USC Signal Integrity Lab Course1
Ansoft High Frequency Structure Simulator (HFSS)
ELCT 762
USC
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Acknowledgement
• Thanks to Ansoft for
– providing free EMS packages to USC / Intel
Signal Integrity Lab
– providing free software to APOGEE students
– allowing us to use some of their training
materials
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Signal Integrity Lab
• Located at Engineering building, 3D22
– Software name: Ansoft HFSS 9
• APOGEE students can get free software
from Ansoft
– Contact: hao1.li@intel.com if you don’t know
how
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What is HFSS
• High Frequency Structure Simulator
• Uses Finite Element Method to solve EM
problems
• Frequency Domain Solution
• Full wave Solver
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5
Different Methods of
Electromagnetic Analysis
MOM
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What is Finite Element Method
(FEM) Software?
• FEM software is a design tool for engineers and physicists,
utilizing rapid computations to solve large problems insoluble
by analytical, closed-form expressions
– The “Finite Element Method” involves subdividing a large
problem into individually simple constituent units which
are each soluble via direct analytical methods, then
reassembling the solution for the entire problem space as
a matrix of simultaneous equations
• FEM software can solve mechanical (stress, strain,
vibration), aerodynamic or fluid flow, thermal, or
electromagnetic problems
• Suggested course: ELCT 891H, computational
electromagnetic.
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FEM Problem Constraints
• Geometry can be arbitrary and 3-dimensional
– Model ‘subdivision’ is generally accomplished
by use of tetrahedral or hexahedral (brick)
elements which are defined to fill any arbitrary
3D volume
• Boundary Conditions (internal and external) can
be varied to account for different characteristics,
symmetry planes, etc.
• Size constraints are predominantly set by
available memory and disk space for storage and
solution of the problem matrix
• Solution is created in the frequency domain,
assuming steady-state behavior
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Example of Adaptive meshing
Waveguide Filter at right (symmetry along top
face) shows effect of mesh adaptation. The
region between posts has a denser mesh,
due to the superposition of reflected energy
found in the solution process.
Post
Post
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When is an FEM solver appropriate for Electromagnetic
Problems (Lower Bound)?
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Example: Finding Signal Integrity
impacts of a Via in the signal path
/100
Example: Coax to WG Transformer
/10
Use a Quasi-Static Solver (OVERLAP)
Problem Scale
Use a FEM Full-Wave Solver
• When the Electrical Length (in wavelengths) requires phase consideration
– /10 is a guideline; there are exceptions
• When radiation from the device must be considered
• When S-Parameters are the desired output
• When lossy dielectric materials have significant effects
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Some Typical High-Frequency Electromagnetic
Applications
Waveguide Components
RF Integrated Circuits
Antenna
EMC
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Example 1: Eigenmode Problem
• Find the resonant frequencies of a perfect
metal box filled with “glass”. The box size
is 3x2x2 inch.
• Draw the electric field inside the box at
those resonant frequencies.
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Ansoft HFSS Project Flow
Configuration
Source
Excitation
Solving
Drawing
Solution
Setup
Boundary
Analyze
Data
Plot
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Configuration
• Click HFSS 9 to start the problem
• Click: File -> Save As -> filename
• Click: Project -> Insert HFSS Design
– Now, HFSS design interface has 6 subwindows: project window, property window,
drawing window, history window, message
window and execution window
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Configuration – cont.
• Click: HFSS ->
Solution type,
• Pop up window
shows three types
• Pick the Eigenmode
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Configuration
• Click: Tool -> Option ->
General Option
• Option window pop up.
• Select Default Units tab
• Change the length to:
“inch”
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Configuration
• Click: View -> Grid
Setting
• Grid setting screen pops
up
• Select grid size as 1 inch
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Structure Drawing
•
•
•
•
Click: Draw -> Box ( You can also
click on the draw box toolbar)
On Drawing window, first click will
set the start point, second click will
set the base end point, and the
third click will set the height of
box. ( draw a 3 inch x 2 inch x 2
inch box)
The property window will pop up.
In the command tap, make sure
the Position is at 0, 0, 0. The xsize, y-size and z-size is what you
wanted.
In the Attribute tab, change the
material to “glass”. Change the
Transparency to be “0.8”
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Drawing
• Here is the picture of
what you get.
• You can always
change the item
properties by clicking
the item, and
modifying them at
property window
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Hint
• Hold the keyboard “Shift” and drag the
mouse, you can PAN the drawing
• Hold the keyboard “ALT” and drag the
mouse, you can rotate the drawing
• Hold the “Shift” and “ALT” and drag the
mouse, you can zoom the drawing
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Boundary
• Click Selection toolbar. See
picture. Change the Selection
from Object to Face
• Now, click the face of box.
Hold down the CTRL key and
click face to add all 6 faces as
selected. You may need to
rotate the BOX so you can
select all 6 faces.
• In menu, click HFSS ->
Boundaries -> Assign ->
Perfect E. This assigns perfect
Electric conductor on all 6
faces of box
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Hint
• You can also set the selection box as
“Object”, and select the whole box to
assign the boundary. In that case, the
software will assign same type of
boundary on every surface of this
objective
• You can also select one face assigned as
“Perfect E” and another face assigned as
“Radiation” or any other type of boundary.
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Question
• If the object is already a metal, you don’t
need to assign the boundary on that face.
Why?
• For Eigenmode solution, you must assign
Perfect E or Finite conductor on all face.
Why?
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Source Excitation
• For eigenmode solution, you don’t need to
add source excitation. The software will
automatically add the EM excitation inside
the boundary.
• For driven modal or driven terminal
projects, you DO need to add source
excitation. And, it is very important you do
it right. ( more on later..)
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Solution Setup
• The structure is ready to
simulate. Click: HFSS ->
Validation check to see if
there’s any mistakes in
drawing or boundary
assignments.
• Click: HFSS-> Analysis
Setup -> Add Solution
Setup
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Solution Setup
• The Solution setup
window pops up.
• Change Minimum
Frequency to: 1Ghz
• Change Number of
Modes to 5. ( find first 5
resonant frequencies)
• Change Maximum
Number of Passes to 5
• Click OK
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Solution Setup 2
• You can enter multiple solution setups. This is
useful and convenient when you are seeking for
multiple answers.
• Go to Solution setup menu again, this time enter
(1) Minimum Freq. 1Ghz, (2) Number of Modes:
1, (3) Number of Pass to 5.
• Now, you have two solutions in the project. If you
check the project manager window, they are
called setup1 and setup2 under Analysis tab.
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Run Simulation
• Click: HFSS -> Analyze
• Relax and wait. This project takes less
than a couple minutes to simulate. Large
projects will take more than 24 hours to
simulate.
• Watch the “execute window” or “message
window” for any errors or warnings.
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Solution Data
• Click: HFSS ->
Results -> Solution
Data
• Click Eigenmode
Data tab. It shows the
results of first 5
modes
• Question: What is first
resonant frequency?
What is 2nd Freq?
What is the 3rd ?
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EM Plot
• Click the BOX1 on
drawing window
• Plot the Electric field
inside the box by
clicking: HFSS ->
Fields -> Plot Fields
-> Mag_E
• Field plot window will
pop up.
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EM plot cont.
• Select Solution
Setup2 Last Adaptive
– Only plot the first
resonant frequency
• Select “BOX1” at In
Volume sub-window.
• Select “Mag_E” at
Quantity sub-window.
• Click: Done
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E Field Plots
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Plot Animation
• Click: HFSS -> Field > Animate
• Select: 18 frames
(steps)
• Click: OK
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4th Resonant Plot
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4th Resonant, Vector Plot
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Homework
•
•
•
•
Design a cylinder cavity
Base Radius = 2 inch
Height = 5 inch
Inside material =
FR4_eposy
• Find: first 5 resonant
frequencies
• Plot: Mag_E field for
5th resonant
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