HFSS Waveguide Combiner

8/16/2019 HFSS Waveguide Combiner

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Getting Started with HFSS:

A 20 GHz Waveguide Combiner

ANSYS, Inc.

275 Technology Drive

Canonsburg, PA 15317

Tel: (+1) 7247463304

Fax: (+1) 7245149494

General Information: [email protected]

Technical Support: [email protected]

May 2010

Inventory ********


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The information contained in this document is subject to change without notice.

Ansoft makes no warranty of any kind with regard to this material, including,

but not limited to, the implied warranties of merchantability and fitness for a

particular purpose. Ansoft shall not be liable for errors contained herein or for

incidental or consequential damages in connection with the furnishing, perfor-

mance, or use of this material.

© 2010 SAS IP Inc., All rights reserved.

ANSYS, Inc.

275 Technology Drive

Canonsburg, PA 15317

USA

Tel: (+1) 724-746-3304

Fax: (+1) 724-514-9494

General Information: [email protected]

Technical Support: [email protected]

HFSS and Optimetrics are registered trademarks or trademarks of SAS IP Inc.. All

other trademarks are the property of their respective owners.

New editions of this manual incorporate all material updated since the previous

edition. The manual printing date, which indicates the manual’s current edition,

changes when a new edition is printed. Minor corrections and updates that are

incorporated at reprint do not cause the date to change.

Update packages may be issued between editions and contain additional and/or

replacement pages to be merged into the manual by the user. Pages that are

rearranged due to changes on a previous page are not considered to be revised.

Edition Date SoftwareVersion

1 Jan 2006 10.0

2 May 2007 11.0

3 February 2009 12.0

4 September 2010 13.0


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Getting Started with HFSS: A Dielectric Resonator Antenna Problem

ii i

Conventions Used in this Guide

Please take a moment to review how instructions and other useful infor-mation are presented in this guide.

• Procedures are presented as numbered lists. A single bullet indicatesthat the procedure has only one step.

• Bold type is used for the following:

- Keyboard entries that should be typed in their entirety exactly asshown. For example, “copy file1” means to type the word copy, totype a space, and then to type file1.

- On-screen prompts and messages, names of options and text boxes,and menu commands. Menu commands are often separated by car-

ats. For example, click HFSS>Excitations>Assign>Wave Port.

- Labeled keys on the computer keyboard. For example, “PressEnter” means to press the key labeled Enter.

• Italic type is used for the following:

- Emphasis.

- The titles of publications.

- Keyboard entries when a name or a variable must be typed in placeof the words in italics. For example, “copy file name” means totype the word copy, to type a space, and then to type a file name.

• The plus sign (+) is used between keyboard keys to indicate that you

should press the keys at the same time. For example, “PressShift+F1” means to press the Shift key and the F1 key at the sametime.

• Toolbar buttons serve as shortcuts for executing commands. Toolbarbuttons are displayed after the command they execute. For example,

“On the Draw menu, click Line ” means that you can click theDraw Line toolbar button to execute the Line command.

Alternatemethodsor

tipsarelistedintheleft

margininblueitalic

text.


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Getting Started with HFSS: A Dielectric Resonator Antenna Problem

iv

Getting Help

Ansys Technical Support

To contact Ansys technical support staff in your geographical area,please log on to the Ansys corporate website, https://www1.anssys.com.You can also contact your Ansoft account manager in order to obtain thisinformation.

All Ansoft software files are ASCII text and can be sent conveniently by e-mail. When reporting difficulties, it is extremely helpful to include veryspecific information about what steps were taken or what stages thesimulation reached, including software files as applicable. This allowsmore rapid and effective debugging.

Help Menu

To access online help from the HFSS menu bar, click Help and select fromthe menu:

• Contents - click here to open the contents of the online help.

• Seach - click here to open the search function of the online help.

• Index - click here to open the index of the online help.

Context-Sensitive Help

To access online help from the HFSS user interface, do one of the follow-ing:

• To open a help topic about a specific HFSS menu command, press

Shift+F1, and then click the command or toolbar icon.• To open a help topic about a specific HFSS dialog box, open the dia-

log box, and then press F1.


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Contents-1

Table of Contents

1. Introduction

TheSampleProblem ............................. 1-2

ResultsforAnalysis .............................. 1-3

2. Creating the New Project

OverviewoftheInterface.......................... 2-2

CreatetheNewProject ........................... 2-4

AddtheNewProject ............................. 2-4

InsertanHFSSDesign........................... 2-4

AddProjectNotes ............................... 2-5

SavetheProject ................................2-5

3. Creating the Model

SelecttheSolutionType.......................... 3-2

SetUptheDrawingRegion ........................ 3-3

Overviewofthe3DModelerWindow................ 3-3

CoordinateSystemSettings.......................3-4

UnitsSettings................................... 3-4

GridSettings ................................... 3-4

TransparencySetting ............................ 3-5

CreatetheGeometry ............................. 3-6

DrawtheWaveguideCombiner .................... 3-6

Table of Contents


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Getting Started wi th HFSS: A 20 Ghz Waveguide Combiner

Contents-2

DrawthePolyline1Object........................ 3-6

VerifythePointsofPolyline1 ...................... 3-10DuplicateandMirrorPolyline1..................... 3-12

UnitePolyline1andPolyline1_1 ................... 3-13

RenamePolyline1 .............................. 3-15

ModifytheWaveguide’sAttributes.................. 3-15

SweeptheWaveguide ........................... 3-17

4. Setting Up the Problem

SetUpBoundariesandExcitations................. 4-2

BoundaryConditions ............................. 4-2

ExcitationConditions............................. 4-2 AssignBoundaries............................... 4-3

AssignaFiniteConductivityBoundarytotheSide

Faces ........................................ 4-3

AssignaFiniteConductivityBoundarytotheBottom

Face......................................... 4-7

AssignaPerfectESymmetryBoundarytotheTop

Face......................................... 4-10

AssignExcitations ............................... 4-13

AssignWavePort1 ............................. 4-14

AssignWavePort2 ............................. 4-15

AssignWavePort3 ............................. 4-16

AssignWavePort4 ............................. 4-17

ModifytheImpedanceMultiplier ................... 4-18

VerifyAllBoundaryandExcitationAssignments....... 4-19

5. Generating A Solution

SpecifySolutionOptions.......................... 5-2

AddaSolutionSetup ............................. 5-2

AddaDiscreteFrequencySweep................... 5-5

ValidatetheProjectSetup ......................... 5-8

GeneratetheSolution ............................ 5-9

ViewtheSolutionData ........................... 5-10


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Getting Started wit h HFSS: A 20 Ghz Waveguide

Contents-3

ViewtheProfileData ............................ 5-10

ViewtheConvergenceData ...................... 5-12ViewtheMatrixData ............................ 5-13

6. Analyzing the Solution

CreateModalS-ParametersReports ................ 6-2

CreateanS-ParametersReportofS11,S12,S13,

andS14....................................... 6-2

CreateanS-ParametersReportofS12andS14 ....... 6-3

CreateFieldOverlayPlots ......................... 6-5

ScaletheMagnitudeandPhaseforthePorts ......... 6-5

CreateaMagEFieldOverlayCloudPlot .............6-6CreateaPhaseAnimationoftheMagECloudPlot.....6-7


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Contents-4


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Introduction 1-1

1 Introduction

This Getting Started guide is written for HFSS beginners as well asexperienced users who are using version 13 for the first time. Thismanual guides you through the setup, solution, and analysis of a two-way, low-loss waveguide combiner.

By following the steps in this guide, you will learn how to perform thefollowing tasks in HFSS:

Draw a geometric model.

Modify a model’s design parameters.

Assign variables to a model’s design parameters.

Specify solution settings for a design. Validate a design’s setup.

Run an HFSS simulation.

Create a 2D x-y plot of S-parameter results.

Create a field overlay plot of results.

Create a phase animation of results.


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1-2 Introduction

The Sample Problem

For this problem, the waveguide combiner is a standard WR42 modelwith a four-port combining junction. Each waveguide is 420 mils wideand 170 mils high. This type of waveguide combiner is used to combinethe output power of two 20 GHz solid state power amplifiers (SSPA) witha very compact size and low insertion loss.

The outputs of the SSPAs are fed into Ports 2 and 4 of the waveguide witha 90-degree out-of-phase separation to steer the output power of theamplifiers to port 1. Port 3 of the waveguide is the isolated port wherethe impedance mismatch at the output (port 1) is absorbed.

This problem is also described and analyzed in the following:

Arcioni, Paolo, Perregrini, Luca, Bonecchi, Fulvio, “Low-Loss Waveguide

Combiners for Multidevice Power Amplifiers,” The Second InternationalConference on Electromagnetics in Aerospace Applications, September1991.

The geometry for this waveguide combiner problem is shown below:

Port 4

Port 2

Combiningjunction Port 3

Waveguidesection

Port 1


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Getting Started wit h HFSS: A 20 Ghz Waveguide Combiner

Introduction 1-3

Results for Analysis

After setting up the waveguide combiner model and generating a solu-tion, you will:

• Create Modal S-parameter reports.• Create a field overlay cloud plot of the magnitude of E.• Create an animation of the mag-E cloud plot.

Time It should take you approximately 2 hours to work through the entireguide.


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1-4 Introduction


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Creating the New Project 2-1

2 Creating the New Project

This guide assumes that HFSS has already been installed as describedin the Installation Guide.

Your goals in this chapter are as follows:

Create a new project.

Add an HFSS design to the project.

Note If you have not installed the software or you are not yet set up to runthe software, STOP! Follow the instructions in the Installation Guide.

Time It should take you approximately 10 minutes to work through thischapter.


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2-2 Creating the New Project

Overview of the Interface

Below is an overview of the major components of the HFSS interface.

Project Manager

window

Displays details about all open HFSS projects. Each projecthas its own project tree, which ultimately includes ageometric model and its boundaries and excitations,material assignments, analysis setups, and analysis results.

Message Manager

window

Displays error, informational, and warning messages for theactive project.

Progress window Displays solution progress information.

Menu bar

Toolbars

Status bar

History tree

Project Managerwindow and the

project tree.

Message Managerwindow

Progresswindow

Propertieswindow

3D Modeler window


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Properties window Displays the attributes of a selected object in the active

model, such as the object’s name, material assignment,orientation, color, and transparency.

Also displays information about a selected command thathas been carried out. For example, if a circle was drawn,its command information would include the command’sname, the type of coordinate system in which it wasdrawn, the circle’s center position coordinates, the axisabout which the circle was drawn, and the size of itsradius.

3D Modeler

window

Displays the drawing area of the active model, along withthe history tree.

History tree Displays all operations and commands carried out on theactive model, such as information about the model’sobjects and all actions associated with each object, andcoordinate system information.

Menu bar Provides various menus that enable you to perform all ofthe HFSS tasks, such as managing project files, customizingthe desktop components, drawing objects, and setting andmodifying all project parameters.

Toolbars Provides buttons that act as shortcuts for executing variouscommands.

Status bar Shows current actions and provides instructions.

Also, depending on the command being carried out, thestatus bar can display the X, Y, and Z coordinate boxes, theAbsolute/Relative pull-down list to enter a point’sabsolute or relative coordinates, a pull-down list to specifya point in cartesian, cylindrical, or spherical coordinates,and the active model’s unit setting.


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Create the New Project

The first step in using HFSS to solve a problem is to create a project inwhich to save all the data associated with the problem. By default,opening HFSS 12 creates a new project named Projectn and inserts a newproject named HFSSDesignn, where n is the order in which each wasadded to the current session.

You can also create a new project and insert a design manually as fol-lows.

Add the New Project

To add a new HFSS project:

• Click File>New.

A new project is listed in the project tree in the Project Manager win-dow. It is named projectn by default, where n is the order in which theproject was added to the current session. Project definitions, such asboundaries and material assignments, are stored under the project name

in the project tree.

Insert an HFSS Design

The next step for this waveguide combiner problem is to insert an HFSSdesign into the new project. By default, a design named HFSSDesignnwith the type as [Driven Modal] appears for the current project.

To manually insert an HFSS design into the project, do one of the follow-ing:

• Click Project>Insert HFSS Design.

• Right-click on the project name in the Project Manager window, and


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then click Insert>Insert HFSS Design on the shortcut menu.

• Click the Insert HFSS Design toolbar button .A 3D Modeler window appears on the desktop and an HFSS Design icon isadded to the project tree, as shown below:

Add Project Notes

Next, enter notes about your project, such as its creation date and adescription of the device being modeled. This is useful for keeping a run-ning log on the project.

To add notes to the project:1 Click Edit>Edit Notes.

The Design Notes window appears.

2 Click in the window and type your notes, such as a description of the

model and the version of HFSS in which it is being created.

3 Click OK to save the notes with the current project.

Save the ProjectNext,saveandnamethenewproject.

Note To edit existing project notes, double-click Notes in the project tree.The Design Notes window appears, in which you can edit the project’snotes.


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ItisimportanttosaveyourprojectfrequentlybecauseHFSSdoes not

automaticallysavemodels.Savingfrequentlyhelpspreventthelossofyourworkifaproblemoccurs.

To save the new project:

1 Click File>Save As.

The Save As dialog box appears.

2 Use the file browser to find the directory where you want to save the

file.

3 Type the name wg_combiner in the File name text box.

4 In the Save as type list, click Ansoft HFSS Project (.hfss) as the cor-

rect file extension for the file type.

When you create an HFSS project, it is given a .hfss file extension bydefault and placed in the Project directory. Any files related to that

project are stored in that directory.

5 Click Save.

HFSS saves the project to the location you specified.

Now, you are ready to draw the objects for this waveguide combinerproblem.

Note For further information on any topic in HFSS, such as coordinatesystems and grids or 3D Modeler commands or windows, you can viewthe context-sensitive help:

• ClicktheHelpbuttoninapop-upwindow.

• PressShift F1.Thecursorchangesto?.Clickontheitemwithwhichyouneedhelp.

• Press F1. This opens the Help window. If you have a dialog open, the Helpopens to a page that describes the dialog.

• UsethecommandsfromtheHelpmenu.


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Creating the Model 3-1

3 Creating the Model

This chapter shows you how to create the geometry for the wave-guide combiner problem described earlier. Your goals are as follows:

Select the solution type.

Set up the drawing region.

Create the objects that makes up the waveguide combiner model,which includes:

a. Drawingtheobjects.

b. Assigningcolorandtransparencytotheobjects.

c. Assigningmaterialstotheobjects.

You are now ready to start drawing the geometry.

Time It should take you approximately 30 minutes to work through thischapter.


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3-2 Creating the Model

Select the Solution Type

Before you draw the waveguide combiner model, first you must specify asolution type. The default solution type is set in theTools>Options>HFSS Options dialog. As you set up your model, theavailable options will depend on the design’s solution type.

To specify the solution type:

1 Click HFSS>Solution Type.

The Solution Type dialog box appears.

2 Select the Driven Modal solution type.

The possible solution types are described below.

3 Click OK to apply the Driven Modal solution type to your design.

Driven Modal For calculating the mode-based S-parameters of passive,

high-frequency structures such as microstrips,waveguides, and transmission lines, which are “driven”by a source.

DrivenTerminal

For calculating the terminal-based S-parameters ofpassive, high-frequency structures with multi-conductortransmission line ports, which are “driven” by a source.

Results in a terminal-based description related tovoltages and currents.

Eigenmode For calculating the eigenmodes, or resonances, of astructure. The Eigenmode solver finds the resonantfrequencies of the structure and the fields at those

resonant frequencies.


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Set Up the Drawing Region

The next step is to set up the drawing region. For this waveguide com-biner problem, you will decide the coordinate system, and specify theunits and grid settings.

Overview of the 3D Modeler Window

The area containing the model is called the drawing region. Models aredrawn in the 3D Modeler window, which appears on the desktop whenyou insert a design into the project.

As shown below, the 3D Modeler window consists of a grid and a historytree. The grid is an aid to help visualize the location of objects. For moreinformation about the grid, see “Grid Settings” on page 3-4.

The history tree displays all operations and commands carried out on theactive model. For more information about the history tree, see “Historytree” on page 2-3.

History

Grid


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Coordinate System Settings

For this waveguide combiner problem, you will use the fixed, defaultglobal coordinate system (CS) as the working CS. This is the current CSwith which objects being drawn are associated.

HFSS has three types of coordinate systems that let you easily orient newobjects: a global coordinate system, a relative coordinate system, and a

face coordinate system. Every CS has an x-axis that lies at a right angleto a y-axis, and a z-axis that is normal to the xy plane. The origin (0,0,0)of every CS is located at the intersection of the x-, y-, and z-axes.

Units Settings

Now, specify the drawing units for your model. For this waveguide com-biner problem, set the drawing units to mils (1 mil = One thousandth ofan inch).

To set the drawing units:1 Click Modeler>Units.

The Set Model Units dialog box appears.

2 Select mil from the Select units drop-down list, and ensure Rescale

to new units is cleared.

If selected, the Rescale to new units option automatically rescales

the grid spacing to units entered that are different than the set draw-

ing units.

3 Click OK to accept mils as the drawing units for this model.

Grid Settings

The grid displayed in the 3D Modeler window is a drawing aid that helpsto visualize the location of objects. The points on the grid are divided bytheir local x-, y-, and z-coordinates and grid spacing is set according tothe current project’s drawing units.

Global CS The fixed, default CS for each new project. It cannot be editedor deleted.

Relative

CS

A user-defined CS. Its origin and orientation can be set relative

to the global CS, relative to another relative CS, or relative toa geometric feature. Relative CSs enable you to easily drawobjects that are located relative to other objects.

Face CS A user-defined CS. Its origin is specified on a planar objectface. Face CSs enable you to easily draw objects that arelocated relative to an object’s face.


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For this waveguide combiner project, it is not necessary to edit any of

the grid’s default properties.To edit the grid’s properties, click Grid Settings on the View menu tocontrol the grid’s type (cartesian or polar), style (dots or lines), density,spacing, or visibility.

Transparency Setting

Set the default transparency for objects to 0.4.

To set the default transparency for new objects:

1 Click Tools>Options>Modeler Options.

The 3D Modeler Options window appears.

2 Click the Display tab.

3 If it is not already there, move the Default transparency slider to thefifth line (which is a transparency of 0.4), and then click OK .


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Create the Geometry

The geometry for this waveguide combiner consists of a single standardWR42 waveguide combiner object with a four-port, low-loss combiningjunction. Each waveguide is 420 mils wide and 170 mils high.

Since this model will be symmetric about the xz plane, first you willdraw the left-half of the structure and then duplicate it to create theright-side and complete the model.

To help reduce the size of this model, you will assign a perfect E symme-try boundary to the top face of the waveguide combiner to split itsheight in half (85 mils). This enables you to model only part of a struc-ture, thereby shortening the solution time.

For a detailed description about this waveguide combiner, see “The Sam-

ple Problem” on page 1-2.

Draw the Waveguide Combiner

You will create the waveguide combiner by first drawing its left-side andthen duplicating it to create the right-side of the model. Then, you willunite these 2-dimensional (2D) sheet objects (geometric objects contain-ing surface area but no volume) to make the single waveguide combinerobject. Next, you will sweep this object in the z-axis direction to createthe final 3D waveguide combiner.

Draw the Polyline1 Object

The first object you will draw is the left-half of the waveguide combiner,

which is created by drawing a polyline object consisting of 25 points.This will result in a 2D sheet object with a default name of Polyline1.

To draw Polyline1, you can use one of two methods.

Method 1: Draw a Polyline and Edit the Point Coordinates

The first, more forgiving method, is to begin by drawing a closed polylinewith 25 mouse clicks. You then use the basic approach described in theVerify the Points of a Polyline section to enter the correct coordinatesfor each point via the CreateLine properites window for each segment.

1 Click Draw>Line, or click the Draw line button on the toolbar.

2 Click a point at the origin, and increment a count of clicks from the

initial click to 25, for convenience following a counter-clockwise

movement that places the last click back at the origin.

3 Right-click to display the shortcut menu.

4 Click Done.


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This displays the properties window for the newly created polyline in

the docked properties window.5 Go to the Verify the Points of a Polyline section and follow the pro-

cedure to enter the correct coordinates for each segment.

Method 2: Enter the Point Coordinates for Each Point

The second method is more direct, but is less forgiving. In this case, youenter the point coordinates for each vertice of the 25 segment polylinein sequence:

1 Click Draw>Line, or click the Draw line button on the toolbar.

The status bar now prompts you to enter the first point of the

polyline.

2 Press the Tab key to move to the X box, and then select the first pointof the line by entering the following values in the coordinate boxes,

pressing Tab to move to the next coordinate text box:

3 Press the Enter key to accept this point.

You can delete the last point you entered by right-clicking in the 3D

Modeler window and then clicking Back up on the shortcut menu.

4 Continue with this same method to enter the following 24 points that

remain:

X coordinate 0

Y coordinate 0

Z coordinate 0

Note Skip the first point, since you just entered its coordinates (0, 0, 0) inthe preceding steps.

Point X Coordinate Y Coordinate Z Coordinate

1 0 0 0

2 0 -53 0

3 -147 -53 0

4 -474 -367 0

5 -474 -710 0

6 -944 -710 0

7 -944 -1130 0

8 -369 -1130 0


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5 Right-click in the 3D Modeler window, and click Close Polyline on

the shortcut menu.

The 2D polyline object appears in the drawing region.

The object is named Polyline1 by default, as displayed in the Proper-

ties window.

9 -27 -792 0

10 -27 -467 011 83 -467 0

12 146 -433 0

13 255 -433 0

14 337 -411 0

15 427 -411 0

16 506 -523 0

17 682 -523 0

18 915 -683 0

19 1562 -683 0

20 1562 -263 0

21 1073 -263 0

22 858 -53 0

23 612 -53 0

24 612 0 0

25 0 0 0

Note Objects are automatically selected immediately after being drawn so

that you can instantly view the selected object’s default attributes inthe Properties window.


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6 Press Ctrl+D to fit the object in the drawing region.

Your completed left-half of the waveguide combiner should appear inthe 3D Modeler window, as shown below:


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Verify the Points o f Polyline1

Before you duplicate the object Polyline1 to create the right-side of thewaveguide combiner, it is important that you make sure all the pointsyou entered are correct.

The image below displays all the point locations required for the objectPolyline1:

To verify the points:

1 In the history tree, click the plus (+) symbol to the left of Sheets to

expand the tree structure to see Unassigned. Expand the structure

under Unassigned to see Polyline1. Expand the structure under

Polyline1 to see Create Polyline. Expand the structure under


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Polyline1 to see the twenty-five CreatePolyline objects.

2 Click the first CreateLine object in the list to view the coordinate

values that you entered for point 1 (0, 0, 0) and point 2 (0, -53, 0).

These values are displayed in the Properties window, as shownbelow:

3 Verify that the values for these points are correct.

Point X Coordinate Y Coordinate Z Coordinate

1 0 0 0

2 0 -53 0

3 -147 -53 0

4 -474 -367 0

5 -474 -710 0

6 -944 -710 0

7 -944 -1130 0

8 -369 -1130 0

9 -27 -792 0

10 -27 -467 0

11 83 -467 0

12 146 -433 0


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4 To edit an incorrect point value:

a. Inthehistorytree,selecttheCreateLineobjectyouwanttoedit.

b. IntheProperties window,enterthecorrectvaluesintheValuecolumn.

ThevalueenteredforPoint2automaticallyappliestothePoint1forthe

nextsegment.Therefore,youneedonlyeditPoint2insubsequentCre-

ateLinewindows.

Asyouenterthevalues,thedisplayofthesegmentupdates.Youmay

needtouseView>Fit All>Active Viewtoresizethedisplayinthe3Dwin-

dow.

c. PressEnter

toapplythenewvaluestothemodel.5 Continue with this same method to verify the values for all the

remaining points.

Duplicate and Mirror Polyline1

Next, you will duplicate and mirror the object Polyline1 object about aspecified plane to create the right-half of the waveguide combiner.Remember, this is possible because the waveguide combiner is symmetricabout the xz plane. This will result in a 2D sheet object with a defaultname of Polyline1_1.

To duplicate the object Polyline1:

1 Select the object Polyline1 by either clicking on it in the 3D Modeler

window or clicking its name in the history tree.

2 Click Edit>Duplicate>Mirror.

3 Press Tab to move to the X box, and then enter (0, 0, 0) to specify

13 255 -433 0

14 337 -411 015 427 -411 0

16 506 -523 0

17 682 -523 0

18 915 -683 0

19 1562 -683 0

20 1562 -263 0

21 1073 -263 0

22 858 -53 0

23 612 -53 0

24 612 0 0

25 0 0 0


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the point on the plane on which you want to mirror the object.

A line drawn from this point to the mirror plane will be perpendicularto the plane.

4 Press Enter.

5 Press Tab to move to the dY box and enter 1 to specify a normal point

on the plane.

6 Press Enter.

The object Polyline1_1, a duplicate of object Polyline1, appears on

the plane you specified, oriented according to the normal point you

specified, as shown below:

Unite Polyline1 and Polyline1_1

Now that you have successfully created both halves of the waveguidecombiner, you will unite, or join, them to make the single waveguidecombiner object.

To unite both halves of the waveguide combiner:

1 Select Polyline1.

2 Press and hold down Ctrl to also select Polyline1_1.

Polyline1 and Polyline1_1 should now both be selected. To verify,both objects should be highlighted in the history tree, and the status


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bar should indicate that the number of objects selected is two.

3 Click 3D Modeler>Boolean>Unite.

The new object that is created inherits its properties (name, color,

boundary, and material assignment) from the first object selected

(Polyline1).

The resulting single, new object appears in the 3D Modeler window,

as shown below:

Note By default, the objects being joined to the first object selected are notpreserved for later use.

For this waveguide combiner problem, you do not need to preserve anyobjects for later use. However, if you want to keep a copy of theobjects being joined to the first object selected, do one of thefollowing:

• Copytheobjects,andthenpastethembackintothedesignafterunitingthem.

• OntheToolsmenu,pointtoOptions>3D Modeler Options,andthenclickClone tool objects before uniteinthe3D Modeler Optionsdialogbox.This

optioninstructsHFSStoalwayskeepacopyoftheoriginalobjectsbeing

joined.


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Rename Poly line1

Next, change the default name of the new, united object to specify thatit is the waveguide combiner object.

To modify the name of Polyline1 object:

1 Under the Attribute tab of the Properties window, click Polyline1 in

the Name row.

2 Type waveguide to rename the object, and then press Enter to

accept the new name.

Modify the Waveguide’s Attributes

The next step in creating the waveguide is to modify its default attri-butes that are displayed in the Properties window, which includes

assigning a color and transparency, and verifying the current materialassignment.

Assign a Color to the Waveguide

To assign a color to the waveguide:

1 Select the object waveguide, if it is not already selected.

2 Under the Attribute tab of the Properties window, click Edit in the

Color row.

The Color palette appears.

3 Select the basic color blue (RGB settings 0, 0, 255) from the Color

palette, and then click OK to assign the color to the object wave-

guide.While the waveguide is selected, it retains the selection color. To see

the assigned color, unselect the waveguide by clicking a location in

the drawing window off the waveguide.

Assign a Transparency to the Waveguide

To assign a transparency level to the waveguide:

1 Select the object waveguide, if it is not already selected.

2 Under the Attribute tab of the Properties window, click the default

value 0.4 in the Transparency row.

The Set Transparency window appears.

3 Move the slider to the right to increase the transparency level, stop-ping when the value is 0.7.

4 Click OK .


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The transparency is now set to .7, which appears as the new value in

the Transparency row after it is set.5 Click outside the object, on the grid background, to deselect wave-

guide and view the resulting color and transparency assignments.

Your waveguide’s color and transparency should resemble the one

shown below:

Verify Lighting Attributes are Disabled

If you want, you can change the default ambient and distant light source

properties at this time, though it is not necessary for this waveguidecombiner problem.

To verify lighting attributes are disabled:

1 Click View>Modify Attributes>Lighting.

The Lighting Properties dialog box appears.

2 Verify that the Do not use lighting option is disabled. Clear this

option if it is selected.

3 Click OK or Cancel, depending on whether or not you had to clear the

lighting option.


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Sweep the Waveguide

Next, you must sweep the 2D object waveguide along a vector to createa 3D solid object as the final waveguide combiner model.

To sweep the waveguide along a vector:

1 Select the object waveguide, if it is not already selected

2 Click Draw>Sweep>Along Vector.

3 Draw the vector you want to sweep the object along:

d. Enter(0,0,0)inthecoordinateboxestospecifythestartpoint,andthen

pressEnter.

e. TabintothedZboxandenter85tospecifytheendpoint,andthenpress

Enter.

The Sweep along vector dialog box appears.

4 Enter 0 in the Draft angle text box.

This is the angle to which the profile is

expanded or contracted as it is swept.

5 Select Round from the Draft type

pull-down list.

This draft type applies rounded edges

to the new object.

6 Click OK to complete the sweep.

Your completed 3D object waveguide should resemble the one shown

below:


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7 Click File>Save, or click the Save a project toolbar button , to

save the geometry.Now you are ready to assign all boundaries and excitatons to the wave-guide combiner.


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Setting Up the Problem 4-1

4 Setting Up the Problem

Now that you have created the geometry and assigned all materialsfor the waveguide combiner problem, you are ready to define itsexcitations and boundaries.

Your goals for this chapter are to:

Define the boundary conditions, such as the locations of finiteconductivity boundaries.

Define the wave ports through which the signals enter and leavethe waveguide combiner.

Verify that you correctly assigned the boundaries and excitations

to the model.Now you are ready to set up the problem.

Time It should take you approximately 15 minutes to work through this chapter.


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4-2 Setting Up the Problem

Set Up Boundaries and Excitations

Now that you have created the waveguide combiner model and definedits properties, you must define the boundary and excitation conditions.These conditions specify the excitation signals entering the structure,the behavior of electric and magnetic fields at various surfaces in themodel, and any special surface characteristics.

Boundary Conditions

Boundaries specify the behavior of magnetic and electric fields at vari-ous surfaces. They can also be used to identify special surfaces —such asresistors— whose characteristics differ from the default.

The following two types of boundary conditions will be used for thiswaveguide combiner problem:

Excitation Conditions

Wave ports define surfaces exposed to non-existent materials (generallythe background or materials defined to be perfect conductors) throughwhich excitation signals enter and leave the structure.

Wave ports represent places in the geometry through which excitationsignals enter and leave the structure. They are used when modeling strip

lines and other waveguide structures, such as this waveguide combinerproblem. Wave ports are typically placed on the perfect E interfacebetween the 3D object and the background to provide a window thatcouples the model device to the external world.

Finiteconductivity

This type of boundary represents an imperfect conductor. HFSSdoes not compute the field inside these objects; the finiteconductivity boundary approximates the behavior of the field atthe surfaces of the objects. Any skin-effect losses will beproperly taken into account.

For this waveguide combiner problem, a finite conductivityboundary is assigned to the side faces (excluding the four ports),and the bottom face of the model.

Symmetry In structures that have an electromagnetic plane of symmetry,such as this waveguide combiner model, the problem can be

simplified by modeling only one-half of the model and identifyingthe exposed surface as a perfect H or perfect E boundary.

For this waveguide combiner problem, a perfect E symmetryboundary is assigned to the top face of the model.


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For this waveguide combiner problem, a wave port is assigned to each

end-face of the model’s four waveguide sections.Assign Boundaries

First, you will assign all boundary conditions to the model. These assign-ments include two finite conductivity boundaries and one perfect E sym-metry boundary.

To review information on the types of boundaries you will assign, see“Boundary Conditions” on page 4-2.

Assign a Fini te Conducti vi ty Boundary to the Side Faces

Finite conductivity boundary to all the waveguide combiner’s side faces,excluding the port faces.

As discussed in “Boundary Conditions” on page 4-2, finite conductivityboundaries represent imperfect conductors. At such boundaries, the fol-lowing condition holds:

where

• E tan is the component of the E-field that is tangential to the surface.

• H tan is the component of the H-field that is tangential to the surface.

• Z s is the surface impedance of the boundary, , where

• istheskindepth, ,oftheconductorbeingmodeled.

• istheangularfrequencyoftheexcitationwave.

• istheconductivityoftheconductor.• isthepermeabilityoftheconductor.

The fact that the E-field has a tangential component at the surface ofimperfect conductors simulates the case in which the surface is lossy.

The surfaces of any objects defined to be non-perfect conductors areautomatically set to finite conductivity boundaries. HFSS does notattempt to compute the field inside these objects; the finite conductiv-ity boundary approximates the behavior of the field at the surfaces ofthe objects.

The finite conductivity boundary condition is valid only if the conductorbeing modeled is a good conductor, that is, if the conductor’s thickness is

much larger than the skin depth in the given frequency range.To assign a finite conductivity boundary to the side faces of the wave-guide combiner:

1 Right-click in the 3D Modeler window, then click Select Faces on the

Etan Z n̂ H tan =

1 j+

2


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shortcut menu.

In this mode you can select or de-select an object’s faces instead ofthe entire object. When the mouse hovers over a face in the 3D Mod-

eler window, that face is outlined, which indicates that it will be

selected when you click.

2 Ultimately, you want to select all of the side faces of the object

waveguide, except the port faces. Here, you do not seek to select

the top or bottom faces. However, given the number and position of

the faces, in this case it is easier to use Edit>Select All, and then use

Ctrl-click to de-select the four port faces, and the top and buttom

faces. You will need to rotate the model to complete the process.

• With Face selection mode on, click Edit>Select All. This high-lights all faces on the object.

• Press and hold down Ctrl and click to de-select the top face andtwo visible port faces.

• Press and hold down Alt and drag the mouse to rotate the modelto a position where you can select the desired side faces.

• Press and hold Ctrl and click to deselect the rotated bottom faceand the remaining port faces.

All side faces of the waveguide combiner are selected.

3 On the HFSS menu, click Boundaries>Assign>Finite Conductivity.


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The Finite Conductivity Boundary window appears.

4 Select the Use Material check box, and click the material button

(where the default vacuum is displayed).

The Select Definition window appears. By default, this material

browser lists all materials in the global material library, as well as the

local material library for the current project, which is a subset of the


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global library.

5 Select aluminum from the list of materials, and then click OK .

The Finite Conductivity Boundary window reappears.

The conductivity and permeability values for aluminum are now

assigned to the finite conductivity boundary.

6 Clear Infinite Ground Plane if it is selected.

If selected, the Infinite Ground Plane option simulates the effects of

an infinite ground plane. This option only affects the calculation ofnear- and far-field radiation during post processing. The 3D Post Pro-

cessor models the boundary as a finite portion of an infinite, per-

fectly conducting plane.

7 Click OK to accept the default name FiniteCond1 and apply the

boundary.

The resulting finite conductivity boundary is applied to the side faces

of the object waveguide and now appears as a subentry of


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Boundaries in the project tree, as shown below:

By default, the geometry, name, and vectors for the boundary are all

shown in the 3D Modeler window. For this waveguide combiner problem,it is not necessary to edit any of the boundary’s visualization default set-tings.

Assign a Fini te Conducti vi ty Boundary to the Bot tom Face

Next, assign a finite conductivity boundary to the bottom face of thewaveguide combiner, using the same procedure you just followed toassign a finite conductivity boundary to the side faces.

Note To edit a boundary’s visualization settings:

1. ClickHFSS>Boundaries>Visualizationifyouwanttoshoworhide

boundaries.

2. CleartheView Geometry,View Name,orView Vectorselectionof

boundariesthatyouwanttohidefromview.Selecttheoptionsyouwant

toshowinthe3D Modelerwindow.

3. ClickClose.

Finite Conductivityboundary added as asubentry ofBoundaries

Finite Conductivity boundaryassigned to the side faces

Properties of thefinite conductivityboundary


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To assign a finite conductivity boundary to the bottom face of the wave-

guide:1 If it is still selected, deselect the finite conductivity boundary you

just assigned to the side faces.

2 In Select Faces mode, do one of the following to select the bottom

face of the object waveguide:

• Press and hold down Alt and drag the mouse to rotate the modelto a position where you can select the bottom face.

• Click the top face, and then click Next Behind on the shortcutmenu, or press B on the keyboard, to select the bottom face.

The bottom face of the waveguide combiner is selected.

3 On the HFSS menu, click Boundaries>Assign>Finite Conductivity.

The Finite Conductivity Boundary window appears.

Hint You can also assign boundaries by selecting the object or object face towhich you want to assign the boundary, and then doing one of thefollowing:

• Right-clickinthe3D Modelerwindow,pointtoAssign Boundary,andthen

clicktheboundarytypeyouwanttoassign.

• Right-clickonBoundariesintheprojecttree,pointtoAssign,andthenclicktheboundarytypeyouwanttoassign.


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4 Select the Use Material check box, and click the material button

(where the default vacuum is displayed).The Select Definition window appears.

5 Select aluminum from the list of materials, and click OK .

The Finite Conductivity Boundary window reappears.

The conductivity and permeability values for aluminum are now

assigned to this finite conductivity boundary.

6 Clear Infinite Ground Plane if it is selected.

7 Click OK to accept the default name FiniteCond2 and apply the

boundary.

The resulting finite conductivity boundary is applied to the bottom

face of the object waveguide.


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Assign a Perfect E Symmetry Boundary to the Top Face

HFSS has a boundary condition specifically for symmetry planes. Insteadof defining a perfect E or perfect H boundary, you define a perfect E orperfect H symmetry plane.

When you are defining a symmetry plane, you must decide which type ofsymmetry boundary should be used, a perfect E or a perfect H. In gen-eral, use the following guidelines to decide which type of symmetryplane to use:

• If the symmetry is such that the E-field is normal to the symmetryplane, use a perfect Esymmetry plane.

• If the symmetry is such that the E-field is tangential to the symmetryplane, use a perfect H symmetry plane.

The simple two-port rectangular waveguide shown below illustrates thedifferences between the two types of symmetry planes. The E-field ofthe dominant mode signal (TE10) is shown. The waveguide has two planesof symmetry, one vertically through the center and one horizontally.

• The horizontal plane of symmetry is a perfect E surface. The E-fieldis normal and the H-field is tangential to that surface.

• The vertical plane of symmetry is a perfect H surface. The E-field istangential and H-field isnormal to that surface.

Since the E-field is symmetric to the height of the waveguide combinermodel in this guide, the height of the waveguide has been split in half inorder to place a perfect E symmetry boundary on the top face.

Electric field of TE10 Mode

Perfect E symmetry plane

Perfect H symmetry plane


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Setting Up the Probl em 4-11

Next, you will assign a perfect E symmetry boundary to the top face of

the waveguide combiner (the symmetry plane for the model).To assign a symmetry boundary to the top face of waveguide:

1 If it is still selected, deselect the finite conductivity boundary you

just assigned.

2 In Select Faces mode, select the top face of the object waveguide.

The top face of the waveguide is selected.

3On the HFSS menu, click Boundaries>Assign>Symmetry.The Symmetry Boundary dialog box appears.

4 Select Perfect E as the symmetry type.

5 Do the following to edit the impedance multiplier:

a. Click Impedance Multiplier .

ThePort Impedance Multiplierdialogboxappears.

b. Enterthevalue2intheImpedance Multiplier box,andthenclickOK.


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6 Click OK to accept the default name Sym1 and apply the boundary.

The resulting perfect E symmetry boundary condition is assigned tothe top face the object waveguide, as shown below:


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Assign Excitations

Now you will assign all excitations to the waveguide combiner model.These excitations include wave ports assigned to each end face of themodel’s four waveguide sections, as shown below:

Wave ports represent places in the geometry through which excitationsignals enter and leave the structure. HFSS assumes that each wave port

you define is connected to a semi-infinitely long waveguide that has thesame cross-section and material properties as the port.

When solving for the S-parameters, HFSS assumes that the structure isexcited by the natural field patterns (modes) associated with thesecross-sections. The 2D field solutions generated for each wave port serveas boundary conditions at those ports for the 3D problem. The final fieldsolution computed must match the 2D field pattern at each port.

For this waveguide combiner model, you will assign four wave ports tothe locations shown in the above image.

Port 1

Port 2

Port 3

Port 4


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The function of each wave port in this waveguide combiner model are as

follows:

Assign Wave Port 1

To assign wave port 1:

1 Deselect the perfect E boundary you just assigned, if it is still

selected.

2 In Select Faces mode, select the face of port 1.

3 On the HFSS menu, click Excitations>Assign>Wave Port.

The Wave Port wizard appears.

4 In the Wave Port:General step, accept the default name WavePort1,

and then click Next.

5 In the Wave Port:Modes step, accept the default settings, and then

click Next.

6 In the Wave Port:Post Processing step, accept the default settings,and then click Finish to complete the wave port assignment for port

1.

WavePort1 is assigned to the waveguide and now appears as a suben-

Port 1 The output port that is fed the output power of the solid statepower amplifiers from ports 2 and 4.

Port 2 The port in which the output of a SSPA is fed.

Port 3 The isolated port where the impedance mismatch at the output(port 1) is absorbed.

Port 4 The port in which the output of a SSPA is fed, with a 90-degreeout-of-phase separation to port 2.


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try of Excitations in the project tree, as shown below:

Assign Wave Port 2

To assign wave port 2, you will use the same procedure you just followedto assign wave port 1, but with the addition of an integration line.

When HFSS computes the excitation field pattern at a port, the direction

of the field at wt = 0 is arbitrary; the field can always point in one of atleast two directions.

For both wave port 2 and wave port 4, you must calibrate the port rela-tive to some reference orientation by defining an integration line in theup direction.


1 Deselect WavePort1 that you just assigned, if it is still selected.




4 In the Wave Port:General step, accept the default name WavePort2,and then click Next.

5 In the WavePort:Modes step, click in the Integration Line list, and

Wave portassignmentadded as asubentry ofExcitations

Properties of thewave port

Port 1

assigned


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then select New Line.

The Wave Port wizard disappears while you draw the vector.6 Define the integration line:

a. Selectthestartpointbyclickingthecenterofthebottomlineontheface.

Yourcursorwillappearasatrianglewhenitisatthisexactlocation.

b. Selecttheendpointbyclickingthecenterofthetoplineontheface,

whichisdirectlyverticaltothestartpointyoujustselected.Again,your

cursorwillappearasatrianglewhenitisatthisexactlocation.

The endpoint defines the direction and length of the integration line.

The Wave Port wizard reappears at the WavePort:Modes step.

7 Click Next.

8 In the Wave Port:Post Processing step, accept the default settings,

and then click Finish to complete the wave port assignment for port

2.

WavePort 2, with its integration line, is shown below:

Assign Wave Port 3

To assign wave port 3, you will use the same procedure you followedwhen you assigned wave port 1.








5 In the Wave Port:Modes step, accept the default settings, and then


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click Next.

6 In the Wave Port:Post Processing step, accept the default settings,and then click Finish to complete the wave port assignment for port

1.

WavePort3 is assigned to the waveguide and now appears as a suben-

try of Excitations in the project tree.

Assign Wave Port 4

To assign wave port 4, you will use the same procedure you followedwhen you assigned wave port 2.



2 In Select Faces mode, select the face of port 4.3 Zoom in on the face of port 4.





6 In the WavePort:Modes step, click in the Integration Line list, and

then select New Line.

The Wave Port wizard disappears while you draw the vector.

7 Define the integration line:

a. Selectthestartpointbyclickingthecenterofthebottomlineontheface.Yourcursorwillappearasatrianglewhenitisatthisexactlocation.

b. Selecttheendpointbyclickingthecenterofthetoplineontheface,

whichisdirectlyverticaltothestartpointyoujustselected.Again,your

cursorwillappearasatrianglewhenitisatthisexactlocation.

The endpoint defines the direction and length of the integration line.

The Wave Port wizard reappears at the WavePort:Modes step.

8 Click Next.

9 In the Wave Port:Post Processing step, accept the default settings,

and then click Finish to complete the wave port assignment for port

4. WavePort4, with its integration line, is assigned to the waveguide


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and now appears as a subentry of Excitations in the project tree.

Modify the Impedance Multiplier

Because you defined a symmetry plane (allowing the model of a struc-ture to be cut in half), the impedance computations must be adjusted by

specifying an impedance multiplier.In cases such as this waveguide combiner problem, where a perfect Eplane of symmetry splits a structure in two, only one-half of the voltagedifferential and one-half of the power flow can be computed by the sys-tem.

Therefore, since the impedance, Z pv , is given by ,

the computed value is one-half the desired value. An impedance multi-plier of 2 must be specified in such cases.

To edit the impedance multiplier:

1 Click HFSS>Excitations>Edit Impedance Mult.

The Port Impedance Multiplier dialog box appears.

2Enter the value 2 in the Impedance Multiplier box, and then clickOK .

Note To edit a wave port assignment:

1. IntheProject Managerwindow,double-clickthenameofthewaveport

assignmentlistedintheprojecttree.

TheWave Portdialogboxappears.

2. Clicktheappropriatetabs(General,Modes,PostProcessing,Defaults)

toeditanyportassignmentinformation.

3. ClickOKtoapplytheassignmentrevisions.

Z pvV V

P-------------=


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Verify All Boundary and Excitation Assignments

Now that you have assigned all the necessary boundaries and excitationsto a model, you should review their specific locations on the model inthe solver view.

When you verify boundaries and excitations in the solver view, youreview the locations of the boundaries and excitations as you havedefined them for generating a solution (solving).

HFSS runs an initial mesh and determines the locations of the boundariesand excitations on the model.

Then, you can select a boundary or excitation from the list in the Bound-ary Display (Solver View) window to view its highlighted area in themodel.

To check the solver’s view of boundaries and excitations:1 Click HFSS>Boundary Display (Solver View).

HFSS runs an initial mesh and determines the locations of the bound-

aries and excitations on the model.

The Solver View of Boundaries window appears, listing all the

boundaries and

excitations for the active model in the order in which they were

assigned.

2 Select a check box in the Visibility column that corresponds with the

boundary or excitation for which you want to review its location on

the model.

The selected boundary or excitation appears in the model in the color

it has been assigned, as indicated in the Color column.

• Visible to Solver appears in the Solver Visibility column for eachboundary that is valid.

• Overridden appears in the Solver Visibility column for eachboundary or excitation that overwrites any existing boundary or


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excitation with which it overlaps.

3 Verify that the boundaries or excitations you assigned to the modelare being displayed as you intended for solving purposes.

4 If required, modify the parameters for those boundaries or excita-

tions that are incorrect.

5 Click Close, and then click File>Save, or click the Save a project

toolbar button , to save the geometry.

You are now ready to set up the solution parameters for this waveguide

combiner problem and generate a solution.

Warning Be sure to save geometric models periodically; HFSS does notautomatically save models. Saving frequently helps prevent the lossof your work if a problem occurs.


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Generating A Solution 5-1

5 Generating A Solution

Now that you have defined and verified all of the boundaries andexcitations for the waveguide combiner problem, you are ready togenerate a solution.

Your goals for this chapter are to:

Set up the solution parameters that will be used in calculating thesolution.

Validate the project setup.

Generate a solution.

View the solution data, such as convergence and matrix data

information.

Time This problem solved in approximately 10 minutes on an 1.4 Ghz PC with1 gigabyte of RAM. Depending on the computing resources you haveavailable, this solution time may vary greatly


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5-2 Generating A Solution

Specify Solution Options

Before you can generate a solution, you need to specify the solutionparameters. This controls how HFSS computes the requested solution.

Each solution setup includes the following information:

• General data about the solution’s generation.

• Adaptive mesh refinement parameters, if you want the mesh to berefined iteratively in areas of highest error.

• Frequency sweep parameters, if you want to solve over a range offrequencies.

You can define more than one solution setup per design; however, youwill define only one solution setup for this waveguide combiner problem.

Add a Solution Setup

Now, you will specify how HFSS will compute the solution by adding asolution setup to the waveguide combiner design.

To add a solution setup to the design:

1 Click HFSS>Analysis Setup>Add Solution Setup.

The Solution Setup dialog box appears.


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The Solution Setup dialog box is divided into the following tabs:

2 Under the General tab, specify the following:

General Includes general solution settings.

Options Includes mesh options, adaptive options, and solutionsettings.

Advanced Includes advanced settings for initial mesh generation andadaptive analysis.Includes mesh generation options for modelports.

Defaults Enables you to save the current settings as the defaults forfuture solution setups or revert the current settings to HFSS’sstandard settings.


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a. Enterthefollowingvalues:

b. Acceptallremainingdefaultsettings.

3 Accept all default settings on the Options, Advanced, and Default

tabs.

4 Click OK .

Setup1 now appears as a solution setup under Analysis in the project

SolutionFrequency

20 GHzFor every modal driven solution setup, you must specifythe frequency at which to generate the solution. Forthis waveguide combiner model, you will solve over arange of frequencies, which will require you to define afrequency sweep in “Add a Discrete Frequency Sweep”on page 5-5. If a frequency sweep is solved, an adaptiveanalysis is performed only at the solution frequency.

MaximumNumber ofPasses

9

The Maximum Number of Passes value is the maximumnumber of mesh refinement cycles that you would like

HFSS to perform. This value is a stopping criterion forthe adaptive solution; if the maximum number of passeshas been completed, the adaptive analysis stops. If themaximum number of passes has not been completed,the adaptive analysis will continue unless theconvergence criteria are reached.

Maximum DeltaS Per Pass

0.001

The delta S is the change in the magnitude of the S-parameters between two consecutive passes. The valueyou set for Maximum Delta S Per Pass is a stoppingcriterion for the adaptive solution. If the magnitude and

phase of all S-parameters change by an amount lessthan this value from one iteration to the next, theadaptive analysis stops. Otherwise, it continues untilthe requested number of passes is completed.


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tree.

Add a Discrete Frequency Sweep

To generate a solution across a range of frequencies, you must add a fre-quency sweep to the solution setup. HFSS performs the sweep after theadaptive solution.

For this waveguide combiner model, you will add a Discrete frequencysweep to the solution setup. A Discrete sweep generates field solutionsat specific frequency points in a frequency range. For this waveguidecombiner problem, you will specify a range of 19.5 GHz to 20.4 GHz,with a Step Size of 0.1 GHz. The result will be ten solutions at incre-ments of 0.1 GHz. By default, the field solution is only saved for the finalfrequency point.

Be aware that HFSS uses the finite element mesh refined during an adap-tive solution at the solution frequency. It uses this mesh without furtherrefinement. Because the mesh for the adaptive solution is optimized onlyfor the solution frequency, it is possible that the accuracy of the resultscould vary at frequencies significantly far away from this frequency. Ifyou wish to minimize the variance, you can opt to use the center of thefrequency range as the solution frequency. Then, after inspecting the

results, run additional adaptive passes with the solution frequency set tothe critical frequencies.

Solution Setupadded as a subentryof Analysis


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To add a Discrete frequency sweep to the solution setup:

1 Click HFSS>Analysis Setup>Add Sweep.The Select dialog box appears.

2 Select Setup1 for the solution setup for which the sweep applies, and

click OK .

The Edit Sweep dialog box appears.

3 Under the Sweep Type section, select Discrete as the frequency

Sweep Type you want to add.

4 Under the Frequency Setup section, select or enter these values to


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define the sweep:

5 Clear Save Fields (All Frequencies), if selected.

If selected, the Save Fields option saves the field solution for a spe-

cific point. The S-parameters are always saved for every frequency

point. The more steps you request, the longer it takes to complete

the frequency sweep.6 Click Display to view each of the sweep values at the 0.1 GHz step

size increment within the frequency range you specified.

7 Click OK .

Sweep1 now appears as a subentry under Setup1 in the project tree.

Type Linear Step

Start 19.5 GHz

Stop 20.4 GHz

StepSize

0.1 GHz


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Validate the Project Setup

Before you run an analysis on the waveguide combiner model, it isimportant to first perform a validation check on the project. HFSS runs acheck on all the setup details of the active project to verify that all thenecessary steps have been completed and their parameters are reason-able.

To perform a validation check on the project wg_combiner:

1 Click HFSS>Validation Check.

HFSS checks the project setup, and then the Validation Check win-

dow appears.

2 View the results of the validation check in the Validation Check win-

dow.

For this waveguide combiner project, a green check mark should

appear next to each project step in the list.

The following icons can appear next to an item:

3 If the validation check indicates that a step in your waveguide com-

biner project is incomplete or incorrect, then return to the step in

HFSS and carefully review its setup.4 Click Close.

5 Click File>Save to save any changes you may have made to your proj-

ect.

Indicates the step is complete.

Indicates the step is incomplete.

Indicates the step may require your attention.


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Generate the Solution

Now that you have entered all the appropriate solution criteria and vali-dated the project setup, the waveguide combiner problem is ready to besolved.

When you set up the solution setup criteria for this model, you specifiedvalues for an adaptive analysis (Maximum number of passes and Maxi-mum delta S per pass). An adaptive analysis is a solution process in whichthe mesh is refined iteratively in regions where the error is high, whichincreases the solution’s precision.

The following is the general process carried out during an adaptive anal-ysis:

1 HFSS generates an initial mesh.

2 Using the initial mesh, HFSS computes the electromagnetic fields thatexist inside the structure when it is excited at the solution frequency.

(If you are running a frequency sweep, an adaptive solution is per-

formed only at the specified solution frequency.)

3 Based on the current finite element solution, HFSS estimates the

regions of the problem domain where the exact solution has strong

error. Tetrahedra in these regions are refined.

4 HFSS generates another solution using the refined mesh.

5 The software recomputes the error, and the iterative process (solve

— error analysis — refine) repeats until the convergence criteria are

satisfied or the requested number of adaptive passes is complete.6 If a frequency sweep is being performed, as with this waveguide com-

biner problem, HFSS then solves the problem at the other frequency

points without further refining the mesh.

To begin the solution process:

1 Click Setup1 solution setup in the project tree.

2 Click HFSS>Analyze. This command solves every solution setup in the

design.

HFSS computes the 3D field solution inside the structure.


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5-10 Generating A Soluti on

The Progress window displays the solution progress as it occurs:

View the Solution Data

While the analysis is running, you can view a variety of profile, conver-gence, and matrix data about the solution.

View the Profile Data

While the solution proceeds, examine the computing resources, or pro-file data, used by HFSS during the analysis.

The profile data is essentially a log of the tasks performed by HFSS dur-ing the solution. The log indicates the length of time each task took andhow much RAM/disk memory was required.

To view profile data for the solution:• Click HFSS>Results>Solution Data.

The Solution Data dialog box appears. The figure shows the Profile

Note The results that you obtain should be approximately the same as theones given in this section. However, there may be a slight variation

between platforms.


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tab selected.

Notice in the Simulation pull-down list that Setup1 is selected as thesolution setup. By default, the most recently solved solution is

selected.

For the Setup1 solution setup, you can view the following profile

data:

Task Lists the software module that performed a task during thesolution process, and the type of task that was performed.

For example, for the task mesh3d_adapt, Mesh3d is thesoftware module that adaptively refined the mesh.

Real Time The amount of real time (clock time) required to performthe task.


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View the Convergence Data

Next, while the solution proceeds, view the convergence data.

To view convergence information for the solution:

• In the Solution Data window, click the Convergence tab.

Based on the criteria you specified for Setup1, you can view the fol-

CPU Time The amount of CPU time required to perform the task.

Memory The amount of RAM/virtual memory required of yourmachine to complete the task. This value includes thememory required of all applications running at the time,not just HFSS.

Information The number of tetrahedra in the mesh that were usedduring the solution.


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lowing convergence data:

• Number of adaptive passes completed and remaining.When the solution is complete, you can view the number of adaptive

passes that were performed. If the solution converged within the

specified stopping criteria, fewer passes than requested may have

been performed.

• Number of tetrahedra in the mesh at each adaptive pass.

• Maximum magnitude of delta S between two passes.

For solutions with ports, as in Setup1, at any time during or after the

solution process, you can view the maximum change in the magnitude

of the S-parameters between two consecutive passes. This informa-

tion is available after two or more passes are completed.

The convergence data can be displayed in table format or on a rect-

angular (X - Y) plot.

View the Matrix Data

You can view matrices computed for the S-parameters during each adap-tive and sweep solution.


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To view matrices:

1 In the Solution Data window, click the Matrix Data tab.

2 In the Simulation pull-down lists, do the following:

a. VerifythatSetup1isselectedasthesolutionsetupyouwantto

view.

b. VerifythatLastAdaptiveisselectedasthesolvedpassyouwanttoview.

3 Select S Matrix as the type of matrix data you want to view.

4 Select Magnitude/ Phase from the pull-down list as the format in

which to display the matrix information.


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You can display matrix data in the following formats:

5 Select the solved frequencies to display:

• To display the matrix entries for all solved frequencies, check AllFreqs.

• To show the matrix entries for one solved frequency, clear All Freqs.and then select the solved frequency for which you want to viewmatrix entries.

For adaptive passes, only the solution frequency specified in the

Solution Setup dialog box is available. For frequency sweeps, the

entire frequency range is available.

Consider the first (S:WavePort1:1) and third (S:WavePort3:1) columnsof the S-matrix at 19.6 GHz. S12, S14, S32, and S34 are all close to

the value .

Furthermore, the phases of S12 and S14 are 90-degrees apart. This is

also true for the phases of S32 and S34, but in the opposite way. This

indicates that if you feed ports 2 and 4 with signals equal in magni-

tude but 90-degrees apart, they will add up constructively in port 1,

while canceling each other in port 3.

Also, S22, S24, S42, and S44 are all small in magnitude, indicating

small return loss and cross-talk to the wrong port.

6 Click Close when done viewing the Solution Data window.

Magnitude/Phase Displays the magnitude and phase of the matrix type.

Real/Imaginary Displays the real and imaginary parts of the matrixtype.

dB/Phase Displays the magnitude in decibels and phase of thematrix type.

Real Displays the real parts of the matrix type.

Imaginary Displays the imaginary parts of the matrix type.

Magnitude Displays the magnitude of the matrix type.

Phase Displays the phase of the matrix type.

dB Displays the magnitude in decibels of the matrix type.

2

2-------


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Analyzing the Solu tion 6-1

6 Analyzing the Solution

Now, HFSS has generated a solution for the waveguide combinerproblem. In general, you can display and analyze the results of aproject in many different ways. You can:

• Plotfieldoverlays—representationsofbasicorderivedfieldquantities—onsurfacesorobjects.

• Create2Dor3DrectangularorcircularplotsanddatatablesofS-param-eters,basicandderivedfieldquantities,and,hadthewaveguidecom-

binermodelemittedradiation,radiatedfielddata.

• Plotthefiniteelementmeshonsurfacesorwithin3Dobjects.

• Createanimationsoffieldquantities,thefiniteelementmesh,anddefinedprojectvariables.

• Scaleanexcitation’smagnitudeandmodifyitsphase.

• Deletesolutiondatathatyoudonotwanttostore.

For this waveguide combiner problem, you will:

Create Modal S-parameter reports.

Create a field overlay cloud plot of the magnitude of E.

Create an animation of the mag-E cloud plot.

Time It should take you approximately 30 minutes to work through this chapter.


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6-2 Analyzing the Solution

Create Modal S-Parameters Reports

Now you are ready to create the modal S-parameters reports.

Create an S-Parameters Report of S11, S12, S13, and

S14

To generate a 2D report of S11, S12, S13, S14:

1 Click HFSS>Results>Create Modal Solutions Data Report>Rectangu-

lar Plot.

The Report dialog box appears.

The Context selections are Setup1: Sweep1 in the Solution pull-

down list, and Sweep from the Domain pull-down list.

2 Under the Y Component pane, specify the following information to

plot along the y-axis:

Category S Parameter

QuantityS(WavePort1,WavePort1)

;S(WavePort1,WavePort2)

;

S(WavePort1,WavePort3); S(WavePort1,WavePort4)

Function dB


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Press and hold down Ctrl to select multiple items in a list.

Freq is the Primary Sweep.This option plots the sweep variables selected under the Families tab

along the x-axis.

3 Click New Report and Close.

The function of the selected quantity is plotted against the plot

domain on an xy graph.

The report XY Plot 1 appears in the 3D Modeler window and is now

listed under Results in the Project tree. Each of the four traces are

also listed in the Project tree.

Notice that the line charted for S11 indicates that this model has its

lowest return loss at 20 GHz, if it were driven at port 1.

Create an S-Parameters Report of S12 and S14

To generate a 2D plot of S12 and S14:

1 Click HFSS>Results>Create Modal Solutions Data Report>Rectangu-

lar Plot.

The Report dialog box appears

The Context selections are Setup1: Sweep1 in the Solution pull-


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6-4 Analyzing the Solution

down list, and Sweep from the Domain pull-down list.

2 Accept X: Freq and All, if they are not already selected.3 Under the Y Component pane, specify the following information to

plot:

4 Click New Report, and then click Close.

The report XY Plot 2 appears in the 3D Modeler window and is now

listed under Results in the project tree.

Notice that at 20 GHz, S12 and S14 are both almost exactly -3 dB.

Category S Parameter

Quantity S(WavePort1,WavePort2); S(WavePort1,WavePort4)

Function dB


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Create Field Overlay Plots

Next, you will create a field overlay plot of the magnitude of E andexamine the resulting E- field pattern.

Scale the Magnitude and Phase for the Ports

Before you proceed with creating the field overlay plot, you must scalethe magnitude of WavePort1, WavePort2, and WavePort4, and you mustmodify the phase for WavePort4. As a result, these settings will makethe model behave as the specific waveguide combiner that is describedin this manual.

To modify the magnitude and phase for the ports:

1 Click HFSS>Fields>Edit Sources.

The Edit Sources dialog box appears.

2 In the Scaling Factor te

Documents

HFSS Waveguide Combiner