CST Notes

OPTIMIZATION FOR THE MINIMIZATION OF PHASE DIFFERENCE BETWEEN TWO SIGNALS: PHASE(S21A)-PHASE(S21b)

"S3(4)2(1)" means Port 3 Mode 4 (OUTPUT) referred to Port 2 Mode 1(INPUT).

INPUT:         PORT 2 MODE 1

OUTPUT:    PORT 3 MODE 4

In CST -  Log(x) is the natural Log

V3mode2
V2mode1

The appropriate Input Signal

The choice of the bandwidth to be simulated may have a strong influence on the simulation time.
From signal theory it is known, that a narrow bandwidth is related to a quite long time signal. For the field updating scheme, the maximum usable time step is fixed, such that a longer input signal needs more simulation time than a shorter signal.
So the best input signal is that one, that covers the entire frequency range up to the maximum frequency of interest.
Do not increase the frequency higher than you are interested in, because this would lead to more mesh points and a smaller time step.
Also, for wave guides, you should (if possible) try to choose the frequency above the cut off frequency of the modes of interest.
Because around cut off there are very slow traveling waves that again take a long time to simulate.

Signal Naming Conventions

The signals calculated by the CST MICROWAVE STUDIO are named by the following conventions:

The substitutes P, Q, M and N are integer values, representing two ports (P,Q) and their corresponding modes (M,N). The general excitation string <Excitation> is then given by the following expressions, depending on a sequential or simultaneous port excitation:

Sequential excitation

<Excitation> = P(N) : excitation of the N'th mode of port P.

Simultaneous excitation

<Excitation> = P1(N1)[a1,p1],P2(N2)[a2,p2],...,[freq] : excitation of different port modes, combined with corresponding amplitudes and phase values (a,p) and finally the phase reference frequency (freq). The amplitude and phase values are referred to a reference signal with amplitude one (1/sqrt(watt)) and zero phase shift.

All calculated Signals are stored in ASCII files. The names of these files are chosen according to the Result File Naming Conventions.

Transient Solver Parameters

Solver settings frame

Accuracy: This setting defines the steady state monitor. It influences the duration of the simulation. It is a value for the accuracy of the frequency domain signals that are calculated by Fourier Transformation of the time signals.

This setting has to be understood only in connection with the processing of the time signals. Errors made by discretizing a structure can only be influenced by manipulating the mesh.

Every simulation stops at some time. This means, that the signals that are calculated are truncated at this point, regardless to their values. If these values are non zero the Fourier Transformation will produce an error, because only a part of the ”whole” signal with all its non zero values has been used for the transformation. So the ”smaller” the signals are, the more accurate the frequency domain values will be.

To get a value for the accuracy not the signal amplitudes itself are used, but the total energy inside of the calculation domain. During the simulation the energy is frequently calculated and related to the maximum energy that has been monitored. This value in a logarithmic scale defines the accuracy.

Store result data in cache: Check here if you want the solver results to be stored in the result data cache. The efficient usage of the result data cache is explained in the printed documentation "Advanced Topics".

Stimulation settings frame

Source type: Define here the type of excitation, choosing between ports and plane wave excitation. You make a selection only if some ports (waveguide or discrete ports) or a plane wave is defined in your structure. Further specifications of the different source types can be done in the corresponding dialog boxes Solve =>Waveguide Ports / Discrete Ports / Plane Wave.

Plane Wave: This selection starts a plane wave excitation.

All ports / Selected ports / Port X: Selecting a port excitation determines also which S-parameter will be calculated. If All ports is selected, the simulation is repeated such that each defined port will be stimulated once. With this setting all N*N elements of the S-parameter matrix of your device will be calculated. In contrast to this if one specific port is chosen to be stimulated, only N S-parameters of a N-port device are calculated. An exception of this rule is a loss free two port device, where all its S-parameters are computed in only one simulation run. There it is made use of the fact, that for all loss free structures the matrix is symmetric. The correspondent modes can be selected below.

Finally it is possible to define a specific selection of port modes by opening the Port mode list... dialog. Here each port mode is listed separately and can be marked for calculation. The simulation runs are then performed one after another, however, it is also possible to choose a simultaneous excitation of the selected port modes.

Example:

Top

Mode: Chooses the number X of the mode that will be used for the stimulation. Usually the S-parameters are calculated for the fundamental mode (number 1) only, the selection All excite each mode separately. Please note, that the calculated S-parameters depend on the selected mode.

Full deembedding: Activate this check button to perform a full deembedding calculation. This implies that the source type is set automatically to All ports/ All modes. If some inhomogeneous ports occur in the structure the port modes will be calculated with broadband information which is added to the result tree. After all solver runs have finished the complete S-parameter matrix is generated considering the broadband behavior of the port modes. The number of frequency samples for this procedure can be defined in the special solver settings/waveguide. For more detailed information see the waveguide port overview.

Calculate modes only: Calculates solely the port modes of your structure, i.e. no solver run is performed.

S-parameter settings frame

Norm to fixed impedance: S-Parameters are always normed to a reference impedance. You may either select to norm them to the calculated impedance of the stimulation port or you may specify a number of your choice.

S-parameter symmetries: Selecting this check button activates the S-parameter symmetry settings made in the S-parameter list... dialog box. These settings should be made due to occurring structure symmetries in order to save simulation time. The solver only starts the necessary calculation runs, all the remaining results will be copied,  including also time signals. The symmetry conditions are only applied to the selected port mode stimulations.

Stimulation signal frame

Gaussian: The stimulation is done with a gaussian pulse.

Rectangular: Enables you to define a digital excitation. Use Ttotal, Trise, Thold and Tfall to define the shape of the function.

User defined: The Edit... button opens the VBA editor which lets you define an excitation function. (See Examples)

Adaptive mesh refinement frame

Adaptive mesh refinement: Mark this check box to activate the adaptive mesh refinement. The mesh will be adaptively optimized by either adding extra grid lines due to the calculation of the electromagnetic field energy or by successively changing the settings of the mesh expert system. Press the Properties... button to edit the current settings for the mesh refinement.

Start solver

Calculates the port modes and starts the time domain calculation.

Modes only

Calculates the port modes of your structure only.

Optimization...

This button opens a dialog box that allows you to set up and start an optimization run.

Par. sweep...

Opens the parameter sweep dialog.

Specials...

This button leads to a dialog where further special settings for the solver can be made. The settings are for expert users only and should generally not be changed.

Apply

Stores the current settings. The dialog box remains open.

Close

Closes this dialog box without performing any further action.

Help

Shows this help text.

See also

Solver Overview, Transient Solver Settings Overview, Special Solver Settings, Ports, Frequency Range Setting, Optimizer, Signals in Time Domain Simulations Overview , Plane Wave , S-Parameter Symmetries, Port Mode Excitation Selection

CST IN BATCH MODE

Command Line Options

It is possible to run CST DESIGN ENVIRONMENT™ in batch mode.

Syntax: Installation Path\CSTStudio.exe -<option> <filename>

Examples for MATLAB - (for DOS batch file remove  "!" )

To start a specific module, to open a help project or to perform some basic settings, the following command line <option> are available:

In general, the following extensions are valid for <filename>

The following options start a calculation after loading a project (and are only valid with a given project file):

If there is need for any other setting, it can be done by executing an appropriate visual basic file. Each module can be controlled through visual basic commands.

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For sheets instead of metalization solids

TOP

MANUAL MESHING

Manual mesh generation

Besides the automatic mesh generation, a manual mesh mode is also available. The automatic mesh generation is switched off as soon as a manual mesh operation is performed.
You may manually add fixpoints by simply clicking at an edge endpoint (Objects /Pick /Pick Point /) or a circular edge (Objects /Pick /Pick Circle Center /), depending on the activated mode. After clicking a proper item, a new fixpoint will be set to the specified location or an existing fixpoint at this location will be selected.
After selecting a fixpoint, it may be deleted by choosing Edit /Delete Object or by pressing the DELETE key.
You may also add, delete and move fixpoints from within the fixpoint list dialog box (Mesh /Fixpoint List, /).
After two fixpoints have been selected (selecting the first one and the holding the CTRL key pressed while selecting the second one) you may also add intermediate fixpoints by choosing the Intermediate option in the fixpoint list dialog box.

AR-Filter

1. original, no monitors.
2. Simulate with !T down to -30 dB accuracy.
3. run AR-Filter in post-processing. Write down all of the settings that give a good answer. <"Results-->Time Signal Calculations-->AR-Filter for Port Signals"> Good results were obtained by using all defaults as they were without clicking any buttons. All settings may be viewed under "Results-->View Logfiles-->AR Filter Logfile for Port Signals".


===================================================================
Analysis 1 of 1 for stimulation port 1
===================================================================

First time step : 1.999046e+000 ns
Skip time steps : 10
Max. frequency : 4.125000e+000 GHz
Max. order of filter : 40
Relative Window length: 2.000000e+000

Input signal samples : 5766
Input signal length : 1.682701e+001 ns

-------------------------------------------------------------------------------
step | window range | rel. wnd. | filter | energy | pulses to
| ns | length | order | error | calculate
------|---------------------------|-----------|--------|-----------|-----------
1 | 6.4787e+000 - 1.2782e+001 | 2.00 | 40 | 4.81e-014 | 8.99e+000
2 | 6.5078e+000 - 1.2811e+001 | 2.00 | 40 | 4.81e-014 | 9.01e+000
3 | 6.5370e+000 - 1.2841e+001 | 2.00 | 40 | 4.81e-014 | 9.03e+000
4 | 6.5662e+000 - 1.2870e+001 | 2.00 | 40 | 5.07e-014 | 9.05e+000
5 | 6.5954e+000 - 1.2899e+001 | 2.00 | 40 | 5.07e-014 | 9.07e+000
6 | 6.6246e+000 - 1.2928e+001 | 2.00 | 40 | 5.23e-014 | 9.09e+000
-------------------------------------------------------------------------------
filter step 1 was chosen for further calculations.
-------------------------------------------------------------------------------

===========================================================
Stimulation at port 1
Average deviation in s-parameter energy balance: 1.593051e-006
Maximum deviation in s-parameter energy balance: 1.717618e-004
===========================================================



===================================================================
Maximum deviation in s-parameter energy balance = 0.000171762
(regarding all successful filter runs)
===================================================================

"Good Results" means when the balance snaps below '1.0000' for closed systems with no energy storage. This doesn't work for antennas, but one additional indication of correct AR Filter settings is the elimination of ripple on |S11|.

4. Now, set-up online AR-Filter (co-processing) with these same settings. Run the simulation in !T, after deleting the results.

5. Make "!T-->Adaptive Mesh Refinement" ACTIVE and re-run the model with no other changes. Expert-based mesh adaption is easier to use than Energy-based. If Energy-based mesh adaption is required, make sure to keep back-up copies of the meshed model.

6. Using the same mesh, from '5' above, turn 'OFF' AR Filter and Mesh Adaption. Add monitors, probes, etc. as needed. In this example add E-field and Farfield monitors at 0.9 and 1.8 GHz. Increase the accuracy from '30' to '50' or '60'. Run the simulation one more time.

NOTE: If S-parameters are not the results of interest, it may be necessary to defeat the automatic check for S-parameter delta (default=0.02) by decreasing this value to some very small number such as '0.000002', followed by setting up a watch for the result which is of interest using Template Based Post Processing. TBPP results will show up in a folder in the navigation tree labeled "Tables".