Training CST 3

First simulation by CST

Microwave Studio

(in Time Domain mode)

Berezin Maksim

Ben-Gurion University.

Course “Antennas and Radiation”.

CST MICROWAVE STUDIO®

Main Features of CST MICROWAVE STUDIO®

• Fast and memory efficient FI-method.

• Good performance due to Perfect Boundary Approximation (PBA™) for solvers using hexahedral grids. The transient and eigenmode solvers also support the Thin Sheet Technique (TST™). Hexahedral grids are supported by all solvers.

• The structure can be viewed either as a 3D model or as a schematic. The latter allows for easy coupling of the EM simulation with circuit simulation.

• Transient solver for efficient calculation for loss-free and lossy structures. The solver does a broadband calculation of S-parameters from one single calculation run by applying DFT’s to time signals.

• Frequency domain solver with adaptive sampling. The general purpose solver supports both, hexahedral and tetrahedral meshes.

• Besides the general purpose solver, the frequency domain solver also contains two solvers being specialized on strongly resonant structures (hexahedral meshes only). The first of these solvers does only calculate S-parameters whereas the second one also calculates fields which requires some additional calculation time.

• Calculation of 3D eigenmodes.

• Expert system based automatic mesh generation with 3D adaptive mesh refinement.

• AR-Filter analysis for resonant structures.

• Farfield (2D, 3D, gain, angular beam width and more) and radar cross section (RCS) calculation.

• Efficient build-in optimizer. (Powell and Quasi-Newton type, advanced multilevel interpolation schemes)

• Parameter Sweeps.

• Network Parameter Extraction.

• Spice Model Extraction.

Basic Shape Creation

The easiest way to create a shape is to define a "primitive." The following table shows the toolbar items, their names and their menu commands.

• Objects Basic Shapes Brick

• Objects Basic Shapes Sphere

• Objects Basic Shapes Cylinder

• Objects Basic Shapes Elliptical Cylinder

• Objects Basic Shapes Cone

• Objects Basic Shapes Torus

• Objects Basic Shapes Bond Wire

• To create such a primitive, you will first need to activate the particular operation as shown in the table. This will lead you to the interactive shape generation mode where you may define the shape's parameters using the mouse (while in this mode, press F1 for more information).

• After the shape has been created, it will appear in the navigation tree under it’s Material folder.

Blend and Chamfer Edges

• The simplest modifications of shapes are the blend and chamfer edge operations.

• To chamfer or blend edges, you will first have to pick these edges. Afterwards, you may activate the proper tool by choosing Objects Blend Edges ( ) or Objects Chamfer Edges ( ).

• Finally, a dialog box will appear where you may define the chamfer width or the blend radius.

SHAPE CREATION

Transformation may be applied to any shape by selecting a shape and then choosing Objects Transform Shape ( ).

With this operation, you may translate, scale, rotate or mirror a shape. The existing shape may either be directly modified by the transformation or the original shape may be kept while new copies will be produced.

Extrude and Rotate Picked Faces

• It often becomes useful to extrude or rotate already existing faces in the model. Therefore, you may pick a particular faceand the activate the Extrude Face (Objects Extrude, ) operation or the Rotate Face (Objects Rotate, ) operation. The latter operation requires the definition of a rotation axis. The axis may be selected by either picking a straight edge from the model or entering a linear edge numerically (Objects Pick Edge from Coordinates, ).

Loft Between Picked Faces

• A more advanced operation to create new shapes is lofting between profiles. This operations requires two faces to be picked between which the loft will be placed. Afterwards, you may activate the loft operation by choosing Objects Loft ( ).

• Finally, a dialog box will appear where you may adjust the tangency of the lofted surface to the adjacent faces.

Shell or Thicken Sheet

• One of the most advanced operations for shape generation is the shelling operation. For shelling, you must first select a shape.

• If you select a solid shape, you may additionally pick faces of the shape that will be opened during the shelling operation.

• Finally, you may activate the shelling operation by choosing Objects Shell Solid or Thicken Sheet from the main menu. A dialog box will open, where you must specify whether the shape is to be shelled or thickened to the inside or to the outside.

Material

• Each shape is assigned to a Material that will describe its material properties and its color. The materials are all shown in the navigation tree .

Component

• The shapes are also associated to "components." Each shape must have a unique name within a certain component. Components are useful to quickly manipulate a larger part of the model.

SHAPE CREATION (continue)

Boolean operations are a very common way to produce complex shapes. With these operations, you may Add

(Objects Boolean Add, ), Subtract (Objects Boolean Subtract, ), Intersect (Objects Boolean Intersect, )

Insert (Objects Boolean Insert, ) and Imprint (Objects Boolean Imprint) shapes into each other.

Boolean Operations

Different kinds of solver modules

Transient Solver

• This is a very flexible time domain simulation module that is capable of solving any kind of S-parameter or antenna problem. It will stimulate the structure at a previously defined port using a broadband signal. Broadband stimulation enables you to receive the S-parameters for your entire desired frequency range and, optionally, the electromagnetic field patterns at various desired frequencies from only one calculation run.

Frequency Domain Solver

• Like the transient solver, the main task for the frequency domain solver module is to calculate S-parameters. Due to the fact that each frequency sample requires a new simulation run, the relationship between calculation time and frequency steps is linear unless special methods are applied to accelerate subsequent frequency domain solver runs. Therefore, the frequency domain solver usually is fastest when only a small number of frequency samples need to be calculated. Hence, a broadband S-parameter simulation with adaptively chosen frequency samples is performed to minimize the number of solver runs. If only S-parameters are required, an alternative method in the frequency domain is the "Resonant: Fast S-Parameter" solver. For this method, one simulation run is performed to obtain the S-parameters for the entire desired frequency range

• If field monitors are required, then the "Resonant: S-Parameter, fields" solver can be used. The S-parameters are again calculated in one simulation run for the entire desired frequency range

• In addition, electric and magnetic field monitors can be calculated in a postprocessing step very quickly at a given frequency marker

Eigenmode Solver

• In cases of strongly resonant loss-free structures, where the resonant fields (= the modes) are to be calculated, the eigenmode solver is very efficient. This kind of analysis is often useful for determining the poles of a highly resonant filter structure. The eigenmode solver directly calculates the first N resonance frequencies and the corresponding field patterns.

Integral Equation Solver

• The areas of application for the integral equation solver are S-Parameter and Farfield/ RCS calculations. The integral equation solver is of special interest for electrically large models. The discretization of the calculation area is reduced to the object boundaries and thus leads to a linear equation system with less unknowns than volume methods. The system matrix is dense. For calculation efficiency the equation system is solved by the Multi Level Fast Multipol Method (MLFMM). The integral equation solver is available for plane wave excitation and discrete face ports. Electric and open boundaries are supported.

Mesh Generation Overview

Hexahedral Mesh GenerationIn general, there are three ways to define a hexahedral mesh: manually, automatically and adaptively.

• PBA mesh: Besides the sufficient sampling of the fields, it is very important to obtain a good approximation of the structure

within the mesh. This is performed by PBA, which ”maps” the structure from the continuous world into the mesh of the discrete

world.

• Staircase mesh: In addition to the PBA mesh, a classic staircase mesh is provided. Choose the staircase mesh for imported

structures that are not solids or that cannot be healed.

• Structure Treatment by Automesh: To make sure that the structure is represented as well as possible, the automatic mesh

generator tries to create the mesh such that critical structure elements are located on mesh lines or planes. This is accomplished

by creating a number of fixpoints and densitypoints . In doing this, the mesh generator creates mesh lines that are very close to

each other. For a very accurate discretization of the structure these mesh lines might be necessary, but small local mesh steps

increase the simulation time.

To avoid such problems, a ratiolimit may be defined. This forces the automatic mesh generator to produce a mesh where the

absolute ratio between the highest and the smallest distance between mesh lines is below the ratiolimit value. The default value of

10 is very often a good compromise to start with

• Mesh and PEC Edges: At PEC edges, you theoretically obtain singularities in the electromagnetic fields. This means that the

fields vary significantly near such edges.

To obtain a good approximation of this behavior, the most straight-forward method is to increase the spatial sampling rate there

A second, more sophisticated possibility is to use the corner correction method. The corner correction uses a singularity model

for PEC edges. It is based on analytical models to obtain a better discretization of the electromagnetic fields.

• Adaptive Meshing

For some structures the automatic mesh generator might not find an optimal mesh. In these cases, an adaptive meshing

procedure might be more successful. This procedure simulates the structure a few times and improves the mesh from run to run.

There are two different strategies for adaptive meshing. One is based on an expert system and the other on the different field

energies within the calculation domain

Tetrahedral Mesh

• Automatic mesh generation

A tetrahedral mesh is generated by an automatic mesh generator. If a solver will be started with a tetrahedral method, the mesh generator will be started automatically, unless a valid tetrahedral mesh already exists.

Alternatively, you may run the mesh generation to view the mesh before you start a specific solver by selecting Mesh Update or by pressing the toolbar button in the Mesh View. Previewing the mesh is not necessary, but is recommended to get obtain insight as to whether the defined problem is sufficiently resolved by the mesh, particularly if you do not use the adaptive mesh refinement.

• Mesh and structure approximation - surface and volume mesh

Shape boundaries and sheets are discretized by the surface mesh consisting of triangles. A fine surface mesh will result in a good approximation of the structure geometry. Each triangle of the surface mesh is a side of one or two adjacent tetrahedrons.

The set of tetrahedrons is called the volume mesh.

• Adaptive mesh refinement

An optional adaptive mesh refinement ensures an accurate numerical solution in combination with a short simulation time. An adaptive solver run simulates the structure several times and locally improves the mesh from run to run. This results in optimal meshes, i.e. the computational power is concentrated to places where it is necessary. A good strategy is to start with a relatively coarse mesh and to use adaptive refinement to improve the results.

Adaptive refinement can be switched on and off in the respective solver dialog.

Mesh Generation Overview

Surface Mesh

Mesh and structure approximation - surface and mesh

Shape boundaries and sheets are discretized by the surface mesh consisting of triangles. A fine surface mesh will result

in a good approximation of the structure geometry

Circular Horn

Units

Solve Units

Solve Background Material

This dialog box helps you to fill the undefined space within the boundaries. You may define its material

properties. Additionally, you may add some space between the bounding box of your model and the

boundaries that will be filled with the background material.

Material properties frame

Material type: The following material types are available:

Sets the background material to a normal material which is loss free

and determined by its Epsilon and Mue.Normal

Sets the background material to a Perfect Electric Conductor.PEC

Epsilon / Mue: In these fields you may enter permittivity Epsilon and permeability Mue if the normal material type is selected.

Themal type: Set the thermal material type of the background material.

Background

Objects Basic Shapes Cylinder

You may interactively define a cylinder by double-clicking its base centerpoint, its radii and its height in the currently

active coordinate system .

Geometry creation

Cylinder Creation Mode –element “solid1”

Geometry creation

Objects Basic Shapes Cone

You may interactively define a cone by double-clicking its base center point, its top and bottom radii and its

height in the currently active coordinate system

Cone Creation Mode – element “solid2”

Objects Basic Shapes Cone

You may interactively define a cone by double-clicking its base center point, its top and bottom radii and its

height in the currently active coordinate system

Cone Creation Mode – element “solid3”

Geometry creation

Transient Solver

Boolean Operations

Probably the most powerful operation to create complex shapes is the combination of simple shapes by boolean operations.

These operations allow you to add two or more shapes together, to subtract one or more shapes from another, to insert

shapes into others, and to intersect two or more shapes.

Subtract “solid3” from “solid2”:

Subtract the first shape from the second to obtain one single shape. The resulting shape will get the name and the

material of the shape from which the other shape is subtracted.

Objects Boolean Subtract

Material setting

Materials: If a specific material is selected all its solids are visualized while the others are

displayed transparently.

To select element right click by mouse “Change material”

The PEC is material for the “solid1” and for the “solid2”.

Excitation Source

• To select the surface of the horn for waveguide port on the “solid1”

You pick a face that is aligned to one of the coordinate axes before entering this dialog box, it will define the

dimensions of the new port region.

Objects Pick Pick Face

Waveguide ports are used to feed the calculation domain with power and to absorb the returning

power. For each waveguide port, S–parameters (and time signals for time domain simulations) will be

recorded during a solver run. In practice, the port can be substituted by a longitudinal homogenous

waveguide connected to the structure

Solve Waveguide Ports

Excitation Source

Solve Boundary Conditions Boundaries

You may double-click on the boundary conditions icon in the main plot window to select one boundary.

By pressing the right mouse button in the main plot window, you can set the type of the boundary

condition for the selected boundary using the popup menu.

Boundary conditions : Xmin / Xmax / Ymin / Ymax / Zmin / Zmax

Due to the fact that a computer is only capable of calculating

problems that have finite expansion, you need to specify the

boundary conditions. This can be done within this dialog box.

If you entered the boundaries property sheet, the modeled

structure is displayed with a surrounding bounding box colored

with regard to the boundary condition at each boundary. The

picture on the right shows an example of such a bounding box.

The assignment of the colors to the boundary conditions is listed

together with the description of the different boundary conditions

below.

Boundary Conditions - Boundaries

Periodic: Connects two opposite boundaries with a definable phase shift such that the calculation domain is simulated to be periodically expanded in the corresponding direction.

Open (add space): Same as Open (PML), but adds some extra space for farfield calculation. This

option is recommended for antenna problems.

Open (PML): Operates like free space: waves can pass this boundary with minimal reflections.

Magnetic: Operates like a perfect magnetic conductor: all tangential magnetic fields and normal electric fluxes are set to zero.

Electric: Operates like a perfect electric conductor: all tangential electric fields and normal magnetic fluxes are set to zero.

Boundary Conditions - Boundaries


Boundary

Frequency Range

Solve Frequency

Field Monitors

Solve Field Monitors

Results

Analyze 1D Results

Results

Analyze 2D/3D Results

Results


100GHz

Results

3D Far Field

Microstrip Antenna –

Rectandular Patch

Units

Solve Units

Solve Background Material

Background

Objects Basic Shapes Brick

.

Geometry creation

Brick Creation Mode –element “solid1”

Geometry creation

To define the additional coordinate system (U,V,W):

WCS Local Coordinate System

To push (Move Local Coordinate System)

Geometry creation

Brick Creation Mode –element “solid2”.(second element)


.

Boolean Operation

Objects Boolean Add

To select these two bricks- “solid1” and “solid2”:

Geometry creation

Brick Creation Mode –element “solid2”.(substrate)


.

To define the other additional coordinate system (U,V,W): dU=-10 dW= -9 (from first local CS)

Material setting

Materials: If a specific material is selected all its solids are visualized while the others are

displayed transparently.

To select element right click by mouse “Change material”

The PEC is material for the “solid1” and the “substrate” for the “solid2”. This dielectric doesn’t locate into internal

material library of the CST and has Epsilon 2.2 and Mue 1.0.

Excitation Source

• To select the surface of the “brick3” for waveguide port.

You pick a face that is aligned to one of the coordinate axes before entering this dialog box.

Objects Pick Pick Face

Waveguide ports are used to feed the calculation domain with power and to absorb the returning

power. For each waveguide port, S–parameters (and time signals for time domain simulations) will be

recorded during a solver run. In practice, the port can be substituted by a longitudinal homogenous

waveguide connected to the structure

To create the “brick3” with dimensions: Xmin=-1.01 Xmax=8; Ymin=-8 Ymax=-4; Zmin=-0.794 Zmax=3

This element must be create into WCS

Excitation Source

Solve Waveguide Ports