U element and W element in Hspice

Hi,
I am now using the transmission line model in Hspice to facilitate my design.
the U element is the lumped RLC transmission line model.
and W element is the distributed RLC transmission line model.

The simulation are quite different between these two models.
I have no idea how these two models work.
So could anybody tell me the reason?

Or could anybody explain why a distributed RLC model is so different from a lumped RLC model?

Thank you.

Have you tried increasing the number of "lumps" in the U models? I would have expected the results to converge if the number of lumps is high enough. I think there are also .options which can affect the accuracy of the true transmission line simulation.

Keith.