Powerful features (1)

Transcription

1 HFSS Overview

2 Powerful features (1) Tangential Vector Finite Elements Provides only correct physical solutions with no spurious modes Transfinite Element Method Adaptive Meshing r E = t E γ i i ( x, y, z) s 11 s 12 s 21 s 22 S Fast Freq. Sweep Fast Frequency Sweep Adapt Freq. Frequency

3 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

4 Limitations - Frequency domain, not time domain Exception: some post processing on S 11 after wide frequency sweep - Linear materials Exception: ferrite applications with M3DFS involved - Passive structures Exception: special application of master/slave boundaries

5 Geometry translation ACIS!! AutoCAD!! Seamless interface with ACIS-based modelers Translators in Maxwell control Panel DXF, STL

6 Printing Any screen or part of it Directly to printer or Print to file: postscript, GIF, bitmap, etc.

7 HFSS flow Driven or Eigenmode Draw Setup Materials Setup Boundaries / Sources Setup Executive Parameters Setup Solution Solve Post Process -Fields -Matrix Data -Matrix Plot

8 Driven or Eigenmode?

9 Eigenmode Solution Resonances in arbitrary closed 3D structures No external excitations in model Lossy possible: Unloaded Q

10 Draw or import the geometry

11 HFSS 3D Modeler

12 Solid-modeling considerations (1) Keep complexity low small number of segments in circles and cylinders omit details if possible Avoid aspect-ratio problems maximum aspect ratio is 1:2500 use 2D objects instead of thin structures Keep solution region small use symmetry whenever possible don t include too much air or transmission line Avoid overlapping objects

13 Solid-Modeling Considerations (2) Few segments around circles and cylinders Thin metal patch is 2D object (aspect ratio!) No overlapping objects (inner conductor is two objects because it goes through two dielectrics)

14 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 radiation boundary (λ/4)

15 Assign material properties

16 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)

17 HFSS Material Manager

18 Materials (2) Some possible materials: air, vacuum perfectly-conducting metal non-perfectly-conducting metal dielectrics, any permittivity, any conductivity magnetic materials, any permeability, any magnetic losses anisotropic materials thin-film resistors, bulk resistors ferrites

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

20 Circulator with Ferrite Puck Ferrite material may be uniformly biased, or use the solution of magnetostatic analysis

21 Assign boundary conditions and excitations

22 HFSS Boundary Manager

23 Sources Power enters the model through (unlimited number of) ports voltage sources current sources incident waves One other kind of source: H bias for ferrites

24 Ports in HFSS Classical Ports: cross section of transmission line HFSS 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

25 Classical Port Surfaces Classical Ports Can Only be Defined on Surfaces Which Are Exposed to a Region Where The Field Does Not Exist Background Perfectly Conducting Objects Simple 2-Port Waveguide: Ports: waveguide cross sections Each port bounds the Background Select faces or appropriate 2D objects to define the ports

26 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

27 Yagi Antenna With Interior Feed Port

28 Example: Microstrip Port PEC Ansoft recommends H = 5-10 h, W = 5 w; H w W h h and w are the substrate height and trace width, respectively. If this leads to a high and narrow port then increase W.

29 Example: CPW port ground trace ground Port

30 Example: stripline port trace port ground ground

31 Example: poor port This microstrip port may be too big waveguide mode possible Remedy: create 2D port object

32 Illegal ports The following two situations are illegal: 1. A port that contains metal only e.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

33 Lumped Gap Source Ports (1) Classical ports or touching gap source ports obtain wrong solution Non-touching gap source ports obtain better solution

34 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

35 Lumped Gap Source Ports (3) A port with multiple conductors per port would take ALL coupling into account. However, modalto-nodal software is needed to make use of this.

36 Example of structure where gap source ports can be useful Lumped Gap Source Ports (4)

37 Example: voltage and current sources Warning: you will get fields but won t get S parameters! load microstrip Two-conductor transmission line Voltage source (<<λ) Current sources (<<λ) Can excite even and odd modes

38 Boundary conditions Perfect E Perfect H / Natural Finite Conductivity Impedance (sheet resistance and reactance) Radiation (= Absorbing Boundary Condition, ABC) Symmetry Master, slave Perfectly-Matched Layer (PML)

39 Perfect E for 2D Conductor Dual Mode Stepped-septum Polarizer Use Perfect E Surface for Thin Septum Infinitely Thin PEC Septum Side View TE 10 /TE 01 Square Waveguide Top View Perfect E Surface Interior to The Problem Space Behaves Like an Infinitely Thin 2D Perfect Electric Conductor (PEC)

40 Perfect H / Natural for 2D Aperture Monopole Over a Ground Plane Ground Plane is Perfect_E boundary How to cut the opening?

41 Perfect H / Natural for 2D Aperture Use Perfect H / Natural For Opening Small Hole Can be Cut in Infinitely Thin Ground Plane Where The Coax Opens Into The Radiation Space Using a Perfect H / Natural Boundary

42 Perfect H / Natural for 2D Aperture Bethe Hole Coupler Small hole can be cut in Infinitely Thin Septum between the Upper and Lower Guide using a Perfect H / Natural Surface at the Hole

43 Radiation boundary for open regions Second-order local absorbing boundary Place this boundary λ/4 away from radiating structures like currentcarrying conductors, radiating apertures Place it closer when not interested in radiation Apply λ/6 or λ/8 seeding on boundary Conformal boundary - reduces model size

44 Perfect E and Perfect H Symmetry TE 10 Mode in Rectangular Waveguide Geometric Symmetry Field Distribution Symmetry Perfect E Surface Perfect H Surface For Symmetry, The Perfect E or Perfect H Surface Must Interface With The Background

45 Periodic Boundaries Phased-array antenna Unit Cell Walls Periodic boundaries enforce phase difference between Unit Cells At large scan angles, Perfectly Matched Layer on top better than Radiation Boundary Master 2 Slave 2 Master 1 Slave 1 Waveguide Radiator Feed Port

46 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!

47 Executive Parameters Often skipped Emissions test Port fields after ports have been solved

48 Setup solution parameters

49 Setup solution (1) Specify initial, previous or current mesh Lambda refinement Number of adaptive passes (5) Frequency Sweep yes or no, discrete of fast?

50 Setup solution (2) Specify frequency number 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 fast starting mesh (manual mesh has a lot to offer) ports-only solution (check!) or all

51 Adaptive solution Create initial or manual mesh Calculate electric fields Calculate S parameters S acceptable? yes no Refine mesh Display parameters and fields, perform frequency sweep post-process data

52 Adaptive meshing Adaptive meshing concentrates points in regions of high field gradients thus focusing the computational effort into the regions that actually need them.

53 Seeding and manual meshing Optional feature User-defined seeding of objects or faces Refine on faces, in objects, in regions

54 Perform the simulation

55 Multi-Frontal Solver Takes optimum advantage of RAM Avoids swapping through Spill Logic Parallel processing is possible on PC

56 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 GHz) Identifies (sharp) resonances

57 Fast frequency sweep Band pass filter

58 Fast frequency sweep Frequency range is very project dependent. This example shows a very wide range. An accuracy check never hurts.

59 Post Process the data Post Process Fields Matrix Data Matrix Plot

60 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

61 E-Field on Cutplane

62 Antenna Example: Sinuous Antenna Geometry Radiation Pattern - Two Ports Excited Radiation Pattern - One Port Excited

63 Horn 3D Far-Field Pattern

64 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. Ω Q u = 2 2 s 2 Γ n H H dγ 2 + dω tgδ Ω H dω

65 Post Processor - Matrix Data Deembed Renormalize Compute Y and/or Z matrices Export to circuit simulators

66 Post processor - Matrix Plot S, Z as function of frequency Linear or Smith Chart db and VSWR options Export plots to data file