Low-Frequency Analysis of Multiconductor Transmission Lines for Crosstalk Design Rules

Abstract

For early risk assessment in the design of cabling in an aircraft, as well as cable bundle optimization, efficient crosstalk estimations, and dependency of crosstalk with respect to designable parameters are required. A low-frequency technique for analyzing crosstalk in multiconductor transmission lines is presented. The result of this analysis is a closed-form expression for crosstalk in a specific cabling configuration. The technique has been validated via measurements and is used in two examples comprising two wire pairs close to a ground plane and in free space. Low-frequency closed-form expressions for near-end crosstalk are derived for both situations, which directly relate any designable parameter to crosstalk levels. Moreover, these expressions clearly show differences between the cases with and without a ground plane. Specifically, with the ground plane, the decrease in crosstalk when doubling the separation distance is 24 dB for pairs close to the ground, while it is 12 dB in free space. The closed-form expressions are utilized to create an overview of sensitivities of crosstalk to all designable parameters for both configurations. Finally, the low-frequency approximations of the chain parameters are applied to more complex nonuniform transmission lines, yielding more than 20 times faster computations when compared with complete MTL simulations.