Getting Started: Ansoft
HFSS 8.0
Section 4: The 3D Modeler
NOTE: The 3D Modeler is the most complex interface in HFSS, and
will likely require the most practice for comfort and proficiency.
However, students already familiar with the use of a detailed 3D
CAD package should find much of the following information can be
rapidly assimilated.
3-1
Synopsis

3D Modeler Basics

Modeler Environment


Geometry Classification



Object Types, Attributes, and Vertices
Command Organization and Standards
3D Modeler “Practice”

Exercise: Draw and manipulate some different objects



View Selection and Manipulation, Grid and Axis Manipulation
Try some basic primitive creations (Box, Cylinder, etc.)
Try some basic drawing operations (Booleans, Sweeps, etc.)
3D Modeler Lab


Exercise: Construct all geometry necessary for a coax-fed
Patch Antenna project
Some Suggestions and Strategies for Geometry Planning
3-2
The 3D Modeler: What is it?

The HFSS 3D Modeler, or “Draw” module, is a
complete 3D CAD package

Utilizes the ACIS 5 3D toolkit from Spatial Technologies


Same 3D geometry kernel as AutoCAD, many others
Supports object-oriented solid geometry creation from
primitives




Construction tools include basic shapes (cylinder, box, planar
polygons)
Basic shapes can be modified via revolutions, linear sweeps
(‘extrusions’) or sweeps along paths
Split, mirror, and duplicate commands exist
Boolean capabilities permit part subtraction, intersection, and
union operations.
3-3
HFSS 3D Modeler Environment: The Layout
Menu
Toolbar
The Side Window
Coordinate Boxes at top
Command Operations
appear below.
Model units are shown in the Side
Window. Units selection is prompted
when the 3D Modeler interface is
first accessed. (Units can be altered
later via the Options menu.)
The Drawing Windows
Four Views by Default
(starting orientation: XY,
XZ, YZ, and isometric)
All are active drawing windows.
All may be rotated, panned,
zoomed, and otherwise
manipulated.
The Status Bar
Provides help text during drawing operations
Displays tool button description if button is ‘held’
The Command Prompt
View or Enter Macro
commands (not open
by default)
3-4
HFSS 3D Modeler Environment: View and
Location Selection
Coordinates displayed as “Absolute” (vs. origin) or “Relative”
(for measurements between two locations/vertices)

Window Selection:

Coordinate Display/Entry Fields. Checked Components
are Active, Unchecked ‘grayed out’



Note: The pointer, as well as
the shape of the cursor at the
selected location, both reflect the
number of components currently
‘active’-Triangular cursor: one
Square cursor: two
Diamond cursor: all three
One drawing window is active
at a time.
 Identified by flashing
cursor, frame
Shift focus to another window
with a single left-click
Shift location within the active
window with any subsequent
left-click
Location Manipulation:

Active Frame Shaded, Cursor Flashing

Moving in 3D or along any
combination of axes achieved
using coordinate checkboxes
in Side Window
 Note checkboxes have
memory!
Right-clicking accesses
movement options as well
3-5
HFSS 3D Modeler Env: View Manipulation

Right-Click Menu also includes View
Manipulation Options


Hotkeys access manipulation as
well:



Rotation Shortcut:
If you double-click near the appropriate region of
the active view menu while in rotate mode, the
view will instantly rotate to a specific orientation.
For example, double-clicking near the top of a
window results in a top down (XY) view, near the
left side a left (XZ) view, and near the center a
front (YZ) view. Double-clicking in the corners
rotates to four different isometric views as well.

Rotate, Pan, Zoom any window
(right click again to release)
CTRL-left-mouse-drag: rotate
SHIFT-left-mouse-drag: pan
CTRL-SHIFT-left-mouse-drag: zoom
(drag up for ‘in’, down for ‘out’)
Zooming also controlled with Toolbar
Icons



Zoom in or out on ‘box’: two leftclicks define opposite corners
“Fit All” tool icon sizes active window
to existing geometry
Hotkey “F” performs “Fit All” on all
views simultaneously
3-6
HFSS 3D Modeler Env: Axis Manipulation

The HFSS Modeler Coordinate
System is malleable


Axis Display Toggle (left)
Switches between large and
small, one and two-sided axis
display modes
Move Origin Icon (right)
Same as Menu Pick for Move
Origin from Coordinates
menu.


Coordinates menu contains axis
manipulation commands



Several Axis Display Options
Origin can be moved, axes
rotated
 Axis changes required for
some drawing commands!
Multiple Local coordinate
systems can be saved
 Starting coordinate system
automatically saved as
Global
Select new origin location before
choosing Move Origin
Select new intercept before
choosing Rotate (X, Y, or Z)
Two Toolbar Icons also provided
3-7
HFSS 3D Modeler Env: Grid Options

The Grid also has multiple options


Grid Display Toggle (left)
Turns Grid visibility on or off
Rotate Grid Icon (right)
Toggles grid between different
coordinate planes. Same
operation as selection in View
menu.


Grid can be rotated to each plane




Grid Settings available under View
Menu, some via Toolbar icons
Can pre-set to open with custom
preferences using Options Menu
 Save Module Preferences under
View Menu
Sizing may be automatic or fixed
 Auto Adjust grid changes with
zoom depth
 Fixed can be set to desired size
(point-to-point spacing)
Toolbar Icon or View Menu
Grid normal identified by dashed axis,
projection lines
Influences active coordinates, rightclick menu operations
Polar Grid also Available
3-8
HFSS 3D Modeler Geometry: Object
Classification and Attributes
Note: The Visibility Icon also allows direct
access to the visibility attribute of each object;
useful in complex models to temporarily ‘hide’
objects so that others may be more easily
viewed or manipulated

HFSS Models have three types of objects:




Only solids and sheets get used in the FEM
solution process




Solids: have volume and surfaces (3D)
Sheets: have only surface area (2 or 3D)
Polylines: have only length (1, 2, or 3D)
Volumes (within solids) can have material
characteristics defined
Surfaces (on sheets or solids) can have
boundary characteristics applied
Polylines can be used in post-processing, but are
ignored in solutions
All HFSS objects have Attributes



Type, name, and color most important
Visibility, ‘Model’, and Wireframe attributes also
available
View/Edit Attributes via the View menu or
highlighted toolbar icon
3-9
HFSS 3D Modeler Geometry: Vertices and
Snap Options

All objects are defined by vertices



Different snap options allow selection of
existing object vertices or features



Snap options are on side window with
coordinate fields. The correct snap
choice can make location selection for
geometry creation very easy.
Even true-curved objects have at least two
wireframe vertices
Many drawing commands require definition
of a base vertex from which you create or
manipulate objects
Grid snap selects a point on (or parallel to)
the drawing grid
Vertex snap selects an existing object’s
vertex.
‘Other’ options allow snapping to different
object features
 Midpoint of object edges and center of
object faces most often used
 The cursor is enlarged to indicate
vertex or ‘other’ snap selection
3-10
HFSS 3D Modeler Geometry: Complex Object
Construction

Basic objects are created as primitives




More complex objects are generated by
manipulation of primitives



Sweeping a line around an axis or along a vector
creates a sheet
Sweeping a sheet around an axis, along a vector,
or along a path creates a solid
Boolean Operations Permit object unions,
intersections, and subtractions

From a simple rectangular or
circular cross-section, detailed
figures of revolution, extrusions,
or helices can be formed.
Polylines: point, polyline (open or closed), arc
Sheets: closed polyline, rectangle, circle
Solids: Box, Cylinder

Remember the solid overlap issue? Boolean
subtraction is one way to handle it.
 Most Booleans result in primitive deletion; use
clipboard to preserve if necessary!
The resulting object will have the name of the
starting construction object
3-11
HFSS 3D Modeler Commands: Drawing
Command Organization
The Lines menu contains commands
which create or modify polyline objects.
Closed polyline objects (rectangles,
circles) which can become sheets are
also generated here.
The Edit menu permits object
selection, copying and pasting
to the clipboard, as well as
duplication of selected objects
along lines, around axis, or
thru mirror planes
The Surfaces menu contains
commands which act upon or
create sheet objects.
The Solids menu contains
commands to create solid objects,
and all Boolean operations
The Arrange menu permits
manipulation of existing objects,
including rotation, movement, and
mirroring. All menu items in Arrange
require at least one object be
selected to be available.
3-12
HFSS 3D Modeler Commands: Drawing
Command Cheat-Sheet
2D Primitive Generation
(Rectangle, Circle)
3D Primitive Generation
(Box, Cylinder)
Arrange Operations
(Move, Mirror, Rotate, etc.)
1. Start from a base or beginning
vertex.
1. Start from a base vertex
(corner for box, end center for cyl)
1. Select object(s) to operate
upon before going to Arrange
2. Define a Normal Axis, size, and
(for circle) vertex count.
2. Define XYZ size (box) or Axis,
radius, height, and # of facets
(cyl)
2. Define vector, axis and rotation
angle, or mirror plane for
operation.
3. Provide name and color.
3. Object attributes (name and
color) unchanged.
Sweep Operations
(Along line, around axis, etc.)
Duplication Operations
(Along line, around axis, etc.)
1. Select Sweep mode (along
vector, etc.)
1. Select object(s) to operate
upon before selecting Duplicate
2. Select profile (cross-section) to
be swept
(may be polyline or sheet)
2. Define vector, axis and rotation
angle, or mirror plane for
operation
3. Define vector, axis of rotation,
or path polyline, depending on
type of sweep
3. Define desired total quantity
(including original)
3. Specify covered (sheet) or not
(polyline).
4. Provide name and color.
Polyline Generation
(polylines and arcs)
1. Define starting point and
subsequent vertices
2. Can be edited, including
insertion, deletion, and movement
of pre-created vertices.
3. If planar and closed, can be
covered (sheet).
4. Require name and color.
4. Resulting solid/sheet has
same name as profile used.
3. Object duplicates created with
increments of original name (e.g.
‘box1’, ‘box2’, ...)
3-13
HFSS 3D Modeler Commands: Boolean
Operation Cheat-Sheet
UNION
SUBTRACTION
1. Select all objects to be united
at once.
1. Select all objects to be
subtracted from (the operands, or
‘stock’)
2. Result of union maintains name
and color of first object selected.
...If you want to keep an object
used in the union available after
the union is completed, first select
that object and copy it to the
clipboard!
STITCH (under Surfaces)
Identical to union, but valid for 2D
sheet objects only
2. Select all objects to subtract
(the operators, or ‘tools’)
3. Result of subtraction is the
objects selected in 1., less any
volume which intersected objects
selected in 2. Objects selected in
2. above are thrown away!
...If you want to keep an object to
be used as a ‘tool’ in a subtraction
operation, first select that object
and copy it to the clipboard!
INTERSECTION
1. Select all objects to be
intersected at once.
2. Result of intersection
maintains name and color of first
object selected.
3. All other objects are discarded
...If you want to keep an object to
be used in an intersection, first
select that object and copy it to
the clipboard!
3-14
HFSS 3D Modeler Commands: Other Drawing
Commands
SOLIDS-->SPLIT
SURFACES-->SECTION
OTHER COMMANDS:
1. Define any necessary
coordinate system translation and
rotation before selecting Split
command
1. Define coordinate system
translation before beginning
Section command
1. Surfaces-->Cover Lines
creates sheets from closed
polylines
2. Section allows creation of a 2D
cross-section of any 3D object,
along the XY, XZ, or YZ planes
2. Surfaces-->Uncover Faces
reverses this process
2. Split command allows ‘splitting’
of objects along XY, YZ, or XZ
planes.
3. Options allow keeping the
positive, negative, or both halves
(with respect to the Normal of the
split plane)
4. You do not need to select
objects first.
5. Parts retain name/color
attributes of original.
3. Sections created will be
uncovered (polyline) objects, and
must be covered to make them
sheets again.
4. You do not need to select
objects first.
5. Objects created will be named
“slice”, “slice1”.... Rename using
Attributes if desired.
UNDO AND REDO: The Edit menu also contains Undo... and Redo...
commands. On the toolbar, these are represented by the
counterclockwise arrow (undo) and clockwise arrow.
3. Surfaces-->Detach Faces
creates sheet objects from the
faces of solids
4. Surfaces-->Connect creates a
sheet connection between two
polylines
4. Solids-->Helix creates a helix
from a provided sheet crosssection profile
5. Solids-->Cover surfaces
creates a solid from a 3D closed
polyline or sheet
3-15
HFSS 3D Modeler Practice: Rectangle
1.
Your instructor should walk you through
opening a new HFSS temporary project,
and entering the Draw Module.
1. From the Lines menu, select Rectangle
2. (not shown)
2. Side window prompts for first point. Type
(2, 2, 0) into the coordinate boxes. Enter
button confirms starting point.
3. Side window prompts for rectangle
plane, size, name, and color.
A. Select XY plane
3.
B. Leave ‘Covered’ checked. This results
in a sheet rather than a hollow outline.
C. Enter x=10, y=15
D. Leave default name “rect1”
E. Pick a color (user option)
4.
4. Enter button finishes object creation;
cursor is left at opposite corner from the
starting vertex.
Note: Rectangle dimensions will be
‘roughed out’ during entry of X and Y sizes;
this feature provides visual feedback before
the object creation is finalized.
3-16
HFSS 3D Modeler Practice: Cylinder
1.
1. From the Solids menu, select
Cylinder
2. (not shown)
2. Side window prompts for axis and
base vertex. Select Z axis. Type (7, 9.5,
0) into the coordinate boxes. Enter
button confirms starting point.
3. Side window prompts for cylinder
radius, height, and vertex count.
A. Select Z axis
B. Enter radius=5, height=10
C. Leave ‘Num segments’ checked.
This results in a faceted cylinder.
Change the value to “16”.
3.
D. Leave name as “cyl1”
E. Pick a color (user option)
4.
4. Enter button finishes object creation,
leaving cursor at the far end of the
cylinder from the base vertex, on the
radius.
Note: Again, solid object will be
‘sketched’ to provide visual feedback
before command is completed. Number
of vertices are not reflected in ‘sketch’
3-17
HFSS 3D Modeler Practice: Polyline (open)
1. From the Lines menu, select Polyline
2. Side Window prompts for name of
polyline to create/edit. (‘rect1’ will show in
this list.) Press ‘OK’ button at bottom to
accept default polyline name of ‘pline1’.
3. Side window changes to polyline draw
mode. Beneath object name and color
selection, the top button defines the action
to occur each time ‘Enter’ is pressed (add
vertex, delete vertex, insert vertex...). The
bottom button defines the type of segment
that will be created between the prior and
current vertex (straight, arc, spline).
A. Move coordinates to (2, 2, 0) and click
“Enter”. An ‘X’ marks first vertex.
B. Move coordinates to (2, 2, 8) and click
“Enter”. (Note: you may wish to use the YZ
view!) A ‘+’ shows subsequent vertices.
C. Repeat, placing coordinates at
(2, -2, 12) and (2, -16, 12).
D. If we wanted to close the polyline at
the first point, we could press “Close”.
Instead, press “Done” to leave open.
4. Side window exits polyline mode; line is
created.
3-18
HFSS 3D Modeler Practice: Sweep
1. From the Solids menu, select Sweep...
Along Vector
Step 3
2. Side Window prompts for name of
profile to sweep. Select ‘rect1’ and press
‘Enter’
3. Side window prompts for vector values.
Enter X=5, Y=5, Z=10 (in vector) boxes
and press ‘Enter’. A canted solid
parallelogram is created.
4. From the Edit menu, select “Undo
Sweep vec”.
5. From the Solids menu, select Sweep...
Along Path
Step 8
6. Side Window prompts for name of
profile to sweep. Select ‘rect1’ and press
‘Enter’
7. Side Window prompts for name of path
to sweep along. Select ‘pline1’ and press
‘Enter’.
8. Side Window prompts for Draft Angle
(growth of profile as it sweeps). Leave at
zero and press ‘Enter’. An extrusion of the
rectangle along the open polyline is
created.
3-19
HFSS 3D Modeler Practice: Duplicate/Mirror
3.
2.
1.
1. Use the Visibility tool icon to ‘hide’ all
geometry but the sweep object from the
prior page (‘rect1’).
2. From the Edit menu, pick Select..., or
use the Selection tool icon (outlined at left)
to select the object ‘rect1’. Press ‘Enter’ to
confirm your selection is finished.
3. From the Edit menu, pick
Duplicate...Mirror. The side window will
now prompt you for a point on the mirror
plane. Select the origin and press ‘Enter’.
4. (not shown)
The Duplicate...Mirror command can utilize any plane of reflection in the
model, and is therefore not tied to the existing coordinate axes. The
reflection plane is defined by its normal vector, with the tail on the plane
and the head orthogonal to the plane. The normal vector need not be of
‘unit’ length.
4. The Side Window will now prompt you
for a point on the normal to the mirror
plane. Select the point (2,2,0) by entering
the coordinate or ‘snapping’ to the
appropriate vertex on the ‘rect1’ object.
5. You should end up with a duplicate of
the original swept part, positioned such
that it is ‘mirrored’ 90 degrees from the
original in the same position from the
origin.
6. Note that in this case the same
operation could also have been performed
using Duplicate...Around Axis.
3-20
HFSS 3D Modeler Practice: Unite and Split
1.
1. From the Solids menu, pick Unite. The
Side Window will prompt you for the names of
all available objects that can be united. Select
‘rect1’ and ‘rect2’, in that order, and press
‘Enter’. The two overlapping solids will be
united into one.
Step 2
Step 4
3. (hidden by menu)
5.
2. Now pick the indicated vertex on the top
face of the object by snapping to it, or entering
coordinate (12, -12, 27). From the
Coordinates menu, pick Set Current
CS...Move Origin. The origin will move here.
3. Be sure your grid plane is displayed with Z
as the normal, using the appropriate icon.
4. Pick the opposite concave corner on the
top face of the united object as shown. From
the Coordinates menu, pick Set Current
CS...Rotate Y. The coordinate axes will rotate
so that this point becomes a Y intercept.
5. From the Solids menu, pick Split. The side
window will now prompt for the split axes and
which parts to keep. Select “YZ” and “Above
plane” and press ‘Enter’. The Side Window
will now list all objects available for splitting:
Select ‘rect1’ and press ‘Enter’. The part will
be cut diagonally along the YZ plane as
shown.
3-21
HFSS 3D Modeler Practice Concluded



This concludes the
introductory 3D Modeler
practice session. Please
select Exit from the File
menu (do not save
changes when
prompted).
When you are returned
to the HFSS Executive
window, click Exit.
We will now walk through
the complete geometry
construction for a Coaxfed Patch antenna
problem. We will only
build the geometry for
this problem; not solve it.
3-22
HFSS 3D Modeler Exercise: Patch Antenna


Drawing Objects Needed:
Boxes: Substrate, Air volume
Cylinders: Coax inner and outer sections, port
‘cap’
Rectangle: Patch
Drawing operations needed:


Split (to prevent coax inner conductor overlap)

This is a coaxial-probe fed
rectangular patch antenna designed
to operate near 2 GHz. The patch
itself is 3 x 4 cm in size.
It is constructed on a 0.32 cm thick
substrate, 10 x 10 cm in size, with
ground plane cladding on the bottom
surface except where the coax
penetrates.
The coaxial probe has an inner
diameter of 0.2 cm and an outer
diameter of 0.46 cm
The entire model will be placed in an
air volume 18 x 18 x 10 cm in size
When instructed, create a New
project in the Project Manager called
“patch” and open the Draw Module.
3-23
HFSS 3D Modeler Exercise: Macro Interface
Step 2
As an introductory illustration of the time saving
features of the Ansoft Macro Language, we will
record our drawing operations as we construct
the patch antenna problem.
1. From the View menu, pick “Command
Prompt”. This will open the direct macro text
interface across the bottom of the modeler
window. Although not necessary for recording,
this will allow you to see visible feedback as
individual commands are enabled thru the
graphical interface.
2. From the File menu, pick Macro...Start
Recording. The interface will prompt you for a
macro name to record to, pre-assuming the name
“mod3.mac” to be saved in the current project’s
directory. Accept this default filename and
proceed to the next page. From here onward, all
commands performed will be recorded into this
file.
Step 1
3-24
Patch Exercise: Create Substrate Solid
1.
We want to create our model centered
at the origin of the coordinate system
with the top of the substrate (the plane
of the patch antenna) at Z=0. For an
antenna model, due to the postprocessing coordinate system used,
we want the antenna’s peak gain at
zenith to be directed along the Z axis.
Therefore we want our substrate to
extend in the XY plane, centered at
the origin.
(ALL UNITS FOLLOW IN CM)
2.
1. From the Solids menu, pick Box.
Set your starting vertex to (-5, -5, 0),
and press the ‘Enter’ button to confim.
3.
2. The Side Window now prompts for
the box size. Enter a size of X=Y=10,
Z= -0.32 . Note that using a negative
Z ‘size’ builds in the negative Z
direction from the starting point at Z=0.
3. Name the object ‘substrate’, select
a color, and press ‘Enter’ to complete
object creation.
4. If the object appears small, you
may zoom or Fit your view.
3-25
Patch Exercise: Create Patch Rectangle
1.
If we assume that the metalization
thickness of the patch is
insignificant compared to its
dimensions, we can model its
geometry as a 2D sheet object
with very accurate results. (The
same is true for much microstrip
and stripline circuitry, where edgeto-edge coupling is not important.)
1. From the Lines menu, select
Rectangle. Define our starting
coordinate as (-1.5, -2, 0) and
confirm.
2.
3.
2. Set the rectangle to exist in the
XY plane, with the dimensions
X=3, Y=4. The rectangle will be
‘sketched’ in as the size values
are entered.
3. Give the rectangle the name
“patch” and choose a color. Press
‘Enter’ to complete the drawing
command.
3-26
Patch Exercise: Create Coaxial Probe Feed
3.
The coaxial probe should contact the
patch, penetrating the substrate. We will
construct this as a faceted cylinder at the
origin.
1.
2.
4.
Why only 8 facets? Since the coaxial feed and probe of the
patch antenna are very narrow and do not need high detail to
properly excite the patch, use fewer facets to save on overall
tetrahedra in the model!
1. In the Side Window, check the box next
to ‘Other...’ in the ‘Snap To:’ options. A
dialog will open with further options.
Check ‘Face center’ and press the ‘OK’
button to confirm. Graphical clicking
operations will now snap us to the center of
any object faces.
2. Click in the graphical window anywhere
in the vicinity of the top face of the
‘substrate’ box or of the ‘patch’ rectangle.
Your cursor should snap immediately to the
origin. (0, 0, 0)
3. From the Solids menu, pick Cylinder.
The Side Window prompts for an axis (pick
Z) and a base vertex. Press ‘Enter’ to
confirm (0, 0, 0) is the base center.
4. Set the cylinder radius to 0.1, height to
-0.82, number of facets to 8. Give the
cylinder the name ‘probe’, select a color
different than the default if desired, and
press ‘Enter’.
3-27
Patch Exercise: Create Coaxial Dielectric
1. The coaxial dielectric will lie beneath
the substrate, concentric with the probe
extending beneath the bottom of the
substrate. We will assume the outer
conductor is of zero thickness, as it will not
influence the antenna fields.
2. Note that following the prior command,
you should have been left at vertex
location (0.1, 0, -.82) on the radius at the
bottom of the ‘probe’ cylinder. Re-set the X
coordinate to ‘0’ using the Side Window,
and from the Solids menu pick Cylinder.
3. The Side Window prompts for an axis
(pick Z) and a base vertex. Press ‘Enter’
to confirm (0, 0, -.82) is the base center.
5. Set the cylinder radius to 0.23, height to
0.5, number of facets to 8. Give the
cylinder the name ‘outer’, select a color
different than the default if desired, and
press ‘Enter’.
Your drawing should look similar to the one
at left upon completion. (Drawing at left
inverted from black background to better
show geometry).)
3-28
Patch Exercise: Create Coaxial Port ‘Cap’
2.
3.
What is a port ‘cap’?
Since we will need to surround the antenna with an air volume for the fields to
radiate into, we cannot leave the back end of the coaxial cable ‘open’ to that
air. We need to provide a cap object to assure that our model excitation can
flow only up the coaxial cable we have created. We will do this by placing a
solid cylinder the same size as the ‘outer’ cylinder on its bottom face.
Although this may look like a ‘short’, it permits the port to behave properly.
(Further discussion in Boundaries)
1. Use the rotation hotkey (CTRLleft-mouse-drag) or double-clicks
to orient a view window so that
your are looking up at the bottom
surface of the ‘substrate’ and
‘outer’ objects. (You may also
wish to zoom in.) If your ‘Other’
Snap mode is still on, a single
mouse-click on the bottom face of
the ‘outer’ cylinder should snap to
the coordinate (0, 0, -.82).
2. Again from the Solids menu,
pick Cylinder. The Side Window
will prompt you for an axis (pick Z)
and a base vertex. Confirm (0, 0,
-.82) is the starting point by
pressing ‘Enter’.
3. Configure the cylinder to have
a radius of 0.23, a height of -0.25,
and 8 facets using the fields in the
Side Window. Give the cylinder
the name ‘cap’, select a color, and
press ‘Enter’ to complete the
geometry creation.
3-29
Patch Exercise: Create Air Volume
1.
The final object we need to create is
the air volume for the structure to
radiate into. Since the antenna is
intended to operate near 2 GHz,
and the substrate is 10 x 10 cm, we
will construct an air volume of 18 x
18 x 10 cm in size. (Sizing of
radiation volumes will be discussed
in the Boundaries presentation.)
1. From the Solids menu, pick Box.
The Side Window will prompt you
for a starting vertex. Set the cursor
to the coordinate (-9, -9, 5) using
the fields in the Side Window, and
press ‘Enter’ to confirm.
2.
3.
2. Set the size of the box to
X=Y=18, Z= -10. The interface
should sketch in a box which
completely surrounds our geometry
created thus far. (You may wish to
zoom out to see it better.)
3. Give the box the name ‘airvol’,
select a color, and press ‘Enter’ to
complete its creation.
3-30
Patch Exercise: Split Probe!!
1. 
3.
2.
4.
5. (illustration shows probe
object after being split)
Remember, objects which intersect one another such that one
is not entirely enclosed by the other will have shared volumes
that the software will not know how to assign conditions to later
on. Splitting the probe into a section inside the ‘substrate’ and
a section inside the ‘outer’ objects will prevent this ambiguity.
1. From the Options menu, pick Check
Overlap. The modeler will check for
overlapping geometry, and should warn you
that some does exist by selecting two
objects. Recall that we created our coaxial
probe to penetrate the substrate, yet extend
beyond its bottom. Therefore the ‘probe’
object is in illegal overlap with both
‘substrate’ and ‘outer’. This must be
corrected before the problem can be
modeled.
2. Zoom in in the vicinity of the coaxial
‘probe’ and ‘outer’ objects. Using the vertex
Snap features, snap the cursor to any
vertex at the Z= -.32 plane (the bottom of
the substrate, or the top of the ‘outer’
cylinder.
3. From the Coordinates menu, select Set
Current CS...Move Origin.
4. From the Solids menu, select Split. The
Side Window will prompt you for the Split
Plane (pick XY) and Keep Fragments
options (pick Both). Press ‘Enter’.
5. The Side Window will give you a list of
objects you may split. Select ‘probe’ and
click ‘OK’ to confirm selection.
3-31
Patch Exercise: Macro Completion
1. From the File menu, pick
Macro...Stop Recording. This will
result in a message informing you the
macro file has been saved.
2. Now from the File menu, pick
Macro...Edit Macro. The macro
we’ve created is automatically
opened in a macro editor interface,
as shown at left.
3. If you wish, highlight one of the
drawing lines (like ‘Box’ or ‘Cyl’) by
clicking on it. The right side panel
contains the alterable arguments for
that command. It should be easy to
see how the macro could be edited to
change the dimensions of some of
the objects we created. The macro
could then be re-run in another fresh
HFSS session to create the entire
geometry, with any changes made.
This page of the presentation is offered as an example of
macro recording and access; full macro use and
construction is covered in Advanced HFSS Training.
4. Exit the Macro Editor from the File
menu. Exit the 3D Modeler from the
File menu. You will be prompted to
save your geometry, choose ‘Yes’.
This completes the 3D Modeler
Lab.
3-32
Geometry Modeling Suggestions

Consider how you want your
geometry oriented and
located before beginning


For antenna problems, a +Z
antenna zenith has advantages
in post-processing patterns
For many problems, centering
at the origin aids geometry
construction, including split
operations for symmetry
utilization
3-33
Geometry Modeling Suggestions, cont.

Thin metal plates connected
by vias look like a solid metal
path to lower frequencies.
Don’t Overspecify: Use only
those details necessary for
the electromagnetic behavior
of the model at the
frequencies you intend to
analyze it.

Each vertex in a problem must be
used by the mesher...are all
these facets necessary for a
mesh at your frequency?

This is especially important
when importing geometry
from other CAD packages.
Often tiny fillet radii or
miniscule screw hole
penetrations exist in the
original data which are
unnecessary for the analysis
at hand.
Don’t overdo facetization on
cylindrical or revolution
objects. In many cases, 1216 facets is sufficient
3-34
Geometry Modeling Suggestions, cont.

Use symmetry wherever possible to
reduce your model volume.

This model may be split by a
perfect_h symmetry plane.


For models with port excitations, don’t
overdo the port extension length.

Port extensions need not be
large fractions of wavelength.
Remember however that geometric
symmetry does not always imply field
symmetry if higher order mode
propagation is involved!!!
(The “Boundary Module” presentation will
describe symmetry planes and their use.)

Extensions on the order of the port
aspect ratio are sufficient for higher-order
mode decay
(The “Boundary Module” presentation will
go into more discussion regarding the
port extension and why it is used.)
3-35
Geometry Modeling Suggestions, cont.

Edge Coupling will be significant
Use trace thickness in planar circuitry
only where necessary

Edge coupling insignificant
The octagonal virtual solid
surrounding the spiral inductor
trace (which has metal
thickness included) helps
transition the mesh out to the
surrounding air volume.

Thickness is necessary when:
 ...it is a significant portion (>15% or
so) of the metal trace width
 ...edge-to-edge coupling is a major
contributor to the device behavior
 ...thickness approaches skin depth
(within a factor of 2 to 3), requiring
meshing interior to metal volumes to
capture true field penetration effects
If you determine thickness must be
considered, use virtual objects or extra
plane breaks to prevent extreme aspect
ratios which can prevent clean meshing

A virtual object is an object that will be
given the same material assignment as
its surroundings, making it a ‘tool’ to
provide additional mesh vertices only.
3-36
The limitation of the modeler
3-37
Virtual Object
3-38
Compensating for the Aspect Ratio
3-39