ECE 484/584
Ansoft HFSS Software Demonstration Example:
Microstrip Transmission Line
Prof. R. W. Ziolkowski
James Cheng
03/23/03 Rev. 2
This exercise will act as an introduction to Ansoft HFSS. It is a short exercise to give
you a general idea of the major steps involved in an HFSS simulation. In this exercise,
you will model a microstrip transmission line driven with a 10 GHz source. The
impedance of the transmission line should match 50 Ω. The model is shown in Figure 1.
Fig. 1
1.
Microstrip Transmission Line
Start a new project in Ansoft HFSS
Start Maxwell by typing
/opt/ansoft8/maxwell
on the command line. The Maxwell toolbar will come up (Figure 2).
1
Fig. 2
Maxwell Toolbar
On this toolbar, click on Projects. The Project Manager window will appear (Figure 3).
Fig. 3
The Maxwell Project Manager
Click on New to create a new project under the default directory. You will be prompted
to give the new project a name. Type transline and make sure the program selection
type is Ansoft High Frequency Structure Simulator 8.5. Click OK. After creating a new
project, the Executive window will appear by default (Figure 4).
2
The buttons on the left indicate the main steps in the simulation: drawing the model,
assigning material properties to the objects in your model, setting up boundary conditions
and sources, setup solver frequency and accuracy parameters, solve and post process.
Fig. 4
2.
Ansoft HFSS Executive Commands window or Main Menu
Draw the geometry of the model
In the Executive window, choose Draw. This brings up the 3D Modeler (Fig. 5). There
are 4 windows representing the xy, yz, zx, and 3D views of the objects drawn.
The modeler then prompts you for units. Select mm as the units for modeling and click
OK.
3
Advanced Topic (Refer to Appendix)
•
If you would like to vary the geometric parameters of your objects, you can
simplify your future sessions by recording the first drawing session. Later
you can edit this macro and edit the parameters. Do not record your session
into a macro until you have experimented some with the drawing package
and understand how to draw the geometry of the model of interest.
•
Choose File/Macro/Start Recording. A file browser appears prompting you
for the name of the macro file to which your session will be recorded. Notice
that the default directory in which the file is saved is called mod3, and the
default file name is mod3.mac. Do not change the defaults. HFSS searches
this directory for the geometry macro file. Choose OK to start recording. All
subsequent actions will be recorded to mod3.mac.
You are now ready to start the drawing process.
Fig. 5
The 3D modeler
Step 1: At the top menu of the 3D Modeler window, select Lines / Rectangle to start the
Rectangle command.
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Step 2: On the left, type the (X,Y,Z) coordinates of the starting point, (0, 0, 0), in the
coordinate spaces in the upper left part of the window. Once you have typed these
coordinates into the boxes, click Enter in the left part of the window for the base vertex.
Step 3: You are now prompted for the Rectangle size, name and color under the
coordinate panel. Type (X, Y) = (28, 12). Type ground in the space for the name. Select
blue as the color of the box by clicking on the gray color button and then selecting the
yellow color. When you have done all this, click Enter.
Notes: The box may be small or not fit right in the windows. In order to see it
better, do one of the following. Press the hot key “f” on the keyboard to fit every
view in all four windows. Or, to fit all in a single window, first click once in a
window to make it active. Then, in the menu on the top, go to View Fit All.
Alternatively, you can click on the following toolbar icon
Now that the ground has been drawn, continue to repeat the step 1 to 3 to draw the
diagram as indicated in the following table.
Object name
Object type
Starting x,y,z
Size
ground
substrate
air
transline
port1
port2
lines / rectangle
solid, box
solid, box
lines / rectangle
lines / rectangle
lines / rectangle
0, 0, 0
0, 0, 0
0, 0, 0
18.79, 0, 0.7874
7.5, 0, 0
7.5, 12, 0
(x,y) 40, 12
40, 12, 0.7874
40, 12, 15
(x,y) 2.42, 12
(x,z) 25, 8
(x,z) 25, 8
Notes:
• Important is that the absorbing boundary or radiation boundary that you
will place on the outer surface of the air box not be too close to any radiating
objects. The rule of thumb is that that boundary needs to be a quarter
wavelength away if you want to obtain an accurate antenna pattern.
•
How large should this port be? Keep in mind that HFSS thinks in terms of
fields. The port should be large enough to accommodate the field pattern of
the TEM microstrip mode. Ansoft recommends that the port be 10 times as
wide as the width of the trace and 10 times as high as the thickness of the
dielectric.
At this point, we’re done with the drawing.
•
If you have been recording the drawing session, please stop it by choosing
File/Macro/Stop Recording.
Go to File Exit in the top menu. You will be prompted to save changes. Select “Yes.”
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3.
Setup Materials
Choose Setup Materials. The Material Setup window appears (Figure 6):
Select the substrate object by either clicking on it in the picture or by clicking on it in
the object list on the left. Notice that the object changes color to indicate selection.
Assign the objects indicated as the following:
Object name
Material
air
substrate
vacuum
duroid (µ=1; ε=2.2)
Fig. 6 Material Setup Window
In the list of materials on the left, select “duroid.” The properties of duroid show up in
the lower right part of the window. Once duroid is highlighted and with the substrate still
selected, click on Assign just above the materials list. The substrate is now assigned the
material properties of duroid as indicated in the object list. Continue to assign the
material value for the air.
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Click on Exit in the lower left part of the window. You will be prompted to save changes
and accept with “Yes.” Back in the Executive window, you should see check marks at
both Draw and Setup Materials, indicating that a drawing exists and that all 3D objects in
that drawing have received a material assignment.
4.
Setup Boundaries / Sources
In the Executive window, choose Setup Boundaries / Sources. This brings up the 3D
Boundary / Source Manager (Figure 7). Since you have not yet assigned any boundaries
and sources, the left bottom square is blank. We want to make the following assignments:
Object name
Select Type
Material Type
ground
transline
air
port1/port2
object
object
face
face
prefect E
prefect E
radiation
port
In the Setup Boundaries / Sources, the following 5-step approach should keep assigning
boundary conditions straightforward and simple. You may skip this 5-step approach
summary and directly follow the detail instructions provided after the summary.
Fig. 7 3D Boundary/Source Manager
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Notes: Five Steps to set up boundaries / Sources
•
First, ensure that nothing is currently selected. You want to make sure
you are starting fresh. To do this, press the deselect button in the tool bar if
it’s not grayed out. You can also achieve this by going to the Edit menu and
selecting “deselect all”.
•
Second, choose the type. Click on the button for either a source or a
boundary. Then, choose the specific type of source or boundary by clicking
on the button to the right that is labeled either PORT or BOUNDARY TYPE.
Ports are the sources; everything else needs to be considered for a type of
boundary condition assignment.
•
Third, select the faces or object surface on which you wish to assign this
source or boundary. For graphical selection, we can choose an object, face
or boundary, in the left-hand panel under graphical pick. If you choose face,
you will be able to select a particular face or multiple faces with the mouse.
If you choose an object, upon clicking on that object with the mouse, all its
faces will be selected. To select by name, go to Edit / Select / By Name, or
use the hot key “s” for selection. A new window listing the object names
appears for selection.
Fourth, type a name for the boundary. Note that the name of the object
you selected will not be its name for the source or the boundary unless you
assign it to be that name. The default names are portj or boundj, j=1, 2, 3, ....
•
•
Fifth, click “Assign”.
First assign perfect conductivity to the two two-dimensional metal objects in our model
that did not yet receive a material parameter assignment.
Choose Edit / Select / By Name. In the little window that appears, make sure the Object
button is selected. Note that we will want to select the 2D objects, not just the faces, that
have created: the ground and the transline. Select the ground. Note that it changes color
in the picture. Below the picture, give the new boundary condition the name ground and
make sure that boundary rather than source is checked. The type of boundary is Perfect
E. This means this object will be treated as a perfectly conductor. Click the Assign
button. Repeat the same procedure to assign the boundary for the transmission line and
give it a name such as strip.
Then assign a radiation boundary to the surfaces through which the energy radiated by
the antenna will propagate. Choose Edit/ Select/ By Name. In the little window that
comes up, make sure Face is checked. Select the air object in the objects list and select
the five faces of that air box that do not coincide with the ground, i.e., the bottom face
(Figure 8). Click Done. Give the new boundary condition the name radiation. Select
Boundary / Radiation. Then click the Assign button.
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Fig.8 Assign boundary condition for radiation surfaces
4.1
Port Definition
Choose Edit / Select / By Name. In the little window that appears, make sure that the
Face button is selected. Select the object port1. Click Done. Below the picture, make
sure that Source rather than Boundary is checked. The source type is port. Don’t click
the Assign button yet.
Let’s define an impedance line. An impedance line is used by HFSS to compute a
voltage in the port, which is needed in two of the three impedance definitions. Impedance
can be calculated from voltage and current, from voltage and power, and from power and
current. Without an impedance line, only power and current are available.
Check the box Use Impedance Line. In the upper-left part of the window, below the
coordinates, change the snap-to mode to other only (not vertex and not grid) and pick
edge center from the options that pop up. Click on the OK button to confirm. Go back to
the impedance line box and click the Edit Line / Set button. We want a line along the zaxis from the edge center of the transmission line to the bottom edge center of the port.
(Fig. 9) Try to snap to the center edge of the transmission line in port1. You do this by
putting the arrow cursor on that edge near its middle and clicking the left mouse button.
Then click the Enter button below the Set Impedance Start button. Then place the
cursor arrow on the opposite edge (bottom edge of port1) and left click. You should then
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see the correct vector appear going from the middle of the edge of the transmission line to
the middle of the bottom edge of port1. Click the Enter button under the Vector Length
button. You have now defined an impedance line.
Fig.9 Assign port impedance and calibration line
Next, we must define the corresponding calibration line. A calibration lines removes a
potential 180-degree phase ambiguity in the impedance calculation by telling the
software in which direction the E field is pointed at phase zero. Check the box in front of
Use Calibration Line. Choose Edit Line / Copy Impedance. The calibration line arrow
and the Impedance arrows will now be coincident.
Click Assign. An “overlapping” boundary message will then appear. In our case, the
overlapping area results from our assignment of a port within a face that has already been
assigned as a radiation boundary. The port assignment will take precedence as the solver
proceeds. Therefore, ignore the warning by clicking the OK button. Continue to assign a
source for Port 2 in the same manner.
4.2
Display Boundary
To check the ports and boundaries, go to Model Boundary Display. HFSS now makes
the initial mesh and comes up with the Boundary Display window. In this window, select
each boundary and source individually from the list on the left and click Toggle Display
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to graphically display the boundary. Once you have checked all the boundaries and ports,
click on Close in the lower-left part of the window. This returns you to the 3D Boundary
/ Source Manager. In that window, select File Exit from the menu at the top. You will be
prompted to save changes. Click “Yes.” After this, you’re back in the Executive window.
5.
Setup Solution
In the Executive window, skip the button “Setup Executive Parameters.” Choose Setup
Solution. The “Solution Setup” window will appear (Figure 10).
Fig. 10 Setup Solution Window
In the top dialog box of that window, make sure “Single Frequency” and “Adaptive” are
checked. Specify the Single Frequency at 12 GHz and Requested Passes 20 with a
Max Delta S of 0.02. The number of requested adaptive passes and the convergence
criterion Max Delta S complement one another. If the convergence criterion Max Delta S
is met before all the adaptive passes have been performed, convergence has been reached
and HFSS will stop and not perform any more passes. Otherwise HFSS will perform all
the requested adaptive passes.
Max Delta S is the maximum magnitude of the complex difference between S-parameters
of the current pass and the corresponding ones from the previous pass. This is a measure
of solution convergence. After two passes, if Max Delta S is still larger than 0.02, the
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mesh is refined again and the fields are recomputed with the denser mesh. The adaptive
mesher refines regions in the volume where the solution has its largest variations.
In the middle dialog box of the window, do not check Sweep at this time.
Accept the other defaults in the lower third panel and click “OK.” This will bring you
back to the Executive window.
6a.
Solve at One Frequency
In the Executive window, click on the Solve button. A status bar in the lower window
informs you on the progress of various processes. Click on Profile in the upper right of
the Executive window. Here we can obtain some statistics of the processes. The first
process is the lambda refinement.
Next the 2D port solution is computed to obtain the modes of this transmission line. After
that, HFSS solves for 3D fields.
A small description of the upper buttons of the Executive window follows:
“Model”, view the model.
“Matrix”, inspect the S parameters, port impedance, and propagation constants.
“Convergence”, view the solution convergence and the growth of the mesh.
“Profile”, view the statistics of the solving project. Listed are all the processes
involved in the solution, the real time and CPU time, memory,
and triangles or tetrahedrons.
6b.
Solve with Frequency Sweep
Once the solver has completed all passes or has reached the requested Max Delta S,
return to the Setup Solution window.
Deselect the adaptive solve button at the top left.
In the middle dialog box of the window, check the Sweep. Specify the Start Frequency
at 5 GHz, Stop Frequency at 15 GHz, and Number of Steps at 1000. Select Fast for fast
sweep.
Accept the other defaults in the lower third panel and click “OK.” This will bring you
back to the Executive window.
In the Executive window, click again on the Solve button.
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7.
Post Process
1. Post Process/Fields
While in the Executive window, click on Post Process Fields. This brings up the Post
Processor, which allows you to inspect the fields. Make a shaded plot and an animated
plot of the electric fields in all of the simulation volume.
Click on Plot Field in the menu near the top. The “Create New Plot” window appears.
Select Mag E in the first column, Volume all in the second, and All in the third. Click
OK. Accept the defaults in the next little window. A shaded plot shows up displaying
the magnitude of the electric fields in the volume.
Now let’s make an animated plot. First make the current plot invisible. Go to Plot
Visibility in the top menu. In the “Plot Visibility” window that comes up, click on Plot1.
Notice that the visibility turns to “No.” Click OK. Now go to Plot Field in the top
menu again. Select Mag E, Volume all, and All. This time, check the “Phase
Animation” box as well. Click OK. The next window that comes up will prompt you
for the range of the phase and step. Accept the defaults and click OK. The next window
will prompt you for the scale. Accept the defaults and click OK. You now get a movie of
the electric fields propagating from port1 to port2.
To terminate the animation, click Stop and Done on the left.
To leave the Post Processor, choose File Exit in the top menu. This brings you back to
the Executive window.
2. Post Process/Matrix Data
Click on Post Process / Matrix Data, make sure Port Zo is selected under “View” in the
right-hand part of the window. Make a note of the input impedance Z of this transmission
line (close to 50 Ohm). Select File / Exit to leave the Matrix Data Post Processor.
3. Post Process/Matrix Plot
Click on the Post Process / Matrix Plot button. The Matrix Plot window will appear. In
that window, select Plot / New Plot in the menu at the top. Plot the S11 and S21 values in
dB’s as a function of the frequency values. Change the scales and the divisions if you like
by double-clicking anywhere in the graph and making changes in the little menu that
pops up.
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8. Re-iterate
Once you have the Fast Sweep for the large range of frequencies, you may want to zoom
in on certain frequency ranges that exhibit interesting behaviors. Use the + magifying
glass in the Post Process/Matrix Plot plot of the S-parameters to zoom in on a particular
frequency regime of interest. Note the values of the frequency interval of interest.
Return to the Setup Solution window, enter the new sweep start and stop frequencies,
exit and hit the Solve button again. Iterate until you have all of the information you need.
9. Print and Exit
To print the plot.
Use HFSS Tool Manager
1) Click "Print" in Maxwell Tool Bar
2) Select output type: PostScript
Destination: Printer
Leave the rest setting and Click Print.
Select the window to print use left bottom of the mouse.
Select window to be printed. A "+" cursor shows up. Use left bottom of the mouse to
select left top corner of the window. Then use right bottom of the mouse to select
the right bottom corner of the window.
To exit HFSS, click on “Exit” in the lower left part of the Executive window, and click
“Yes” to confirm. This brings you back to the Project Manager. To exit from there, click
“Exit” in the lower-left part of the window. This brings you back to the Toolbar. To exit
from there, click “Exit” and click “Yes” to confirm.
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8.
Model of a patch antenna
Simulation and Layout Requirement:
•
•
•
•
•
•
Use mm in the designed structure.
Use 35mm x 35mm as the ground plane.
Layout patch antenna as indicated in Fig. 12.
Set 15 GHz as single frequency.
Set ∆S = 0.05.
The width of the gap should be greater than 0.5mm.
Notes: The number of the tetrahedras typically is around 15000. The total
simulation time is around 30 minutes.
An example model of a rectangle patch antenna should look like the following:
Fig 11. Model of a rectangle patch antenna
15
35mm
17.5mm
35mm
Fig.12 Layout of the patch antenna
8.1
Plot Antenna Patterns
Choose Post Process Fields from the Main Menu. The Post Processor 3D window will
appear.
Choose Radiation / Compute Far Field. The next window that appears will ask you to
specify angles over which you want the radiation pattern. Take a moment to understand
the angles. HFSS works with angles theta and phi in spherical coordinates. Theta, θ, is
the angle from the z-axis and phi, φ, is the angle from the x-axis. Hence, an antenna
pattern in the x,z plane will have φ = 0 and an antenna pattern in the y,z plane will have
φ = 90 degrees. In the boxes for phi, φ, enter start=0, stop=90, steps=1. Both antenna
patterns will have θ going “full circle”. In the boxes for θ, enter start=0, stop=360,
steps=72. Click OK.
Use the next window that appears to plot the antenna directivity pattern for φ = 0 and φ =
90. The patterns are proportional to the radiated power (square of the fields), and are
relative to the power that would be radiated from an isotropic radiator, i.e. a source that
radiates power equally in all directions. An example of antenna directivity pattern is
shown in Figure 13. (Note that the following antenna pattern does not have the same
structure as in Fig. 11. Therefore, you need to understand your own antenna structure
and then generate a right pattern for it and explain the meaning of the pattern in the
report.)
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Fig. 13 Antenna directivity patterns example, phi=0 (x,z plane) and phi=90 (y,z plane)
To produce an antenna gain pattern, choose Plot Far Field, and make the appropriate
selections.
Explore some menu selections like Window Tile, Window Cascade, Plot Modify, Plot
Delete and Window Close.
9. Create and Submit a DXF file for the Mask
1. Copy your project to another name. Select the Model Only button.
2. Open up your new project and enter the 3D Drawing Routine (Select Draw Button)
3. You should see your original project drawing. Make sure the unit is in mm. If not, go
to Solid/Unit to display the drawing as mm. You need to move the coordinate origin so
that the x-y plane coincides with the plane of the drawing that your patch is in.
Change the origin to the layer where the patch antenna is located. For example, move the
origin from (0,0,0) to (0,0,0.7874) if the height of the substrate is 0.7874mm. You can
use the mouse to do this – simply move the arrow to one of the 3D drawing windows
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(Figure 15) and select the window by clicking the left mouse button. Then move the
arrow to the point in that window where you want the origin and click the left mouse
button again. Then
Choose Coordinates / Set Current CS / Move Origin.
The coordinate axis should now appear with the x-y plane being the plane containing the
patch antenna.
4. Save 2D Modeler file
Fig.15 3D Modeler Window
Go to File/Export/2D Modeler File. This brings up a window as shown in Figure 16.
Give a name for the file and click OK to save the file. Remember the folder to which
you have written the file.
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Fig. 16 Pop up window to save the 2D modeler file
5. Translate file
Go to Maxwell Tool Bar. Click Translators. This brings up the translators windows
(Figure 17). Choose Maxwell 2D Ver.6 in the Source box, and AutoCAD DXF in the
Destination box. In the Source file, find and select the 2D modeler file you just saved and
choose the destination directory you would like to save DXF file. The default unit for
translator is set to mm. Click Start.
Fig. 17 Translators Windows
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6. Send your project to Dr.Z.
Send the resulting DXF file, which will be used to generate a mask, to Dr. Z at
ziolkowski@ece.arizona.edu.
Name your file according to the last name of your
“computer account” team member. We will correlate all of the files and layout the masks
to minimize the number of actual masks that are created. Your final masks will be cut
out from one of these monster masks and will be provided to you by the scheduled clean
room times. ☺
10.
Reference
1. HFSS Help
2. More examples can be found under Ansoft Online technical support:
http://www.ansoft.com/support.cfm
Note: There is a memory limitation (500Mb)
associated with your Unix account. A typical
HFSS simulation requires 100Mb to 300Mb of
disk space. You will not be able to have many
cases saved in your account. Please always print
out your simulation results and delete the old
cases to free up disk space. (You can check your
disk space by typing ecequota at the unix
command prompt.)
HAVE FUN
AND
GOOD LUCK !!!!
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Appendix. ADVANCED TOPIC: Example of Editing a Macro
To edit the recorded session, choose File/Macro/Edit Macro to access the recorded
macro. Click Yes in the little window that will appear. This brings up the Macro Editor
(Figure 1). On the left side of the Macro Editor, these are all of the commands that have
been recorded while you were drawing the model.
Fig.1 Macro Editor
In the transmission line example, you may want to vary the width of the transmission line
to move the port impendence closer to 50 Ω. You can assign the width of the
transmission line as a parameter so that you may adjust it easily.
Click the command line corresponded to the correct object you wish to edit. In our case,
click New Object (0.492815 0 0.031) 2 0.09547 0.44488 “transline” 1. Once you click
it, the detail information shows up at the right side of the macro editor (Figure 2).
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Fig.2 Macro Editor for editing transline
Fig. 3 Assign parameters for transline
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Replace the start point (0.492815,0,0.031) with (trline_x, 0, 0.031) and Size
(0.09547,0.44488) with (w, 0.44488) (Figure 3). Click Accept.
The following message appears (Figure 4). Click Yes to add variables.
Fig. 4 Add parameters
Click
Rectangle (0,0,0) 2 1.0811 0.44488 “ground” 1
Replace Size (1.0811, 0.44488) with (x, 0.44488).
Repeat this procedure if you feel that you will want to change the shapes or sizes of the
ground and substrate.
Choose Edit/All Parameters to edit parameters in the macro. This brings up the
parameters editor. (Figure 5)
Fig. 5 Parameters Editor
23
Select trline x and type the equation (x-w)/2 at the right box of the equal sign. Click
Update and Done. Choose File/Apply Changes. Exit the Macro Editor.
If you have simulated one case and would like to vary some of the parameters for the
next series of runs, it is now very easy to accomplish. Under Maxwell Project Manager,
click: Copy, select the project you wish to copy, and give a name for the new project.
Make sure the Model Only is checked. Click OK. Open the new project, go to Draw and
choose File/Macro/Edit Macro. You should select the macro that you had in the
previous project. It will have the same parameters that you input for the previous case.
Choose Edit/ All parameters. Change the value of any of the parameters. Then select
Apply the changes. You are now able to adjust the width of the transmission line easily
by changing the value of x in the Parameters Editor.
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