Near end crosstalk in twisted pair cables - a comparison of simulation versus measurement

A method of geometry modeling and simulating near end crosstalk for twisted-pair cables is discussed and verified experimentally. Description of the cable design environment is provided. A graphical user interface is used for entering cable design data including materials, plating, stranding, twisting, and wire naming. The design information is then processed in order to calculate a realistic 3D model of a twisted pair cable. The collapsing of the cable's initial geometry under the pressure of external insulation and shield and in the presence of core twisting is automatically calculated along the cable. The resulting model of the cable is subsequently analyzed numerically using a combination of finite element and boundary element methods. The skin depth value is used for optimizing meshing. Extracted unit parameters are used to build accurate circuit models of cable sections. These models are used subsequently to calculate chain parameters, which are eventually translated into S-parameters representing near end crosstalk. A 50 meter long four twisted-pair cable was used to verify simulation results against crosstalk measurement. The measurements were carried out with a vector network analyzer. Both ends of the cable were connected to special fixtures, which were designed to eliminate reflections. Simulation and measurement are plotted in the frequency range of 1 MHz to 1 GHz. Good agreement between simulation and measurement of near end crosstalk is reported