Electronics

Electronics

How to setup a voltage source with internal impedance in HFSS

    • tomas.monopoli
      Subscriber

      I have a simple stripline over a dielectric in HFSS. I want to excite the line with a 1V source with impedance 50 Ohm. The termination of the stripline is also connected to a 50 Ohm impedance. I expect the voltage along the line to be around 0.5 V

      From what I understand, setting incident voltage should be equal to setting the forward wave voltage, is that correct? 

      How can I set up a 1V source with an internal 50 Ohm impedance?

      I tried adding port post-processing but I still obtain values around 1V. 


      Thank you

    • Chinmay T
      Ansys Employee

      Please provide more details on how you are exciting the stripline and which port type you are using.
      Can you share the screenshots of your simulation model?
      Thanks Chinmay
    • tomas.monopoli
      Subscriber
      Of course!!
      I selected a terminal solution type.
      I am using lumped ports.

      This is a screenshot of the design:

      I think the problem is that I don't fully understand the excitation types:

      I used Q2D to extract the characteristic impedance:
      As you can see the char impedance is quite different from 50 Ohms (that is the one I set to the lumped ports).
      However, setting the sources to "incident voltage" I get a voltage across the line that is close to 1.
      I believe this is quite strange, it should be close to 1 if the characteristic impedance were close the characteristic impedance of the port I think.
      Here is a comparison with the transmission line formulas, where I set the forward wave voltage to 1:

      Thank you
      Tomas


    • Chinmay T
      Ansys Employee

      You can directly see the impedance in HFSS design.
      To plot the impedance,In the project manager window right mouse click on Results, go to terminal solution data report.
      A new window pops up, in the category, select Terminal Port Zo and after this select quantity and function and click on a new report to see the impedance plot.
      Thanks Chinmay
    • tomas.monopoli
      Subscriber
      Thank you both for your answers!
      indeed, the impedance was set correctly and setting incident voltage to 1V is the same as setting the forward wave arriving to the port to 1V.
      From the HFSS manual I read:
      I(0)Zref = Vfw - Vbw and V(0) = Vfw+Vbw => 2Vfw = V(0)+I(0)Zref ; 2Vbw = V(0)-I(0)Zref;
      Therefore if you want to create the classical voltage source with internal impedance Zo, you can set the incident voltage to Vs/2 and the port impedance to Zref = Zo.

      Tomas
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