Suppression of alien crosstalk in communication systems is an increasingly important practice for improving systems' reliability and the quality of communication. As the bandwidth of a communication systems increases, so does the importance of reducing or eliminating alien crosstalk.
In wired communication systems, crosstalk is caused by electromagnetic interference within a communication cable or between cables. Crosstalk resulting from interaction between cables is known as alien crosstalk. Alien near-end crosstalk (alien NEXT) occurs when signals transmitted on one cable disturb signals in another cable. Alien NEXT travels in the disturbed cable in the direction opposite the direction of signal travel in the disturbing cable. As communications signal frequencies and data transmission rates increase, alien NEXT becomes problematic and is a barrier to increased signal frequencies and data transmission rates. Alien crosstalk degrades or destroys performance, for example, in 10 Gbps Ethernet communications over installed cable such as Cat 5e, Cat 6, or Cat 6e cable.
The magnitude of alien crosstalk increases with increased capacitance between nearby cables. Thus, alien crosstalk can be decreased by decreasing this capacitance. Capacitance, in turn, may be decreased in two ways: by increasing the distance between cables, and by decreasing the effective dielectric constant of the material between the two cables. Because there are physical barriers to increasing the distance between two cables—including cable size considerations—it is desirable to space cables (or conductors within a cable) at an acceptable distance from each other while minimizing the effective dielectric constant of the material between cables.
Air is the most effective low-dielectric-constant material, but other materials must be placed between cables to provide insulation and physical separation. The present invention is directed to structures and methods that decrease the effective dielectric constant between cables while maintaining a desirable physical separation between the cables. Structures and methods according to some embodiments of the present invention may be applied to previously installed cabling.