Electronics

Electronics

Computing Zpi impedance in Eigenmode Simulation (HFSS)

    • cbiurrun
      Subscriber

      I am facing some issues when trying to use the Fields Calculator in ANSYS Electromagnetics Desktop (HFSS). The version I am using is 2020 R2.4.

      I am simulating a standard Grounded Coplanar Waveguide with HFSS. I have two different setups: one being a Driven Modal analysis and the second being an Eigenmode analysis. In the former, I have a Wave Port consisting of a 2D Rectangle. This Wave Port, after Driven Modal simulation, will give me a Zpi impedance. In principle, the impedance given by the simulator is computed from a 2D Eigenmode problem that is solved for the Waveport. I would like to do the same, directly on the Eigenmode simulation setup.

      In the Eigenmode simulation, there are no Waveports. I just have Primary and Secondary boundaries on the faces perpendicular to the longitudinal axis (X-axis, in this case) and PEC boundaries on the other faces. With this analysis, I get information regarding several modes propagating in the structure and their complex frequencies for a given phase delay in between the primary-secondary boundaries (namely, a phase constant Betta). I am also generating and saving the fields information of the simulation, therefore I should be able to compute the Zpi impedance of the crosssection of this transmission line (I created a rectangle). I am, however, not very familiar with the use of the Fields Calculator tool and therefore I feel stuck in obtaining this result.

      For this impedance, I should get the Power and divide it by the current squared to the power of 2. However, I keep receiving errors when I try to integrate the fields/currents in the geometry of interest.

      Could anyone provide some help?

    • cbiurrun
      Subscriber
      Follow up:


      I programmed these functions (see file attached) in the Field Calculator for obtaining V, I and P , following the Zpi, Zpv and Zvi impedance definitions found in the HFSS Help. However, for a 50-Ohm CPW I got really strange results (Zvi = 350 Ohm, Zpi=450 -j290 Ohm, Zpv=1.8E17 Ohm), so I guess I am doing something wrong (maybe the equations or maybe the geometries selected).

    • cbiurrun
      Subscriber

      I updated the definition of P but still do not get the proper results. Nevertheless, at least I don't get so crazy values.
      Now I get:
      Zpi: -120 Ohm
      Zpv: -20.52 -j33.53 Ohm
      Zvi: 60.14 +j33.71 Ohm
      I understand that the (-) sign doesn't matter and is probably due to the path of integration. However, the results are still far from the expected (50 Ohm)
    • manny
      Ansys Employee
      I suspect that is something to do with your geometry. Your formulae look ok. It probably has to do with your integration line and geometry. For more information, please see the Fields Calculator cookbook in the online help.
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