Hello, I have a question regarding the schematic feature in CST Microwave Studio (CST MWS).

I'm trying to analyze a coaxial cable using the schematic interface in CST MWS and perform a TDR (Time Domain Reflectometry) analysis.
In the post-processing step, I selected "TDR from Time Signals" under the PP (Post-Processing) templates,
but I keep getting the error "Selected port is not a signal source."

In the 3D layout, I only used one waveguide port for excitation, and in the schematic, I assigned one external port.
However, the post-processing still complains that the port is not a signal source.

Interestingly, when I run "TDR from S-Parameters", I get results just fine.

Could you please help me understand what the issue might be?
Any help would be much appreciated. Thank you!