hfss smith chart

Dear all,

I am a novice in HFSS and I encountered a problem trying to simulate a 4:1 transformer on a PCB and your advices/help will be very much appreciated.

Please find the attached zip file of the HFSS file of the 4:1 transformer.

The problem is that the simulation ran o.k.. But the S11 and S22 results do not agree with measurements, though S21 agrees reasonably well.

Simulation results said they are two independent inductor with no coupling between them. For instance, S11 in Smith chart looks like an inductor of about 1nH and S22 looks like a 15nH inductor. The experiment (via a network analyzer) said the S11 looks like a small resistance of a few ohms and S22 looks like a large resistance of one/two hundred ohms. The experimental results make sense because of the 4:1 transformation and I have other evidences to support the experimental results.

So the question is why the HFSS simulation results of S11 and S22 show in the Smith chart as if they are two independent inductors with no coupling between the two? Is there anything wrong with the setup?

Please note that the attached model shows how the balun is measured: one arm of the primary and secondary is grounded and signals are injected into the other arms. The centre tap is left floating. Shorting the ground of the primary and secondary only affects S21 but not S22 or S11.

Again your advices are very much appreciated.

Terence

I cann't open the attached file,bless

Did anyone ever figure this out? I am trying to simulate two inductively coupled rings, but I'm new to HFSS and can't find any examples that are helpful.

Does anyone know how to do inductive coupling in HFSS? What boundaries, etc. need to be set?

Thanks,
LFegely