Inhomogeneous Dielectric Induced Skew Modeling of Twinax Cables

To understand the skew in twinax cables of separately extrusion and co-extrusion design, the impact of inhomogeneous dielectric in copper twinax cables is analyzed, with an emphasis on signal integrity performance. The inhomogeneity is treated as a perturbation to the RLGC parameters, and analytical equations for the calculation of scattering parameters from RLGC parameters are derived to analyze the effects of this perturbation on signal integrity. The inhomogeneity leads to a modulation behavior in the scattering parameters, which decreases asymmetry-induced skew at high frequencies and eliminates the resonance of skew in the differential insertion loss. Mathematical analysis, physical explanation, and various design cases are presented for validation.