HFSSv12

HFSS v12 training:

2008 Ansoft, LLC All rights reserved.

Ansoft High Frequency Structure Simulator v12 Training Course

Ansoft, LLC Proprietary

Agenda HFSS : 3D Full-wave Electromagnetic Fields Simulator Introduction : What is HFSS ? What Information does HFSS Compute? Parts of HFSS : GUI, Mesh ,Solver, Post-Process How HFSS is working ? Theory and principle (FEM method , Adaptative mesh,..) Design Flow Ansoft Desktop and overview of the 3D Modeler Building an HFSS Model Step by Step Drawing, Excitations, Boundaries conditions, set-up, frequency sweep, analyses, post-processing

Handling HFSS with examples ------------------- HFSS Options HFSS 12 Advanced Training Questions and Answers




INTRODUCTION




What is HFSS? HFSS High Frequency Structure Simulator - circa. 1990 Arbitrary 3D Volumetric Full-Wave Field Solver Ansoft Desktop Advanced ACIS based Modeling (v19.2) True Parametric Technology Dynamic Editing Powerful Report Generation Dynamic Field Visualization Design Flow Automation: Optimetrics/Ansoft Designer/AnsoftLinks/e-physics Advanced Material Types Frequency Dependent Materials (eg r, vs freq) Non-linear (ferrites) and Anisotropic Materials Advanced Boundary Conditions Radiation and Perfectly Matched Layers Symmetry, Finite Conductivity, Infinite Planes, RLC, Layered Impedance, Screening Impedance Master/Slave Unit Cells Advanced Solver Technology Automatic Conformal Mesh Generation Adaptive Mesh Generation, Fault tolerant Mesher Internal/External Excitations Includes Loss ALPS Fast Frequency Sweep Direct and Iterative solvers (32/64bit) / Eigenmode Analysis (32/64bit)bAnsoft High Frequency Structure Simulator v12 Training CourseAnsoft, LLC Proprietary


What Information does HFSS Compute?0.00 Matrix Data Modal/Terminal/Differential -10.00 S-, Y-, and Z-Parameters VSWR -20.00 Excitations Complex Propagation Constant (Gamma) -30.00 Characteristic Impedance Zo -40.00 Full-Wave Spice Full-Wave Spice Broadband Model -50.00 Lumped RLC Low Frequency Model Partial Fraction Matlab -60.00 9.50 9.75 10.00 Freq [GHz] W-Elements Port Solution Export Formats HSPICE, PSPICE, Cadence Spectre, and Maxwell SPICE Common Display Formats: Rectangular, Polar Smith Chart Data Tables Common Output Formats: Neutral Models Files (NMF) (Optimetrics only) Parametric Results Touchstone, Data Tables, Matlab, Citifile Graphics Windows ClipboardAnsoft Corporation Response HFSSModel1

Y1

Curve Info dB(S(WavePort2,WavePort1)) XBandSweep : Sweep1 dB(S(WavePort1,WavePort1)) XBandSweep : Sweep1

10.25

10.50




What Information does HFSS Compute? Fields Modal/Terminal/Differential Electric Field Magnetic Field Current (Volume/Surface) Power Specific Absorption Rate Radiation 2D/3D Far-/Near-Fields Arrays Regular and Custom Setups RCS Field Calculator User Defined Field Calculations Common Display Formats Volume Surface Vector 2D Reports Rectangular, Polar, Radiation Patterns Common Output Formats: Animations AVI, GIF Data Tables Graphics Windows Clipboard, BMP, GIF, JPG, TIFF, VRML




What Information does HFSS Compute? Eigen Mode Analysis Eigen Mode Data Eigen Mode Frequency, Q Common Display Formats Volume Surface Vector Data Tables Common Output Formats: Animations AVI, GIF Data Tables Graphics Windows Clipboard, BMP, GIF, JPG, TIFF, VRML

DRO

Dipole



Parts of HFSS Four differents parts : GUI Graphical User Interface

MESH Divides the full problem space into thousands of smaller regions.

SOLVER Compute the data using the corresponding solve

POST-PROCESSING Exploit the results of the simulation

Ansoft Corporation

Response

HFSSModel1

0.00

-10.00

-20.00

Y1

-30.00

-40.00Curve Info dB(S(WavePort2,WavePort1)) XBandSweep : Sweep1 dB(S(WavePort1,WavePort1)) XBandSweep : Sweep1

-50.00



-60.00 9.50

9.75

10.00 Freq [GHz]

10.25

10.50


THEORY & PRINCIPLE




Finite Element Method (FEM) software Geometry can be arbitrary, 3-dimensional

Boundary Conditions within and on the problem space boundary 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 created is in the frequency domain, assuming steady-state harmonic behavior




What is the Technology Behind the HFSS Field Solver? Volumetric Field Solver Type: Full-Wave Solution Method: 3D Finite Element Method (FEM) Accuracy: If there were no limits on the size of the matrix and on the number of digits for computation, there would be no limit to the accuracy of the Finite Element Method! Mesh Type: Conformal Mesh Element: Tetrahedron Vertex: Explicitly Solved Mesh Process: Adaptive Convergence: Complex Magnitude Edge: Explicitly Solved Change in S-Parameters (Delta S) Excitations - Port Solver Solution Method: 2D Finite Element Method Face: Interpolated Mesh Process: Adaptive Frequency Sweeps Discrete Sweep Generates field solutions at specific frequency points in a frequency range. Interpolating Sweep Adaptive Discrete Sweep with curve fitting Up to 10000 data points, number of discrete solution points varies with response. Fast Frequency Sweep: ALPS (Adaptive Lanczos-Pad Sweep) Matrix Data and Fields at every frequency in sweep, up to 10000 data points.Ansoft High Frequency Structure Simulator v12 Training CourseAnsoft, LLC Proprietary


Pre-Processing: Geometry definition

Patch antenna

On chip spiral inductor

Air box /4 Air box /4 /4 Symmetry plane

Symmetry should be used to reduce solve time and improve accuracy For radiating structure: antenna airbox should be drawn (lambda/4 to lambda/2 in all directions) and radiation boundary or PML used.12 2008 Ansoft, LLC All rights reserved.

Airbox needs to be drawn far enough here to remove the outer boundary influence For non radiating structure (several times smaller than wavelength a smaller box - approx lambda/10 - is more efficient.Ansoft, LLC Proprietary


HFSS solution type

Used in most RF/microwave designs where excitations (ports) are defined to get S,Y,Z parameters, field, radiation pattern

Used for Signal integrity application where multiple excitations are defined at the port. Solution can be exported as Full Wave Spice model

Mainly used to model cavity and get eigen frequencies and Q factor.

Note: in project where one single excitation mode is used at the port, both modal and terminal based model should provide similar answer




Accuracy Accuracy of the model

All the relevant details needs to be defined Proper material properties. Proper port definition and model size Accuracy of the mesh

The EM field value can strongly vary in some part of the model and less in other: HFSS adaptive process automatically refines the critical area so that a denser mesh will better represent the field.



Adaptive MeshGeometry (no mesh data)

Create Initial Mesh

Adaptive meshing example 11.5 GHz patch antenna Mesh elements concentrate about the perimeter of patch. Optimal mesh automatically generated by HFSS

Calculate Field

Calculate Field Accuracy

S Acceptable? Yes Display Simulation Results

No

Refine Mesh




3D Example : Microstrip Via Transition through a Ground Plane

Hole for via Ground metal Air

Substrate

Model Definition16 2008 Ansoft, LLC All rights reserved.



Initial mesh

View of initial mesh

The projection of the 3-dimensional mesh onto the substrate surface creates a triangular mesh. The initial mesh is as coarse as possible while still representing all geometric features. The solver then starts the solve process, progressing around the solve loop, adapting the mesh and checking the solution.

17 2008 Ansoft, LLC All rights reserved.



Adaptative process Mesh after 2 passesMax(|S|)

Convergence

Mesh after 4 passesMax(|S|)

Convergence




Adaptative process Mesh after 6 passesMax(|S|)

Convergence

Mesh after 8 passesMax(|S|)

Convergence




Final Converged Mesh

ConvergenceMax(|S|)Magnetic field |H| magnitude at 13 GHz (1V input to microstrip feed with 50 ohm termination on the opposite port).

Electric field |E| magnitude at 13 GHz (1V input to microstrip feed with 50 ohm termination on the opposite port).




Accuracy of the solution When a project is properly defined (dimensions, material, ports), the accuracy of the solution in HFSS only depends on the accuracy of the mesh. Many inaccurate results just get better with asking for more adaptative passes.




Design Flow Definition :Design flows are the explicit combination of electronic design automation tools to accomplish the design of an integrated circuit/system. The challenges of rising interconnect delay led to a new way of thinking about and integrating design closure tools. New scaling challenges such as leakage power, variability, and reliability will keep on challenging the current state of the art in design closure.

The notion of flexibility is essential in order to get the most integrated Design Flow as possible. Each tool should respect : Interaction between the differents simulation tools.

Data Importation / Exportation with the biggest choice of format. Ex : (Mechanical : Step, Sat, Iges, Catia, ProE Electrical: Touchstone, Spice,.) Capability of scripting. Availability on several Operating Systems (OS) : Windows, Linux, Sun




HFSS Design Flow SummaryLayout under the pre-defined constraints using 3rd party layout toolsCadence Allegro/ APD Mentor Board Station /ExpeditionTM Sigrity UPD Zuken CR-5000 DXF / GDS

3D-Model import from CAD-fileProE Catia V4/V5 Sat / Step / Iges

Ansoft Links

Results export : Sparameter Spice :touchstone

HFSSTM Fullwave extractionDynamic Link

Geometry export: 2D : dxf and GDS 3D : SAT, STEP and IGES

FullwaveSpice

Ansoft Designer/NexximCircuit / EM cosimulation : Time and frequency domain



Ansoft DesktopMenu bar Toolbars

3D Modeler Window Project Manager with project tree

Message Manager

Progress Window

Status bar Coordinate Entry Fields

Property Window




Ansoft Desktop Project Manager Multiple Designs per Project Multiple Projects per Desktop Integrated Optimetrics Setup Requires License for Analysis Project Manager Window

Project Design

Design Setup

Design AutomationParametric Optimization Sensitivity Statistical

Design Results




3D Modeler Demo




HFSS Analysis Design Flowchart

Construct Geometry (User Input) Define Volume Conditions (User Input) Define Surface Conditions (User Input)

2D Excitation Solution (Automatic) View/Plot S-Parameters (User Input) 3D Mesh Generation (Automatic, User Input Optional) View/Plot Fields (User Input) Solve 3D Matrix (Automatic)

Define Solution Requirements (User Input)

PRE-PROCESSING

SOLUTION

POST-PROCESSING




Boundary conditions




Boundary Conditions




Boundary conditions Why do I Care? They Force the fields to align with the definition of the boundary condition As a user I should be asking

What assumptions, about the fields, do the boundary conditions make? Are these assumptions appropriate for the structure being simulated? Model Scope To reduce the infinite space of the real world to a finite volume, Ansoft HFSS automatically applies a boundary to the surface surrounding the geometric model

Outer boundary Default Boundary: Perfect E Model Complexity To reduce the complexity of a model, the boundary conditions can be used to improve the:

Solution Time Computer ResourcesFailure to understand boundary conditions may lead to inconsistent results 2008 Ansoft, LLC All rights reserved.



Boundary conditions What are Common Ansoft HFSS Boundary Conditions? Excitations Wave Ports (External) Lumped Ports (Internal) Surface Approximations Perfect E or Perfect H Surface Finite Conductivity Surface Impedance Surface Layered Impedance Surface Lumped RLC Symmetry Planes Radiation Surface Perfectly Matched Layer (PML)

Largely the users responsibility

Strictly not a surface approximation Master/ Slave Material Properties Boundary between two dielectrics Finite Conductivity of a conductor

Transparent to the user




Surface Approximations Perfect E Forces the electric field perpendicular to the surface Outer Surface Default Boundary PEC/Perfect Conductor Material Property Perfect E Surface Model complexity: Reduced by eliminating conductor loss Perfect H Forces the electric field tangent to the surfacePerfect H Surface

Finite Conductivity Lossy electric conductor. Forces the tangential electric field at the surface to: Zs(n x Htan). The surface impedance (Zs) is equal to, (1+j)/(), Model complexity: Reduced by eliminating conductor thickness




Impedance Impedance Represent surfaces of a known impedance Specified in terms of the surface impedance (Zs), Rs + jXs (Ohms/Square) The tangential electric field at the surface is the given by Zs(n x Htan).Thin film Resistor modeled as Impedance boundary, where geometry controls the impedance.

Layered Impedance Models multiple thin layers in a structure as a single Impedance Surface

Lumped RLC Similar to the Impedance boundary above, but represents a surface as a parallel combination of R, L, & C explicitly. The R, L & C can be used to incorporate lumped element component values into a model, without including the 3D model of the component e.g. a matching capacitor network or terminating resistor etc Boundaries can be concatenated to build up more complex impedances e.g.

C L

R

Microstrip line with series L and C and a load modeled as lumped R. 2008 Ansoft, LLC All rights reserved.

33Ansoft, LLC Proprietary

Screening Impedance Boundary Used to efficiently represent periodic screens or grids with impedance boundary condition Can be anisotropic (different values in x and y directions) Can be frequency-dependent Dynamic link support to import impedance values from unit cell Includes effects of polarization Resistance and reactance (/square) Coordinate system if anisotropic HFSS design for dynamic link

Periodic grid characterized by unit cell

Parameters




Symmetry Enables you to model only a part of a structure Perfect E or Perfect H Symmetry Planes Must be exposed to the outer surface Must be on a planar surface Impedance multiplier used to correct extracted impedance Single E, set impedance multiplier to 2, Single H, set impedance multiplier to 0.5

Model complexity: Reduced by eliminating part of the solution volume

Perfect E Symmetry

Full Model

Perfect H Symmetry

Remember! Mechanical Symmetry may not Equal Electrical Symmetry 2008 Ansoft, LLC All rights reserved.



Open structures Radiation Surface Allows waves to radiate infinitely far into space. The boundary absorbs wave at the radiation surface Can be placed on arbitrary surfaces Accuracy depends on The distance between the boundary and the radiating object The radiation boundary should be located at least one-quarter of a wavelength from a radiating structure. If you are simulating a structure that does not radiate, the boundary can be located less then one-quarter of a wave length (The validity of this assumption will require your engineering judgment). The incident angle The radiation boundary will reflect varying amounts of energy depending on the incidence angle. The best performance is achieved at normal incidence. Avoid angles greater then ~30degrees. In addition, the radiation boundary must remain convex relative to the wave.

Perfectly Matched Layer (PML) Allows waves to radiate infinitely far into space. Not a Boundary Condition. Fictitious materials that fully absorb the electromagnetic fields impinging upon them. These materials are complex anisotropic. Types Free Space Termination or Reflection Free Termination Can only be placed on planar surface Model complexity: They do not suffer from the distance or incident angle issues, but should be place at least one-tenth of a wave length from strong radiatorsAnsoft High Frequency Structure Simulator v12 Training CourseAnsoft, LLC Proprietary


Radiation Boundary Mimics continued propagation beyond boundary plane Absorption achieved via 2nd order radiation boundary Place at least /4 from strongly radiating structure Place at least /10 from weakly radiating structure Absorbs best when incident energy flow is normal to surface Must be concave to all incident fields from within modeled space

Parameters Advanced options used for incident wave and HFSS DataLink problems

Boundary is /4 away from horn aperture in all directions

Radiation boundary functions well for incident angles less than 25 -30




Perfectly Matched Layer (PML) Fictitious lossy anisotropic material which fully absorbs electromagnetic fields Two types of PML applications PML objects accept free radiation if PML terminates free space PML objects continue guided waves if PML terminates transmission line Use PML setup wizard for most cases Manually create a PML when base object is curved or inhomogeneous Uniform thickness Minimum frequency Minimum radiating distance (between PML and antenna)

Guidelines for assigning PML boundaries

Parameters

PML functions well for incident angles less than 65 -70




Radiation Boundary vs PML

Radiation Boundary Type Incident angle from normal Distance from radiator Setup complexity 2D < ~30 > /4 Low

PML 3D (occupies volume) < ~70 > /10 Medium




Excitations




Excitations can take several forms : Ports Ports are a unique type of boundary condition, and the most common excitation. Allow energy to flow into and out of a structure. Defined on 2D planar surface Arbitrary port solver calculates the natural field patterns or eigen modes Assumes semi-infinitely long waveguide Same cross-section and material properties as port surface 2D field patterns serve as boundary conditions for the full 3D problem

Floquet ports Used with master/slave boundary for periodic antenna array FSS/PBG

Incident field Used to illuminate a model with a plane wave or other type of incident field. The field can be the near/far field from another Ansoft EM solver enabling linked problems to be setup. Magnetic Bias Used for non circulator, isolator.

Voltage or Current sources Used to apply a specific voltage or current to an object No network parameters etc available, only fields and derived quantities




Port Type Wave Port (Waveguide) External Recommended only for surfaces exposed to the background PEC Supports multiple modes (Example: Coupled Lines) Supports reference plane de-embedding and arbitrary mode re-normalization 2D Port solver computes modal Zo, Gamma, lambda and Epsilon. Computes Generalized S-Parameters Frequency dependent Characteristic Impedance (Zo) Perfectly matched at every frequency Note: this may differ from measurements or other simulations, use re-normalization to make comparisons. Wave ports are well suited for closed structures like waveguide, coax, etc. For open structures like microstrip, coplanar waveguide etc., waveports are typically defined on the face of the surrounding airbox as shown - refer to sizing guides.



WavePort External Examples Wave ports are well suited for closed structures like waveguide, coax, etc. For open structures like microstrip, coplanar waveguide etc., waveports are typically defined on the face of the surrounding airbox as shown - refer to sizing guides.Port 1

Port 4

Differential Stripline with waveport defined between upper and lower ground planes

Port 3 Port 2

Port 1

Microstrip with wave port defined on face of surrounding airbox, with deembedding arrow shown.

Wave ports defined on faces of coaxial model.

Port 2




WavePort Internal Examples Wave Port (Waveguide) Internal In some cases waveports may be placed internally using an inner void or on the surface of a 3D PEC object drawn within the model. Note: The 3D PEC object may well influence the solution if not PEC Block placed on placed/sized carefully. PCB to enable insertionof internal Waveport for impedance calculations Dipole in large airbox (not shown) with internal wave port on PEC object.




Excitation (continued) Wave Port Boundary Conditions Perfect E or Finite Conductivity Default: All outer edges are Perfect E boundary. Port is defined within a waveguide. Easy for enclosed transmission lines: Coax or Waveguide Challenging for unbalanced or non-enclosed lines: Microstrip, CPW, Slotline, etc.Narrow Port MS Mode

Symmetry or Impedance Recognized at the port edgesPerfect E Edges Larger Port MS Mode

Radiation Default interface is a Perfect E boundary.

Narrow Port Higher Order Mode




WavePort Properties Waveports have various properties controlled by the user. These can be set during definition of the port or after, by selecting the port and clicking properties. Ports can also be re-assigned to other surfaces etc. General Tab Used to set the Name e.g. WavePort1




WavePort Properties Modes Tab Enables definition of number of allowed Modes at the Port default is one. For each mode allowed, a set of s-parameters is generated in the 3D model solution. i.e. 1 port,1 mode = 1 x 1 s-matrix. 1 port, 2 modes = 2 x 2 matrix etc. Integration line can be defined (recommended) for each mode: Defines orientation of the mode (for 3D solution) and the Integration path over which integral is computed to determine mode VoltageV. dl E. If defined, Zo can be determined from voltage (v) , current (i) and power (p). E-Field can be forced to align with Integration line by selecting Polarize E FieldExamples: WG Appropriate for structures with degenerate modes e.g. square or circular WG. Coax Microstrip




WavePort Properties Post Processing Tab Port Renormalization enables re-normalization of all or specific port modes to a desired impedance. Enables direct comparison with measured data e.g. s2p file or data where Zo is fixed w.r.t. frequency. Deembedding can be enabled and used to move the solution reference plane in or out of the model a specific distance.

Ensure good port solution for accurate de-embedding




Wave Port Sizing Guidelines Microstrip port height between 6h and 10h Tend towards upper limit as dielectric constant drops and fringing fields increase Make bottom edge of port co-planar with upper face of ground plane 10w for w h 5w, or on order of 3h to 4h, for w < h

Extend stripline port height from upper to lower groundplane (h) Stripline port width 8w for w h 5w, or on order of 3h to 4h, for w < h

Microstrip port width

Can also make side walls of port Perfect H boundaries

10w, w h or 5w (3h to 4h), w < h

8w, w h or 5w (3h to 4h), w < h

w h 6h to 10h w h Port sizing guidelines are not inviolable rules. If meeting height and width requirements result in rectangular aperture larger than /2 in one dimension, the substrate and trace may be ignored in favor of a waveguide mode. When in doubt, run a ports-only solution to determine which modes are propagating.Ansoft, LLC Proprietary


Wave Port Sizing Guidelines Slotline port height at least 4h or 4g (whichever is larger) Include air above and below substrate If ground plane is present, port should terminate at ground plane

Coplanar waveguide port height at least 4h or 4g (whichever is larger) Include air above and below substrate If ground plane is present, port should terminate at ground plane

Port width should contain at least 3g to either side of slot or 7g total minimum Port boundary must intersect both side ground planes or they will float and become signal conductorsApprox 7g minimum

Port width should contain 3-5g or 3-5s of side grounds (whichever is larger) Total width ~10g or ~10s Port outline must intersect both side grounds or they will float and become signal conductorsLarger of approx. 10g or 10s

Larger of 4h or 4g g h h For Driven Modal solutions, use Zpv for impedance calculation g Larger of 4h or 4g s



Wave Port Implications Modes, reflections, and propagation It is possible for 3D field solution generated by excitation signal of one specific mode to contain reflections of higher-order modes which arise due to discontinuities If higher-order mode is reflected back to excitation port or transmitted onto another port, its S-parameters should be calculated If higher-order mode decays before reaching any port (because of attenuation or because it is a non-propagating evanescent mode), there is no need to obtain its S-parameters

Wave ports require a length of uniform cross-section HFSS assumes that each port is connected to semi-infinitely long waveguide with same cross-section as wave portNo uniform cross section at wave ports Uniform cross-section added for each wave port




Internal Wave Ports Wave ports can be placed internal to model by providing boundary condition normally seen by external wave port Create PEC cap to back the wave port and enable excitation in proper directionExample coax feed within solution volume

Coaxial antenna feed with coaxial wave port capped by PEC object




Integration Lines Applicable to driven modal solution types Port vector which can serve several purposes Calibration line which specifies direction of excitation electric field pattern at port Define separate integration line for each mode on multi-mode ports

Impedance line along which to compute Zpv or Zvi port impedance Select two points with maximum voltage differential

Microstrip line Waveguide

Slotline




Lumped PortsRecommended only for surfaces internal to model Single TEM mode with no de-embedding Uniform electric field on port surfaceNormalized to constant user-defined Z0 Perfect E or finite conductivity boundary for port edges which interface with conductor or another port edge Perfect H for all remaining port edges

Lumped port boundary conditionsDipole element with lumped port

Zo

Uniform electric field User-defined Zo




Wave Ports vs Lumped Ports

Wave portAccessibility Higher order modes De-embedding Re-normalization Setup complexity External Faces Yes Yes Yes Moderate

Lumped port Internal to Model No No Yes Low




HFSS source : Floquet ports A Floquet port is like a Wave port except: Adjacent boundaries must be LBCs Material touching Port must be isotropic and homogeneous. Modes are generated from analytic projection instead of eigensolution. Floquet ports are used for FSS where it replaces the incident plane wave excitation and PML or in antenna infinite array simulation as a replacement for PML. Floquet ports provide both amplitude and phase for FSS analysis.




HFSS Source : Incident Wave Other Incident Wave: Plane Wave: Regular/evanescent/Eliptically polarized. Commonly used for FSS (frequency selective surface analysis) or RCS (radar cross section) analysis. Hertzian dipole, linear antenna, Gaussian beam: analytical Wave patterns. Far Field Wave/near field Wave: Commonly used for dynamically linked model: HFSS/Siwave/maxwell3D. The field pattern of another project is used as an excitation. Commonly used in EMI/EMC application or for large antenna simulation. Siwave Board

HFSS model Note: If model complexity permits it, it is recommanded for accuracy to perform full model simulation




Solution type :Driven Terminal




Terminal Assignment Terminals defined by edge or face selection Terminals appear in the project tree Listed under ports Can be selected, edited, independently No need to draw terminal lines, which is tedious and error prone

Terminals defined by face selection. 2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary

Auto-Assign Ports and Terminals

Select Ports and Assign

Choose References Auto-Assign



Solution type : Eigen Mode




EigenMode An Eigenmode solution is a direct solution of the resonant modes of a closed structure As a result, some of the sources and boundaries discussed so far are not available for an Eigenmode project. These are: All Excitation Sources: Ports Voltage Drop and Current Sources Magnetic Bias Incident Waves

The only unavailable boundary type is: Radiation Boundary (A Perfectly Matched Layer construction is possible as a replacement)




EigenMode Eigen solution is very sensitive to the mesh/order- If the mesh/order is too low, it would support many, unexpected field patterns, ex : When using zero order elements, you loose on the accuracy so much, that you can not get a reasonable solution.

In general Mesh operations is required to start from a better mesh. improve the conformal mesh as your geometry has true curves Improve accuracy

Low convergence criteria (0.1%) so increase adaptive passes Use Symmetry planes if you are only interested in mode 1 Eigenmode solver :- The more mode you ask for, the longer will be the simulation. - In the same way, you must define the minimum frequency close of the 1st mode frequency when you know it. This reduces the computation time and improve the accuracy also. 2008 Ansoft, LLC All rights reserved.



Solution Setup & Solution Data




Solution Setup - General Solution Setups are added in the Project manager under the Analysis Tree . Multiple Setups can be added if required. The General Tab is used to set critical solution controls. Solution Frequency Defines the frequency at which model is meshed and solved adaptively (adaptive solve loop). Maximum no of Adaptive Passes: Default is six, more may be required. Maximum Delta S: default is 0.02 i.e. 2% This controls convergence of the adaptive pass solve loop. 1-2% is generally accurate enough. Option to solve Ports Only can be set Use this to study port eigen modes, optimize Zo etc




Solution Setup - Options The Options tab is used to refine the solution controls and initial mesh options. Initial Mesh Options: Do Lambda Refinement - enabled by default. This refines the initial mesh based on material dependent wavelength. Target: sets goal for number of tetrahedra per unit wavelength - 0.333 default for 1st order solution, i.e. minimum of three tetrahedra per unit wavelength. Free space lambda can be used in some circumstances e.g. very lossy dielectrics. Adaptive Options: Max refinement per pass: 30% Min No of Passes: default 1 Min Converged passes: 1 or more >1 forces solution process to continue beyond convergence.




Solution Setup - Options Interpolation scheme of the basis functions is controlled by the Solution Options tick box: zero order: uses Linear interpolation: saves RAM and CPU 6 Unknowns per Tetrahedra Application: structures which are small compared to wavelength - e.g. structures on chip, LTCC arrangements, MEMS, packages etc Default First order: uses Quadratic interpolation 20 Unknowns per Tetrahedra Application : electrically large structures - e.g. antennas, resonators etc Second order: 45 unknowns per tertrahedra Application: More effective to mesh model with electrically large uniform medium. Mixed order (new with v12!) 0,1,2nd order elements are mixed. Adaptative refinement will refine on both mesh size and element order. Generally the most effective for speed and accuracy.Ansoft High Frequency Structure Simulator v12 Training CourseAnsoft, LLC Proprietary


Basis Functions - Hierarchical and Higher Order Vector Basis FEM uses Basis Functions to interpolate the field at any point within the element. HFSS v12 currently supports low order , 1st order and 2nd order basis functions : Low order basis function is a linear function Model size is small compared to wavelength This results in linear interpolation, the field varies linearly inside each tetrahedron Field quantities are solved in 6 points 1st order basis function is quadratic function i.e. 2nd order polynomial This results in 2nd order interpolation Field quantities are solved in 20 points 2nd order basis function with regard to electrically large, geometrically simple models. Improve accuracy around sharp edges and corners Provide accurate solutions in large volumes with a smaller mesh, resulting in memory and time savings Field quantities are solved in 45 points

(Default order)



Choice of Solver: Direct / Iterative HFSS12 has two matrix solvers: direct matrix solver Iterative matrix solver (enabled for 1st and 2nd order basis element)Time to solve Direct Iterative Memory to solve Scale with X excitations ~= 1 ~= X

N^1.6 N^1.3 N^1.3 N^1.1

With a couple of sources, the iterative solvers is usually faster than the direct solver and can be multiple times faster for large model. The iterative solver always uses less memory than the direct solver. Recommandation: antenna problem usually having one or two sources Packaging/ mult-pin connector usually many sources use iterative solver use direct solver

Note: Fast Sweep takes significantly longer with iterative solve. Prefer Direct+fast sweep or Iterative + interpolating



Iterative Solver How does it work? The Iterative Matrix Solver works by guessing a solution to the matrix of unknowns, and then recursively updating the guess until an error tolerance has been reachedInitial guess

Preconditioner

What is the advantage? Reduced RAM and Simulation Timeno

Update solution and search direction

Where do you control the Iterative Solver? Options Tab from Solution Setup dialog. The iterative solver residual default value 0.0001 yields to identical result for S parameters and Field than a direct solution. 0.001 usually provide same S parameters.

Converges ? yes



Solution Setup - Initial Mesh and Lambda Refinement Initial Mesh generated based on geometry, boundaries and any surface approximations (seeding) i.e. not an electrical aware mesh Under Solution Setup > Options Tab, Lambda Refinement is enabled (by default). Target is typically 0.333 => Minimum of three tetrahedra per unit wavelength. Mesh is then Lambda Refined based on the material dependent wavelength (or free space wavelength if ticked), where Solution Freq is defined in Solution Setup > General Tab For example, hollow metal box 300x300x300mm, varying r and solution freq:

Initial Mesh = 6 Tetrahedra

Mesh A

~23 x Mesh A

~33 x Mesh A

~ 63 x Mesh A

r=1

Solution Freq=1GHz Lambda Refine = 641 Tetrahedra(1 cubic wavelength) 2008 Ansoft, LLC All rights reserved.

r=1, Solution Freq=2GHzLambda Refine = 5520 Tetrahedra(8 cubic wavelengths)

r=9, Solution Freq=1GHzLambda Refine = 17898 Tetrahedra(27 cubic wavelengths)

r=9, Solution Freq=2GHzLambda Refine = 144765 Tetrahedra(216 cubic wavelengths)Ansoft, LLC Proprietary


Solution Setup Advanced/Expression cacheAdvanced: Import mesh: can import a mesh from a different design (same geometry, different material properties/boundaries) Port Options: can force default accuracy on the port (can reduce numerical noise) Enable Thermal feedback from Ansys Mechanical:

Expression cache - Multiple Expression from S param/fied/farfield will be computed for every passes and can be used as a convergence criteria.




Solution Setup - derivative-Ask for derivative computation on defined variables -Allow sensitivity analysis with same mesh. -Variables can be define on geometry, material properties, imepdance boundaries. -Allow to tune the result. -Optimetrics licence usedRigh click on Results/Tune reports




Solution Data - Profile Solution data should be monitored during solve process. Right click on Solution Setup and select Profile or click toolbar icon. Profile tab gives real time update of solution process: Job status. Number of tetrahedra/unknowns. Adaptive pass number. Frequency points etc.

Additionally, Length of time each task took. Which Matrix Solvers are being used. How much physical memory/disk memory was required.Ansoft High Frequency Structure Simulator v12 Training CourseAnsoft, LLC Proprietary


Solution Data Profile Memory Usage is indicated in the Solver Line of the profile. Matrix size (no of unknowns) is indicated.Disk usage during the matrix solution is indicated if offcore is shown after disk, it indicates HFSS could not fit the matrix entirely in memory, so had to partition the matrix and solve parts in memory whilst storing parts on disk. This will slow down the solution process (real time > CPU time)

Mesh maker

Note: Multi processors or multiple cores will result in reduced Real time compared to CPU time ~3.7x speedup due to 4 processors, indicated by MCS4 solver. ~500 MB memory, 0 disk

75 2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary

Solution Data Profile - Solvers Different Matrix Solvers in HFSS identified in the Profile Solver pdsn line where p (precision): M (Mixed) or D (Double) or L (iterative) d (data type): R (Real) or C (Complex) s (symmetry type): S (Symmetric), A (Asymmetric) or H (Hermitian) n (no of processors or cores) : e.g. 4 Typical examples: MRS (Mixed, real, symmetric) : used in completely lossless structures MCS4 (Mixed, complex, symmetric, 4 cpus) : the preferred multifrontal solver for complex matrices, i.e in all lossy structures. LCS2 (Iterative, complex, symetric, 2cpus): when iterative solver converged, otherwise, it will revert to direct solver. DCS2 (double-precision, complex solver, 2 cpus ): activated in cases where the MCS is unable to solve the matrix with enough precision ( eg. When aspect ratio is still very bad; very low frequencies); very memory intensive. Note: HFSS chooses the correct solver automatically!Ansoft, LLC Proprietary


Solution Data - Convergence Convergence tab gives data on solution convergence. Inspection of this data is recommended to ensure solution process proceeds correctly and achieves convergence. Delta S as a function of adaptive pass number can be viewed in tabular or XY plot form, in real time. Other info regarding no of passes etc is also displayed. Correctly setup models should show good convergence profile, with delta S proceeding towards target delta S (red line) in relatively smooth fashion. If model fails to converge; If profile looks as if it is proceeding towards convergence, increase number of adaptive passes and rerun If profile shows delta S oscillating or continuing to increase from pass to pass, inspect model for incorrect setups, ports, boundaries etc.

Target

Note: Using solution data from a model which is not converged will give inaccurate answers.Ansoft High Frequency Structure Simulator v12 Training Course



Solution Data Matrix Data Matrix tab displays the matrix data calculated based the model setup S,Y,Z parameter data can be displayed by ticking the relevant tick boxes. Port Gamma and Zo can also be displayed. Data can be displayed in various formats mag/ang, dB/ang etc as relevant. Default is to view the data for the Last Adaptive pass, but this can be changed to any previous pass if required. All freqs tick box enables display of data for all current valid frequency points. Export Matrix Data enables export of data to various formats including touchstone/citifile etc. If the Solution type was set to terminal and a frequency sweep is completed, Equivalent circuit export is enabled. - This enables generation of Spice models, both Full Wave and RLC types




Solution Data Mesh Statistics

Displays statistics about mesh on an object by object basis. Useful for debugging and model validation. Verify mesh element edge lengths comply with mesh operations.




Frequency sweep




Frequency Sweep - Discrete Frequency Sweeps can be added to an analysis setup in the project tree or using menu HFSS>Analysis Setup> Add Sweep. Choice of Discrete, Fast or Interpolating. Discrete Sweep generates field solutions at the specified frequency points in a frequency range. The sweep can be a single point, linear step or linear count. Multiple sweeps can be added under any Analysis setup if required. Option to Save Fields at all frequencies in the sweep can be ticked. The model is explicitly solved for every discrete point specified so high frequency resolution is computationally expensive. Discrete Sweep is thus most useful where a small no of points is required or where fields are required at only specific frequency points.




Frequency Sweep - Interpolating Calculation of the rational polynomial for a simple Transmission Line Example 5cm long transmission line Computed S-parameters are shown below



S11 (dB)


Frequency Sweep - InterpolatingS11 (dB) S11 (dB)Rational Polynomial (2 solutions) Rational Polynomial (3 solutions)

Adaptive Frequency

S11 (dB)

Rational Polynomial (4 solutions)



S11 (dB)



Frequency Sweep - InterpolatingS11 (dB) S11 (dB)Rational Polynomial (6 solutions) Rational Polynomial (9 solutions)

S11 (dB)



S11 (dB)


15 solutions)

DONE!


Frequency Sweep - Fast Fast Frequency Sweep Uses an Adaptive Lanczos-Pad Sweep (ALPS) based solver to extrapolate the field solution across the requested frequency range from the center frequency field solution (solution frequency if in band). Performs one solve process to obtain the broadband data, field data is known at all frequencies, very sensitive to high Q resonances. Provides matrix data and fields at every frequency in sweep, up to 10000 data points Fast sweep uses more memory than the interpolating sweep, and cannot handle frequency dependent material properties Generally used for narrower band high Q type problems.




Post-Processing Demo




Friendlier report interaction

Dynamic view interaction using Alt/Shift keys

Hide/Show various entities

Selected curves are emphasized using transparency 2008 Ansoft, LLC All rights reserved.

Tool tips and hover cursor changesAnsoft, LLC Proprietary


MiscellaneousProject Files Everything regarding the project is stored in an ascii file File: .hfss Double click from Windows Explorer will open and launch HFSS v12 Drag and drop .hfss file onto HFSS desktop will open the project. Results and Mesh are stored in a folder named .hfssresults Lock file: .lock.hfss Created when a project is opened Auto Save File: .hfss.auto When recovering, software only checks date If an error occurred when saving the auto file, the date will be newer then the original Look at file size (provided in recover dialog) Default Script recorded in v12 Visual Basic Script & Javascript enabled Tools > Options > General Options > Analysis OptionsAnsoft, LLC Proprietary

NOTE: You should make backup copies of all HFSS projects created with a previous version of the software before opening them in a later version of HFSS.

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Scripts

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Remote Solve


Miscellaneous Supported Operating Systems HFSS v12 Windows XP Professional, 32 and 64bit Windows Server 2003, 32 and 64bit Windows Vista Business Linux RHE v4 & v5, 32 and 64bit SUSE Enterprise Server v9, 32 and 64bit Updating Drivers Update your Microsoft DirectX drivers to latest version, 9.0c http://www.microsoft.com/directx Update your video drivers to the latest available from the card manufacturers website. Memory allocation HFSS v12 HFSS v12 can access up to 3GB of Ram on a 32bit PC All about 3GB switch, supported OS http://support.microsoft.com/default.aspx?scid=kb;en-us;291988 How to use /3GB switch http://msdn.microsoft.com/library/default.asp?url=/library/en-us/ddtools/hh/ddtools/bootini_1fcj.asp Increasing Memory allocation for HFSS With a 64bit operating system theoretically there is no RAM limitation Practically, you can typically access up to 64GB of RAM due to hardware limitations. For optimum performance on a 64bit system, set windows swap file size = 2 x physical memory available




HFSS options

Options




HFSS Design Flow SummaryLayout under the pre-defined constraints using 3rd party layout toolsCadence Allegro/ APD Mentor Board Station /ExpeditionTM Sigrity UPD Zuken CR-5000 DXF / GDS

3D-Model import from CAD-fileProE Catia V4/V5 Sat / Step / Iges

Ansoft Links

Results export : Sparameter Spice :touchstone

HFSSTM Fullwave extractionDynamic Link

Geometry export: 2D : dxf and GDS 3D : SAT, STEP and IGES

FullwaveSpice

Ansoft Designer/NexximCircuit / EM cosimulation : Time and frequency domain




Option : 3DCAD Standart available import/export .DXF, .GDS, .SAT,

Optional import: STEP, IGES, Pro-E, CATIAv4, CATIAv5, Parasolid, Unigraphics, Nastran,

Optionnal export: STEP, IGES, CATIAv4, Parasolid.




Option : Multiprocessing Works on the solver part. To set up under tools/options/hfss options

~3.7x speedup due to 4 processors, indicated by MCS4 solver. ~500 MB memory, 0 disk




Option : OptimetricsMultiple types of analysis: Parametrics Optimization ( quasi-newton , pattern search, SNLP, genetic) Sensitivity Statistical




Option : Pre/Post Processing License It is a powerful pre- and post-processing tool based on the appropriate tools : HFSS,Q3D Extractor , Ansoft Designer and Maxwell With an easy-to-use interface, Pre - Post Processing allows you to create and edit geometry, set-up the project in order to have a project ready to solve . It also includes post processing tools.

Construct Geometry (User Input) Define Volume Conditions (User Input)

Define Surface Conditions (User Input) Define Solution Requirements (User Input)

View/Plot S-Parameters (User Input)

View/Plot Fields (User Input)

PRE-PROCESSING POST-PROCESSING




HFSS 12 Advanced Training




HFSS 12 Advanced Training Healing Defeaturing Manual mesh operations Visual Basic Scripts GDSII Import




HealingNo purge history required. Model will be auto purged on healing.

Manual healing option for advanced users.

Control permitted object properties change for feature or small entities removal



ACIS Errors and Healing Auto healing during import tries to address api_check_entity errors, i.e. geometry and topology errors non-manifold edges and vertices, allowed by ACIS but not by our mesher

Manual healing can be used to address - api_check_entity errors - non-manifold edges and vertices - undesired small features Small feature removal during manual healing can be instrumental in correcting ACIS errors, and is beneficial to the mesh as a bonus.




ACIS Errors and Healing Identify non-manifold edges

Zero thickness makes ACIS complain about non-manifold




Face Alignment



DefeaturingDetected features are displayed in the analysis results dialog

Select multiple features and delete



Defeaturing



Principal reasons for inaccurate simulation resultsIn principle there are only two possible reasons for wrong results in a 3D Simulation tool ( independent from method ):

1) Wrong modeling ( i.e wrong geometry , wrong material characteristics, inadequate boundaries or ports, ) Attention should always be paid towards modeling of ports and boundaries as these are artificial assumptions which are not present in reality

2) Insufficient mesh quality : - Because of bad aspect ratios in some relevant areas - Because of insufficient refinement to capture all relevant field behavior




Influence on the overall mesh procedure1) Initial Mesh 2) Lambda refinement 3) Seeding/ virtual objects 4) Selecting frequency of adaptive refinement and convergence criteria 5) Port accuracy




Initial Mesh In most cases this will be sufficient to provide a good solution, but occasionally it is necessary to assist the mesher when autodaptive meshing alone is not sufficient. HFSS has the possibility to influence the initial mesh by applying user defined mesh operations on an object by object basis:

Approximation of true curved surfaces via surface approximation (not needed for facetted objects). Aspect ratio of mesh elements on surfaces via surface approximation. Length or volume based seeding.

Select objects or surfaces and define operations




Defining Surface Approximation and Aspect Ratio

Default: 22.5

default: 10 for curved surfaces 200 for planar surfaces 2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary

Recommended Settings of Surface Approximation: Normal deviationConductors with inductive character ( bondwires, vias, .. diameter PML setup wizard Distance : /6 @ Fmin from radiating structure No closer than /10




Scripts available

Antenna design kit:



Questions and Answers




Documents

HFSSv12