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Getting Started with HFSS: 20 GHz

Waveguide Combiner

Release 2020 R2
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Getting Started with HFSS: 20 GHz Waveguide Combiner

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Getting Started with HFSS: 20 GHz Waveguide Combiner

Conventions Used in this Guide

Please take a moment to review how instructions and other useful information are presented in this
guide.
l Procedures are presented as numbered lists. A single bullet indicates that the procedure
has only one step.
l Bold type is used for the following:
o Keyboard entries that should be typed in their entirety exactly as shown. For example,
“copy file1” means the word copy must be typed, then a space must be typed, and
then file1 must be typed.
o On-screen prompts and messages, names of options and text boxes, and menu com-
mands. Menu commands are often separated by carats. For example, “click
HFSS>Excitations>Assign>Wave Port.”
o Labeled keys on the computer keyboard. For example, “Press Enter” means to press
the key labeled Enter.
l Italic type is used for the following:
o Emphasis.
o The titles of publications.
o Keyboard entries when a name or a variable must be typed in place of the words in ital-
ics. For example, “copy file name” the word copy must be typed, then a space must
be typed, and then name of the file must be typed.
l The plus sign (+) is used between keyboard keys to indicate that you should press the keys
at the same time. For example, “Press Shift+F1” means to press the Shift key and the F1
key at the same time.

Ribbons, menu bars, and short-cut menus are three methods that can be used to see what
commands are available in the application.

l Ribbons are the rectangular area on top of the application window and contain multiple tabs.
Each tab has relevant commands that are organized, grouped, and labeled. An example of a
typical user interaction is as follows:

"On the Draw ribbon tab, click the Box primitive" means you can click the Box icon on the
Draw tab and execute the Box command to draw a box.

l The menu bar (located above the ribbon) is a group of the main commands of an application
arranged by category such File, Edit, View, Project, etc. An example of a typical user inter-
action is as follows:

"On the File menu, click the Open Examples command" means you can click the File menu
and then click Open Examples to launch the dialog box.

l Another alternative is to use the short-cut menu that appears when you click the right-mouse
button. An example of a typical user interaction is as follows:

3
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Getting Started with HFSS: 20 GHz Waveguide Combiner

“Right-click and select Assign Excitation> Wave Port” means when you click the right-
mouse button with an object face selected, you can execute the excitation commands from
the short-cut menu (and the corresponding sub-menus).
Getting Help: ANSYS Technical Support
For information about ANSYS Technical Support, go to the ANSYS corporate Support website,
https://www.ansys.com/Support. You can also contact your ANSYS account manager in order to
obtain this information.
All ANSYS software files are ASCII text and can be sent conveniently by e-mail. When reporting dif-
ficulties, it is extremely helpful to include very specific information about what steps were taken or
what stages the simulation reached, including software files as applicable. This allows more rapid
and effective debugging.
Help Menu
To access help from the menu bar, click Help and select from the menu:
l HFSS Contents - click here to open the contents of the help.
l HFSS Search - click here to open the search function of the online help.
Context-Sensitive Help
To access help from the user interface, do one of the following:
l To open a help topic about a specific menu command, press Shift+F1, and then click the
command or toolbar icon.
l To open a help topic about a specific dialog box, open the dialog box, and then press F1.

4
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information of ANSYS, Inc. and its subsidiaries and affiliates.
Getting Started with HFSS: 20 GHz Waveguide Combiner

Table of Contents
Table of Contents Contents-1
1 - Introduction {chapnum)-1
The Sample Problem {chapnum)-1
Results for Analysis {chapnum)-2
Overview of the Interface {chapnum)-2
2 - Creating the New Project 2-1
Add the New Project 2-1
Insert an HFSS Design 2-2
Add Project Notes 2-3
Select the Solution Type 2-3
Save the Project 2-4
3 - Set Up the Drawing Region 3-1
Overview of the Modeler Window 3-1
Coordinate System Settings 3-2
Units Settings 3-3
Grid Settings 3-3
Transparency Setting 3-4
4 - Creating the Model Geometry 4-1
Draw the Polyline1 Object 4-1
Method 1: Draw a Series of Polylines Graphically and Edit the Point Coordinates After-
ward 4-1
Method 2: Enter the X and Y Coordinates for Each Point 4-2
Verify the Points of Polyline1 4-5
Duplicate and Mirror Polyline1 4-9
Unite Polyline1 and Polyline1_1 4-10
Modify the Waveguide’s Attributes 4-12
Rename Polyline1 4-12
Assign a Color to the Waveguide 4-12

Contents-1
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Getting Started with HFSS: 20 GHz Waveguide Combiner

Assign a Transparency to the Waveguide 4-13

Verify that Lighting Is Enabled and Using Default Attributes 4-14
Sweep the Waveguide 4-15
5 - Setting Up the Problem 5-1
Set Up Boundaries and Excitations 5-1
Boundary Conditions 5-1
Assign Boundaries 5-2
Assign a Finite Conductivity Boundary to the Bottom and Side Faces 5-2
Assign a Perfect E Symmetry Boundary to the Top Face 5-9
Excitation Conditions 5-14
Assign Excitations 5-15
Assign Wave Port 1 5-16
Assign Wave Port 2 5-17
Assign Wave Port 3 5-18
Assign Wave Port 4 5-19
Verify All Boundary and Excitation Assignments 5-20
6 - Set up and Generate a Solution 6-1
Specify Solution Options 6-1
Add a Solution Setup 6-1
Add a Discrete Frequency Sweep 6-4
Validate the Project Setup 6-6
Generating the Solution 6-7
Analyze the Setup You Defined 6-8
View the Solution Data 6-9
View the Profile Data 6-9
View the Convergence Data 6-11
View the Matrix Data 6-12
7 - Analyzing the Solution 7-1
Create an S-Parameters Report of S11, S12, S13, and S14 7-1
Create an S-Parameters Report of S12 and S14 7-3

Contents-2
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information of ANSYS, Inc. and its subsidiaries and affiliates.
Getting Started with HFSS: 20 GHz Waveguide Combiner

Scale the Magnitude and Phase for the Ports 7-5

Create a Mag E Field Overlay Cloud Plot 7-6
Create a Phase Animation of the Mag E Cloud Plot 7-8
Self-Study Challenge: 7-9

Contents-3
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Getting Started with HFSS: 20 GHz Waveguide Combiner

Contents-4
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information of ANSYS, Inc. and its subsidiaries and affiliates.
Getting Started with HFSS: 20 GHz Waveguide Combiner

1 - Introduction
This Getting Started guide describes how to set up and solve a two-way, low-loss waveguide com-
biner.
By following the steps in this guide, you will learn how to perform the following tasks in HFSS:
l Draw a geometric model.
l Modify a model’s design parameters.
l Assign variables to a model’s design parameters.
l Specify solution settings for a design.
l Validate a design setup.
l Run an HFSS simulation.
l Create plots and a field overlay of the results (see Results for Analysis).

The Sample Problem

For this problem, the waveguide combiner is a standard WR42 model with a four-port combining
junction. Each waveguide is 420 mils wide and 170 mils high. This type of waveguide combiner is
used to combine the output power of two 20 GHz solid state power amplifiers (SSPA) with a very
compact size and low insertion loss.
The outputs of the SSPAs are fed into Ports 2 and 4 of the waveguide with a 90-degree out-of-
phase separation to steer the output power of the amplifiers to port 1. Port 3 of the waveguide is the
isolated port where the impedance mismatch at the output (port 1) is absorbed.
This problem is also described and analyzed in the following reference:
Arcioni, Paolo, Perregrini, Luca, Bonecchi, Fulvio, “Low-Loss Waveguide Combiners for
Multidevice Power Amplifiers,” The Second International Conference on Electromagnetics in
Aerospace Applications, September 1991.
The geometry for this waveguide combiner problem is shown below:

Introduction {chapnum)-1
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Getting Started with HFSS: 20 GHz Waveguide Combiner

Results for Analysis

After setting up the waveguide combiner model and generating a solution, you will:
l Create Modal S-parameter reports (2D x-y plot).
l Create a field overlay cloud plot of the magnitude of E.
l Create an animation of the mag-E cloud plot.

Overview of the Interface

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

Note:

The background color can be changed from View> Modify Attributes> Background
Color.

Introduction {chapnum)-2
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Getting Started with HFSS: 20 GHz Waveguide Combiner

Project Manager window Displays details about all open HFSS projects. Each project has
its own project tree, which ultimately includes a geometric
model and its boundaries and excitations, material assign-
ments, analysis setups, and analysis results.
Message Manager window Displays error, informational, and warning messages for the act-
ive project.
Progress window Displays solution progress information.

Introduction {chapnum)-3
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Getting Started with HFSS: 20 GHz Waveguide Combiner

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 that has
been carried out. For example, if a circle was drawn, its com-
mand information would include the command’s name, the type
of coordinate system in which it was drawn, the circle’s center
position coordinates, the axis about which the circle was drawn,
and the size of its radius.
Modeler window Displays the drawing area of the active model, along with the
History Tree.
History Tree Displays all operations and commands carried out on the active
model, such as information about the model’s objects and all
actions associated with each object, and coordinate system
information.
Menu bar Provides various menus that enable you to perform all of the
HFSS tasks, such as managing project files, customizing the
desktop components, drawing objects, and setting and modi-
fying all project parameters.
Toolbars Provides buttons that act as shortcuts for executing various com-
mands.
Status bar Shows current actions and provides instructions.
Also, depending on the command being carried out, the status
bar can display the X, Y, and Z coordinate boxes, the Abso-
lute/Relative pull-down list to enter a point’s absolute or rel-
ative coordinates, a pull-down list to specify a point in Cartesian,
Cylindrical, or Spherical Coordinates, and the active model’s
unit setting.
Component Libraries Component libraries contain ready-to-insert 3D Components,
which are stored in the PersonalLib and in the SysLib folders.
Component Libraries allow easy access to the 3D Components.

Introduction {chapnum)-4
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Getting Started with HFSS: 20 GHz Waveguide Combiner

2 - Creating the New Project

Your goals in this chapter are as follows:
l Create a new project.
l Add an HFSS design to the project.
l Optionally add project notes.
l Select the Solution Type
l Save the project with a user-specified name.

This chapter describes how to create a project in which to save all the data associated with the prob-
lem. By default, when you launch the Ansys Electronics Desktop a new project named Projectn is
automatically created into which you can insert a new design HFSS design type.

You can also create a new project and insert a design manually.

Time It should take you approximately 10 minutes to work through this

chapter.

Add the New Project

1. Launch the Electronics Desktop application, if it is not already running.
2. If you have just started Electronics Desktop, a new project has already been created for you
automatically. You can skip this step. However, if you previously opened Electronics
Desktop and then closed the project you had been working on, do one of the following to cre-
ate a new project:
l From the menu bar, click File> New.

l From the Desktop tab of the ribbon, click New

A new project is listedat the top of the Project Manager in the Project Manager window. It is
named Projectn by default, where n is the order in which the design type was added to the

Creating the New Project 2-1

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Getting Started with HFSS: 20 GHz Waveguide Combiner

current session. Project definitions, such as boundaries and material assignments, are
stored under the project name in the Project Manager.

Insert an HFSS Design

The next step for this waveguide combiner problem is to insert an HFSS design into the new pro-
ject. On adding an HFSS design type, a design named HFSSDesignn with the solution type as
[Driven Modal] appears for the current project.
3. Select the project name (Projectn) at the top of the Project Manager window.
4. To manually insert an HFSS design into the project, do one of the following:
l Using the menu bar, click Project> Insert HFSS Design.
l Right-click the project name in the Project Manager window, and then select Insert>
Insert HFSS Design from the shortcut menu.

l In the Desktop tab of the ribbon, click Insert HFSS Design

l In the Desktop tab of the ribbon, choose HFSS from the Insert HFSS Design
pull-down.
An HFSS Design icon and heading are added to the Project Mnager, as shown below:

Creating the New Project 2-2

Add Project Notes

You can enter notes about your project, such as its creation date and a description of the device
being modeled. These notes are useful for keeping a running log of the project details and for future
reference.
To add notes to the project:
1. In the Project Manager, right-click the HFSS design type heading (default = HFSSDesignn)
and select Edit Notes from the short-cut menu.
The Design Notes window appears.
2. Click inside the window and type your notes, such as a description of the model, assumed
conditions, and the version of HFSS in which it is being created.
3. Click OK to save the notes with the current project.

Note:

To edit existing project notes, double-click Notes in the Project Manager. The Design
Notes window appears, and you can edit its content as needed.

Select the Solution Type

Before you draw the geometry, specify a solution type as follows:
1. Access the Solution Type dialog box using one of the following two methods:
l Using the menu bar, click HFSS> Solution Type.
l In the Project Manager, right-click HFSSDesignn and choose Solution Type from
the shortcut menu.

The Solution Type dialog box appears.

2. Ensure that the Modal solution type is selected.

Creating the New Project 2-3

Some of the possible solution types are described below:

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.
Terminal For calculating the terminal-based S-parameters of passive, high-fre-
quency structures with multi-conductor transmission line ports, which are
“driven” by a source.
Results in a terminal-based description related to voltages and currents.
Eigenmode For calculating the eigenmodes, or resonances, of a structure. The Eigen-
mode solver finds the resonant frequencies of the structure and the fields at
those resonant frequencies.

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

Save the Project

Next, save and name the new project.

Creating the New Project 2-4

It is important to save your project frequently to prevent loss of your work if a problem occurs.

Note:

By default, ANSYS Electronics Desktop autosaves your projects every ten edits. Auto-
save settings are found in the General> Desktop Configuration section of the General
Options. You can change the autosave interval or disable the feature.

To save the new project:

1. From the menu bar, 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, accept ANSYS Electronics Desktop Project File (*.aedt) as the
correct file type.
When you create an HFSS project, it is given an .aedt file extension by default and placed in
the project directory. Any files and subfolders related to that project are stored in the same
directory.
5. Click Save.
The project is saved to the specified location.

Note:

For more information on any topic in HFSS, such as coordinate systems and grids or
Modeler commands or windows, you can view the context-sensitive help:

l Click the Help button in a pop-up window.

l Press Shift+F1. The cursor changes to ?. Click on the item with which you need
help.
l Press F1. This opens the Help window. If you have a dialog open, the Help opens
to a page that describes the dialog.
l Use the commands from the Help menu.

At this point you are ready to set up the drawing region in preparation for drawing the waveguide
combiner.

Creating the New Project 2-5

PDF layout 2-6

3 - Set Up the Drawing Region

The next step is to set up the drawing region.
In this chapter, you will:
l Look at an overview of the Modeler window
l Learn about settings for the following four items:
l Coordinate System
l Units
l Grid
l Transparency

For this waveguide combiner problem, use the default coordinate system, specify the units, and
define the grid settings.

Overview of the Modeler Window

The area containing the model is called the drawing region. Models are drawn in the Modeler win-
dow, which appears in the desktop after you insert a design into the project.
As shown below, the Modeler window consists of a grid, coordinate axes, a scale indicator (Ruler),
and a History Tree. The grid is an aid to help visualize the location of objects. For more information
about the grid, see “Grid Settings”.
The History Tree displays all operations and commands carried out on the active model. See “His-
toryTree” for more information.

Set Up the Drawing Region 3-1

Coordinate System Settings

For this waveguide combiner problem, use the fixed, default global coordinate system (CS) as the
working CS. This is the current CS with which objects being drawn are associated.
HFSS has three types of coordinate systems that let you easily orient new objects: a global coordin-
ate system, a relative coordinate system, and a face coordinate system. Each of these coordinate
systems has an x-axis that lies at a right angle to 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.

Global CS The fixed, default CS for each new project. It cannot be edited or 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 to a geometric feature. Rel-
ative CS enables you to easily draw objects that are located relative to other
objects.

Set Up the Drawing Region 3-2

Face CS A user-defined CS. Its origin is specified on a planar object face. Face CS
enables you to easily draw objects that are located relative to an object’s
face.

Units Settings
Specify the drawing units for your model. For this waveguide combiner problem, set the drawing
units to mils (1 mil = One thousandth of an inch).
To set the drawing units:
1. Access the Set Model Units dialog box using one of the following two methods:
l Using the menu bar, click Modeler> Units.
l From the Draw tab of the ribbon, click Units.
2. Select mil from the Select units drop-down menu, and ensure Rescale to new units is
cleared.

Note:
l When Rescale to new units is not selected, the dimensions of any existing
geometry are updated to keep the size and location of the objects
unchanged. For example, a 1 in cube would become an equivalent 25.4 mm
cube when changing units from inch to mm.
l When Rescale to new units is activated, the numerical values of any exist-
ing dimensions remain unchanged, but the units are redefined. This process
changes the physical size and location of the previously drawn objects. For
example, a 1 inch cube with its lower left corner placed 1 inch in the +X dir-
ection from the origin would become a 1 mm cube placed 1 mm from the ori-
gin. Use this option to correct objects drawn using the correct numerical
values but the wrong units setting.
l In either case, the grid spacing is adjusted to reflect the new units.

3. Click OK to accept mils (thousandths of an inch) as the drawing units for this model.

Grid Settings
The grid displayed in the Modeler window is a drawing aid that helps to visualize the location and
size of objects. In addition, the cursor can snap to grid points when drawing objects graphically,
depending on the settings under 3D Modeler> Snap in the General Options. The points on the
grid are divided by their local x-, y-, and z-coordinates, and grid spacing is set according to the cur-
rent project’s drawing units.
To edit the grid’s properties, click Grid Settings on the View menu. You can control the grid type
(Cartesian or polar), style (dots or lines), density, spacing, or visibility.

Set Up the Drawing Region 3-3

For this waveguide combiner project, it is not necessary to edit any of the grid’s default properties.

Transparency Setting
Set the default transparency for objects to 0.4.
To set the default transparency for new objects:
1. Access the Options dialog box using one of the following two methods:
l From the menu bar, click Tools> Options> General Options.

l In the Desktop tab of the ribbon, click General Options.

Set Up the Drawing Region 3-4

2. Expand the 3D Modeler option and, under Display, click Rendering.

3. Change Default transparency to 0.4 and click OK.

Set Up the Drawing Region 3-5

PDF layout 3-6

4 - Creating the Model Geometry

This chapter shows you how to create the geometry for the waveguide combiner problem
described earlier. Your goals are as follows:
l Drawing the objects that make up the waveguide combiner.
l Assigning color and transparency to the objects.
l Assigning materials to the objects.

The geometry for this model consists of a single standard WR42 waveguide combiner object with a
four-port, low-loss combining junction. Each waveguide is 420 mils wide and 170 mils high.
The waveguide combiner starts out as a 2D sheet object (a geometric object containing surface
area but no volume). You draw the sheet object on the XY plane as a series of polylines enclosing
an area. Since this model is symmetrical about the xz plane, just draw the left-half of the structure's
outline. Then, complete the outline of the sheet object by duplicating and mirroring the left side to
create the right side. Finally, merge (that is, Union) the two sides together.
Create the 3D waveguide combiner by sweeping the 2D sheet object in the Z direction. To reduce
the size of this model, only sweep the outline half of its actual height (170 mils / 2 = 85 mils). Assign
a perfect E symmetry boundary to the top face of the waveguide combiner to represent the other
(unmodeled) half of the device. This technique reduces the mesh volume to half that of the full
model, thereby shortening the solution time.
For a detailed description about this waveguide combiner, see “The Sample Problem”.
You are all set to draw the geometry.

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

Draw the Polyline1 Object

The first object to be drawn is the left half of the waveguide combiner. Do this by drawing a polyline
object consisting of 25 points. This procedure results in a 2D sheet object with a default name of
Polyline1.
To draw Polyline1, you can use one of the following two methods:

Method 1: Draw a Series of Polylines Graphically and Edit the Point

Coordinates Afterward
The first method is to begin by graphically drawing a closed polyline sequence with 25 mouse
clicks. You then use the basic approach described in the Verify the Points of a Polyline section

Creating the Model 4-1

to specify the correct coordinates for each point. Revise the coordinates via the docked Properties
window for each CreateLine segment in the History Tree.

1. Using the menu bar, click Draw> Line or, on the Draw ribbon tab, click Draw line.
2. Click an initial point at the origin (click 1), and incrementally count your clicks from the initial
one to the 25th click. For convenience, follow a counter-clockwise series of movements
where no line segment crosses over the path of a previous segment and place the last click
back at the origin.
3. Right-click in the Modeler window and choose Done from the shortcut menu.
The resultant sheet object is shaded and named Polyline1, and the Properties dialog box
appears.
4. Click OK to dismiss the Properties dialog box.
5. Go to the Verify the Points of a Polyline section and follow the procedure to specify the
correct coordinates for each segment.
Method 2: Enter the X and Y Coordinates for Each Point
The second method is more direct than the first. In this case, you enter the point coordinates in
sequence for each vertex of the 25 polyline segments while creating them.

1. From the menu bar, click Draw> Line or, on the Draw ribbon tab, click Draw line.

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

2. Press Tab to move to the X text box along the bottom of the program window. Then, specify
the first point of the line by typing the following X, Y, and Z values, pressing Tab to jump to
the next coordinate text box. (You can also press Shift+Tab to jump to the previous text
box.):

X Coordinate 0
Y Coordinate 0
Z Coordinate 0

Note:

Ensure that the drop-down menu to the right of the coordinate text boxes is set to
Absolute for the first point and for all subsequent points. Also, be careful not to
move the mouse while typing coordinates into the text boxes. Doing so will cause
the numerical values to revert to the graphical location of the cursor.

3. Press Enter to accept the first point.

Creating the Model 4-2

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

Note:

If you accidentally enter an incorrect set of coordinates, you can delete the last
point you entered by right-clicking in the Modeler window and then clicking Undo
Previous Segment on the shortcut menu.

Point X Coordinate Y Coordinate Z Coordinate

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
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

Creating the Model 4-3

5. Right-click in the Modeler window, and click Close Polyline on the shortcut menu.

A sheet object appears in the History tree, it is shaded (selected) in the drawing region, and
the Properties dialog box appears.

Note:

Objects are automatically selected immediately after being drawn so that you can
instantly view the default attributes and optionally modify them.

6. The object is named Polyline1 by default, as displayed in the Attributes tab of the Prop-
erties dialog box.

7. Click OK to dismiss the Properties dialog box.

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

The completed left-half of the waveguide combiner should appear in the Modeler window, as
shown below:

Creating the Model 4-4

Verify the Points of Polyline1

Before you duplicate and mirror the object Polyline1 to create the right-side of the waveguide com-
biner, it is important that you make sure all the points you entered are correct. You will not obtain
the expected simulation results if the geometry is not exactly as described in this exercise.
The image below shows all the point locations used to define the segments for the object
Polyline1:

Creating the Model 4-5

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 Polyline1 to
see 24 CreateLine commands under CreatePolyline.

Creating the Model 4-6

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 docked Properties window, as shown below:

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

Creating the Model 4-7

9 -27 -792 0
10 -27 -467 0
11 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

4. To edit an incorrect point value:

a. In the History Tree, select the CreateLine object you want to edit.
b. In the Value column of the docked Properties window, enter the correct x, y, and z
coordinates (separated by commas).
The value entered for Point2 automatically applies to Point1 for the next segment.
Therefore, you need only edit Point2 for each of the subsequent CreateLine seg-
ments.
c. Press Enter to apply the new values to the model.

As you enter the values, the display of each segment updates. You may need to click
Fit All in the Draw ribbon tab to resize the object view within the Modeler window.

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

Creating the Model 4-8

Duplicate and Mirror Polyline1

Since the waveguide combiner is symmetric about the xz plane you can duplicate and mirror the
object Polyline1 and create the right-half of the waveguide combiner. This results in a 2D sheet
object with a default name of Polyline1_1.
To duplicate the object Polyline1:
1. Select the object Polyline1 by either clicking it in the Modeler window or selecting it in the
History Tree.
2. You can initiate the duplicate and mirror command using either of the following two methods:
l Using the menu bar, click Edit>Duplicate>Mirror.
l In the Draw ribbon tab, click Thru Mirror (Mirror Duplicate).
3. Press F3 to use the coordinate-text-box method of defining the mirror plane (rather than
filling in the DuplicateMirror dialog box).
4. Press Tab to move to the X text box at the bottom of the program window and then enter 0
Tab 0 Tab 0 to specify the origin (X=0, Y=0, Z=0) as a point on the mirror plane.
5. Press Enter.

This point and the next point you specify define a line perpendicular to the mirror plane, fully
locating and orienting the plane.

6. Press Tab to move to the dY text box and enter 1 to specify the normal point. (Ensure that
the X and Z coordinates are both 0.)
The normal line defined by this point lies along the Y axis.
7. Press Enter. The object is duplicated and mirrored, and the Properties dialog box appears.

8. Click OK to dismiss the Properties dialog box.

The object Polyline1_1, a duplicate of object Polyline1, appears on the opposite side of the

Creating the Model 4-9

mirror plane you specified and should look like the following image:

Unite Polyline1 and Polyline1_1

After successfully creating both halves of the waveguide combiner, unite them to make a single
waveguide combiner object.
To unite both halves of the waveguide combiner:
1. Select Polyline1.
2. While holding down the Ctrl key, also select Polyline1_1.

Both objects (Polyline1 and Polyline1_1) are highlighted in the History Tree, and the status
bar indicates that the number of objects selected is two.

Creating the Model 4-10

Note:

By default, the objects being joined to the first object selected are not preserved for
later use. However, they do become part of the first object selected.

For this waveguide combiner problem, you do not need to preserve any objects for
later use. However, if you wanted to keep a copy of the objects being joined to the
first object selected, you could use one of the following methods:

l Copy the objects, perform the Boolean Unite operation, and then paste the
original objects back into the design after uniting them.
l From the menu bar, click Tools> Options> General Option, go to 3D
Modeler> Operation, and then select the Clone tool objects before unit-
ing option. This option instructs the 3D Modeler to always keep a copy of the
original objects being joined. Finally, perform the Boolean Unite operation.

3. Click 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 united object appears in the Modeler window, as shown below:

Creating the Model 4-11

Modify the Waveguide’s Attributes

The next step in creating the waveguide is to modify its default attributes that are displayed in the
docked Properties window. You will rename the object, assign a color, adjust the transparency
level, and verify the material assignment. You will also verify the global lighting attributes.

Rename Polyline1
Change the default name of the united object to specify that it is a waveguide combiner. To modify
the name:
1. Reselect Polyline1 if it is not already selected.
2. Under the Attribute tab of the docked Properties window, click Polyline1 in the Name row.
3. Type waveguide to rename the object, and press Enter to accept the new name.

Assign a Color to the Waveguide

With the waveguide still selected and the Attribute tab of the Properties window still displayed:
4. Click the currently displayed color bar in the Value column of the Color row. The Color
palette appears.

Creating the Model 4-12

5. 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 waveguide.

Note:

While the waveguide is selected, it retains the selection color. To see the assigned
color, deselect the waveguide by clicking a location in the drawing window outside
of the waveguide.

Assign a Transparency to the Waveguide

To assign a transparency level to the waveguide:
1. Reselect the object waveguide, if it is not already selected.
2. Under the Attribute tab of the docked Properties window, click the default value 0.4 in the
Values column of the Transparency row.

The Set Transparency window appears.

3. Move the slider to the right to increase the transparency to 0.7, or type this value into the text
box.
4. Click OK to accept the new transparency value.
5. In the Modeler window, click outside the waveguide object to deselect it for viewing the res-
ulting model appearance.

Creating the Model 4-13

Verify that Lighting Is Enabled and Using Default Attributes

It is not necessary to adjust the global lighting parameters for this waveguide combiner problem.
However, if you want, you can change the default ambient and distant light source properties at this
time.
To verify that default lighting attributes are enabled:
1. Using the menu bar, click View> Modify Attributes> Lighting.

The Lighting Properties dialog box appears.

2. Verify that the Do not use lighting option is cleared (to enable lighting effects).
3. Click Reset from default to restore default settings.

Note:

Optionally, if you have customized lighting settings that you wish to retain, click
Save as default to make your settings the default configuration.

4. Click OKto accept the settings and close the Lighting Properties dialog box.

Creating the Model 4-14

Sweep the Waveguide

Next, you must sweep the 2D object waveguide along a vector to create a 3D solid object as the
final waveguide combiner model.
To sweep the waveguide along a vector:
1. Select the object waveguide.
2. Execute the Sweep command using one of the following three methods:
l From the menu bar, click Draw> Sweep> Along Vector.
l In the Draw ribbon tab, click Sweep along vector.
l Right-click in the Modeler window and choose Edit> Sweep> Along Vector from
the shortcut menu.
3. Specify the vector along which you want to sweep the object:
a. Enter (0, 0, 0) in the X, Y, and Z coordinate text boxes to specify the start point and
press Enter.
b. Tab into the dZ text box (if the cursor is not already there), type 85 to specify the end
point, and press 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 (positive angles) or contracted (negative
angles) as it is swept.

5. You can keep whatever the current Draft type setting is, since this setting will only matter
when a non-zero draft angle is specified or the object is swept along a nonlinear path.

For more information, see Draft Type Options.

6. Click OK to complete the sweep.

The Properties dialog box appears.

7. Click OK to dismiss the Properties dialog box.

Your completed 3D object waveguide should resemble the one shown below:

Creating the Model 4-15

8. Click File>Save, or click the Save icon ( ) available on any ribbon tab , to save the geo-
metry.
Now you are ready to assign all boundaries and excitations to the waveguide combiner.

Creating the Model 4-16

5 - Setting Up the Problem

Now that you have created the geometry and assigned all materials for the waveguide combiner
problem, you are ready to define its excitations and boundaries.
Your goals for this chapter are to:
l Define boundary conditions, in this case finite conductivity boundaries.
l Define the wave ports through which the signals enter and leave the waveguide combiner.
l Verify you correctly assigned the boundaries and excitations to the model.

Set Up Boundaries and Excitations

Now that you have created the waveguide combiner model and defined its properties, you must
define the boundary and excitation conditions. These conditions specify the excitation signals enter-
ing the structure, the behavior of electric and magnetic fields at various surfaces in the model, and
any special surface characteristics.
You are ready to set up the problem.

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

chapter.

Boundary Conditions
Boundaries specify the behavior of magnetic and electric fields at various surfaces. They can also
be used to identify special surfaces —such as resistors— whose characteristics differ from the
default.
The following two types of boundary conditions will be used for this waveguide combiner problem:

Finite con- This type of boundary represents an imperfect conductor. HFSS does not com-
ductivity pute the field inside these objects; the finite conductivity boundary approximates
the behavior of the field at the surfaces of the objects. Any skin-effect losses will
be properly taken into account.
For this waveguide combiner problem, a finite conductivity boundary is assigned
to the bottom face and the side faces of the model (excluding the four ports).

Symmetry In structures that have an electromagnetic plane of symmetry, such as this wave-

Setting Up the Problem 5-1

guide combiner model, the problem can be simplified by modeling only one-half
of the model and identifying the exposed surface as a perfect H or perfect E
boundary.
For this waveguide combiner problem, a perfect E symmetry boundary is
assigned to the top face of the model.

Assign Boundaries
First, assign all boundary conditions to the model. These assignments include two finite con-
ductivity boundaries and one perfect E symmetry boundary. For more about the different types of
boundaries available in HFSS, see “Boundary Conditions”.

Assign a Finite Conductivity Boundary to the Bottom and Side Faces

Assign a finite conductivity boundary to all the waveguide combiner’s side faces, excluding the four
port faces.
As discussed in “Boundary Conditions”, finite conductivity boundaries represent imperfect con-
ductors. At such boundaries, the following condition holds:

where
l Etan is the component of the E-field that is tangential to the surface.
l Htan is the component of the H-field that is tangential to the surface.
l Zs is the surface impedance of the boundary, , where

l d is the skin depth, , of the conductor being modeled.

l w is the angular frequency of the excitation wave.
l s is the conductivity of the conductor.
l m is the permeability of the conductor.
The fact that the E-field has a tangential component at the surface of imperfect conductors sim-
ulates the case in which the surface is lossy.
The surfaces of any objects defined to be non-perfect conductors are automatically set to finite con-
ductivity boundaries. HFSS does not attempt to compute the field inside these objects; the finite
conductivity boundary approximates the behavior of the field at the surfaces of the objects.
The finite conductivity boundary condition is valid only if the conductor being modeled is a good con-
ductor, and if the conductor’s thickness is much larger than the skin depth in the given frequency
range.

Setting Up the Problem 5-2

To assign a finite conductivity boundary to the side faces of the waveguide combiner:
1. Right-click in the Modeler window, then click Select Faces on the shortcut menu.

In this mode you can select or de-select an object’s faces instead of the entire object. When
the mouse hovers over a face in the Modeler window, that face is outlined, which indicates
that it will be selected when you click.

2. Select all the side faces of the waveguide object except for the four port faces. Additionally,
select the bottom face. Exclude the top face. Hold down the Ctrl key when clicking to select
multiple faces.

Note:
o To minimize or eliminate the necessity of changing the model viewpoint, you
can select a face that's behind another face. Click on the face you want to
select (even though another face is in front of it). The face in the foreground
is initially selected. Then, press B on the keyboard (or right-click and choose
Next Behind from the shortcut menu) to select the next face behind the one
just selected.
o You can also be creative with techniques for selecting multiple items in one
operation. For example, click and drag to draw selection rectangles, noting
that the direction you drag affects the selection behavior:
n When dragging left-to-right, only items that are fully enclosed within
the rectangle are selected.
n When dragging right-to-left, all items that are fully enclosed withing
the rectangle and all items that the rectangle crosses through are
selected.

The selected faces should look like the figure below. Note that the two port faces in the fore-
ground (+X end) appear to be selected in the first image, but they are not. Due to the model
viewpoint, the bottom highlighting is seen through these two faces.

Setting Up the Problem 5-3

If you rotate the model viewpoint, you will see that these two faces are not selected, but from
that viewpoint, the other two ports will then look like they're selected.

Setting Up the Problem 5-4

3. On the HFSS menu, click Boundaries> Assign> Finite Conductivity or, right-click in the
Modeler window and choose Assign Boundary> Finite Conductivity.

The Finite Conductivity Boundary window appears.

Setting Up the Problem 5-5

4. Set the material to aluminum. To do this:

a. Select the Use Material check box.
b. Click the material button (where the default vacuum is displayed).

The Select Definition window appears. By default, this material browser lists all mater-
ials in the global material library, as well as the local material library for the current pro-
ject, which is a subset of the global library.

Setting Up the Problem 5-6

c. 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 the finite
conductivity boundary.

5. Clear Infinite Ground Plane if it is selected.

If selected, this option simulates the effects of an infinite ground plane, and it only affects the
calculation of near- and far-field radiation during post processing. The 3D Post Processor
models the boundary as a finite portion of an infinite, perfectly conducting plane.

6. Click OK to accept the default name FiniteCond1 and apply the boundary.
7. The resulting finite conductivity boundary is applied to the side faces of the object waveguide
and now appears as a subentry of Boundaries in the Project Manager. Select FiniteCond1
to highlight the assigned boundary if it is not already displayed. Your model should look like
the following image:

Setting Up the Problem 5-7

By default, the geometry, name, and vectors for the boundary appear in the Modeler win-
dow. For this waveguide combiner problem, it is not necessary to edit any of the boundary’s
default visualization settings.

Setting Up the Problem 5-8

Note:

To edit a boundary’s visualization settings:

1. Click HFSS> Boundaries> Visualization if you want to show or hide

boundaries.
2. Clear the View Geometry, View Name, or View Vector selection of bound-
aries that you want to hide from view. Select the options you want to show in
the Modeler window.
3. Click Close.

Assign a Perfect E Symmetry Boundary to the Top Face

HFSS has a boundary condition specifically for symmetry planes. Instead of defining a perfect E or
perfect H boundary, you define a perfect E or perfect H symmetry plane.
When you are defining a symmetry plane, you must decide which type of symmetry boundary
should be used, a perfect E or a perfect H. In general, use the following guidelines to decide which
type of symmetry plane to use:
l If the symmetry is such that the E-field is normal to the symmetry plane, use a perfect E sym-
metry plane.
l If the symmetry is such that the E-field is tangential to the symmetry plane, use a perfect H
symmetry plane.
The simple two-port rectangular waveguide shown below illustrates the differences between the
two types of symmetry planes. The E-field of the dominant mode signal (TE10) is shown. The wave-
guide has two planes of symmetry, one vertically through the center and one horizontally.
l The horizontal plane of symmetry is a perfect E surface. The E-field is normal and the H-field
is tangential to that surface.
l The vertical plane of symmetry is a perfect H surface. The E-field is tangential and H-field is

Setting Up the Problem 5-9

normal to that surface.

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

Setting Up the Problem 5-10

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.

3. On the HFSS menu, click Boundaries> Assign> Symmetry.

The Symmetry Boundary dialog box appears.

Setting Up the Problem 5-11

4. Select Perfect E as the symmetry type.

5. Because you defined a symmetry plane (allowing the model of a structure 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 E plane of symmetry
splits a structure in two, only one-half of the voltage differential and one-half of the power
flow can be computed by the system.

Therefore, since the impedance, Zpv, is given by , the computed value is one-
half the desired value. An impedance multiplier of 2 must be specified in such cases.

Do the following to edit the impedance multiplier:

a. Click Edit Port Impedance Multiplier.

The Edit Port Impedance Multiplier dialog box appears.

Setting Up the Problem 5-12

b. Enter the value 2 in the Impedance Multiplier box, and then click OK.

Note:

You can also set the impedance multiplier from the HFSS menu by clicking
Excitations> Edit Port Impedance Multiplier.

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

The resulting perfect E symmetry boundary condition is assigned to the top face the object
waveguide, as shown below. Select Sym1 in the Project Manager if the boundary is not
already displayed.:

Setting Up the Problem 5-13

Excitation Conditions
Wave ports define surfaces exposed to non-existent materials (generally the background or mater-
ials defined to be perfect conductors) through which excitation signals enter and leave the struc-
ture.
Wave ports represent places in the geometry through which excitation signals enter and leave the
structure. They are used when modeling strip lines and other waveguide structures, such as this
waveguide combiner problem. Wave ports are typically placed on the perfect E interface between
the 3D object and the background to provide a window that couples the model device to the
external world.
For this waveguide combiner problem, a wave port is assigned to each end-face of the model’s four
waveguide sections.

Setting Up the Problem 5-14

Assign Excitations
Now you will assign all excitations to the waveguide combiner model. These excitations include
wave ports assigned to each end face of the model’s four waveguide sections, as shown below.
The model orientation in this image is Trimetric, and the ports have been selected for clarity:

Wave ports represent places in the geometry through which excitation signals enter and leave the
structure. HFSS assumes that each wave port you define is connected to a semi-infinitely long
waveguide that has the same cross-section and material properties as the port.
When solving for the S-parameters, HFSS assumes that the structure is excited by the natural field
patterns (modes) associated with these cross-sections. The 2D field solutions generated for each
wave port serve as boundary conditions at those ports for the 3D problem. The final field solution
computed must match the 2D field pattern at each port.
For this waveguide combiner model, you will assign four wave ports to the locations shown in the
above image.

Setting Up the Problem 5-15

The functions of each wave port in this waveguide combiner model are as follows:

Port 1 One of two output ports, along with Port 3.

In a later procedure, each of the opposite two ports (2 and 4) will
receive the output from a solid-state power amplifier (SSPA). The out-
put at Port 1 depends on the phase angle between the inputs applied to
Ports 2 and 4. With the Port 4 input 90-degrees out-of-phase with Port
2, we expect all of the power to flow out of Port 1, fully combining the
SSPA outputs.
Port 2 One of two input ports, along with Port 4, to which the output of an
SSPA will be fed.
Port 3 One of two output ports, along with Port 1.
The output at Port 3 depends on the phase angle between the inputs
applied to Ports 2 and 4. With the Port 4 input 90-degrees out-of-phase
with Port 2, we expect Port 3 to be isolated with essentially zero output.
Port 4 One of two input ports, along with Port 2, to which the output of an
SSPA will be fed.
Port 4 will receive the output of the SSPA but 90-degree out-of-phase
relative to Port 2.

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 or, right-click in the Modeler
window and choose Assign Excitation> Wave Port.

The Wave Port wizard appears.

4. In the Wave Port: General dialog box, enter the name WavePort1, keep the default Mode
settings, and click Next.
5. In the Wave Port: Post Processing dialog box, accept the default settings and click Finish to
complete the wave port assignment for port 1.

WavePort1 is assigned to the waveguide and now appears as a subentry of Excitations in

the Project Manager. Select WavePort1 if it is not already displayed on the model.

Setting Up the Problem 5-16

Assign Wave Port 2

To assign wave port 2, you will use the same procedure you just followed to 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 ωt = 0 is arbit-
rary; the field can always point in one of at least two directions.
For both wave port 2 and wave port 4, you must calibrate the port relative to some reference ori-
entation by defining an integration line in the up (that is, +Z) direction.
To assign wave port 2:
1. Deselect WavePort1 that you just assigned, if it is still selected.
2. In Select Faces mode, select the face of port 2.
3. Zoom in on the face of port 2.
4. On the HFSS menu, click Excitations> Assign> Wave Port.

The Wave Port wizard appears.

5. In the Wave Port: General dialog box, enter the name WavePort2.
6. Click in row 1 of the Integration Line column and choose New Line from the drop-down
menu.

The Wave Port wizard disappears while you draw the vector.

Setting Up the Problem 5-17

7. Define the integration line:

a. Select the start point by clicking the center of the bottom edge of the face. Your cursor
will appear as a triangle when it is at this exact location, and it will snap to this midpoint
when clicked.
b. Select the end point by clicking the center of the top line on the face, which is directly
vertical to the start point you just selected. Again, your cursor will appear as a triangle
when it is at this exact location.

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

The Wave Port wizard reappears, still at the Wave Port: General step.

8. Click Next.
9. In the Wave Port: Post Processing dialog box, accept the default settings and click Finish to
complete the wave port assignment for port 2.

WavePort1 is assigned to the waveguide and now appears as a subentry of Excitations in

the Project Manager. This wave port, with its integration line, is shown below:

Assign Wave Port 3

To assign wave port 3, use the same procedure you followed when you assigned wave port 1:
1. Deselect WavePort2 that you just assigned, if it is still selected.
2. In Select Faces mode, select the face of port 3.
3. On the HFSS menu, click Excitations> Assign> Wave Port.

The Wave Port wizard appears.

4. In the Wave Port: General dialog box, enter the name WavePort3, keep the default Mode
settings, and click Next.
5. In the Wave Port:Post Processing step, accept the default settings and click Finish to com-
plete the wave port assignment for port 3.

Setting Up the Problem 5-18

WavePort3 is assigned to the waveguide and now appears as a subentry of Excitations in

the Project Manager.
Assign Wave Port 4
To assign wave port 4, you will use the same procedure you followed when you assigned wave
port 2:
1. Deselect WavePort3 that you just assigned, if it is still selected.
2. In Select Faces mode, select the face of port 4.
3. Zoom in on the face of port 4.
4. On the HFSS menu, click Excitations> Assign> Wave Port.

The Wave Port wizard appears.

5. In the Wave Port: General dialog box, enter the name WavePort4.
6. Click in the first row of the Integration Linecolumn and select New Line from the drop-
down menu.

The Wave Port wizard disappears while you draw the vector.

7. Define the integration line:

a. Select the start point by clicking the center of the bottom line on the face. Your cursor
will appear as a triangle when it is at this exact location, and it will snap to this midpoint
when clicked.
b. Select the end point by clicking the center of the top line on the face, which is directly
vertical to the start point you just selected. Again, your cursor will appear as a triangle
when it is at this exact location.

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

The Wave Port wizard reappears at the Wave Port: General step.

8. Click Next.
9. In the Wave Port: Post Processing dialog box, accept the default settings and click Finish to
complete the wave port assignment for port 4.

WavePort4, with its integration line, is assigned to the waveguide and now appears as a
subentry of Excitations in the Project Manager.

Setting Up the Problem 5-19

Note:

To edit a wave port assignment:

1. In the Project Manager window, double-click the name of the wave port
assignment listed in the tree.

The Wave Port dialog box appears.

2. Click the appropriate tabs (General, Post Processing, Defaults) to edit any
port assignment information.
3. Click OK to apply the assignment revisions.

Verify All Boundary and Excitation Assignments

Now that you have assigned all the necessary boundaries and excitations to a model, you should
review their specific locations on the model in the solver view.
When you verify boundaries and excitations in the solver view, you review the locations of the
boundaries and excitations as you have defined them for generating a solution (solving).
HFSS runs an initial mesh and determines the locations of the boundaries and excitations on the
model.
Then, you can select a boundary or excitation from the list in the Boundary Display (Solver
View) window to view its highlighted area in the model.
To check the solver’s view of boundaries and excitations:
1. Click HFSS> Boundary Display (Solver View) or right-click the HFSSDesignx entry in
the Project Manager and choose HFSS> Boundary Display (Solver View) from the short-
cut menu.

HFSS runs an initial mesh and determines the locations of the boundaries 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.

Setting Up the Problem 5-20

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.

l Visible to Solver appears in the Solver Visibility column for each boundary that is
valid.
l Overridden appears in the Solver Visibility column for each boundary or excitation
that overwrites any existing boundary or excitation with which it overlaps.
3. Verify that the boundaries or excitations you assigned to the model are being displayed as
you intended for solving purposes.
4. If required, modify the parameters for those boundaries or excitations that are incorrect.
5. Click Close, and then, from the File menu, click Save. Or, in any tab of the ribbon, click Save
.

Warning:

Be sure to save your models frequently. While ANSYS Electronics Desktop does

periodically autosave models, the most convenient way to prevent loss of work in
the event of a problem is to save frequently.

You are now ready to set up the solution parameters for this waveguide combiner problem and gen-
erate a solution.

Setting Up the Problem 5-21

PDF layout 5-22

6 - Set up and Generate a Solution

Now that you have defined and verified all the boundaries and excitations for the waveguide com-
biner problem, you are ready to set up and generate a solution.
Your goals for this chapter are to:
l Set up the solution parameters that will be used in calculating the solution.
l Validate the project setup.
l Generate the solution.
l View the solution data, such as convergence and matrix data information.

Time Aside from the solution time, it should take about 15 minutes for you to complete
the setup steps and to review the solution data.
Depending on your computing resources, the solution time may vary con-
siderably. This problem solved in approximately 10 minutes on a 1.4 GHz PC
with 1 gigabyte of RAM. On a 12-core, 3 GHz, Xeon-processor-based PC with
64 GB of RAM, the solution took approximately 50 seconds to complete.

Specify Solution Options

Before you can generate a solution, you need to specify the solution parameters. This controls how
HFSS computes the requested solution.
Each solution setup includes the following information:
l General data about the solution’s generation.
l Adaptive mesh refinement parameters, if you want the mesh to be refined iteratively in areas
of highest error.
l Frequency sweep parameters, if you want to solve over a range of frequencies.
You can define more than one solution setup per design. However, you will 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 a solution setup to the wave-
guide combiner design.
To add a solution setup to the design:

Set up and Generate a Solution 6-1

1. Use one of the following three methods to add a solution setup to the desigh:
l From the HFSS menu, click Analysis Setup> Add Solution Setup> Advanced.

l From the Simulation ribbon tab, click Setup> Advanced.

l From the Project Manager, right-click Analysis and choose Add Solution Setup>
Advanced.

The Driven Solution Setup dialog box appears.

Set up and Generate a Solution 6-2

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

General Includes general solution settings.

Options Includes mesh options, adaptive options, and solution settings.

Advanced Includes advanced settings for initial mesh generation and adaptive analysis.
Includes mesh generation options for model ports.
Defaults Enables you to save the current settings as the defaults for future solution
setups or revert the current settings to HFSS’s standard settings.

2. Under the General tab:

a. Specify the following values:

Solution Fre- 20 GHz

quency For every modal driven solution
setup, you must specify the fre-
quency at which to generate the solu-
tion. For this waveguide combiner
model, you will solve over a range of
frequencies, which will require you to
define a frequency sweep in “Add a
Discrete Frequency Sweep”. If a fre-
quency sweep is solved, an adaptive
analysis is performed only at the solu-
tion frequency.

Maximum Number 9
of Passes The Maximum Number of Passes
value is the maximum number of
mesh refinement cycles that you
would like HFSS to perform. This
value is a stopping criterion for the
adaptive solution; if the maximum
number of passes has been com-
pleted, the adaptive analysis stops. If
the maximum number of passes has
not been completed, the adaptive

Set up and Generate a Solution 6-3

analysis will continue unless the con-

vergence criteria are reached.

Maximum Delta S 0.001

per Pass The delta S is the change in the mag-
nitude of the S-parameters between
two consecutive passes. The value
you set for Maximum Delta S Per
Pass is a stopping criterion for the
adaptive solution. If the magnitude
and phase of all S-parameters
change by an amount less than this
value from one iteration to the next,
the adaptive analysis stops. Other-
wise, it continues until the requested
number of passes is completed.

b. Accept all remaining default settings.

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 MANAGER.
Add a Discrete Frequency Sweep
To generate a solution across a range of frequencies, you must add a frequency sweep to the solu-
tion setup. HFSS performs the sweep after the adaptive solution.
For this waveguide combiner model, you will add a Discrete frequency sweep to the solution setup.
A Discrete sweep generates field solutions at specific frequency points in a frequency range. For
this waveguide combiner 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 increments of 0.1 GHz. By default, the field solu-
tion is only saved for the final frequency point. Be aware that HFSS uses the finite element mesh
refined during an adaptive solution at the solution frequency. It uses this mesh without further refine-
ment. Because the mesh for the adaptive solution is optimized only for the solution frequency, it is
possible that the accuracy of the results could vary at frequencies significantly far away from this fre-
quency. If you wish to minimize the variance, you can opt to use the center of the frequency range
as the solution frequency. Then, after inspecting the results, run additional adaptive passes with
the solution frequency set to the critical frequencies.
Add a discrete frequency sweep to the solution setup:

Set up and Generate a Solution 6-4

1. Select Setup1 under Analysis in the Project Manager.

2. Begin adding a frequency sweep using one of the following three methods:

a. From the Simulation ribbon tab, click Sweep.

b. From the HFSS menu, click Analysis Setup> Add Frequency Sweep.
c. Right-click Setup1 and choose Add Frequency Sweep from the shortcut menu.

The Edit Frequency Sweep dialog box appears.

3. From the Sweep Type drop-down menu, select Discrete.

4. In the Frequency Sweeps table, select or enter these values to define the sweep:

Type Linear Step

Start 19.5GHz
Stop 20.4GHz
Step Size 0.1GHz

The table title should indicate [10 points defined] after Frequency Sweeps.

5. Clear Save Fields (All Frequencies), if it's currently selected.

When selected, the Save Fields option saves the field solution for a specific point. The more
steps you request, the longer it takes to complete the frequency sweep. However, the S-
parameters are always saved for every frequency point.

The dialog box should look like the following image:

Set up and Generate a Solution 6-5

6. Click Preview to view each of the sweep values at the specified 0.1 GHz step size increment
within the frequency range you specified.
7. Click OK.

Sweep now appears as a subentry under Setup1 in the Project Manager.

Validate the Project Setup

Before you run an analysis on the waveguide combiner model, it is important to first perform a val-
idation check on the project. HFSS runs a check on all the setup details of the active project to
verify that all the necessary steps have been completed and their parameters are reasonable.
To perform a validation check on the project wg_combiner:
1. From the menu bar, click HFSS> Validation Check or, from the Simulation ribbon tab,

click Validate.

HFSS checks the project setup, and then the Validation Check window appears.

Set up and Generate a Solution 6-6

2. View the results shown in the Validation Check window.

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:

Indicates the step is complete.

Indicates the step is incomplete.

Indicates the step may require your attention.

3. If the validation check indicates that a step in your waveguide combiner project is incomplete
or incorrect, then return to the corresponding 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 project.

Generating the Solution

Now that you have entered all the appropriate solution criteria and validated the project setup, the
waveguide combiner problem is ready to be solved.

Set up and Generate a Solution 6-7

When you set up the solution setup criteria for this model, you specified values for an adaptive ana-
lysis (Maximum number of passes and Maximum delta S per pass). An adaptive analysis is a solu-
tion process in which the mesh is refined iteratively in regions where the error is high, which
increases the solution’s precision.
The following is the general process the program carries out during an adaptive analysis:
1. HFSS generates an initial mesh.
2. Using the initial mesh, HFSS computes the electromagnetic fields that exist inside the struc-
ture when it is excited at the solution frequency. (If you are running a frequency sweep, an
adaptive solution is performed 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 adapt-
ive passes is complete.
6. If a frequency sweep is being performed, as with this waveguide combiner problem, HFSS
then solves the problem at the other frequency points without further refining the mesh.

Analyze the Setup You Defined

Begin the solution process using any one of the following three methods:

l From the Solution ribbon tab, click Analyze All . This command solves every solution
setup in the design.
l Right-click Setup1 under Analysis in the Project Manager and choose Analyze. This com-
mand only solves the setup that you right-clicked.
l From the menu bar, click HFSS> Analyze All. This command solves every solution setup in
the design.

HFSS computes the 3D field solution inside the structure.

The Progress window displays the solution progress as it occurs:

Set up and Generate a Solution 6-8

Note:

The results that you obtain should be approximately the same as the ones given in this
section. However, there may be a slight variation between platforms and between dif-
ferent versions of the ANSYS Electronics Desktop software.

View the Solution Data

While the analysis is running, you can view a variety of profile, convergence, and matrix data about
the solution. The subsections that follow cover the available solution data.
View the Profile Data
While the solution proceeds, examine the computing resources, or profile data, used by HFSS dur-
ing the analysis.
The profile data is essentially a log of the tasks performed by HFSS during the solution. The log
indicates the length of time each task took and how much RAM/disk memory was required.
To view profile data for the solution:
l From the HFSS menu, click Results> Solution Data or, right-click Setup1 in the Project
Manager and choose Profile from the shortcut menu.

The Solution Data dialog box appears with the Profile tab selected.

Set up and Generate a Solution 6-9

Notice in the Simulation drop-down menu that Setup1 is selected as the solution 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 the
solution process, and the type of task that was performed.
For example, for the task mesh3d_adapt, Mesh3d is the
software module that adaptively refined the mesh.

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

Set up and Generate a Solution 6-10

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

Memory The amount of RAM/virtual memory required of your

machine to complete the task. This value includes the
memory required of all applications running at the time, not
just HFSS.

Information The number of tetrahedra in the mesh that were used dur-
ing the solution.

View the Convergence Data

To view convergence information for the solution:
l In the Solution Data window, click the Convergence tab.

Based on the criteria you specified for Setup1, you can view the following convergence
data:

Set up and Generate a Solution 6-11

l Number of adaptive passes completed and remaining.

When the solution is complete, you can view the number of adaptive passes that were per-
formed. If the solution converged within the specified stopping criteria, fewer passes than
requested may have been performed.

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

l 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 con-
secutive passes. This information is available after two or more passes are completed.

The convergence data can be displayed in table format or on a rectangular (X - Y) plot.

Note:

You can see that the solution is NOT CONVERGED. The Max. Mag. Delta S value
at the ninth pass is greater than the value that was specified in the setup (0.001).
You may decide that the level of accuracy achieved is acceptable. To achieved a
converged status, you could either relax the Max. Delta S requirement (to 0.004 or
0.005) or increase the Maximum Number of Passes (for example, to 15).

For the purpose of this exercise, the current solution is sufficient.

View the Matrix Data

You can view matrices computed for the S-parameters during each adaptive and sweep solution.
To view the matrices:

Set up and Generate a Solution 6-12

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

2. In the Simulation drop-down menus, do the following:

a. Verify that Setup1 is selected as the solution setup you want to view.
b. Verify that LastAdaptive is selected as the solved pass you want to view.
3. Select S Matrix as the type of matrix data you want to view.
4. Click the Format subtab and ensure that Magnitude/ Phase (deg) is selected from the
drop-down menu as the format for displaying the matrix information.

You can display matrix data in the following formats:

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

Real/Imaginary Displays the real and imaginary parts of the matrix type.

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

Set up and Generate a Solution 6-13

5. Select the solved frequencies to display:

l To display the matrix entries for all solved frequencies:
a. In the second Simulation drop-down menu, select Sweep.
b. Check Display All Frequencies.
l To show the matrix entries for one solved frequency:
a. Clear Display All Frequencies.
b. Select the solved frequency for which you want to view matrix 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-matrix column (S:WavePort1:1) and third S-matrix column
(S:WavePort3:1) at 20 GHz. Notice that S12 and S32 (second row) as well as S14 and S34

(fourth row) are all close to the value .

Furthermore, the phases of S12 and S14 are 90-degrees apart. This angle is also true for
the phases of S32 and S34, but in the opposite way. These values indicates that if you feed
ports 2 and 4 with signals equal in magnitude but 90-degrees apart, they will add up con-
structively 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.

Set up and Generate a Solution 6-14

7 - Analyzing the Solution

Now, HFSS has generated a solution for the waveguide combiner problem. In general, you can dis-
play and analyze the results of a project in many different ways. You can:
l Plot field overlays — representations of basic or derived field quantities — on surfaces or
objects.
l Create 2D or 3D rectangular or circular plots and data tables of S-parameters, basic and
derived field quantities, and, had the waveguide combiner model emitted radiation, radiated
field data.
l Plot the finite element mesh on surfaces or within 3D objects.
l Create animations of field quantities, the finite element mesh, and defined project variables.
l Scale an excitation’s magnitude and modify its phase.
l Delete solution data that you do not want to store.
For this waveguide combiner problem, you will:
l Create Modal S-parameter reports.
l Create a field overlay cloud plot of the magnitude of E.
l Create an animation of the mag-E cloud plot.

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

chapter.

Create an S-Parameters Report of S11, S12, S13, and S14

You are now ready to create the modal S-parameters reports.
1. To generate a 2D report of S11, S12, S13, S14, use one of the following three methods:
l From the HFSS menu, click Results> Create Modal Solutions Data Report>
Rectangular Plot.
l From the Results ribbon tab, choose 2D from the Modal Solution Data Report

drop-down menu.
l Right-click Results in the Program Manager and click Create Modal Solutions
Data Report> Rectangular Plot.

The Report dialog box appears with the Trace tab initially selected.

Analyzing the Solution 7-1

The Context selections are Setup1: Sweep in the Solution drop-down menu, and Sweep
in the Domain drop-down menu.

2. Accept Primary Sweep: All and X: Default (Freq), if they are not already specified.
3. In the three option lists located below the Y text box, specify the following information to plot
along the Y-axis:

Category S Parameter
Quantity S(WavePort1,WavePort1); S(WavePort1,WavePort2);
S(WavePort1,WavePort3); S(WavePort1,WavePort4)
Function dB

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

The Primary Sweep option is Freq, which is also the default X: value to plot.

This option plots the sweep variables selected under the Families tab along the X-axis.

4. Click New Report and Close.

The function of the selected quantity is plotted against the plot domain on an xy graph.

Analyzing the Solution 7-2

The report window XY Plot 1 appears, and S Parameter Plot 1 is now listed under Results in
the Project Manager. Each trace is also listed under S Parameter Plot 1 (four total).

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. From the Results ribbon tab, choose 2D from the Modal Solution Data Report
drop-down menu.

The Report dialog box appears

Analyzing the Solution 7-3

The Context selections are Setup1: Sweep in the Solution drop-down menu, and Sweep
in the Domain drop-down menu.

2. Accept X: Freq and All, if they are not already selected.

3. In the three option lists located below the Y text box, specify the following information to plot
along the Y-axis:

Category S Parameter
Quantity S(WavePort1,WavePort2); S(WavePort1,WavePort4)
Function dB

4. Click New Report and Close.

The report window S Parameter Plot 2 appears and is listed under Results in the Project
Manager.

Analyzing the Solution 7-4

Notice that between 19.9 GHz and 20 GHz, S12 and S14 are both approximately -3.1 dB.

Scale the Magnitude and Phase for the Ports

You will soon create a field overlay plot of the magnitude of E and examine the resulting E- field pat-
tern. But, before doing that, you must first scale the magnitude of the ports to represent equal
power input to WavePort2 and WavePort4, and zero at the other two ports. You must also modify
the phase angle for WavePort4. As a result, these settings will make the model behave as the spe-
cific waveguide combiner that is described in this exercise. WavePort1
To modify the magnitude and phase for the ports:
1. From the menu bar, click HFSS> Fields> Edit Sources or right-click Field Overlays in the
Project Manager and click Edit Sources.

The Edit post process sources dialog box appears.

2. In the Magnitude text box for WavePort1:1 and WavePort3:1, enter 0.

3. In the Magnitude text box for WavePort2:1 and WavePort4:1, enter 1.

This magnitude is the factor by which the excitation value is scaled. WavePort2:1 and
WavePort4:1 are each to be fed the output of a separate solid state power amplifier
(SSPA).

Analyzing the Solution 7-5

Note:

Since this is a half-symmetry model of the actual waveguide combiner, the 1 W port
excitations are equivalent to 2 W at each input port of the full device that the model
represents.

Additionally, you may have noticed that, when you first accessed the Edit post pro-
cess sources dialog box, the default magnitude at WavePort1:1 was 0.5 (not 1).
The reason is that you previously applied a symmetry boundary and, accordingly,
specified a port impedance multiplier of 2. Therefore, the program decreased the
source magnitude from the default value of 1 W to 0.5 W and, by default, placed the
excitation at the first port. The fact that you are applying a full watt of power to each
of the half-symmetry input ports is perfectly acceptable. Just be aware that
whatever excitation you apply is only half of the equivalent magnitude going into the
full part the model represents (due to the use of symmetry).

4. In the Phase text box for WavePort4:1, enter 90.

This value is the phase of the excitation entering the port. WavePort4 is the port to which the
output of an SSPA is fed 90 degrees out-of-phase relative to the WavePort2 excitation.

5. Click OK.

The correct magnitude and phase are now assigned to all ports.

Create a Mag E Field Overlay Cloud Plot

Now that you have scaled the magnitude and phase for each port, you are ready to create a field
overlay plot of the magnitude of E and examine the resulting E- field pattern.
1. In Select Faces mode (Edit> Selection Mode> Faces), click the top face of the object
waveguide.
2. Use one of the following three methods to begin creating the mag E field overlay:
l On the HFSS menu, click Fields> Plot Fields> Mag_E.
l Right-click Field Overlays in the Project Manager and click Plot Fields> E> Mag_E.
l Right-click in the Modeler window and click Plot Fields> E> Mag_E from the short-
cut menu.

The Create Field Plot dialog box appears.

Analyzing the Solution 7-6

3. Select Mag E from the Quantity list.

This selects the magnitude of the real part of the electric field |E|(x,y,z,t) as the quantity to
plot.

4. Select AllObjects from the In Volume list to specify that HFSS will plot over the entire
volume of the model.
5. Accept Setup1: LastAdaptive and 20 GHz as the Solution and Freq options, respect-
ively. In this case, these are the only available options.

The Freq pull-down menu includes a list of frequencies for which a field solution is available.

6. Select 0deg from the Phase drop-down menu.

7. Click Done.

The Mag_E1 field overlay cloud plot appears in the Modeler window and is now listed under
Field Overlays in the Project Manager.

The resultant E-field pattern shows that input from wave ports 2 and 4, with a 90-degree out-
of-phase separation, combine at port 1. The E-field at port 3 is approximately 0.0001 V/m,
which is very close to zero. So, you can see that the waveguide combiner behaved as expec-
ted with a 90-degree phase angle between the two inputs.

Analyzing the Solution 7-7

Create a Phase Animation of the Mag E Cloud Plot

Next, you will create an animation of the field overlay plot of the magnitude of E to examine a
frame-by-frame animated behavior of the plot.
To create a phase animation of the Mag E plot:
1. Select the Mag_E1 field overlay plot from the Project Manager.
2. Click HFSS>Fields>Animate.
The Select Animation dialog box appears.
3. Click New.
The Setup Animation dialog box appears.
4. Accept the default name Animation1 in the Name text box.
5. Optionally, type a description of the animation in the Description text box.
6. Under the Swept Variable tab, select Phase from the Swept variable list.

Analyzing the Solution 7-8

7. Accept the remaining default settings.

8. Click OK.

The animation begins in the Modeler window.

The Animation panel appears in the upper-left corner of the desktop, enabling you to stop,
restart, reverse, and control the speed of the frames.

Self-Study Challenge:
You may wish to experiment with different phase angles for the excitation at WavePort4. For
example, you could try an angle of 45 degrees, which should produce output at both WavePort1
and WavePort3, with the latter having the weaker field. At a phase angle of zero, the output at
each port should be equal. Finally, at a phase angle of -90 degrees, all of the output should go to
WavePort3, with the field at WavePort1 being approximately zero.
To adjust the phase angle at WavePort4, edit the port sources as described on the page, Scale the
Magnitude and Phase for the Ports. Simply adjust the angle specified in step 4 of that page. You
can keep the animation running and keep the Edit post process sources dialog box open while
applying different phase angles. When you click Apply, the animation will be updated immediately
and will continue to play.

Analyzing the Solution 7-9

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