HFSS Trouble Converging at Resonant Frequency of High Q Cavity

Hello everyone,

I am interested in finding the field distribution inside a large resonant cavity at the resonant frequency. I can successfully simulate the cavity near the resonant frequency and use interpolating sweeps to zero in on the exact resonant frequency. Because the Q factor is so high (simulated at over 10,000), the sweep must necessarily be very fine to find the resonant frequency. But if I actually want the fields at f0, I must move the solution frequency to exactly the resonant frequency (I picked to about three decimal places: 348.219 MHz).

But now my simulation will not converge given my previous criteria (max delta S = 0.002). In fact I have to change my max delta S to about 0.05 to get any convergence. Does anyone have any insight why simulating the resonant frequency is so much more difficult for HFSS than merely near it? And possibly a way to get around it?

Hi,

I think that because you're near or exactly at the resonant frequency, the field change rapidly, so HFSS doesn't find an ideal adaptative mesh. I mean that between to simulations the S parameters evolve rapidly so the difference in S parameters changes and the convergence is not reached. A solution will be to take a solution frequency greater than the resonant frequency and make a sweep around the resonant frequency.
Bye

A non-converging simulation typically means the mesh is not adequate. Assign an initial seed mesh ("mesh operation") to the cavity dielectric, and make sure it's relatively dense. This should speed up convergence.

Thank you for your help.

@eraste: Thank you for your insight, I thought something like that might be happening but that is a better articulation. Yes your frequency sweeping solution is what I typically do and it works for finding the S parameters at f0, but you see if the center frequency is not the resonant frequency of the cavity, then the fields I am plotting are not truly the resonant fields.

@planarMetamaterials: Seeding is not something I've tried, thanks that's sure to help with other cavity simulations. But for this application, I don't think it will help. I'm afraid I don't have the convergence data on me, but its pretty clear after about 30 passes that the max mag delta S is still around 0.05 after about 8 passes and just oscillates there. To me, that seems a high delta S to converge to, but maybe that's OK? I do not have a lot of intuition for this.