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HFSS - Antennas, Arrays and FSS's
David PerryApplications Engineer
Ansoft Corporation
Synopsis
w Some Excerpts from “What’s New”w Enhancements to HFSS
w Wave Guide Simulator (WGS)w What is it?w Why you would use it?
w Analytical Simulator (AS)w Good compliment to WGS
w Perfect Matched Layer (PML)
What’s New in Recent Versions of HFSS
HFSS Graphics: Animation Exports
w Animated Magnitude or Vector Plots can be exported as animated *.gif files
w Macro wizard interfaces walks user through animation settings
w Animations are cross-platform and can be used in presentations
HFSS Graphics: Post-Processor Improvements
w Lighting Control Option prevents 3D object lighting or shadows from washing out magnitude field plots
w 3D Polar Antenna Patterns scale shape as well as color to plot min/max settings
Macro Language Enhancementsw User-customizable menu
structure via macro commands
w Bitmaps in Wizard graphical windows
w “Splash” screensw Graphical diagrams to aid
macro data entry
w Local or private scoped variables
w Macro debugger executablew …and MORE! Please refer
to separate Macro presentation for additional details.
L R
C
Lumped RLC Circuit Elements
w Additional boundary condition permits inclusion of lumped circuit elements in HFSS
w Model assumes parallel RLC circuit
w Build several in a row for serial circuit topography
Z(f) R L C
w Direct computation of “Total” field, rather than computation of “Scattered” field only
w Higher Accuracy, Fewer Unknowns per excitation
RCS/Scattering Solution Improvements
HFSS 8 Interpolative Sweep
w Falls between ‘fast’ and ‘discrete’ in capabilities
w Multi-decade bandwidthw Faster than Discretew No modal cutoff issuesw Fields only at mesh
frequency
w Provides wide-band sweep resultsw Calculator tool aids sweep setup if using FWS
Wide-band behavior including several sharp resonances was properly identified using very few frequency points (approximately 20).
HFSS 8 Interpolative Sweep Example
Lumped Port
Wave Port
Internal Portsw Internal ports defined with a single sheet object
at the end of the trace - no cap required.
w 2 options on how to define these ports:
w Traditional-style ports assume a perfect-H boundary on all edges that do not contact metal (wave ports)
w Gap source style (lumped ports).
Gap Source - Dipole
w Utilizing a Gap Source at feed point can improve accuracy
Meshing Improvements
Initial Lambda-Refined Mesh on a block of Vacuum and a block of
Alumina, displaying material-sensitive refinement.
w Lambda Refinement now recognizes object material assignments
w Less need to seed simply due to material conditions
w Improved convergence
w Improved mesh generation for high aspect ratios and true curved surfaces
Post3 - Moving the originw The origin can be moved
and far/near field results computed without resolving
Enough Of What’s New - So How Do I Use This Stuff?
Large Arrays Modeled as Infinite
NOT!
Probably Still Not
w So what is “large” anyway?w How many adjacent
elements cause most of the coupling?
w How much of the array sees edge affects?
w 1948 Wheeler published “The radiation resistance of an antenna in an infinite array orwaveguide”… A waveguide simulator
w 1960’s others followed
Waveguide Simulators
w Approximation of large array with an infinite array
w No edge affectsw Pairs of Perfect E’s or
Perfect E’s and Perfect H’s
Modes in a Waveguide Simulator
w Waveguide modes correspond to plane waves at angles
w Various sizes of cross sections result in different scan angles
Waveguide & Analytical Simulatorw Waveguide simulators (WGS) solve for multiple
scan anglesw Analytical simulator (AS) solves for one scan
angle. User SELECTS this angle!
* Spreadsheet is available!
Unit Cell Model of End-Fire Waveguide Array
WG Port(bottom) Ground Plane
Perfectly Matched Layer(top)
Slave BoundaryMaster Boundary
Origin
V-axis
U-axis
HFSS Boundary Descriptions: Master/Slave Boundaries
w Parameters: Coordinate system, master/slave pairing and phasing
w Master and slave boundaries used to model a unit cell of a repeating structure
w Master and slave boundaries always paired: one master to one slave
w The fields on the slave surface are constrained to be identical to those on the master surface, with phase shift
w Constraints:w The master and slave surfaces must be of
identical shapes and sizesw A coordinate system must be identified on
the master and slave boundary to identify point-to-point correspondence
Periodic Boundaries in Ansoft HFSS
w Periodic BC, Linked BC, Master/Slave Pairsw Yeah they are all the same thing!
w Adds to ability to model phased array antennasw Useful for any large uniform or periodic structurew Use to impose phase shift between two boundaries
w Multiple pairs (two or more) of matching boundariesw Can solve “staggered” antenna arrays
w Arbitrary orientation of matching boundaries in model coordinate system
How Does a LBC Operate?w The LBC enforces a phase difference Φ between
the two linked boundaries.
w Eslave = eiΦ Emasterw where Φ = d/λ sin θ cos(φ)w here Φ depends on scan angles, θ and φ
θ
x
z
d/λ
Φw φ angle measured
from X axisw θ angle measured
from Z axis
Periodic Boundaries in Ansoft HFSS (cont)
w Boundary manager screen allows easy set-up of master and slave boundaries
w Checks that u-v coordinate choices for master and slave planes are consistent
w User provides scan angles θ and ϕ in model coordinate system
w Automatic calculation of array parameters based on model geometry
w Only model coordinate system
w Works with ABC, PML and impedance boundaries on “space port”
Space Port
Port Boundary (should NOT touch periodic boundary in HFSS)
Matching Boundary(slave)
Matching Boundary(master)
Unit Cell Boundary Conditions
MASTER 1
SLAVE 1
MA
STE
R 2
SLA
VE
2
MASTER 3 SLAVE 3
MASTER 4 SLAVE 4
Example of Skewed Array, Top View
Wondering how to create this unit cell?A macro exists to help with this!
Skewed Array (2)
w The triangular spaced array -other methods
App Note is Available
Applications of Simulatorsw Arrays of driven elements
w Excitationw Traditional portw Gap Source port
w Space portsw WGS can use ports or PML’sw AS must use appropriate termination
w Frequency Selective Surface (FSS)w Excitation
w Traditional port or incident wave for WGSw Incident wave for AS
w Transmission/Reflection characteristics computed using the POST 3 calculator
w Macro exists to aid in this effort (fsswiz4.mac)
w Space portsw Same as above
PML and How to Approach the Setup
w Perfect Matched Layer (PML) w fictitious material that fully absorbs the
electromagnetic field impinging upon it w independent of incident angle
w PML requirement:w both the permeability and the permittivity be
complex anisotropic
Use “pmlcoversetup” or “dpPML” macros
Solution Space Terminationsw Absorbing Boundary Condition (ABC)
w Most effective when incident waves normal to the absorbing surface
w ABC surface should be placed approx λ/4 away from radiating surface z
-100
-80
-60
-40
-20
0
20
Ref
lect
ion C
oef
fici
ent
(dB
)
0 10 20 30 40 50 60
theta (deg)
Reflection Coefficient (dB)
70 80 90
ABC
r E TM
θ
Solution Space Terminationsw PML
w Works well for steep angles of incidence (often occurs with wave guide simulators)
w PML does not suffer from λ/4 separation requirement (main concern is meshing)
Integration Surface for Far-Field Computation
w Default: far-fields computed through an integration over the radiation boundary or inside of PML surface
w User defined interior surface:alternate integration surface can be chosen
w “Custom Surface” must enclose all radiating surfaces
w Advantages: potential for better accuracy
w Useful for mesh manipulationw Due to material discontinuity and meshing,
integration on inside of PML surface is not typically the best choice
Alternate Interior Surface (AIS)
w AIS Defined in Post-Processing
w Far-Field computation only allowed by Post 3 if:
w Radiation boundary existsor
w PML with objects names beginning with “PML…”
w Suggestion - Define face list (customer surface) first
Method:1) In the Post Processor, select radiation > compute > far field/near field2) In the “Compute Far Field” menu, check box next to “Customer Surface” then click “Set”3) This will direct you to define a set of faces from which the far fields will be calculated
Farfield Plots of FINITE arraysw Array calculations use unit cell farfield as element
pattern
So What about FSS’s?
w Use unit cell approximationw Can use either WGS or ASw Space port at both top and
bottomw Transmission/Reflection
Characteristicsw Ports + WGS - S-parametersw Incident Wave + AS -
integrate poynting vector (*fsswiz.mac and app note available)
Further Material Availablew Docs
w AppNotePhasedArrays2.doc App Note on infinite triangular arrayw MicroJournPML.doc Discussion of LBC's and PML'sw PeriodicBCsGuide8/28/00.doc Discussion of infinite arrays in HFSSw UnitCellWriteup2.doc Discusses unit cell shapesw PML-LBC pres.pdf Further info on LBC's and PML'sw CalcCookBook.doc Great writeup on Post3 Calculator WITH
EXAMPLES!!w FSSTesting3.Doc How to for FSS’s in HFSS (draft form)
w References (Essential to understanding WGS/AS)w Hansen, Microwave Scanning Antennas Vol 2 if they are separatew IEEE AP 13 1965 page 342 Hannan Simulation of Phased Array Antenna in
Waveguidew Proc IRE Vol 36 1948 Wheeler The Radiation Resistance of an Antenna in
anInfinite Array or Waveguidew IEEE AP 13 1965 page 475 Phased Array Simulators in WG for Triangular
arranged elementsw IEEE AP 11 1963 page 377 A Technique to Simulate the Self and Mutual
Impeadances of an Array
Further Material Available Cont.w Macros (Only a partial list … Ask your favorite AE for further details)
w ArrayCalcWiz4.mac Macro to calc array pattern based on Unit Cell solutionw UnitCellWiz2.mac Macro to assist setting up unit cell for triangular arrayw FSPatGen.mac Generates many plots from a fast swept projectw Pmlcoverstepup Built in macro in Draw that creates PML Objectsw Pmlmatsetup Built in macro in Material Manager to set materialsw dpPMLWiz5.mac Will create Rectangular as well as quasi Cylindrical or
Sphereical PML’sw Should be more accurate than pmlcoversetup
w dpPMLMat2.mac Works with PMLGeom4.mac to set material parametersw FarFieldFix.mac Post3 will not allow computation of farfield without PML
or radiation BCw FSSWiz.mac Calculates transmitted and reflected power from incident
wave
w Spreadsheetsw PMLWorksheet.xls Aid to calc PML parameters for non rect
w Also available in formats for MapleV, Mathcad, EqnEval
w WvGdSim.xls Aid to calc wg mode - scan angle
Closingw HFSS V8 provides both evolutionary and
revolutionary improvements to an already-powerful tool in the antenna engineer’s arsenal
w Usability Enhancements improve day to day interaction with the software
w Improvements to Existing Features speed solution times, improve accuracy, and expand the usage possibilities
w New Features permit analysis applications previously unavailable to antenna designers
w Please continue to request enhancements and added capabilities. Ansoft realizes this software is for YOUR use!