21.12.2009
Workflow Example
Horn Antenna
Purpose : Optimize the
aperture of the horn
antenna such that the gain
is maximized at 10 GHz.
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CST MWS - Standard Workflow
Choose a project template.
Create your model.
 parameters + geometry + materials
Define ports.
Set the frequency range.
Specify boundary and symmetry conditions.
Define monitors.
Check the mesh.
Run the simulation.
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Cylindrical Horn Antenna 8 – 12 GHz
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0.5
0.5
dia=2, rad=1
zlength=2
units: inch
waveguide: 1.0 in x 0.5 in x 0.5 in
aperture radius: 1.0 in, length: 0.25 in
shell thickness: 0.01 in (outside)
monitors: E-field, H-field & far field at 10 GHz
0.25
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Project Template
At the beginning choose
“File” -> “New”
For an existing project you may choose
to create a new project.
“File” -> “Select Template”.
The project templates customize the default settings
for particular types of applications.
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Project Template
background material
Antennas should be modeled with
vacuum as background material.
PEC is very practical for closed structures.
(e.g. waveguides, connectors, filters)
The project templates customize the default
settings for particular types of applications.
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Change the Units
Define units.
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Horn Antenna – Construction (I)
Define a brick (1.0 x 0.5 x 0.5 in)
made of PEC.
Define a cylinder (outer radius: 1.0 in,
height: 0.25 in) made of PEC.
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Pick face.
Align the WCS with the
face.
Move the WCS by 2.0
inches.
Horn Antenna – Construction (II)
Pick two opposite faces.
Perform a loft.
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Horn Antenna – Construction (III)
Perform a
Boolean add.
Select multiple objects
(ctrl or shift + left mouse button).
shell solid: 0.01 in
(outside)
Pick two faces.
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Port Definition
Pick point
inside corner.
Define a waveguide port.
Pick edge.
Define the port on the internal profile.
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Set the Frequency Range
Set the frequency range.
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Boundary Conditions and Symmetry Planes
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3D Monitors
Add field monitors for E-field, H-field, and far field at 10 GHz.
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Mesh View (I)
mesh properties
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Mesh View (II)
TST at work!
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Transient Solver: Start Simulation
The accuracy defines the steadystate monitor.
The simulation is finished when
the electromagnetic energy in the
computational domain falls below
this level.
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Analyze 1D Results
port signals
S-parameter
energy
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Analyze 2D/3D Results
port information:
• cut-off frequency
• line impedance
• propagation constant
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Electric Field at 10 GHz
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Far Field at 10 GHz
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Polar Plot for Far Field at 10 GHz
phi=90
phi=0
Create a new folder “Comparison” to compare different 1D results.
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Parameterization
Optimization
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Parameterization (I)
r1
outer radius r1 = variable
goal: maximize gain
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Parameterization (II)
outer
radius
r1
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Result Processing Templates (Shift+P)
1D results
Define gain(theta) at phi=0.
Postprocessing templates provide a convenient way to calculate
derived quantities from simulation results.
Each template is evaluated for each solver run.
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Result Processing Templates (Shift+P)
0D results
Define max of gain(theta).
Read the online help to learn more
about the postprocessing in CST MWS.
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Result Processing Templates (Shift+P)
Alternative solution:
The maximum gain can be computed using
the “Farfield” template in “0D Results”.
Define max of gain(theta).
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Parameter Sweep - Settings
1
2
3
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Parameter Sweep - Settings
Add a S-parameter watch.
The results will be automatically listed
in the “Tables” folder.
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Parameter Sweep – Table Results
Right click on plot
window and select
“Table Properties…”.
Choose the result curve for each
parameter value with the slider.
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Parameter Sweep – Table Results
parameter values
parameter values
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Automatic Optimization
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Automatic Optimization
Define the parameter space.
Define the goal function.
Template based postprocessing 0D results can be
used to define very complex goal functions.
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Automatic Optimization
Choose the “Classic Powell” optimizer.
Follow the optimization.
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Automatic Optimization - Results
parameter values
1D results
goal:
maximize gain
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Optimization - Summary
Define a variable.
Parameterize the structure.
Define the goal function.
Set the parameter space.
Run the optimizer.
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Far Field Postprocessing
 terminology
 broadband far field
analysis
 co-/cross-polarization
 phase center
 tips and tricks
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Broadband Far Field Analysis
How to plot the antenna gain for the complete
frequency range?
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Broadband Far Field Monitors
Create a broadband far field monitor
from the available monitors.
After monitor definition, start T-solver again!
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Result Processing Templates (Shift+P)
1D Results
Define maximum value of gain.
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Broadband Far Field Monitors
far field 3D pattern
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Broadband Far Field Monitors
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“Tables” -> “1D Results” -> “Broadband gain 3d”
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Co- / Cross-Polarization
The co-polarized far field component has the same polarization
as the excitation (y-oriented in our case).
The cross-polarized far field component is orthogonal to the
co-polarized component and main lobe direction.
In order to use different polarizations for transmitting/receiving,
an antenna design goal might be to maximize the co-polarized
and minimize the cross-polarized component.
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Co- / Cross-Polarization
1. Select the tab “Axes“.
2. Click “Main lobe/polarization
alignment“.
3. Choose the “Ludwig 3“ coordinate
system.
polarization vector direction
(arbitrary user input possible).
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If “Main lobe ... “ is not selected, the user
can enter arbitrary directions for:
-polarization plane normal (z„) (= theta axis)
-cross-polarized component (x„) (= phi axis).
Co- / Cross-Polarization
co-polarized = Ludwig 3 vertical
cross-polarized = Ludwig 3 horizontal
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Co & Cross Polarization
Result Templates for Parameter Sweep and Optimization
co-polarized= Ludwig 3 vertical
cross-pol. = Ludwig 3 horizontal
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Phase Center Calculation
Finding the best location to place the horn
inside a parabolic antenna. The best position
is to match the focal point of the dish
with the phase center of the horn.
= y‘z‘ plane
= x‘z‘ plane
?
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Check Phase Center
Check the phase center by plotting the Ludwig 3 vertical phase.
Plotting the phase of Ludwig 3 vertical (=dominant component of co-polarized
fields) does not result in a 180° jump of the phase (=color jump) at theta=0.
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Check Phase Center
Check the phase center by moving the origin to the phase center.
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See also article (Phase Center comparison with measurements)
on www.cst.com. -> application article ID=256
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