Not sure about Zeland, but HFSS uses an algorithm (Adaptive Lanczos-Pade Sweep) to reduce the order of the finite element matrix . This enables it to provide an accurate solution over a wide frequency range by only simulating the model at a few discrete frequency points within that range. In HFSS you typically assign your mesh to adapt at the center frequency of your band when performing a fast sweep. I have found the fast sweep to be accurate over a 3:1 BW.
There's a section on the Adaptive Lanczos-Pade fast Sweep in "Multigrid Finite Element Methods for Electromagnetic Field Modeling" by Zhu, Y. Cangellaris, A. C., ISBN: 0471786373
Dear
I seem Fast sweep in hfss at first, calculated some frequency in Bandwitdh and then uses the interpolation to calculated the all frequency Bandwitdh.
but I think what you are talking about is the interpolating sweep, which tries to interpolate the response of the structures by calculating its poles and zeros. I cannot see the difference between the interpolating and the fast sweeps in this case ?
I believe the Fast Sweep in HFSS is equivalent to the Adaptive Intelli-Fit (AIF) in IE3D. However, FastEM in IE3D is a complete different concept. It is a process to build a model with variables geometry dimensions. You are able to find the geometry and s-parameters of a structure with a new set of dimensions in real-tiome. FastEM allows users to do real-time EM tuning. You just slide the bars and see the change in geometry and y, z, s-parameters, equivelant circuits in real time. The s-parameters are from full-wave EM simulations and they are off high accuracy. The FastEM allows users to do real-time EM tuning and optimizations. It really changes the definition of EM designs because you really can use it for synthesis. Regards.
but I think what you are talking about is the interpolating sweep, which tries to interpolate the response of the structures by calculating its poles and zeros. I cannot see the difference between the interpolating and the fast sweeps in this case ?
In HFSS, the Fast Sweep allows one to calculate the fields at any frequency, but the Interpolatory Sweep does not. Both are rational function fits, but the Fast Sweeps is fitting the fields and the Interpolatory Sweep is fitting the S parameters.