Woven low impedance electrical transmission cable and method

A woven electrical transmission cable A is illustrated which includes a plurality of warp elements (12, 12, 14) interwoven with a weft element (16). A number of the warp elements are ground conductors (10) and a number are signal conductors (12). The ground and signal conductors are arranged in clusters (D, E) which include signal conductor pairs (12a, 12b and 12c, 12d) isolated by ground conductors (10a-10c and 10d-10f), respectively. An input signal is split at the input (20, 24) of the cluster between the signal conductor pair which is then combined at the output to provide a single output signal (28, 30). The location of the ground conductors relative to the signal conductors is fixed in the cable by interweaving of the weft (16) and warp binder yarns (14) together with the warp conductors (10, 12) whereby the characteristic impedance is controlled.

BACKGROUND OF THE INVENTION 
The invention relates to electrical transmission cables of the type which 
are woven and typically include a plurality of conductor elements 
extending in a warp direction of the cable which transmit high frequency 
signals. Woven cables of this type are being utilized more and more in 
computer systems, communications systems, and other sophisticated 
electronic systems. The controlling of the characteristic impedance of the 
cable so that the impedance of the cable and the input are matched so that 
a representative and error free output signal is produced is a problem to 
which much attention must be given. The need for controlling the impedance 
becomes more acutely necessary when considering the fast operating speeds 
of present sophisticated electronic equipment wherein the rise time of the 
switching pulses is faster than one nanosecond. If the characteristic 
impedance of the cable is not controlled accurately so that the impedance 
of the line driver and the cable are matched, ringing in the output signal 
can occur which results in false triggering or other erroneous signals 
being produced at the output. 
Prior attempts to provide controlled impedance cables in flat flexible type 
cables of the non-woven type are illustrated in U.S. Pat. Nos. 3,634,782 
and 3,818,117. 
U.S. Pat. No. 4,143,236 illustrates a woven controlled impedance cable 
wherein each signal line is provided with a ground conductor on each side 
thereof to control the impedance. The signal conductors are woven in an 
undulating woven pattern in the cable. The relative distances between the 
ground and signal conductors are fixed by the woven warp and weft yarns in 
the cable. The characteristic impedance of the cable is thus accurately 
controlled. 
The spacing between the, ground wires on either side of the signal wire and 
the signal wire itself determines to a large extent the characteristic 
impedance of the cable. The closer the ground wires are brought towards 
the signal wire, the lower the impedance of the cable. The relative 
distances between the ground and signal conductors are fixed by the woven 
warp and weft yarns in the cable. The characteristic impedance of the 
cable is thus accurately controlled. However, a problem exists in such a 
woven construction, which also includes warp binder yarns between the 
signal and ground conductors, in that there is a limit to the closeness in 
the positioning of the ground wires next to the signal wires due to this 
woven construction. Thus, the characteristic impedance of the cable 
reaches a point below which lower impedances are difficult to provide in 
the woven cable. 
Accordingly, an important object of the present invention is to provide a 
woven electrical transmission cable having a low characteristic impedance 
value and method therefore. 
Another important object of the present invention is to provide a woven 
transmission cable having a controlled characteristic impedance which may 
be lower than heretofore provided in a woven cable construction. 
Still another important object of the present invention is to provide a 
woven transmission cable having a low characteristic impedance value in 
which cross-talk between the signal wires is reduced. 
SUMMARY OF THE INVENTION 
The above objectives are accomplished according to the present invention by 
providing a woven high frequency transmission cable which includes a 
plurality of warp elements extending in a warp direction in the cable and 
a weft element woven with the warp elements in a weft direction in the 
cable. A number of the warp elements are conductor elements which include 
signal conductors and ground conductors. By arranging the signal and 
ground conductors in clusters, and by splitting each transmission signal 
between a pair of the signal conductors in the cluster, the impedance of 
the cable may be substantially lowered. The characteristic impedance of 
the cable may still be accurately controlled by fixing the position of the 
signal and conductor warp elements in the woven pattern of the cable. In a 
preferred embodiment, each cluster includes a first ground conductor, a 
first signal conductor, a second ground conductor, a second signal 
conductor, and a third ground conductor, arranged in juxtaposed relation 
with respect to one another. A plurality of the clusters are woven in the 
cable in juxtaposed relation across the weft direction of the cable. The 
signal conductors of each cluster are woven in an undulating pattern in 
phase with one another. The signal conductors of adjacent clusters 
undulate out of phase with one another so that cross-talk between the 
signal conductors of adjacent clusters is reduced.

DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring now in more detail to the drawings, FIG. 1 illustrates a woven 
transmission cable which may be woven on a conventional loom as is well 
known in the weaving art. The woven cable includes a plurality of warp 
elements which include a number of ground conductors 10 and a plurality of 
signal conductors 12. The warp elements further include a number of warp 
binder yarns 14 woven together with the warp elements 10 and 12 and a weft 
element 16. The warp elements are illustrated as being woven with the weft 
elements 16 in an undulating pattern that will be more fully described 
hereinafter. The warp binder yarns 14 and weft yarns 16 may be any 
suitable yarn such as Nomex brand nylon with each element 14 and 16 being 
a bundle of yarns. 
The warp conductor elements are arranged in clusters as can best be seen in 
FIG. 3 wherein a first cluster D and a second cluster E are illustrated in 
juxtaposed relation. Cluster D includes a first ground conductor element 
10a, a first signal conductor element 12a, a second ground conductor 
element 10b, a second signal conductor element 12b, and a third ground 
conductor element 10c. Likewise, cluster E includes a first ground 
conductor element 10d, first signal conductor element 12c, a second ground 
conductor element 10e, a second signal conductor element 12d, and a third 
ground conductor element 10f. 
As many clusters as desired may be arranged in juxtaposed relation across 
the weft direction and woven in the cable. Each cluster would contain the 
ground conductors and signal conductors as described above for clusters D 
and E. 
As illustrated in FIG. 3, each cluster, such as D, includes a pair of 
signal conductors, such as 12a and 12b. The signal conductors are input by 
a single input signal 20 (FIG. 6) which is split between the conductor 
pairs 12a and 12b. The conductors 12a and 12b are terminated such that the 
signal is output as a single output signal representing the input signal 
20. An input means such as a line driver 22 may provide the input signal 
to the cluster. Cluster E likewise includes a line drive input at 24 which 
is a single signal that is split between the signal conductor pairs 12c 
and 12d. By isolating the signal conductors in each cluster by means of a 
ground conductor on either side thereof, the impedance of the signal 
conductors is fixed whereby the overall impedance characteristic of the 
cable may be controlled and fixed. The grounds may be terminated at a 
common ground plane 26 in a conventional manner. The signal conductor pair 
of each cluster D, E is terminated to combine the split input signal and 
provide a single output signal at outputs 28 and 30, respectively. 
It is preferred that the signal conductors such as 12a and 12b in cluster D 
of each cluster undulate in the woven pattern in phase with one another as 
can best be seen in FIGS. 2 and 4-5. In this manner, the single signal 
which is input at 20 is split between the conductors and travels in phase 
until it is output again as a single signal. The adjacent signal 
conductors in adjacent clusters such as 12a, 12b and 12c, 12d of clusters 
D and E are, however, woven so as to undulate approximately one hundred 
and eighty degrees out of phase with each other. This provides for woven 
fabric stability and minimization of cross-talk between adjacent signal 
pairs and adjacently transmitted signals. As illustrated, the signal 
conductors are woven over two picks of the weft element 16, such as 16a 
and 16b, in an over and under pattern as can best be seen in FIGS. 4 and 
5. The ground conductor 10, however, alternates and undulates over and 
under each single pick such 16b of the weft yarn elements. The conductor 
elements B and C may be terminated by proper terminal connections as is 
well known in the art by any suitable terminal connector. 
Thus, it can be seen that an advantageous construction can be had for a 
woven high frequency transmission cable whereby a low impedance 
characteristic value can be provided in a woven cable construction 
utilizing the space available for the weaving of the cable in a 
conventional manner on the loom. The positions of the signal and ground 
conductors in the woven cable are fixed in the woven pattern of the cable 
such that their position does not shift during use and such that the 
positioning of the various conductors is maintained at all times so that 
the impedance characteristic is not varied but is maintained constant. 
Thus, with the impedance characteristic of the cable constant, the 
impedance of the line driver and cable may be matched with reliability 
whereby the output signal is representative of the input signal without 
error. The lower impedance of the cable means that less power is required 
to drive and deliver the signal through the cable. 
While a preferred embodiment of the invention has been described using 
specific terms, such description is for illustrative purposes only, and it 
is to be understood that changes and variations may be made without 
departing from the spirit or scope of the following claims.