lecture 8: introduction to hybrid fem...

Release 2015.0 May 6, 2015 1 © 2015 ANSYS, Inc.

2015.0 Release

Lecture 8: Introduction to Hybrid FEM IE

ANSYS HFSS for Antenna Design


Hybrid FEM-IE Solution Using HFSS and HFSS-IE

• Advantages of Hybrid Solution • Leverage the strength of both Finite Element (HFSS) and Integral Equation (HFSS-IE) methods in a single problem

• Conformal and discontinuous air region to minimize solution volume required for FEM solution

• IE solution used to solve for field propagation through free space and conductors outside of FEM volume, no volume mesh required

• IE solution can overlap with FEM solution (i.e. currents are continuous from one solution domain to another)

IE Solution

Surface current on metal

block solved with IE

FEM Only Solution Hybrid FEM-IE Solution

FEM Solution


Invoking the Hybrid Finite Element-Integral Equation Solution

• The Hybrid FEM-IE Solution • The hybrid FEM-IE solution is invoked with special boundary

conditions in an HFSS design type called FE-BI and IE-Regions

• A hybrid solution can contain FE-BI boundary conditions and/or IE-Regions.

• Finite Element Boundary Integral (FE-BI) • Similar concept as an ABC or PML, boundary condition that

truncates the FEM solution volume with infinite free space

– Applied to an air volume that surrounds a geometry

– Unlike ABC or PML, FE-BI can be any arbitrary shape, and any distance from radiator

– The IE solution on the outer boundary also allows for discontinuous FEM solution spaces

• For example 2 antenna’s separated by a distance could be solved using 2 separate air boxes surrounding each antenna with FE-BI applied to each airbox

• Applying “Model exterior as HFSS-IE domain” when setting up a Radiation Boundary Condition

• IE-Regions • Assigning an object as an IE-Region

– When an object is assigned as an IE-Region, the IE solver will be used to solve for currents on the surface of this object

FEM Solution in Volume

IE Solution on outer surfaces

and IE Regions

Iterate

FEM Solution IE Solution on Reflector and Outer

Surface of Airbox

Hybrid Solution Process


Hybrid Finite Element-Integral Equation

• Hybrid Solution Using Finite Element – Boundary Integral

• Hybrid FEM-IE significantly reduces required computer resources • Large air volume inside of radome is removed from the FEM solution

– Air volume is required if using PML or ABC

– Discontinuous solution space made possible using FE-BI

• FE-BI applied to 2 separate air boxes around -

– Airbox conformal to radome

– Airbox conformal to horn antenna

– IE solution is used to solve for fields between FEM domains

PML

26 GHz RAM Elapsed Time

PML 259G (DDM) 840min

FE-BI 64G 205min

19143 λ³

FEBI shows 4.1x speedup factor and 75% less RAM

FEM-IE

FEM-IE Surface

2860 λ³


Hybrid IE-Regions

• Metal objects that are outside of the FEM solution volume can be directly solved using the integral equation solution • Removes the need for air box to surround metal objects

• Fully coupled FEM and IE domains

IE Region: Applied to reflector

FE-BI: Applied to outer surface of airbox. FEM solution of

horn inside of airbox

Reflector Analysis with Hybrid FEM-IE solution

Hybrid solution of reflector fully

couples the solutions of the FEM and IE

Domain

Blockage due to feed


Hybrid IE-Regions: Interior Dielectrics

• Not only can metal objects that are exterior to the FEM solution be solved using a hybrid solution, but also models with uniform dielectrics interior to the FEM solution volume • When a model contains a uniform dielectric inside of an FEM volume, the

integral equation solver can solve for the surface currents only on the surface of the dielectric, forgoing the need to solve for the fields directly inside of the dielectric

Hybrid FEM-IE Solution

❶Dielectric IE-Region

Metal

Dielectric εr = 4

FEM Solution

Hybrid solution uses ~70% less RAM than FEM only solution

❷Metallic IE-Region

Solution Type RAM (GB)

FEM Only 20

Hybrid FEM-IE 6.2


Hybrid FEM-IE Solution with Overlapping Domains

• Advanced hybrid FEM-IE solution allows FEM and IE domains to overlap • Useful in situations where the FEM and IE domains are not physically separated

• Currents will be continuous across domains

• Region of overlap should be placed at least λ/4 away from an antenna element

FEM-IE

IE-Region

Co-site Analysis Reflector Analysis

FEM Solution for Antenna Elements

IE Solution for metallic fuselage


Hybrid FEM-IE Solution: Examples

FEM DDM IE Domain

FE-BI applied to conformal Airbox 10x RAM reduction over FEM only solution

15x RAM reduction over FEM only solution

Beam Waveguide Antenna

FEM-IE

IE-Region 3

Full Wave, Accurate Solution in 37G RAM, 3.2 hours

60λ


IE-Regions: Boundary Condition Setup

• IE-Regions can be applied to metal or dielectric objects inside of an HFSS Design • Metal Objects

• Typically exterior to air box region with FE-BI outer radiation boundary or

• Internal to dielectric IE Region

• Dielectric Objects

• Must be interior to air box region

• Assignment: • Select Object

– Select the menu item HFSS > IE Regions > Assign As IE Region

Air Volume truncated with FE-BI radiation boundary condition

IE Solution Applied to Metal outside of air box and dielectric inside of air box


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lecture 8: introduction to hybrid fem...

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