Question about s-parameter causality changes on the same PCB

[yefj]

Hello , I am measuring two differential lines one is 3 inch the other is 6 inch over a span of 70 GHz.
one differential line shows 92% percent causality CQMi while the other is 66% CQMicausality.The PNA is well calibrated.
why is that ? causality means the quality of the s-params is not good .
Why one trace give good quality s-params while the other in not?
Thanks.

 

[Rive]

FR4?
Weave effect can do that.

 

[Baluncore]

3 inch : 92% percent causality.
6 inch : 66% percent causality.
Is what you would expect if the line was not correctly terminated.
How do you terminate the line?
What is the impedance step at the driven end, and at the termination end of the line?