Evaluation of the propagation constants of differential PCB interconnections

Today the telecommunication equipments are characterized by transmission bandwidths of tents of GHz. Consequently the digital signals into play reach data rates of some Gbps with rise/fall times of few picoseconds. In this context it is important to correctly characterize the transmission lines on boards for studying the signal propagation as a function of the frequency. The more effective technique starts from measurements, connecting the studied traces to the measurement instruments by means of transition networks or fixtures. But in this case the connective errors due to the connector mismatches and discontinuities have to be removed. The paper proposes different mathematical de- embedding procedures to evaluate the propagation constant of differential traces, de-embedded by the effects of the SMA´s connecting them to the VNA.