Unbalance & Mode Transfer in Shielded Pairs


AUTHORS: M. Josefsson and J. Poltz

VENUE: Presented at the 59th IWCS/Focus Conference, November 8-10, 2010, Providence, RI, USA

ABSTRACT - The capacitive unbalance of four selected samples of individually screened pairs was correlated with the measurement of intra pair skew and differential to common mode transfer. The intra pair skew was measured directly with a 4-port Vector Network Analyzer. It was noticed that the intra pair skew characteristics was frequency dependent, with smaller time delay values at higher frequencies. Differential to common mode transfer was measured with a 2-port and a 4-port Vector Network Analyzer. Different measurement techniques were compared and time domain response was calculated. Only step response of the differential to common mode transfer produced unexpected amplitude levels for cables with small capacitive unbalance. Simulation of non-uniform cables with geometrical and dielectric asymmetry in different locations allowed interpretation of time domain measurement results. Transmission quality of the selected samples was finally tested by generating eye diagrams.

Modeling balanced and unbalanced cable segments

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