Technique to improve the accuracy of mixed-mode S-parameters derived from single-ended results and application to shorter test coupon design

In this paper we present an approach to improve the accuracy of mixed-mode S-parameters including differential insertion loss calculations using the single-ended simulation or/and measurement results for transmission lines. A correction term is derived to improve the conversion from 4-ports single-ended S-parameters to differential insertion loss. The approximation, which assumes odd mode impedance = even mode impedance in the conventional transform formula S_DD21=0.5×(S_SE21-S_SE23-S_SE41+S_SE43), is revised in the new equation. The new equations to calculate the whole mixed-mode s-parameters are also derived. The equation can be used not only for improving the accuracy of the characterization from single-ended S-parameters to differential insertion loss, but also for reducing the length of test structures and coupons. Simulation results are showed to validate the method.