ELCT 361 Introduction to ANSYS HFSS

Brandon Gore 1st Edition

Sam Wang 2nd Edition

Special Thanks

Thanks to ANSYS Corporation for

donation of HFSS licenses to University of

South Carolina classrooms

Content from HFSS 14.0 help files: <install>\Ansoft\HFSS14.0\Help\HFSSinto.pdf where

<install> is typically C:\Program Files\

Agenda

Introduction and Applications

Microstrip Start to End Tutorial

Extras as backup

What is HFSS?

High Frequency Structure Simulator

A full wave electromagnetic field simulator for 3D

volumetric modeling of passive devices

Finite Element Method (FEM)

– Structure is subdivided into finite elements

– One element is a tetrahedra (tet)

– Entire collection of tets called the mesh

– Electromagnetic fields are found within each tet

– Maxwell’s equations are satisfied across element

boundaries

What is HFSS? (continued)

Adaptive meshing: automatically tuned

most accurate and efficient mesh possible

Model arbitrary shapes

Visualize in Windows based GUI

– 3D Model

– Field Results

– S-matrix Results

What is HFSS? (continued)

Possible HFSS Modeling

Package Modeling – BGA, QFP, flip-chip

PCB Board Modeling – ground planes, vias

Silicon/GaAs – spiral inductors, transformers

EMC/EMI – coupling, near/far field radiation

Antennas/Mobile Communications – patches, dipoles, horns, cell phone antennas

Connectors – coax, backplanes, SFP/XFP, vias

Waveguides – filters, resonators, couplers

Filters – cavity filters, microstrip, dielectric

Signal Integrity Uses

Typical server board

Signal Integrity Uses

PCIe

Device

CAP

CPU

SL

OT

PCIe

Connector

Socket

DIEPackage

CAP

PCIe link between CPU and

connector

2-D

representation

of PCIe link

Signal Integrity Uses

PCIe

Device

CAP

CPU

SL

OT

PCIe

Connector

Socket

DIEPackage

CAP

PCIe link between CPU and

connector

Red Dash:

modeled in 3D

simulator

HFSS GUI

progress

properties

Project

manager

3D modeler Design tree

messages

Microstrip Example

The purpose of this segment is to use a

simple microstrip example as a walk-

through for discussion of basic concepts

and terminology such as

– boundaries and excitations

– model creation (drawing)

– analysis setup

– data reporting

5 Step for HFSS

Microstrip

Wave

ports

Trace Ground

FR4

Air

Microstrip Design

Simple stack up

– trace

– dielectric

– ground

1.3 mil

5 mil

1.3 mil

These can be made

variables to facilitate

optimization or quick

redraw

Project Settings

Open HFSS and click insert HFSS design icon from the toolbar

File save as “Project Examples”

Rename design “single microstrip”

From menu HFSS > Solution Type > Driven Terminal – Driven Modal

– Driven Terminal

– Eigen mode

– Transient

Menu: Modeler > Units > mils

Draw Ground Plane Place a 200mil x 200mil x 1.3mil ground

Select 3D box from toolbar

Click once on the origin, and twice

more at arbitrary points in space Right Click

(on CreateBox) >

Properties

Can add as variable instead

of static number

Ground Plane Properties

Attribute Tab:

Set attributes:

Name: ground

Material: copper

Transparent 0

Viewing and Rotating

Mouse + Hot Keys

Rotate

– Hold ALT

Zoom

– Hold ALT+SHIFT

Pan

– Hold SHIFT

Fit to screen (no mouse

click)

– Control + D

Predefined views

– Hold ALT, and double

click one of 9 regions

Dielectric

Draw another box on top the ground plane

Set properties – Position 0,0,0

– X size 200 mil

– Y size 200 mil

– Z size 5 mil

Set attributes – Name Sub

– Material fr4_eproxy

– Transparency 0.5

To open attributes and properties again…

Click for properties

Click for attributes

Signal Trace

Draw a 3D box at an arbitrary location

Set properties – Position 0, 95, 6.3

– X size 200 or Ground_x

– Y size 10 or Line_y

– Z size 1.3

Set attributes – Name trace_a

– Material copper

– Color orange

– Transparency 01

What if these

were variables? (0,($y/2-$w/2),$vss+$die_h)

Draw Ports

Select YZ from the

drawing plane drop down

Draw a 2D rectangle

with the following

Properties

– Position 0, 50, 1.3

– Y size 100

– Z size 50

Attributes

– Name port1

– Transparency 0.9

Create another 2D

rectangle

Properties

– Position 200, 50, 1.3

– Y size 100

– Z size 50

Attributes

– Name port2

– Transparency 0.9

Possible to make a copy

of port1

5 Step for HFSS

Assign Port 1

Right click on port1 from design tree. Assign excitation, wave port

To create name, next

Select ground as

reference, OK Repeat for port2

Air Box

Draw 3D box

Properties – Position 0,0,0

– X size 200

– Y size 200

– Z size 100

Attributes – Name Air BOX

– Material air

– Transparency 1

Removing Intersections

Two 3D geometries cannot overlap or intersect within one another

The signal trace is currently intersecting the air box!(In HFSS 14, this is not considered to be intersection)

– But how do you know!? Press Validate Design

Use the design tree to select both the Air BOX and wire

Right click in the design window and select edit > boolean > subtract or press

Removing Intersections(Not right

in HFSS14 for this case) Trace is the tool part. It will tool a hole in

AirBOX, the size of wire.

To keep trace as part of the design, be sure to

check “clone tool objects before

subtracting”!(Just learn how to do it but do not

really do it in HFSS14)

Default

material

override also

available

Validate again!

Is the intersection

fixed?

Assigning Boundaries

Select Airbox from

the Design Tree

Right Click >

Boundaries > Radiation

5 Step for HFSS

Analysis Settings

In the project manager,

right click Analysis to Add

Solution Setup

General Tab

– Solution Freq 20 GHz

– Max number of passes 25

– Maximum Delta S 0.01

Everything else is default

20Ghz

Analysis Sweep

Right click setup1 to

add Add Sweep

Sweep type

interpolating

Freq Step

– Linear Count

– 50Mhz to 20Ghz

– Step size: 0.01GHz

Analysis Sweep

Interpolation Setup

New window in HFSS v14

New setting in HFSS v14

5 Step for HFSS

Solve

Validate

– This is ok. The wave port boundary will over-

ride the radiation boundary

– No such warnings for this case in HFSS 14

Right click setup1 … Solve

Check Convergence

HFSS menu > Results > Solution Data

Convergence Tab

Did solution converge in less than the maximum

number of passes, below my delta S target?

S-Parameters can be

extracted from here. Make sure to select your sweep

S-Parameters

Scattering parameter models are one of HFSS’s output capabilities – R,L,G,C, time delay, and impedance can be extracted

from s-parameters

– S-parameters can be used as equivalent circuits in simulation

– Characteristics of s-parameters can be used to gain intuition about circuit behavior for signal integrity problems

For more on s-parameters, refer to Frequency Domain slides from ELCT 762 & 865

View S11, S21

Create Report by right clicking

on results in project manager

Report type is Terminal S Parameters on

Rectangular Plot

Click St(wire_T1,wire_T1) and hold Ctrl and then

click St(wire_T2_T1)

Double

click

Plot E-Fields

Eye Candy

Select trace

Right click in drawing window. Select plot fields, E, magE.

Press Done, notice you are plotting at at 20GHz

You can animate

Extra

Frequency Sweeps

Discrete: full solution at every freq.

Fast: adaptive solver to extrapolate solution from center frequency. Good for high Q-devices; but not for devices that pass through a cut-off. Fields can be displayed at any frequency.

Interpolating: solves at discrete points that are fit by interpolating. The field solution is available only at the last solved fequency.

Definitions of Excitation Boundaries

Excitation – permits energy to flow into

and out of a structure

Perfect E/H – perfect electrical or

magnetic conductor

Radiation –The wave is absorbed,

essentially modeling the boundary as an

infinitely open space

Definitions of Excitation Boundaries

Wave Port – assumed to be a semi-

infinitely long waveguide to the solver.

Each wave port is individually excited and

contains one watt of time-averaged power.

It is used to calculate impedance, complex

propagation constant, and s-parameters

Solution Types

HFSS > solution type

Driven Modal – Modal based s-parameters where matrix solutions are

expressed in terms of incident and reflected powers of waveguide modes

Driven Terminal – Terminal based s-parameters of multi-conductor

transmission line ports that are expressed in terms of voltages and currents

Eigenmode – Calculates the Eigen modes – that is the resonant

frequencies and fields of a structure

History Tree

Organization by material

Expand design tree to undo an operation

The last operation on an object must be undone first

Select multiple objects that are hard to select in design view, and properties of all selected objects

To Clone, Copy, or Paste

You can copy and paste designs in a project – Warning (you will do this): when you copy a design, CLOSE the

drawing window. For example, you think you are editing your new design but you are still using the original!

You can copy and paste in the design tree – Now there are two traces, but they are overlap, occupying the

same space! You must move it!

An alternative to copy: duplicate (clone)

Clones

To clone, select object: edit>duplicate

Along Line option allows you to draw a vector on which to duplicate objects

The image created here, by selecting a vector of two points and selecting 3 total number when prompted

The vector drawn…

Clones_1

A copy is independent of it’s original

For a clone, what happens to the original, happens to the clone!

Notice the naming convention – John

– John1 (copy of john)

– John_1 (clone of john)

Even though the clone

operation has been

completed, you edit it in the

history tree. For example,

edit the vector and increase

the amount of space

between the original and

clone.

Miscellaneous Topics

When drawing any 2D line or 3D box, you

can enter the coordinates manually at the

lower right corner of the screen by hitting

tab

You can control what vertices your mouse

snaps to by opening menu Modeler >

Snap Mode

Miscellaneous Topics

Relative Coordinate Systems – One use is to ‘split’ or remove all objects on one side of an axis

If HFSS crashes, a .lock file is created that prevents you from opening the project. You may need to delete this file.

Dembedding under wave port allows you to remove a length transmission line from the model

Design List under HFSS menu is useful for operating on all objects with in the design

Differential S21:

(S(Port2,Port1)-S(Port4,Port1)-S(Port2,Port3)+S(Port4,Port3))/2

Visibility

To select a hard-to-reach face of an

object, hold the mouse above the desired

face and press “b” until that face is

selected

Don’t forget the View menu has a handy

render>wireframe option and a visibility

menu to turn objects on and off in the

drawing window

Uniting Intersecting Parts

Touching conductors should be united to

simplify design for solver

– Unite trace_top, via1, and trace_top_2

– Repeat for the second trace

The vias are intersecting with all 3

dielectric layers and possibly the air box

– Subtract