Measurement & Simulation of Unbalances in Symmetrical Transmission Lines


AUTHORS: J. Poltz and M. Josefsson

VENUE: Presented at the 58th IWCS/Focus Conference, November 8-11, 2009, Charlotte, NC, USA

ABSTRACT - The results of simulation and measurement of unbalance parameters in individually screened twisted pairs and parallel pairs are presented in this paper. The impact of geometrical, conductive and dielectric asymmetry of the pair on unit parameters and the concept of quasi-common and quasi-differential modes of propagation and modal dispersion in an unbalanced pair is discussed. It is demonstrated that the differential skew is proportional to the cable length only if the unbalance results from geometrical asymmetry. However, the dielectric asymmetry creates unbalance which cannot be correlated with cable length. The ability of the pair to propagate unbalance is linked to its common mode attenuation. A double coaxial link and two different samples of shielded pairs with low- and high-skew were selected for laboratory tests. The differential skew (intra pair skew) was measured directly with a 4-port Vector Network Analyzer.

Parallel screened pair photograph and model

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