Impact of Connectors on NEXT in Twisted Pair Cables

摘要

A procedure for modeling, simulating and measuring near end crosstalk (NEXT) for twisted-pair cable (TPC) and connector assemblies is discussed in the paper. First, a model of the cable and RJ45 connector is constructed and simulated using a combination of finite element and boundary element methods. Extracted frequency dependent parameters of the connector and a standard TPC were used to build accurate circuit models. These models were used to calculate chain parameters, which are eventually translated into S-parameters and NEXT. The RJ45 connector was then measured and compared with the simulated model. The measurements were carried out with a Vector Network Analyzer (VNA) and showed very good correlation with the model. Subsequently the measured connector S-parameters were used to model an assembly with the simulated cables. Once selected, the cable was measured with the RJ45 connectors and as a raw cable using two types of fixtures which allow accurate raw cable termination or board side termination of RJ45 connectors. Simulation and measurement results are plotted for frequencies of 1 MHz to 1 GHz. Good agreement between NEXT simulation and measurement is reported. Dominant effects of near-end and far-end RJ45 connectors on measured NEXT was observed.