For years the finite element method (FEM) has been the key design and simulation tool for engineers working in a wide range of disciplines. Due to its flexibility in implementation, the finite element method has attracted so many people to work on a wide spectrum of problems such as structural, fluid, and thermal problems. Those working in the area of high frequency electromagnetics (from radio frequencies, RF, to optics) have, on the other hand, relied more on analytical approaches, when-ever possible, empirical and semi-empirical models, or simple solution techniques with limited accuracy and range of applicability. Several numerical difficulties associated with the nature of the high frequency electromagnetic fields and their representation in a discretized space have slowed the introduction of the FEM as a reliable tool in RF, microwave, millimeter-wave, and optical designs.
In 1995, Integrated Microwave Technologies Inc. and Structural Research and Analysis Corporation developed HFESAP (High Frequency Electromagnetic Simulation and Analysis Package), an FEM package for the analysis and design of passive microwave and digital circuits with accuracy, speed, efficiency and ease of use. The package included two-dimensional, axisymmetric and three-dimensional modules for the analysis of waveguides and transmission lines as well as axisym-metric and 3D resonant structures. HFESAP, now called COSMOSHFS 2D and COSMOSCAVITY, is complemented by COSMOSFS 3D to provide a full wave solution for high frequency electromagnetic problems.
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1 Introduction
COSMOSHFS 3D is a program that simulates arbitrary three-dimensional passive structures, including scattering parameters, port propagation parameters and animated full-wave field solutions
Based on the Finite Element Method, COSMOSHFS 3D uses tangential vector basis functions along with options to use iterative or direct solvers. COSMOS
HFS 3D is available as part of Structural Research’s COSMOSM® finite element analysis system which comes with a standard pre- and postprocessor, called GEOSTAR, that is used for all analysis types provided by SRAC. While you may build your geometry directly in GEOSTAR, you may use your favorite solid model-ing package to build the geometry and then import it to GEOSTAR. GEOSTAR supports almost all popular CAD systems (refer to the next chapter for a list).
Most of the practical problems to be solved by COSMOSHFS 3D has more than one material. GEOSTAR accepts assemblies from several CAD systems where each component of the assembly can be exported to GEOSTAR as a part which may be assigned a different material. COSMOSWorks, a program fully integrated with SolidWorks, is particularly powerful for this kind of problems since it provides a very friendly environment to export SolidWorks assemblies directly to GEOSTAR where you assign the desired materials, mesh the assembly, specify boundary conditions, run the analysis, and visualize the results. Refer to the COSMOSM Getting Started manual for details.
In addition to the S-parameter field solver, COSMOSHFS 3D offers you an optional access to a full-wave resonant cavity field solver that directly determines the resonant frequencies and corresponding modal fields of arbitrary three-dimensional structures. You can then perform subsequent S-parameter analysis at and around the resonant frequencies for a complete characterization of the structure. You may also export the calculated S-parameters to external files in various circuit simulator formats including Compact, Citifile, and Touchstone.
COSMOSHFS 3D application areas include radio frequencies, microwave, millimeter-wave, wireless, passive waveguide components, MHMIC, MMIC, microstrip, stripline, launchers, coupling structures, connectors, transitions, discontinuities, spiral inductors, interdigitated capacitors, filters, hybrids and vias.
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2. Using GEOSTAR for COSMOSHFS 3D
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Electromagnetics in GEOSTAR
GEOSTAR is the standard pre- and postprocessor of all analysis modules of the COSMOSM finite element system. In addition to electromagnetics, the COSMOSM system includes modules to perform stress analysis, fatigue analysis, thermal analysis, and fluid flow analysis.
The COSMOSHFS Suite includes COSMOSHFS 2D and COSMOSCAVITY (High Frequency Simulator and Cavity Solvers, previously called HFESAP) and COSMOSHFS 3D.
COSMOSHFS 2D and COSMOSCAVITY
COSMOSHFS 2D is a finite element-based package for the analysis and design of
2D and axisymmetric passive mircrowave and digital circuits. COSMOSHFS 2D
is an integrated program that combines quasi-static, frequency-dependent and time domain analyses. It invokes one or more sub-modules to analyze transmission-line or waveguide structures and simulate their time domain response under specified excitation and termination conditions.
COSMOSCAVITY is a general frequency domain program for the analysis of resonant structures. Its applications include the analysis and design of cavities, dielectric resonators, frequency meters, connectors, cavity filters, and oscillators. It
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solves the vector wave equation for the resonant frequency and the corresponding modal field distributions.
This chapter will show you how to use GEOSTAR to use COSMOSHFS 3D to model and calculate S-parameters only. Separate manuals are available for COSMOSHFS 2D and COSMOSCAVITY.
Modeling Geometry
There are two ways to model your geometry:
1. Create your geometry directly in GEOSTAR.
2. Create your geometry in your favorite solid modeling package and then export it to GEOSTAR.
Creating Geometry in GEOSTAR
You may use GEOSTAR to create 3D geometries. The geometric entities in GEOSTAR include: keypoints, curves, surfaces, contours, regions, polyhedra, volumes, and parts. COSMOSHFS 3D requires the creation of parts or volumes which are the only two entities that you may mesh to create tetrahedral elements with nodes. To learn how to create geometry in GEOSTAR, refer to COSMOSM User’s Guide, Command Reference, and on-line help.
Exporting Geometry from Other Solid Modeling Systems
Modern CAD systems provide parametric, feature-based solid modeling environment which simplifies geometric modeling and modification. For this reason, many users prefer to create their geometry in their favorite CAD systemthen import it to GEOSTAR.
GEOSTAR supports the following solid modeling CAD systems:
• SolidWorks,
• Pro/Engineer and PT/Modeler (Parametric Technologies Corp.),
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• Solid/Edge (Intergraph),
• MicroStation Modeler (Bentley Systems),
• Helix Design Systems (MICROCADAM)
• Eureka (Cad.Lab),
• CADDS5 (ComputerVision),
• I-DEAS (SDRC), and
• Other generic CAD systems.
Integrated analysis packages are available for SolidWorks, Solid/Edge (Intergraph), MicroStation Modeler, Pro/ENGINEER and PT/Modeler, Helix Modeling, AutoCAD, and Eureka.
After creating your geometry in the favorite CAD system, you will be able to generate a COSMOS GEO file or an IGES file that you may import to GEOSTAR.
Exporting SolidWorks Models to GEOSTAR
SRAC has developed a fully-integrated interface with Solid/Works. The interface is currently 100% fully integrated for stress, frequency, buckling, and thermal analyses. When COSMOSWorks is installed, an FEM menu appears in SolidWorks.
Although the interface is not fully integrated for use with electro- magnetic analysis, it is still very useful since it lets you import SolidWorks geometry in both part and assembly modes to GEOSTAR.
To export SolidWorks geometry:
1. Build your part or assembly as usual.
2. Verify the units used in your model by choosing Tools, Options, clicking the Grid/Units tab, and checking the Length Unit field.
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3. Choose FEM > Preferences.
4. Click the Export tab.
5. In the Cosmos Setting, click Geometry Only.
6. From the Unit drop-down menu, choose the unit system used in SolidWorks.
✍ If you choose a unit that is different from that used in SolidWorks, COSMOSWorks will do the conversion from the unit in SolidWorks to the unit specified in the Preferences, Export dialog box.
7. If you like to launch GEOSTAR automatically after exporting a model, check the Launch GEOSTAR box.
8. Click OK.
9. From the FEM menu, choose Export. The Save As dialog box opens.
10. From the Save as type drop-down menu, choose COSMOS Files (*.geo). This is the file that you will load into GEOSTAR using the File, Load command (in GEOSTAR). The File will be loaded automatically if the Launch GEOSTAR option is activated in the Preferences, Export dialog box.
Getting Your Model to GEOSTAR
If you have generated a GEO file, you need to import it to GEOSTAR through the File > Load command.
IGES files are imported to GEOSTAR through the Control > CAD_System > Read CAD Input command. This command will open a dialog box in which you may specify the source CAD system. You may choose the type of the file from the CAD System menu shown in the figure.
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✍ You may not modify or change geometry that you have imported from a CAD system. Such geometries must be used as is. If you need to make a change, go back to your CAD system, make the change, and export the new geometry to GEOSTAR. The only operations that you may use are: Identify, List, and Plot.
What to Do in GEOSTAR
GEOSTAR is large program that supports many types of analyses including structural, thermal, fluid flow, and electromagnetics. The remainder of this chapter will emphasize the commands related to COSMOSHFS 3D.
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List Parts
If you exported SolidWorks geometry in the part mode, you will have only one part in GEOSTAR. If you exported an assembly, you will have a number of parts that is equal to the number of components in your assembly.
To list parts:
1. From the Geometry menu, choose Parts.
2. Choose List. The PARTLIST dialog box opens.
3. Click OK. The parts are listed.
Dimensions of the Model
Once your model has been imported into GEOSTAR, it is important to verify that it has the proper dimensions. Use the Control, Measure command to measure the length of a curve in the model. If the length does not match your expectations, go back to your CAD system, set the length units properly, and try again.
Viewing Your Model
Use buttons in the Geo Panel and commands in the Viewing menu to get a good view of your model by rotating, zoomin in, etc. Use the on-line help if you need more information.
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Define Material Properties
Material properties are defined through the Propsets menu. In general, several attributes are needed to completely define a finite element in GEOSTAR. These include the element group type, real constant set, and the material property set. For COSMOSHFS 3D, the only attribute needed is the material property set.
Defining Material Sets
GEOSTAR provides flexible ways to define material properties. You may define properties on-line or you may select materials from a material library. The COSMOSM Material Library for electromagnetics is included in a text file called usermat.lib which may be edited to define new materials or properties as desired. The file Pickmat.lib contains the COSMOSM Material Library for other modules. It is important to remember that whenever you mesh a part, it will assume the properties of the active material set. Material set number 1 is active by default. In cases where you have multiple materials, the recommended procedure is to activate (or define) the proper material property set before meshing the desired part(s). If there is only one material set, you may define it at any time before running the analysis (before or after meshing).
If you ran an analysis and you just need to study the effect of changing the material, just redefine the material set and run the analysis again.
The material properties that are used in COSMOSHFS 3D are:
• PERMIT_R: Real part of relative permittivity.
• PERMIT_I: Imaginary part of relative permittivity.
• MPERMIT_R: Real part of relative permeability.
• MPERMIT_R: Imaginary part of relative permeability.
• ECON: Electrical conductivity.
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Picking a Material from the COSMOSM Material Library
To pick a material from the library:
GROSTAR comes with a fairly extensive library of microwave materials for printed circuits, coaxial cables, and semiconductors. This library is separated from the regular COSMOSM Material Library for convenience.
1. To choose a material from this library, select User Material Library, from the Propsets menu, the USER_MAT dialog box opens.
2. In the Material Property set field, enter the label of the material set. The default is the last material number you have defined + 1.
3. From the Material Name drop-down menu, choose the desired material to be assigned to this set.
4. The Unit label is not used for COSMOSHFS 3D.
5. Click OK. The material set you just defined becomes active.
To list material property sets:
1. From the Propsets menu, choose List Material Props. The MPLIST dialog box opens.
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2. Click OK. Material sets and properties are listed. The Temp/BH-Cr field is not used by COSMOSHFS. The label A indicates that the set is active which means that elements generated at this time will be associated with this material.
To make a material lossless:
1. Pick a material from the User Library as described above.
2. From the Propsets menu, choose User Material Library. The USER_MAT dialog box opens.
3. In the Material Set Number field, make sure to enter the material set number you want to make lossless (do not accept the default).
4. From the Material Name drop-down menu, choose LOSSLESS.
5. List the material as shown above to verify that PERMIT_I is set to zero (it will not be listed). Other properties remain unchanged.
Activating a Material Set
The last defined material set becomes active by default. You may define a material set, mesh the associated part(s), define another set, mesh its associated parts and so on, or you may define all material property sets at once and then activate the desired set and mesh the associated part(s).
To activate a material set:
1. From the Control menu, choose Activate > Set Entity. The ACTSET dialog box opens
2. From the Set Label drop-down menu, choose MP: Material Property.
3. Click Continue. Another dialog box opens.
4. In the Material Set Number field, enter the desired set number.
5. Click OK. The specified material set number becomes active.
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Meshing the Model
Because the analysis results depend on the quality of the model’s mesh, beformeshing, it is important to specify a reasonable element size. The element sizshould be small enough to accurately predict the S-parameters matrix for the highest frequency of interest.
Element Size
Calculate the element size based on the highest frequency of interest. It helps default element size suggested by GEOSTAR. It is suggested to use the smalthe two numbers.
Typically, an average of 10 elements per wavelength, corresponding the highefrequency of interest in the part’s material should be kept. Occasionally, additiomesh control may be required on regions and/or surface to locally to increasedecrease the mesh density in and around areas of high field concentration andfield variation.
✍ A polyhedron is the air-tight surface area of a 3D object. A part is made uone or more polyhedra. Multiple polyhedra in a part represent cavities copletely enclosed by the outer polyhedron. If you are importing geometry fra CAD system, polyhedra and parts are automatically created.
To list polyhedra, choose Geometry, Polyhedra, List. Listing polyhedra is important because:
1. It lists the element size suggested by GEOSTAR to generate a reasonably mesh, and
2. It lists the regions forming the part. This is particularly useful when you havmultiple parts since it helps identify the common regions. For example, we mconclude from the list below that regions 2 and 14 are common to polyhedrand 2.
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The suggested size is used by default but may be easily changed as will be shown in the next section.
Changing Element Size
To change the element size:
1. From the Meshing menu, choose Mesh Density.
2. Choose Mesh Density. The PHDENSITY dialog box opens.
3. Specify the desired polyhedra. It is recommended to use the same element size for all polyhedra unless it is required to minimize the number of elements due to machine resources.
4. Set the desired Element Size.
5. Specify Tolerance. Using a tolerance larger than the default helps speed and some times in avoiding meshing problems.
6. Click OK.
✍ The Mesh Density menu lets you specify different element sizes for different regions, contours, and even curves. It is suggested to use these features only if you have to like in the case where you have large as well as very small fea-tures in your model. Small features that are not important in your model should be suppressed in the CAD system. If you use different dimensions for different polyhedra, make sure that their common regions have the same den-sity. This can be insured through the Meshing, Mesh Density menu.
To mesh the model:
1. Define a material set or activate an existing material set.
2. From the Meshing menu, choose Auto_Mesh, Parts. The MA_PART dialog box opens.
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3. Pick the beginning part or type its able in the Beginning part field.
4. Pick the ending part or type its label in the Ending part field.
5. In the Increment field, key in the increment between parts in the pattern
6. From the Element Order drop-down menu, choose 0:Low. High order elements are not used in COSMOSHFS 3D, so make sure to choose the Low order.
7. Click OK. Meshing of the specified parts starts. Each element will have a tetrahedral shape defined by 4 nodes. The elements will be associated with the active material set.
8. Repeat steps 1 through 7 as many times as needed to mesh all other parts.
To display the elements in different colors based on material:
1. From the Meshing menu, choose Elements> Activate Elem. Color. The ACTECLR dialog box opens.
2. From the Color flag drop-down menu, choose 1: Yes.
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3. From the Set label drop-down menu, select MP: Material Property.
4. Accept the Default colors flag set to 1:On.
5. Click OK.
6. From the Meshing menu, choose Elements > Plot. The EPLOT dialog box opens.
7. Accept the default entries, and Click OK. The elements are redisplayed in different colors based on their material.
Boundary Conditions
For COSMOSHFS 3D, only three types of boundary conditions can be used:
GC: Grounded Conductor
This boundary condition should be used on metallic surfaces. It imposes a perfect electrical conductor boundary condition by setting the tangential component of the field to 0.
PMC: Perfect Magnetic Conductor
This boundary condition should be used for symmetric surfaces where the magnetic field is purely normal to surface, i.e., this boundary condition forces the tangential component of the magnetic field to be 0.
PORT: Port
Define access ports to the structure. Use this boundary condition to define the ports of your model. Ports should be numbered sequentially starting at 1.
To apply boundary conditions:
1. From the LoadsBC menu, choose E-Magnetic, HiFreq_B.C, Define By Regions. The CBRG dialog box opens.
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2. Point to the desired region and click the left button of the mouse. A regions highlights.
3. If the highlighted region is correct, click the left button again to accept. If some other region is highlighted, click the right button to reject.
✍ If the desired region is not highlighted, keep rejecting until the proper region highlights and then accept by clicking the left button.
4. From the Boundary Conditions Type drop-down menu, choose GC: Grounded Conductor, PORT: Port, or PMC: Perfect Magnet Conductor.
5. Click Continue.
6. Continue to specify input based on the selected boundary condition.
Important Points to Remember
• Boundary conditions should be only applied to parts that have been meshed. All boundary conditions applied to boundaries of parts that have not been meshed will be ignored.
• All boundary conditions are applied from the LoadsBC menu.
• The only types accepted by COSMOSHFS 3D are GC: Grounded Conductor, PORT: Port, and PMC: Perfect Magnet Conductor.
• If you need to apply a boundary condition to too many regions, it may be more efficient to create a selection list and then apply the boundary condition to all the entities at once.
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• If you imported the geometry from a CAD system, you will nat have surfaces in your model. All the boundaries of the model will consist of regions. Native GEOSTAR geometry may have surfaces and regions.
• Re-applying a boundary condition to a region (or faces of elements) will overwrite all previous assignments. As an example, if you defined a port at a region and then you applied a ground conductor to the same region, the port condition will be replaced by the ground conductor condition for that region.
• Every outer boundary of the model must be assigned a boundary condition.
• Ports must be labeled sequentially starting from 1.
Detailed steps to define ports:
In general, a port may be made up of many different regions or surfaces. In defining that port, the same port number must be given to all the regions/surfaces associated with it.
1. From the LoadsBC menu, choose E-Magnetic, HiFreq_B.C, Define By Regions. The CBRG dialog box opens.
2. Pick the Beginning region.
3. From the Boundary Condition Type drop-down menu, choose PORT: port.
4. Click Continue.
5. In the Port Number field, enter the Port number. Start with number 1.
6. Pick the ending region.
7. In the Increment field, enter the increment between regions in the pattern. If two regions are used, use (Ending Region - Beginning Region).
8. Click OK. The port condition will be displayed at the specified regions.
9. You may continue to add regions as described above for port 1.
10. You may continue to define up to 10 ports.
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✍ Ports must be labeled sequentially starting at 1.
Detailed steps to apply perfect magnetic conductor condition:
1. From the LoadsBC menu, choose E-Magnetic, HiFreq_B.C, Define By Regions. The CBRG dialog box opens.
2. Pick the Beginning region.
3. From the Boundary Condition Type drop-down menu, choose PMC: Perfect Mag. Conductor.
4. Click Continue.
5. Pick the ending region.
6. In the Increment field, enter the increment between regions in the pattern. If two regions are used, use the difference between the two labels.
7. Click OK. The PMC condition will be displayed at the specified regions.
8. You may repeat the steps above as many times as needed.
✍ It may be more efficient to create a selection list and then apply the PMC to all regions. In this case use 1 for the beginning region, type RGMAX for the ending region, and 1 for the increment.
Detailed steps to apply ground conductor condition:
1. From the LoadsBC menu, choose E-Magnetic, HiFreq_B.C, Define By Regions. The CBRG dialog box opens.
2. Pick the Beginning region.
3. From the Boundary Condition Type drop-down menu, choose GC: Ground Conductor.
4. Click Continue.
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5. In the Conductor Number field, enter the ground conductor number. Start from 1.
6. In the Relative Permeability Value field, enter the relative permeability value.
7. Pick the ending region.
8. In the Increment field, enter the increment between regions in the pattern. If two regions are used, use the difference between the two labels.
9. Click OK. The GC condition will be displayed at the specified regions.
10. You may repeat the steps above as many times as needed.
About Selection Lists
Selection lists are filters that can be applied to a group of entities in GEOSTAR. When a selection list is active for a given entity, GEOSTAR will only recognize the members of that entity that are in the selection list. For example if you like to apply an identical boundary condition to many regions, you may have to repeat thecorresponding command several times. To simplify this process, you may create a selection list that contains all such regions and then apply the boundary conditions to all regions which results in applying the condition to regions in the active selection list.
Operations related to selection lists are available in the Control, Select and Unselect menus. Several ways are available to create, modify, initialize, and complement selection lists. Up to 10 selection lists may be defined for each entity (like regions). It should be noted that selection lists work for postprocessing also. For example, if you generate a nodal field plot while a selection list is active for nodes, then the field will be plotted for the selected nodes only. Similarly if you plot or list all nodes, only nodes in the selection list will be plotted.
Set operations are also available for selection lists. For example you can define a new selection lists that is the union or the intersection of two existing selection lists.
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The status of selection lists may be conveniently viewed and controlled by the STATUS3 Table accessed by clicking the Status3 button in the Geo Panel or from Control, Select, Status Table 3.
Use the online help to get information on the various operations for the selection lists.
Running Analysis
Before running the analysis, it is important to set your analysis and output options.
To set analysis options:
1. From the Analysis menu, choose HiFreq_Emagnetic > Analysis Option. The A_HFRQEM dialog box opens.
2. From the Analysis option drop-down menu, choose SPARAMETER.
3. In the Units field verify that the proper unit is selected.
✍ This flag is the only way the program knows about the units used in your geometry. Even if you imported your geometry from COSMOSWorks or other CAD systems, to GEOSTAR they are just numbers. Make sure to specify the proper unit that corresponds to your model. Use the Control, Measure menu to verify the dimensions of your model.
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4. From the Analysis menu, choose HiFreq_EMagnetic > S-parameters > Set Options. The A_HFRQEM dialog box opens.
5. In the Number of ports field, enter the number of ports you have defined in your model.
✍ You must enter the exact number of ports you have defined. Ports must have been numbered sequentially starting from 1.
6. In the Starting frequency (GHz) field, enter the lowest frequency of interest.
7. In the Ending frequency (GHz) field, enter the highest frequency of interest. Remember that you should have used this number to specify the element size.
8. In the Frequency increment (GHz) field, enter the desired number.
9. In the Impedance Multiplier field, enter the impedance multiplication factor.
✍ If a GC or PMC boundary condition is used as a symmetry boundary condi-tion, this field must be set to 2 or 0.5 so that the impedance computed by the simulator corresponds to the impedance of the entire structure and not the half model.
10. In the field matrix solution method, choose direct or iterative.
✍ The direct method performs a matrix factorization and requires more memory while the interactive method uses less memory, i.e., can be used for very large problems, but may be slower.
11. If the Renormalized Smatrix flag field, indicate whether or not the simulator should compute the renormalized scattering matrix. This is needed in order to be able to output the scattering parameters in various circuit simulator formats.
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12. Click Continue. A dialog for setting more solution parameters is displayed.
13. The number of modes to be considered and the de-embedding length should be specified for each port.
14. For each port, specify the additional solution parameters. The number of modes to be considered and the de-embedding length should be specified for each port.
✍ Depending on the solution parameters chosen, the amount of data output by the simulator may be very large. To control the amount of disk space used, the output options give you some control over what the simulator writes out.
To set output options (optional):
1. From the Analysis menu, choose HiFreq_EMagnetic > S-parameters > Set Output. The HF_SPAROUT dialog box opens.
2. From the Circuit Simulator Flag drop-down menu, select the desired format. The available formats are Citifile, Compact, and Touchstone. Note that the dominant mode S-parameters only are output to these files.
3. From the Output Option drop-down menu select None, Nodal, Elemental, or both Nodal and Elemental. This controls which field quantities are to be written by the simulator. Note that only the solution based on dominant mode excitation at each port is written.
4. Click OK.
To run the analysis:
1. From the Analysis menu, choose Run Analysis. GEOSTAR will start preparing information needed by COSMOSHFS.
✍ Preparing data is currently slow. It will be improved in future releases.
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Visualizing the Results
After finishing the analysis, you are ready to visualize the results. COSMOSHFS 3D generates results for port propagation characteristics as well as various scattering parameters matrices and impedance and admittance matrices. These results may be viewed by listing them in a text format or alternatively by plotting them versus frequency.
To list the S-parameters matrix:
1. From the Results menu, choose List, HF Emag Result. The HF_RESULT window opens, showing the Port Propagation Parameters and the Generalized S-Matrix at each frequency. If additional calculations were requested, i.e., renomalization or de-embedding, they are also displayed in this window.
✍ The generalized S-parameters have four indices, i, n, j, and m. The entry jm” corresponds to the ratio of the wave associated with mode n at port i when port j is excited with mode m.
S-parameter Versus Frequency
Multiple S-parameters may be displayed on the same plot by assigning each othem to a separate graph. Selected graphs can subsequently be plotted.
✍ Only S-parameters for the dominant mode at each port can be plotted.
To activate Sij graph:
1. From the Display menu, choose XY-Plots > Activate Post Proc. The ACTXYPLOT dialog box appears.
2. In the Graph Number field, enter 1 for the first graph or the appropriate number for the other graphs.
3. In the Row Number, enter i, the desired row index of the desired matrix.
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4. In the Column Number field, enter j, the desired column index of the desired matrix. by entering i in step 3 and j in step 4 we have chosen to plot the ij entry of the matrix to be selected in step 5.
5. From the Y Variable drop-down menu, choose the proper matrix and format of the plot. For example MatrixS Mag, will select the magnitude of Sij.
6. Click Continue.
7. From the Graph Color drop-down menu, choose the color you want for the graph line.
8. From the Graph Line Style drop-down menu, choose Solid.
9. From the Graph Symbol Sign drop-down menu, select Circle.
10. Set the Graph ID field to the desired label, for example Mag (Sij).
11. Click OK.
12. You may repeat the steps above to activate more graphs by changing the graph number in step2, and the i and j values in steps 3 and 4.
To generate the XY plot:
1. From the Display menu, choose XY Plots, Plot Curves,. The XYPLOT dialog box opens with a list of all available graphs.
2. From the Plot Graph drop-down menu, you may choose which curves you want to graph. “1: Yes” for example, indicates that you want to generate the first curve.
3. Press OK. The graph is displayed in the active window.
In addition to the scattering parameters, you may also view field distribution inmodel for a given frequency and a given port excited by its dominant mode. Treal and imaginary parts of the electric field, magnetic field and current densitimay be plotted.
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To plot the electrical field intensity:
1. From the Results menu, choose Plot > Electromagnetic. The ACTMAG dialog box opens.
2. In the Frequency Number (frequency step) field, enter the desired frequency step (step 1 is the lowest requested frequency).
3. In the Port Number field, enter the desired port number. This means that the solution to be used is the one where the specified port is excited with its dominant mode.
4. From the Entity Flag drop-down menu, choose Node.
5. From the Component drop-down menu, choose ER_R: Resultant Electrical Field Intensity (Real part).
6. Click Contour Plot, Vector Plot, Iso Plot, or Section Plot. Another dialog box will open based on the type of plot you select.
7. Set desired values and click OK. The default element number is the highest element label available in the database. The variable ELMAX may be entered instead of writing a number. Similarly RGMAX and NDMAX refer to the highest region and node labels in the database.
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✍ Other fields can be plotted similarly. The available components may be selected from the component drop-down menu in the ACTMAG dialog box as shown.
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Introduction
• This simple tutorial will guide you step-by-step through your first COSMOSHFS 3D analysis.
• This tutorial assumes that you have used Microsoft Windows before and know how to run programs, resize windows, and manipulate parts within COSMOSM GEOSTAR.
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What is GEOSTAR?
GEOSTAR is the basic pre- and postprocesser of COSMOSM products. You may create your geometry in GEOSTAR or import it from your favorite CAD system. Steps to Perform Electromagnetic Analysis
The following steps describe the general procedure for performing electromagnetic analysis:
To perform electromagnetic analysis:
• Create your geometry in GEOSTAR or use your favorite CAD system.
• If you are not using GEOSTAR to create your geometry, generate a COSMOS file or an IGES file from your CAD system,
• Mesh your model,
• Assign material from a library or specify the desired material properties,
• Specify ports and other loads and boundary conditions,
• Set your options for the electromagnetic analysis,
• Run the analysis, and
• Visualize the results in graphical and tabulated formats.
• COSMOSHFS 3-D provides coupling with thermal analysis, so you may continue to perform thermal analysis and visualize the results. Results of your electromagnetic analysis will still be available after running thermal analysis.
In this example, you will learn how to:
1. Import the geometry to GEOSTAR through a GEO file.
• The GEO file for this example was created in COSMOSWorks which is a fully integrated interface with SolidWorks for structural and thermal analyses.
2. Define element attributes,
3. Mesh the model,
4. Assign ports and apply other boundary conditions,
5. Set your analysis options,
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6. Run electromagnetic analysis, and
7. List the S-parameters, generate the S-parameters versus frequency plots, and visualize electric and magnetic fields.
Step 1: Importing the Geometry to GEOSTAR
To start a new problem in GEOSTAR:
1. Start GEOSTAR. GEOSTAR starts and the Open Problem Files dialog box opens.
2. In the Look in field, browse to the directory which you want to use for the new problem.
3. In the File name field, enter the name you like to give to the new problem.
4. Click Open. GEOSTAR sets the new problem. All related database files will be created in the specified folder.
To import the geometry file:
1. From the File menu, select Load. The File dialog box opens.
2. Click the Find... button and browse to the vprobs\HFS folder under your COSMOSM directory.
3. Choose the COAX.GEO file and click Open.
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4. Click OK. The file will be imported. The message window will echo the progress of loading the file. The geometry will be constructed on the screen. Reconstructing the model should take a few seconds for this model.
Step 2: Assigning Materials
To define material properties, you may select a material from a library, or you define material properties directly.
• There are two material libraries available for use with COSMOSM. The COSMOSM Material Library and the InfoDex Material Library. The COSMOSM Material Library is available by default. The InfoDex Material Library is more extensive and may be optionally acquired.
• You may also edit the COSMOSM Material Library to add more materials and electromagnetic properties as desired.
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To define material property set number 1:
1. From the PropSets menu, select Material Property. The Mprop dialog box opens.
2. In the message Material Property Set field, verify that 1 is entered.
3. From the Material Property Name drop down menu, choose PERMIT_R.
4. Click Continue.
5. In the Property Value field, enter 1.0 (for air).
6. Click OK. The first MPROP dialog box opens again to let you define more properties.
7. Click Cancel to exit the dialog box.
• It is recommended to list and examine material property sets before continuing with rest of the steps.
To List material property sets:
1. To list material property set 1, choose List Material Props from PropSets. The MPLIST dialog box opens.
2. Click OK to accept default numbers for beginning, ending, and the increment to list material set number 1. Each row lists a material property. NUXY is defined by default as 0.3 for structural models and is not used for electromagnetic analyses.
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• The letter A indicates that Material Set (Label) 1 is active. Any mesh generated at this point will assume the active material set.
Step 3: Meshing
Once the geometry and material specifications were determined, the model is ready to be meshed. You may want to list the default element size and change it if you like.
To list the default element size selected by the program:
1. From the Geometry menu, choose Polyhedra > List. The PHLIST dialog box opens.
2. Click OK. The element size is listed as shown.
• The default element size is 2.7711 (mm). All regions making up the polyhedron are listed. You may make it smaller for finer mesh or larger for a coarser mesh. The element size and tolerance list here will be used unless changed as shown next.
To change the default element size:
1. From the Meshing menu, choose Meshing Density > Polyhedron Elem Size. The PHDENSITY dialog box opens.
2. In the Beginning Polyhedron field, key in 1. There is only one polyhedron in this model.
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3. In the Ending Polyhedron field, key in 1.
4. In the Increment field, key in 1.
5. In the Average elements size field, key in 0.5.
6. In the Tolerance field, key in 0.001.
7. Click OK.
To Mesh the Model:
1. From the Meshing menu, select Auto-Mesh > Parts. The MA_PART dialog box opens.
2. In the Beginning Part field, verify that 1 is entered. There is only one part in this model.
3. In the Ending Part field, verify that 1 is entered.
4. In the Increment field, verify that 1 is entered.
5. In the Hierarchy check flag field, verify that No is active.
6. In the Element Order Flag filed, verify that Low order is selected.
• High order mesh is not used in COSMOSHFS 3D.
7. In the Number of Smoothing Iterations field, verify that 4 is entered.
8. Click OK. GEOSTAR starts building the mesh. After few seconds, the mesh will be generated. You will see the nodes as shown.
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nd
To view the mesh:
1. From the Meshing menu, choose Elements > Plot. The EPLOT dialog box opens.
2. In the Beginning Element field, enter 1.
3. In the Ending Element field, use the default number given in the dialog box. This is the highest element number in the model.
4. In the Increment field, verify that 1 is keyed in.
5. Click OK. The elements are plotted as shown.
Sep 4: Assigning Boundary Conditions
The purpose of this stage is to assign boundary conditions to the model.
• Metallic surfaces are assigned “Grounded Conductor” condition,
• The plane of symmetry is assigned “Perfect Mag. Conductor” conditions, a
• Ports are assigned the “Port” conditions.
To plot regions:
1. From the Geo Panel window, click the CLS button to clear the screen.
• You may also enter CLS in the Message window. You will be prompted to set a color. See the STATUS1 table for color code. 16 is white.
2. From the Geometry menu, choose Regions > Editing > Plot. The RGPLOT dialog box opens.
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3. In the Beginning Region field verify that 1 is keyed in.
4. In the Ending Region field, enter the maximum number of regions in the model (default). In this model there are 10 regions.
5. In the Increment field, verify that 1 is keyed in.
6. Click OK. The regions will be plotted on the screen.
To define ports:
Three ports will be defined for this structure as shown.
1. From the LoadsBC menu, choose E_Magnetic > Hi-freq_B-C > Define by Regions. The CBRG dialog box opens.
2. Point to region 6 and click the left button of the mouse. Region 6 highlights and 6 appears in the Beginning Region field.
3. Click once more to accept. If a wrong region highlights, reject using the right button until region 6 highlights and then click the left button to accept.
4. In the Boundary condition type drop down field, choose Port.
5. Click Continue. Another dialog box opens.
6. In the Port Number field, enter 1.
7. In the Ending Region field, input a large number, accept the default number 6.
8. In the Increment field, verify that 1 is keyed in.
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9. Click OK. Port 1 is defined as shown.
10. Repeat the steps above to define port 2 (Region 7) and port 3 (Region 8).
To assign perfect magnetic conductors to symmetrical regions:
Perfect Magnetic Conductor condition will be assigned to regions representing the plane of symmetry as shown. These are regions 1, 2, and 5 as shown in the figure.
1. From the LoadsBC menu, choose E_Magnetic > Hi-freq_B-C > Define by Regions. The CBRG dialog box opens.
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2. Point to region 1 and click the left button of the mouse. Region 1 highlights and 1 appears in the Beginning Region field.
3. Click once more to accept. If a wrong region highlights, reject using the right button until region 1 highlights and then click the left button to accept.
4. In the Boundary condition type drop down field, choose PMC: Perfect Mag. Conductor.
5. Click Continue. Another dialog box opens.
6. Point to region 2 and click the left button (or just type 2 in the Ending Region field). 2 appears in the Ending Region field.
7. In the Increment field, verify that 1 is keyed in.
8. Click OK. Perfect Magnetic Conductor condition is assigned to regions 1 and 2 as shown.
9. Repeat the steps above to assign a Perfect Mag. Conductor to region 5.
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To assign Ground Conductor condition to all other regions:
Ground Conductor condition will applied to the rest of the regions in the structure. Namely regions 3, 4, 9, and 10. You may continue the procedure above to apply ground conductor condition to regions 3 and 4 with an increment of 1 in one step and similarly repeat for regions 9 and 10. We will use the selection list utility instead.
The utility is particularly useful when many regions are to be assigned an identical condition. The regions (or other entities) are chosen in a selection set and then the condition is applied to all regions while the proper selection list is active. All regions mean all selected regions in this case. This procedure lets you apply the condition in one shot to all regions in the selection set. Alternatively, you may repeat the command to apply the condition. There are many ways to select and unselect entities to selection lists.
To create a selection list:
1. From the Control menu, choose Select > by Picking. The SELPIC dialog box opens.
2. From the Entity name for Selection Set 1 drop down menu, choose RG:Region.
3. Click Continue. The SELPIC dialog box opens.
4. Using the left mouse button click on one of the curved regions, the region will highlight. If the program highlights the desired region, click the left mouse button again to
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accept. The region number appears in the SELPIC dialog box. The first set includes all regions with electrical boundary conditions.
• If the wrong region was chosen, press the right mouse button to reject the selection, another region highlights. Keep rejecting until the proper region highlights then click the left button to accept.
5. Click in the Selection Entity RG 2 field and then click on region 4.
6. Similarly select regions 9 and 10. The SELPIC dialog box should look as shown in the figure.
7. Click OK. Selection list number 1 is created and activated. Now all regions means regions 3, 4, 9, and 10.
8. Click the CLS button to clear the screen.
9. From the Geometry menu, choose Regions > Editing > Plot. The RGPLOT dialog appears.
10. Press OK. Only the regions which belong to the activated set are displayed. While a selection list is active, GEOSTAR will only see the members that are in the selection list.
To assign Ground Conductor boundary condition:
1. From the LoadsBC menu, choose E_Magnetic > Hi-freq_B-C > Define by Regions. The CBRG dialog box opens.
2. Click Continue.
3. In the Beginning Region field, verify that 1 is keyed in.
4. In the Boundary condition type drop down field, choose Grounded Conductor.
5. Click Continue.
6. In the Conductor Number field, key in 1.
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7. In the Conductivity value field is set to 5.8e+007 value by default.
8. In the Relative permeability value field, verify that 1 is keyed in.
9. In the Ending Region field, key in RGMAX. This forces the system to assign the given BC to all the regions in the active selection list. RGMAX is a variable that refers to the highest region number in the database.
10. In the Increment field, verify that 1 is keyed in.
11. Click OK. The boundary condition is applied as shown.
To deactivate selection set number 1:
1. Click the Status3 button in the Geo Panel window. The Status Table 3 dialog box opens.
• Notice that Selection Set number 1 is active and that Region (RG) selection is on.
2. Click on ON twice to turn off the selection set.
3. Click Save. The selection set may be activated at any time later.
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4. To get help for the STATUS3 (Status of Selection Lists), click the Help icon.
Step 5: Performing Analysis
In this stage, we setup the solver and output options.
To setup analysis options:
1. From the Analysis menu, choose HiFreq_Emagnetic > Analysis Option. The A_HFRQEM dialog box opens.
2. From the Analysis option drop down field, choose SPARAMETER.
3. In the Units field verify that the 0:mm option is chosen.
4. Click OK.
To setup analysis options:
1. From the Analysis menu, choose HiFreq_EMagnetic > SParameters > Set Options. The HF_SPARSOLN dialog box opens.
2. In the Number of ports field, enter 3.
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3. In the Starting frequency (GHz) field, enter 1.
4. In the Ending frequency (GHz) field, enter 10.
5. In the Frequency increment (GHz) field, input 0.5
6. In the Impedance multiplier field, input 0.5.
7. You can keep the other entries as given by the default values.
8. Click Continue.
9. In the Port Number field, enter 1.
10. In the Number of Modes field, enter 1.
11. In the De-embedding Length field, enter 0.
12. Repeat steps 8 to 10 for port 2 and 3 as shown.
13. Click OK.
✍ For the number of ports you should enter the total number of ports in the mod-el. Also remember that ports must be numbered sequentially starting from 1.
To setup analysis options:
1. From the Analysis menu, choose Hi-Freq_EMagnetic > SParameters > Output Options. The HF_SPAROUT dialog box opens.
2. From the Circuit Simulator drop-down menu, choose Citifile, Compac, Touchstone, or None.
3. From the Output Option drop-down menu, select Nodal.
4. Click OK.
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To run analysis:
1. From the Analysis menu, choose HiFreq_EMagnetic > Run Analysis. Analysis starts.
2. After analysis is completed. Click the OK button in the Solution Complete window.
Step 6: Visualizing Results
Once the analysis is completed, you may visualize results in both graphical and tabular formats as shown below.
To list the S-Matrix:
1. From the Results menu, choose List > HF Emag Result. The HF_RESULT window opens, showing the Port Propagation Parameters and the Generalized S-Matrix at each requested frequency.
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To plot resultant electrical field:
1. From the Results menu, choose Plot > Electromagnetic. The ACTMAG dialog box opens.
2. In the Frequency number field, enter 1.
3. In the Port number field, enter 1.
4. In the Entity flag drop down field, choose Node.
5. From the Component drop down field, choose ER_R: Resultant Electrical Field Intensity (Real).
6. Click Contour Plot button. The MAGPLOT dialog box opens.
7. From the Line flag drop-down menu, choose 0: Fill.
8. In the Beginning Element field, enter 1.
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9. In the Ending Element field, keep the default number given by the program. That is the highest element label in the model.
10. In the Increment field, verify that 1 is keyed on.
11. Click OK. The results are displayed in the main window.
To generate a vector plot for the electric field:
1. Repeat steps 1 through 5 in the procedure above.
2. Click the Vector Plot button. The MAGPLOT dialog box opens.
3. In the Line flag drop-down menu, choose 2: Vector.
4. In the Beginning Node field, input 1.
5. In the Ending Node field, choose the default number. The default number is the highest node number in the model.
6. In the Increment field, verify that 1 is active.
7. In the Vector scale factor field, verify that 1 is keyed in.
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8. Click OK. The mesh and the vector plot are displayed.
To generate a section plot of the electric field:
1. Again repeat steps 1-5 as described above.
2. Click the Section Plot button. The SECPLOT dialog box opens.
3. From the Orientation of section planes drop-down menu, choose 0: X.
4. Click Continue.
5. In the Number of section planes field, enter 10.
6. From the Section plan positions drop-down menu, choose 0: Defaults.
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7. Click Continue. The field on the symmetrical planes is displayed.
To generate a graph of an S-Parameter Versus Frequency:
First we will activate and setup options for the first graph.
To activate the S11 element graph and setup options:
1. From the DISPLAY menu, choose XY_Plots > Activate Post Proc. The ACTXYPLOT dialog box appears.
2. In the Graph number field, enter 1.
3. In the Row number, enter 1.
4. In the Column number field, enter also 1. By entering 1 in steps 2 and 3 we have chosen to plot the S11 element of the S-Matrix.
5. From the Y variable drop-down menu, choose MatrixS_Mag, to display the magnitude of S11.
6. Click Continue. A dialog box opens for plotting options.
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7. From the Graph color drop-down menu, choose the desired color for the graph line.
8. From the Graph line style drop-down menu, choose t: Solid.
9. From the Graph symbol sign drop-down menu, choose t:Circle.
10. Set the Graph id field to R1_C1 or any desired name.
11. Click OK.
• You may continue the above procedure to activate other elements of the S-Matrix.
To generate the graph:
1. From the DISPLAY menu, choose XY Plots > Plot Curves. The XYPLOT dialog box opens.
2. From the Plot graph drop-down menu, choose 1: Yes.
3. Click OK. The graph is displayed as shown.
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Introduction
The Magic Tee, also called the Hybrid Tee junction, has important properties which make it suitable for microwave bridges, discriminators and many other applica-tions. In this example, we will analyze the Hybrid Tee junction shown below:
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The magic Tee junction has the following properties:
1. The S-parameter matrix is symmetrical for each mode.
2. Feeding in power to port 3 couples equal magnitude, opposite phase powers to ports 1 and 2. No power appears at port 4.
3. Feeding in power to port 4 couples equal magnitude, in-phase powers to ports 1 and 2. No power appears at port 3.
4. All 4 ports are completely matched.
These properties will be verified by the solution of this problem.
Step 1: Importing the Geometry to GEOSTAR
To start a new problem in GEOSTAR:
1. Start GEOSTAR. GEOSTAR starts and the Open Problem Files dialog box opens.
2. In the Look in field, browse to the directory in which you want to create the new problem.
3. In the File name field, enter the name you like to give to the new problem. In this example, we will use Magic-T
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4. Click Open. GEOSTAR sets the new problem. All related database files will be created in the specified folder.
To import the geometry file:
The geometry of this example can be easily created in GEOSTAR. We will however import a part file that was created by Solid/Works.
✍ We will show you how to create the geometry of this example in GEOSTAR at the end of this tutorial.
1. From the File menu, select Load. The File dialog box opens.
2. Click the Find... button and browse to the vprobs\HFS folder under your COSMOSM directory.
3. Choose the Magic-Tee.GEO file and click Open.
4. Click OK. GEOSTAR will start constructing the geometry. The message window will echo the commands in the GEO file (ASCII file). Reconstructing the model should take only a few seconds for this model.
Step 2: Assigning Materials
To define material properties, you may select a material from a library, or you define material properties directly.
To define material property set number 1:
1. From the PropSets menu, select User Material Lib. The User_Mat dialog box opens.
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2. In the message Material Property Set field, verify that 1 is entered.
3. From the Material Name drop down menu, choose Air.
4. Ignore the Unit Label field. It is not used in this library.
5. Click OK.
• It is recommended to list and examine material property sets before continuing with rest of the steps.
To List material property sets:
1. To list material property set 1, choose List Material Props from PropSets. The MPLIST dialog box opens.
2. Click OK to accept default numbers for beginning, ending, and the increment to list mate-rial set number 1. Each row lists a material property. NUXY is defined by default as 0.3 for structural models and is not used for electromagnetic analyses.
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• The letter A indicates that Material Set (Label) 1 is active. Any elements that you generate will assume the active material set.
Step 3: Meshing
Once the geometry and material specifications were determined, the model is ready to be meshed. You may want to list the default element size and change it if you like.
To list the default element size selected by the program:
1. From the Geometry menu, choose Polyhedra > List. The PHLIST dialog box opens.
2. Click OK. The element size is listed as shown.
• The default element size is 1 (mm). All regions making up the polyhedron are listed. You may make it smaller for finer mesh or larger for a coarser mesh. The element size and tolerance list here will be used unless changed as shown next.
To change the default element size:
1. From the Meshing menu, choose Meshing Density > Polyhedron Elem Size. The PHDENSITY dialog box opens.
2. In the Beginning Polyhedron field, key in 1 (or point to the model and click left button). There is only one polyhedron in this model.
3. In the Ending Polyhedron field, key in 1 (or point to the model and click left button).
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4. In the Increment field, verify that 1 is keyed in.
5. In the Average elements size field, key in 12.
✍ The selected element size of 12 mm satisfies the requirement that the element size may not exceed 1/10 of the wave length of the operating signal.
6. In the Tolerance field, key in 0.01.
7. Click OK.
To verify the new mesh density setting:
1. From the Geometry menu, choose Polyhedra > List. The PHLIST dialog box opens.
2. Click OK.
To Mesh the Model:
1. From the Meshing menu, select Auto-Mesh > Parts. The MA_PART dialog box opens.
2. In the Beginning Part field, verify that 1 is entered. There is only one part in this model.
3. In the Ending Part field, verify that 1 is entered.
4. In the Increment field, verify that 1 is entered.
5. In the Hierarchy check flag field, verify that No is active.
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6. In the Element Order Flag filed, verify that Low order is selected.
• High order mesh is not used in COSMOSHFS 3D.
7. In the Number of Smoothing Iterations field, verify that 4 is entered.
8. Click OK. GEOSTAR starts building the mesh. In few seconds, the mesh will be generated. You will see the nodes as shown.
To view the mesh:
1. From the Meshing menu, choose Elements > Plot. The EPLOT dialog box opens.
2. In the Beginning Element field, enter 1.
3. In the Ending Element field, use the default number given in the dialog box. This is the highest element number in the model.
4. In the Increment field, verify that 1 is keyed in.
5. Click OK. The elements are plotted as shown.
Sep 4: Assigning Boundary Conditions
The purpose of this stage is to assign boundary conditions to the model.
• Metallic surfaces are assigned “Grounded Conductor” condition, and each the 4 ports is assigned the “Port” condition.
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To plot regions:
1. From the Geo Panel window, click the CLS button to clear the screen.
• You may also enter CLS in the Message window. You will be prompted to set a color. See the STATUS1 table for color code. 16 is white.
2. From the Geometry menu, choose Regions > Editing > Plot. The RGPLOT dialog box opens.
3. In the Beginning Region field verify that 1 is keyed in.
4. In the Ending Region field, enter the maximum number of regions in the model (default). In this model there are 18 regions.
5. In the Increment field, verify that 1 is keyed in.
6. Click OK. The regions will be plotted on the screen.
To define ports:
Four ports will be defined for this structure as shown.
1. From the LoadsBC menu, choose E_Magnetic > Hi-freq_B-C > Define by Regions. The CBRG dialog box opens.
2. Point to region 9 and click the left button of the mouse. Region 9 highlights and 9 appears in the Beginning Region field.
Port 1
Port 2Port 3
Port 4
Region 9
Region 7
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3. Click once more to accept. If a wrong region highlights, reject using the right button until region 9 highlights and then click the left button to accept.
4. In the boundary condition type drop down field, choose Port.
5. Click Continue. Another dialog box opens.
6. In the Port Number field, enter 1.
7. In the Ending Region field, accept the default region number (9).
8. In the Increment field, verify that 1 is keyed in.
9. Click OK. Port 1 is defined as shown.
10. Repeat the steps above to define port 2 (Region 7) and port 3 (Region 18). Do not forget to type in the proper port number in the Port Number field of the CBRG dialog box.
11. Port 4 must be defined using the 3 regions which make it up. You can repeat the steps for each of the 3 regions as shown above, or you may define the port in 2 steps by applying the condition to 2 of the regions using the proper beginning, ending and then defining it for the third region.
Region 1
Region 2
Region 12
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For example, you may use 1, 2, 1, or 1, 12, 11, etc. for the beginning region, ending region, and increment. Note that selecting 12, 1, and 11 for the beginning region, ending region, and increment will also apply the condition to regions 1 and 12.
✍ If you define Port 4 in 2 or 3 steps, make sure to enter 4 for the port number each time.
✍ Instead, you may use selection lists to apply boundary conditions to many entities in one step. This will be demonstrated in the next step.
To assign Ground Conductor condition to all other regions:
Ground Conductor condition will be applied to all regions except the ones we used to define the ports. You may continue the procedure above to apply ground conductor condition to all these regions. Instead we will use the selection list utility.
About Selection Lists
Selection lists are very useful during pre- and post-processing. A selection list acts like a filter. When a selection list is active for an entity, GEOSTAR will only recognize the members of this entity that are on the selection list. Up to 10 selection lists may be created for each entity. There are several convenient ways to select and unselect entities including specifying labels, picking using the pointing device, specifying a window, using reference (selecting members of entity associated with another) entity, specifying a window in 3D space, and selecting elements based on their attributes.
Refer to the Control, Select, and Unselect menus for details). In this example, we will create a selection list for regions by unselecting the regions that we used for ports. We will then apply the ground conductor condition to all regions which will be interpreted by GEOSTAR as the regions on the selection list.
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To create a selection list:
1. From the Control menu, choose Unselect > by Picking. The UNSELPIC dialog box opens.
2. From the Entity name for Selection Set 1 drop down menu, choose RG: Region.
3. Click Continue. The UNSELPIC dialog box opens.
4. Using the left mouse button click on region 9 (port 1), the region will highlight. If the program highlights the desired region, click the left mouse button again to accept. Otherwise click the right button to reject until the proper region highlights and then accept by clicking the left button.
5. Keep selecting regions used to define the ports (regions 9, 7, 18, 1, 2, and 12) as shown in the figure.
6. Click OK. Selection list number 1 is created and activated. Now GEOSTAR filters out the specified region from the list of regions that it recognizes.
7. Click the CLS button to clear the screen.
8. From the Geometry menu, choose Regions > Editing > Plot. The RGPLOT dialog appears.
9. Press OK. Only the regions which belong to the active set are plotted. While a selection list is active, GEOSTAR will only see the members of the entity that are in the selection list.
To assign Ground Conductor boundary condition:
1. From the LoadsBC menu, choose E_Magnetic > Hi-freq_B-C > Define by Regions. The CBRG dialog box opens.
2. Click Continue.
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3. In the Beginning Region field, verify that 1 is keyed in.
4. In the Boundary condition type drop down field, choose Grounded Conductor.
5. Click Continue.
6. In the Conductor Number field, key in 1. In the Conductivity value field, verify that 5.8e+007 is keyed in.
7. In the Relative permeability value field, verify that 1 is keyed in.
8. In the Ending Region field, key in RGMAX. This instructs GEOSTAR to assign the given BC to all the regions in the active selection list. RGMAX is a variable that refers to the highest region number in the database.
9. In the Increment field, verify that 1 is keyed in.
10. Click OK. The boundary condition is applied as shown.
To deactivate selection set number 1:
1. Click the STATUS3 button in the GeoPanel window. The Status Table 3dialog box opens.
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• Notice that Selection Set number 1 is active and that Region (RG) selection is on.
2. Click on ON (under RG) twice to turn off the region selection set.
3. Click Save. The selection set may be activated at any time later.
4. To get help for the STATUS3 (Status of Selection Lists), click the Help icon.
Step 5: Performing Analysis
In this stage, we setup the solver and output options.
To setup analysis options:
1. From the Analysis menu, choose HiFreq_Emagnetic > Analysis Option. The A_HFRQEM dialog box opens.
2. From the Analysis option drop down field, choose SPARAMETER.
3. In the Units field, verify that the 0: mm option is chosen.
4. Click OK.
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To setup analysis options:
1. From the Analysis menu, choose HiFreq_EMagnetic > SParameters > Set Options. The HF_SPARSOLN dialog box opens.
2. In the Number of ports field, enter 4.
3. In the Starting frequency (GHz) field, enter 1.8.
4. In the Ending frequency (GHz) field, enter 2.25.
5. In the Frequency increment (GHz) field, input 0.05.
6. In the Impedance multiplier field, input 0.5.
7. You can keep the other entries as given by the default values.
8. Click Continue.
9. The HF_SPASOLN window opens. Click OK to accept the default values.
✍ For the number of ports you should enter the total number of ports in the model. Also remember that ports must be numbered sequentially starting from 1.
To setup analysis options:
1. From the Analysis menu, choose Hi-Freq_EMagnetic > SParameters > Output Options. The HF_SPAROUT dialog box opens.
2. From the Circuit Simulator drop-down menu, choose Touchstone.
3. From the Output Option drop-down menu, select Nodal.
4. Click OK.
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To run analysis:
5. From the Analysis menu, choose HiFreq_EMagnetic > Run Analysis. The analysis starts.
6. After analysis is completed. Click OK in the Solution Complete window.
Step 6: Visualizing Results
Once the analysis is completed, you may visualize results in both graphical and tabular formats as shown below.
To list the S-Matrix:
1. From the Results menu, choose List > HF Emag Result. The HF_RESULT window opens, showing the Port Propagation Parameters and the Generalized S-Matrix at each requested frequency.
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To plot resultant electric field intensity produced by exciting a port at 2.0 GHz:
1. First we create four windows for the four plots. To do so, choose Create from the Windows menu. Repeat this process for three times. To tile the windows, choose Tile from the Windows menu.
2. Activate the first window simply by clicking in it.
3. From the Results menu, choose Plot > Electro-magnetic. The ACTMAG dialog box opens.
4. In the Frequency number field, enter 5 (corresponds to a frequency of 2 GHz).
5. In the Port number field, enter 1.
6. In the Entity flag drop down field, choose Node.
7. From the Component drop down field, choose ER_R: Resultant Electrical Field Intensity (Real).
8. Click Contour Plot button. The MAGPLOT dialog box opens.
9. From the Line flag drop-down menu, choose 0: Fill.
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10. In the Beginning Element field, enter 1. In the Ending Element field, keep the default number given by the program. That is the highest element label in the model.
11. In the Increment field, accept 1.
12. Click OK. The plot are in generated in the active window
13. Repeat steps 2 through 11 for the other three windows to produce the plots corresponding to ports 2, 3, and 4. Make sure that you enter the proper port number in step 5 each time.
✍ It is instructive to notice the electric field distribution inside the T-junction. For example, when Port 4 is excited with 2 GHz field, a standing wave is cre-ated at Port 4 waveguide due to the reflection of the applied field at the junc-tion. You may also notice the equi-amplitude fields at Ports 1 and 2 waveguides and, most importantly, the zero-field at Port 3 waveguide.
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To generate a section plot of the electric field:
1. Again repeat steps 1-5 as described above.
2. Click the Section Plot button. The SECPLOT dialog box opens.
3. From the Orientation of section planes drop-down menu, choose 0: X.
4. Click Continue.
5. In the Number of section planes field, enter 10.
6. From the Section plan positions drop-down menu, choose 0: Defaults. Click Continue.
7. Section plot is generated in the active window. Repeat same steps again to generate the other sectional plots. Make sure to enter the proper port number each time.
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✍ For the section plot generated for Port 4, it is more informative to change the orientation of the section planes to be parallel to the Z-axis. This would need to change only the Orientation of section planes field in the SECPLOT dia-log box to Z-axis option.
To generate X-Y plots for the magnitude and phase of the first element in the scattering matrix versus frequency:
To plot magnitude versus frequency
1. From the Display menu choose XY_Plots > Activate post-Proc. The ACTXYPOST dialog box opens.
2. In the Graph number field, enter 1.
3. In the Row number field, enter 1.
4. In the Column number field, enter 1.
5. From the Y variable drop-down menu choose MatrixS_Mag option. Then click Continue.
6. The ACTXYPOST dialog box opens. Accept the default values and click OK.
7. To display the plot, choose XY_Plots > Plot Curves from the Display menu. The plot is generated.
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To plot phase versus frequency:
1. From the Display menu choose XY_Plots > Activate Post-Proc. The ACTXYPOST dialog box opens.
2. In the Graph number field, enter 1.
3. In the Row number field, enter 1.
4. In the Column number field, enter 1.
5. From the Y variable drop-down menu choose MartixS_Phase option and click Continue.
6. The ACTXYPOST dialog box opens. Accept the default values and click OK.
7. To display the plot, choose XY_Plots > Plot Curves from the Display menu. The plot is generated.
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A. Material Constants
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Table A.1 Dielectric\Constant and Conductivity of Some Materials (at 25°C)
