For SERDES signals with a characteristic impedance of 85 ohms where the single ended impedance could be different from 50 ohms, how do we terminate the unused ports as its impedance may be differnt from the standard available
match of 50 ohms?
You can use a 50-80 T or Pi converter. Otherwise normalize ports to a different impedance in VNA. The S-paramter can be normalized to a non-50oihm impedance.