## 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

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