, 
causes the conductive sheaths 22', 24' to overlie a respective surface of 
the septum 30' and contact the ridges thereon to define the envelopes 44'. 
In the alternate arrangement shown in FIG. 9 the septum 30' is provided 
with a pair of flaps 86, 88 integrally formed along the opposed 
longitudinal edges of the septum 30'. The conductive sheaths 22', 24' are 
provided on a respective one of the flaps 86, 88. In this instance when 
each of the flaps 86, 88 is folded along an appropriate fold line 90, 92, 
respectively, the conductive sheaths 22', 24' are brought into overlying 
position with respect to a surface of the septum 30' thereby to contact 
the ridges 34' thereof to define the axially extending tubular envelopes 
44'. 
As is the case in the embodiment of the invention shown in FIG. 7 the 
layers of adhesive 79 are disposed on the inner surface of the single flap 
82 (FIG. 8) and on the inner surfaces of the flaps 86, 88 (FIG. 9). 
Large drain wires 59' are disposed in the grooves at at each lateral edge 
of the septum so as to lie at each lateral end of the linear array of 
conductors 48 provided in the cable 10'. The drains 59' should have outer 
diameter dimension of the same as those of the conductors 48. The drains 
59' are provided primarily to terminate the sheaths. Secondly, when the 
foamed conductors are used as the conductors 48, the drains 59' at each 
lateral end of the linear array provide protection for the fragile foamed 
conductors. It should also be appreciated that the drains or other 
protective wires (whether or not interconnected in an electrical circuit) 
can be interspersed along the width of the linear array of conductors in 
order to provide mechanical protection for foamed conductors, if they be 
used in the cable. Thirdly, the drains 59' serve as strain relief for the 
cable 10' when a connector is added. 
A suitable insulating jacket 58' is formed over the septum 30', whether or 
not the septum 30' is overlaid with the conductive sheaths 22', 24'. 
As is the case in the circular cable discussed in conjunction with FIGS. 1 
through 6, each tubular envelope 44' in the flat cable 10' may contain 
multiple conductors, or alternate ones of the envelopes may contain single 
conductors 48 while the other of the envelopes contain multiple conductors 
48. 
A flat cable 10' in accordance with the present invention may be fabricated 
using the steps shown in FIGS. 10A through 10E. 
As shown in FIG. 10A an array of conductors is laid against on surface 30'I 
of the septum 30'. The septum is compressed against the array of 
conductors, thus imparting the corrugated shape thereto. A second array of 
conductors 48 may then be laid into the grooves 34' formed in the septum 
30'. Alternately, as shown in FIG. 10B an array of conductors 48 is laid 
simultaneously against each surface of a resilient material used to form 
the septum 30'. The conductors 48 are laid with a gap defined therebetween 
such that when the conductors 48 and the septum 30' are exposed to a 
compressive force the corrugated shaped is imparted to the septum 30'. In 
each instance the compressive force must be applied either from the center 
of the septum 30' outwardly or from one side toward the other. By whatever 
alternative used, the structure shown in FIG. 10C is produced. 
If sheaths 22', 24' are eliminated, the resultant structure shown in FIG. 
10C is thereafter covered with a suitable insulating jacket. However, if 
sheaths 22', 24' are used, the further steps of the manufacturing process 
are dependent upon the form which the sheaths take. If each edge of the 
septum 30' is provided with a flap 86, 88, respectively (as illustrated in 
FIG. 10C), the flaps 86, 88 are provided with the adhesive layer 79 and 
folded, as shown in FIG. 10D; along their appropriate fold lines 90, 92, 
respectively to dispose the sheaths 22', 24' in their overlapping 
relationship to the septum 30'. If the single flap 82 is used, as shown in 
FIG. 10E, the single flap 82 provided with the adhesive 79 on those 
portions of the inner surface of the flap 82 and the flap 82 is folded 
along the fold lines 84A, 84B as shown in FIG. 10E to dispose the sheaths 
22', 24' carried on the flap 82 in their overlapping relationship with 
respect to each surface of the septum. The resultant structure is then 
covered with the insulating jacket. The drain wires 59', if used, are 
provided on the flap (or flaps) so as to appropriately locate the drain. 
As an alternate mode of manufacture a metallized plastic foil used to form 
the septum may be unwound from a supply reel and corrugated using a 
corrugator having a series of contoured rollers therein. The septum is 
corrugated first in the central region thereof, with the corrugations 
being formed progressively toward the lateral edges of the septum as the 
septum moves through the corrugator. Conductors and drains, as 
appropriate, are laid into selected grooves on each surface of the septum. 
The adhesive layer is then applied to the exposed portions of each surface 
of the septum and the conductors and drains. The backing of the transfer 
tape (identified earlier) is stripped therefrom as the tape is drawn from 
a supply roll and pressed onto the septum, conductors and drains as the 
assembly passes through a pair of nip rolls. Outer sheaths (whether of 
conducting or nonconducting material) are laid onto both surfaces of the 
septum. The lateral edges of the assembly so produced are trimmed to an 
appropriate width. The cable assembly may then be jacketed with a suitable 
insulating jacket 58, preferably formed of polyvinylchloride (PVC). 
In view of the foregoing, those skilled in the art may readily appreciate 
that a cable, in round or flat form, in accordance with the present 
invention provides electrical performance substantially equal to that 
produced by a corresponding coaxial cable. However, since ordinary 
shielded cable has been used to form the cable 10, such performances has 
been achieved at a fraction of the cost. Those skilled in the art, having 
benefit of the teachings of the present invention as hereinabove set forth 
may effect numerous modifications thereto. However, such modifications are 
to be construed as lying within the scope of the present invention, as 
defined by the appended claims.