Problem with extrapolating DC solution in HFSS

Hi everyone,

I am new in HFSS and I have a question regarding the DC solution in HFSS.

I designed a coupled-line transformer, solved between 100MHz and 10GHz, and simulated it in HFSS. I then generated the s-parameters file of the structure. The S11 and S12 plots are close to my hand calculations. Since I want to run the s-parameters in Spectre, I choose to extrapolate the solution to DC in the sweep and the s-parameters.

But the problem is that when I transport the s-parameters file into Spectre and run a DC and transient simulations, the DC simulations of the structure is completely wrong, even though the AC simulations look correct.

So is there anything I need to do to get a better estimate of the DC solution in the s-paramters in HFSS?

Many thanks.

Tony

I don't think it'll do you any good to extrapolate the S-parameters to DC. They're
meaning less.

The S-parameters are meaning less in DC, as there is no need to calculate normalized power waves to voltage or current waves in DC as the DC is much simpler than that.

For your coupled line filter, you can consider just extracting the parasitic caps and resistance between the coupled lines for DC simulation only.

Extracting the inter-wire resistance would be advisable.

So my word is, just don't use the S-parameters for DC, and use an inter-wire resistance extraction tool to help you do the DC simulation. If you're using it in a circuit, then the DC would just be like a set of series caps with resistances parallel to them.