Single-Port Model/Circuit Element on Coax in HFSS

    • Dustin Pieper


      I have been attempting to use HFSS's Single-Port Model feature (covered in Ch 19 of the help manual) in a simulation to represent a complex Circuit Element for a system that I am simulating. However, when I apply this tool to a coaxial port, I have not been getting reasonable behavior, and instead the system is just behaving as an open circuit. I've been able to get a Single-Port Model to work on a microstrip format, so I believe I'm otherwise using the feature correctly. Is there something I'm missing in the Circuit Element behavior?

      An example coaxial simulation is provided below for reference:

      I'm feeding the other end with just a simple lumped port. I've simulated this geometry with lumped ports on both ends to make sure the model is valid, so that's not the issue.

      Here's the example s1p file I've used to define the Circuit Element for the Single-Port Model:

      Since this is just a simple matched coax line, the S11 of my lumped port should basically just look like that, right? However, instead it just looks like a mostly open circuit. Observe:

      I've also seen that the E-fields at the Circuit Element definition boundary at the end of the coaxial line don't conform to the expected TEM distribution (while they do for the feed at the other end), which leads me to believe that there is an extra definition that I need to do.

      Any advice or help would be appreciated!

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