Flat multi-signal transmission line cable with plural insulation

Abstract

A multi-signal transmission line is formed of a flat cable having a plurality of generally parallel conductors embedded in a dielectric core material, with an insulator jacket encasing the flat cable and being made of a dielectric material having a higher dielectric constant than the dielectric core material of the flat cable. The resulting composite transmission line cable insures that substantially all of the transverse electromagnetic propagation field created by the passage of a fast rise time pulse in a signal conductor is confined to the geometric area of the cable and the cable functions in a manner to greatly reduce the far end line-to-line interference (crosstalk) between the signal conductor and adjacent quiet lines.

What is claimed is: 
     
       1. A composite multi-signal transmission line cable for transmitting fast rise time electrical pulses with minimum far-end crosstalk comprising: a flat multi-conductor cable including a plurality of generally parallel conductors embedded in a planar sheet of insulation material having a dielectric constant, .Iadd.adjacent conductors being spaced apart at a predetermined pitch .Iaddend.with selected conductors adapted to be connected to ground, while remaining conductors are used as signal-carrying conductors .Iadd.the ratio of the thickness of the insulation material to said pitch being at least 2.0 such that at least about 98 percent of the transverse electromagnetic (TEM) field propagates within said insulation material.Iaddend.; and   an insulator jacket surrounding the flat multi-conductor cable and in intimate contact with said insulation material; said insulator jacket being made of a dielectric material having a dielectric constant greater than the dielectric constant of said insulation material whereby the electrical effect of the composite of the insulation material and the insulator jacket is to establish a balance between the inductive and capacitive coupling coefficients between adjacent signal-carrying conductors thereby minimizing the far-end cross-talk.   
     
     
       2. A composite multi-signal transmission line cable as in claim 1 wherein the insulation material is polyethylene, and the insulator jacket is made of vinyl. 
     
     
       3. A composite multi-signal transmission line cable as in claim 1 wherein the flat cable includes alternating flat and round conductors, with the round conductors being the signal carrying conductors, and wherein the characteristic impedance of the cable (Z d ) is expressed by the following relationship:   .[.Z.sub.d =(1/√ε) 42 cosh.sup.-1 (1.8×.sup.2 -(1.25×.sup.2 -1) ).]. .Iadd.       Z.sub.d =1/(ε).sup.1/2 42 cosh.sup.-1 (1.8×.sup.2 -(1.25×.sup.2 -1) .sup.1/2).Iaddend.     where   
     
     
       d=diameter of round conductors; 
     
     
       p=spacing between a round conductor and an imaginary round conductor falling within the confines of the adjacent flat conductor; 
     
     
       x=p/d; and ε=relative dielectric constant of insulation dielectric material to air dielectric. 
     
     
       4. A composite multi-signal transmission line cable as in claim 1 wherein the signal conductors are round in cross-section, while the ground conductors are rectangular in cross-section. 
     
     
       5. A composite multi-signal transmission line cable as in claim 1 wherein the insulator jacket is extruded over the flat cable. .[.6. A composite multi-signal transmission line cable as in claim 1 wherein the thickness of the jacket is approximately two-thirds that thickness of a theoretical cable core capable of confining approximately 98 percent of the TEM 
     
     
        field..]. 7. A composite multi-signal transmission line cable as in claim 
     
     
        4 wherein the insulator jacket is bonded to the flat cable. 8. A composite multi-signal transmission line cable as in claim 1 wherein the total thickness of the insulation material of the flat cable is sufficient to contain substantially all of the transverse electromagnetic field area 
     
     
        generated by a signal passing through a conductor. 9. A composite multi-signal transmission line cable as in claim 1 wherein the insulator jacket is made of a material which is self-extinguishing when exposed to a 
     
     
        flame. 10. A composite multi-signal transmission line cable for transmitting fast rise time electrical pulses with minimum far-end crosstalk comprising: a flat multi-conductor cable including a plurality of generally parallel conductors alternating in cross-section between round and rectangular, and embedded in a planar sheet of insulation material having a dielectric constant and a low dissipation factor.Iadd., the center to center distance between a round conductor and the center of an imaginary round conductor tangent with the facing wall of an adjacent rectangular conductor defining a pitch therebetween, the ratio of the thickness of the insulation material to said pitch being at least 2.0 such that at least about 98 percent of the transverse electromagnetic (TEM) field propagates within said insulation material.Iaddend.; and   an insulator jacket extruded over said flat cable, and completely surrounding and in direct contact with said flat cable, said insulator jacket being made of a material having a dielectric constant greater than the dielectric constant of said insulation material, whereby the electrical effect of the composite of the insulation material and the insulator jacket is to establish a balance between the inductive and capacitive coupling coefficients between adjacent signal-carrying   
     
     
        conductors thereby minimizing the far-end cross-talk. 11. A composite multi-signal transmission line cable as in claim 10 wherein the insulation material is made of polyethylene, and the insulator jacket is formed of 
     
     
        vinyl. 12. A composite multi-signal transmission line cable as in claim 10 wherein the characteristic impedance (Z d ) of the cable is expressed in the following relationship:   .[.Z.sub.d =(1/√ε) 42 cosh.sup.-1 (1.8×.sup.2 -(1.25×.sup.2 -1) ).]. .Iadd.       Z.sub.d =1/(ε).sup.1/2 42 cosh.sup.-1 (1.8×.sup.2 -(1.25×.sup.2 -1).sup.1/2) .Iaddend.     where   
     
     
       d=diameter of round conductors; 
     
     
       p=spacing between a round conductor and an imaginary round conductor falling within the confines of the adjacent flat conductor; 
     
     
       x=p/d; and 
     
     
       ε=relative dielectric constant of insulation dielectric material to air dielectric. .[.13. A composite multi-signal transmission line cable as in claim 10 wherein the thickness of the jacket is approximately two-thirds that thickness of a theoretical cable core capable of confining 
     
     
        approximately 98 percent of the TEM field..]. 14. A composite multi-signal transmission line cable as in claim 10 wherein the insulator jacket is 
     
     
        formed of a material which is self-extinguishing. 15. A composite multi-signal transmission line cable as in claim 10 wherein the insulator 
     
     
        jacket is bonded to the insulation material. 16. A composite multi-signal transmission line cable as in claim 10 wherein the dissipation factor of the dielectric material of the insulator jacket is greater than the dissipation factor of the insulation material of the flat cable.