SIwave-PSI Best Practices: Frequency Sweep

Typically, 3D full-wave solvers have difficulty in solving the vector Helmholtz equation at low frequencies due to decoupling of electric and magnetic fields. This low frequency limit could be as high as 1 to 10MHz. But the PSI solver employs a tree-cotree splitting on the edge elements to overcome this instability, so that a simulation can be extended to extremely low frequencies (as low as 1Hz). Good accuracy is maintained in the S- and Y- parameters at such low frequencies. But the open-ended Z-parameters could exhibit non-monotonic behavior below the KHz range since the z-parameters try to capture open circuit responses coming from 1/wC. To circumvent this behavior, select Enforce DC point and Causality, which enables the PSI solver to explicitly solve for the DC point and start simulation from a suitably higher frequency point.

Using the Interpolating Sweep is strongly recommended as it improves the performance significantly, with the same level of accuracy as Discrete sweep. Since the convergence of sweep requires more simulations at low frequencies, it is recommended to use a higher starting frequency in MHz region unless the application demands otherwise.