Frequency Domain, Modal Method
Bandpass-frequency responses of a passive circuit often result from a combination of multiple resonances. Eigenfrequency analysis is used for capturing the resonance frequencies of a device. In a subsequent step, the information from the Eigenfrequency solutions can be reused in a Frequency Domain, Modal study to generate a solution for the driven problem.
Eigenfrequency Study Step Settings
To perform a Frequency Domain, Modal analysis, it is necessary to configure the Eigenfrequency study step properly. As the output of the Eigenfrequency study may include unphysical results (so called spurious modes), appropriate settings help refine the Eigenfrequency study results.
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Set Eigenfrequency search method to Manual
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Adjust Desired number of eigenfrequencies if necessary
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Set Search for eigenfrequencies around to the estimate of the lowest passband frequency
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Set Eigenfrequency search method around shift to Larger real part
Data Management
The Store fields in output checkbox in the Values of Dependent Variables section can be applied to the Frequency Domain, Modal study — if you are interested only in S-parameters. By storing solutions only on port boundaries, the saved model file size will decrease a lot.
Note that the phase of the computed S-parameters in the Frequency Domain, Modal study can be different from that of the regular frequency sweep model due to that all relevant eigenmodes might not be included in the simulation. It is recommended to perform an initial eigenfrequency investigation, to find all relevant eigenfrequencies contributing to the frequency response. If not all relevant eigenfrequencies are included in the simulation, the results are compatible only for phase-independent S-parameter values, such as dB-scaled, absolute value, reflectivity, or transmittivity.