HFSS Overview

Powerful features (1)

Tangential Vector Finite ElementsProvides only correct physical solutions with no spurious modes

Transfinite Element Method

Adaptive Meshing

Fast Frequency Sweep

r E = Ei

t∑ γ i x, y, z( )

s11 s12

s21 s22

⎡ ⎣ ⎢

⎤ ⎦ ⎥

Fast Freq. Sweep

Frequency

S

Adapt Freq.

Powerful features (2)

ACIS-Based Modeler, “Undo”, Macros

Materials include lumped RLC elements and

ferrites

Perfectly-Matched Layer (PML)

Periodic Boundaries or Linked Boundaries

Optimetrics Module: Parametrics and Optimization

3D Eigenmode Solver

Limitations

- Frequency domain, not time domainException: some post processing on S11 after wide frequency

sweep

- Linear materialsException: ferrite applications with M3DFS involved

- Passive structuresException: special application of master/slave boundaries

Geometry translation

ACIS!! AutoCAD!!Seamless interface with ACIS-based modelers

“Translators” in Maxwell control PanelDXF, STL

Printing

Any screen or part of it

Directly to printeror

Print to file:

postscript, GIF, bitmap, etc.

HFSS flow

Driven or EigenmodeDrawSetup MaterialsSetup Boundaries / SourcesSetup Executive ParametersSetup SolutionSolvePost Process

- Fields- Matrix Data- Matrix Plot

Driven or Eigenmode?

Eigenmode Solution

Resonances in arbitrary closed 3D structuresNo external excitations in modelLossy possible:Unloaded Q

Draw or import the geometry

HFSS 3D Modeler

Solid-modeling considerations (1)

Keep complexity lowsmall number of segments in circles and cylindersomit details if possible

Avoid aspect-ratio problemsmaximum aspect ratio is 1:2500use 2D objects instead of thin structures

Keep solution region smalluse symmetry whenever possibledon’t include too much air or transmission line

Avoid overlapping objects

Solid-Modeling Considerations (2)

Few segments aroundcircles and cylinders

Thin metal patch is 2Dobject (aspect ratio!)

No overlapping objects(inner conductor is twoobjects because it goesthrough two dielectrics)

Solid-Modeling Considerations (3)

Some transmission line between port and

antenna(length line not much

smaller than cross section port)

Some air between antenna and radiationboundary (λ/4)

Assign material properties

Materials (1)3D objects get material parameters, 2D objects get a boundary condition.

Materials are valid in interior region of object.A waveguide is made of air.

No fields need be computed inside very good conductors (metals)

HFSS Material Manager

Materials (2)Some possible materials:

air, vacuumperfectly-conducting metalnon-perfectly-conducting metaldielectrics, any permittivity, any conductivitymagnetic materials, any permeability, any magnetic lossesanisotropic materialsthin-film resistors, bulk resistorsferrites

HFSS: Ferrites

Ferrite modeling capability enables simulation of circulators, isolators, and other non-reciprocal devices.Ferrite permeability tensor properties are determined using either uniform magnetic bias field or (optional) 3D magnetostatic field solution.

Circulator with Ferrite Puck

Ferrite material may be uniformly biased, or use the solution of magnetostatic analysis

Assign boundary conditions and excitations

HFSS Boundary Manager

Sources

Power enters the model through (unlimited number of)

portsvoltage sourcescurrent sourcesincident waves

One other kind of source:Hbias for ferrites

Ports in HFSS

Classical Ports: cross section of transmission lineHFSS finds propagating and evanescent modes and determines characteristic impedances

Lumped Gap Source Ports: use when Classical Ports don’t work (will be explained shortly)You specify characteristic impedance of the line

Classical Port Surfaces

Classical Ports Can Only be Defined on Surfaces Which Are Exposed to a Region Where The Field Does Not Exist

BackgroundPerfectly Conducting Objects

Simple 2-Port Waveguide:Ports: waveguide cross sectionsEach port bounds the BackgroundSelect faces or appropriate2D objects to define the ports

Example: coax port

Port is coax’cross section

To define it,select a face or a 2D object

Port and coax are inside a larger

model⇒ cap behind port

Yagi Antenna With Interior Feed Port

Example: Microstrip Port

H’

W’

w

h

PECAnsoft recommends

H’ = 5 -10 h , W’ = 5 w;

h and w are the substrate height and trace width, respectively.If this leads to a highand narrow port thenincrease W’.

Example: CPW port

ground trace ground

Port

Example: stripline port

ground

groundport

trace

Example: poor portThis microstrip

port may be too big

⇒ waveguide mode

possible

Remedy: create2D port object

with

Illegal portsThe following two situations are illegal:

1. A port that contains metal onlye.g. the port is just the cross section of a signal trace

2. A port that is split in disconnected parts e.g. port extends below ground plane

HFSS will not be able to find a field that “fits”

Lumped Gap Source Ports (1)

Classical ports or touching gap source ports obtain wrong solution

Non-touching gap source ports obtain better solution

Lumped Gap Source Ports (2)

Traces close together ⇒ classical ports don’t fit

Gap source port has other boundary conditions on sides that don’t touch metal ⇒ much better solution

Gap source port is internal port but does not get a metal cap

Coupling between traces not part of port solution but included in rest of 3D model ⇒ not perfect but often as accurate as measurements

You specify port impedance

Gap source port provides S parameters just like classical port

Lumped Gap Source Ports (3)

A port with multiple conductors per port would take ALL coupling into account. However, modal-to-nodal software is needed to make use of this.

Lumped Gap Source Ports (4)

Example of structure where gap source ports can be useful

Example: voltage and current sources

Warning: you will get fields but won’t get S parameters! load

Two-conductor transmission line

microstrip

Voltage source (<<λ) Current sources (<<λ)

Can excite even and odd modes

Boundary conditions Perfect EPerfect H / NaturalFinite ConductivityImpedance (sheet resistance and reactance)Radiation (= Absorbing Boundary Condition,

ABC)SymmetryMaster, slavePerfectly-Matched Layer (PML)

Perfect E for 2D Conductor

Dual Mode Stepped-septum PolarizerUse Perfect E Surface for Thin Septum

TE10/TE01 SquareWaveguide

Infinitely ThinPEC Septum

Side View Top View

Perfect E Surface Interior to The Problem Space BehavesLike an Infinitely Thin 2D Perfect Electric Conductor (PEC)

Perfect H / Natural for 2D Aperture

Monopole Over a Ground Plane

Ground Plane isPerfect_E boundary

How to cut the opening?

Perfect H / Natural for 2D Aperture

Use Perfect H / Natural For Opening Small Hole Can be “Cut”in Infinitely Thin GroundPlane Where The CoaxOpens Into The RadiationSpace Using a Perfect H / Natural Boundary

Perfect H / Natural for 2D Aperture

Bethe Hole Coupler Small hole can be “cut”in Infinitely Thin Septumbetween the Upper andLower Guide using aPerfect H / Natural Surface at the Hole

Radiation boundary for open regions

Second-order local absorbing boundary

Place this boundary λ/4 away fromradiating structures like current-carryingconductors, radiating apertures

Place it closer when not interested in radiation

Apply λ/6 or λ/8 seeding on boundary

Conformal boundary - reduces model size

All l l ti f f d

Perfect E and Perfect H Symmetry

TE10 Mode in Rectangular WaveguideGeometric SymmetryField Distribution Symmetry

Perfect E Surface

Perfect H Surface

For Symmetry, The Perfect E or Perfect H Surface MustInterface With The Background

Periodic Boundaries

Phased-array antenna

Periodic boundaries enforcephase difference between “Unit Cells”

At large scan angles,Perfectly Matched Layer on topbetter than Radiation Boundary

Master 1Slave 1

Master 2

Slave 2

WaveguideRadiator

Unit Cell Walls

Feed Port

Boundaries

Boundary conditions are order dependent -a new one can (partially) overwrite an existing one

HFSS puts Perfect_E on non-assigned outer boundary

Always check boundaries before proceeding!

Executive Parameters

Often skippedEmissions testPort fields afterports have been solved

Setup solution parameters

Setup solution (1)

Specify initial, previous or current meshLambda refinementNumber of adaptive passes (5)FrequencySweep yes or no, discrete of fast?

Setup solution (2)Specify

frequencynumber of adaptive passes (5 or more)tet refinement (accept default in most cases)convergence criterion (e.g. ∆S<0.05)frequency sweep yes or no, discrete or faststarting mesh (manual mesh has a lot to offer)ports-only solution (check!) or “all”

Adaptive solution Create initial or manual

meshCalculate electric fields

Calculate S parameters

Display parameters and fields, perform frequency sweep

post-process data

Refine mesh

yes

∆S acceptable? no

Adaptive meshing

Adaptive meshing concentrates pointsin regions of high field gradients thusfocusing the computational effort intothe regions that actually need them.

Seeding and manual meshing

Optional feature

User-defined seeding of objects or faces

Refine on faces, in objects, in regions

Perform the simulation

Multi-Frontal Solver

Takes optimum advantage of RAM

Avoids swapping through “Spill Logic”

Parallel processing is possible on PC

Fast frequency sweep

Starts with (existing) field solution at center frequency

Searches for poles and zeros of a linear transfer function

Provides S parameters and fields over large bandwidth

(e.g. 8-12 GHz)

Identifies (sharp) resonances

Fast frequency sweep

Band pass filter

Fast frequency sweepFrequency

rangeis very projectdependent.

This exampleshows a verywide range.

An accuracycheck never

hurts.

Post Process the data

Post Process

FieldsMatrix DataMatrix Plot

Post Processor (Fields)Important features:

Data - edit sources menu to switch sources on and off

Fields in ports to check excitations

Shaded plot on cut plane, phase animation

2D antenna pattern, 3D antenna pattern

Calculator

E-Field on Cutplane

Geometry

Radiation Pattern - Two Ports Excited Radiation Pattern - One Port Excited

Antenna Example: Sinuous Antenna

Horn 3D Far-Field Pattern

Fields Calculator

Enables many operations on fields:♦ Dot and cross products with field vectors and geometric vectors

♦ Integration over lines, surfaces, volumes

♦ Etc, etc, etc.

∫ ∫

∫

Γ Ω

Ω

Ω+Γ×

Ω=

dtgds

dQu

22

2

2HHn

H

δ

Post Processor - Matrix Data

Deembed

Renormalize

Compute Y and/or Z matrices

Export to circuit simulators

Post processor - Matrix Plot

S, Z as function of frequency

Linear or Smith Chart

dB and VSWR options

Export plots to data file