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Reference Value and Normalizing

CST MICROWAVE STUDIO offer several sources for exciting a given structure, e.g. waveguide ports or plane waves. The common reference signal for these sources is indicated in the Navigation Tree as explained in the Excitation Signal View. This reference signal itself is unitless. The input signals for the different source types are defined as the reference signal mutliplied by a certain fixed or user-defined scaling factor. This scaling factor also carries the specific units of the source types and is described in more detail below. The input signal is given as peak values.

For simultaneous excitations or combined calculations, the input signal can be additionally multiplied with user defined factors.

Please see also the Power View page for details about the stimulated and accepted power of a simulation and the corresponding power loss results in frequency domain.

Amplitude and phase of time domain signals

The scaling factor for the input signal depends on the corresponding excitation type:

This means that, e.g., a waveguide port realizes an input power of 1 Watt (peak) over its entire port face; therefore, the field amplitude itself changes with the size of the port. In contrast, a Plane wave is excited with a constant field amplitude, independent of the size of the boundary plane where the wave is excited.

Field sources (RSD, FSM, or NFD imports) are excited at the amplitudes given in the input data. No normalization is performed and these field values are fixed by the input data.

Stimulation of multiple ports and user defined excitation function

When exciting multiple ports or combining calculations, the input signal is multiplied additionally by the given amplitude and phase factors.

Note: The user-defined phase values for the excitation of multiple ports or combined calculations with time domain monitors are converted into corresponding time shifts for the time signals by use of the given reference frequency or can be set directly as user-defined time shifts. A broadband phase shift of 180 degrees can be achieved by: amplitude = &endash;1 and phase = 0.

S-Parameter and F-Parameter calculation

In general, S-Parameter results are given as the ratio of incident and reflected voltage wave spectra at a port, where only one port is excited and all others are perfectly matched. Consequently, for transient simulations, all port signals first have to be transformed into the frequency domain, providing broadband results for one port excitation with only one simulation run.

However, in the case of simultaneous excitation several ports are stimulated at once, so it is not possible to apply the general S-Parameter definition. Now the incident and reflected spectra are given as so-called incident and reflected F-Parameters, all normalized to the spectrum of the reference signal. Furthermore, as an additional result and for a better analysis of the structure's behavior, the reflected spectra of all excited ports are normalized to their own incident spectra, respectively, providing so-called active S-Parameters. Since there might be more energy absorbed at a specific port than it itself has injected, the resulting curves could show active behaviour with values greater than one.

Please note that also in the case of a plane wave or field source excitation, the outgoing signals at ports are used to determine F-Parameters as described above.

Spectral results from transient solvers

All frequency domain results like probes or monitors are in general normalized to the default Gaussian signal to offer comparable results to any solutions from frequency domain solvers. Thus the results correspond to a peak excitation with the input signal scaling factor. For example for a waveguide port excitation, this means 1 Watt stimulated peak power.

In case that other signals than the default Gaussian signal are used, then no normalization is applied at all. However, you can still activate normalization to the selected reference signal for the transient solver on the Special Solver Parameters - Solver dialog page.

In case of a transient co-simulation the normalization is by default driven from CST DESIGN STUDIO, i.e. when the co-simulation is excitated with the default Gaussian signal inside CST DESIGN STUDIO then all results inside CST MICROWAVE STUDIO are normalized to this signal. Otherwise the results are unnormalized. This behavior can again be changed by activating normalization to the selected reference signal inside CST MICROWAVE STUDIO for the transient solver on the Special Solver Parameters - Solver dialog page.

Eigenmode solutions

All eigenmode solutions are normalized to 1 Joule total stored energy.

See also

Waveguide Port Overview, Discrete Port Overview, Field Source Overview

Excitation of multiple ports, Combined calculations, User defined excitation function, Power View

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