How does HFSS calculate Z Parameters?

[christopherdean]

Hi,

I am new to HFSS (a few weeks ago I was asked to learn it without any prior knowledge of it or antenna simulation), and I have a model of an Interdigitated Capacitor, which we are trying to find the capacitance of. I have a lump port across the two "digits" for an excitation and I recently added a dielectric(Polyamide, Er=4.3) and PEC under the capacitor(the cap will be applied to a metal surface). I plotted the Z parameters, notably the imaginary component as the real was ~=0. From this I calculated C from Z= 1/(jwC) \[\to\] C = -1/(2*pi*f*z), with ~=1pF results. My advisor liked this but wanted to know how HFSS calculates Z parameters. I tried to look online and through the help but I cannot figure it out. Any help would be greatly appreciated. I attached the file I've been using if that helps.

View attachment IDC.zip


Thanks.

 

[Leegit]

The Z-Parameters will be constructed in a similar fashion as all other parameters which involve signals such as S-Parameters. The program sends in a unitary signal into the first port and then detects the signal which arrives back out of this port, S11, and detects the signal which transmits through the structure and comes out the other port, S21. For the Z-Parameters, most likely it sends in a unitary current signal, 1A, then calculates the voltage sent by using the V=IZ relationship. It receives the current coming out of the other ports and uses the complex form of Ohm's Law to get the other impedances.

Relevant Information: Impedance parameters - Wikipedia, the free encyclopedia

 

[christopherdean]

Thanks for the reply.

So, the Z11 parameter is found by sending a 1A current through the Lump Port, and calculating the the impedance of the port with a known voltage? I'm a little confused how it calculates V and Z.

 

[ksugahar]

Thanks for the reply.

So, the Z11 parameter is found by sending a 1A current through the Lump Port, and calculating the the impedance of the port with a known voltage? I'm a little confused how it calculates V and Z.

Please check how HFSS calculate the S-parameter.
As far as I remember, HFSS computes the S-parameter and
the other parameters like Z and Y are converted from the
S-parameter. Therefore I guess hfss does not do any
calculations mentioned above.