© 2011 ANSYS, Inc. May 24, 2012 1

HFSS with HPC for Large Finite Antenna Array Design

8-23-2011

© 2011 ANSYS, Inc. May 24, 2012 2

Introduction

• Domain Decomposition Review

• Challenges of Solving Finite Arrays

• Finite Array Tool

Examples:

1. Vivaldi array

2. Patch array

Efficiency Enhancements

Conclusion

Overview

© 2011 ANSYS, Inc. May 24, 2012 3

• Finite Array DDM Expands the DDM Capabilities

• DDM was first released in HFSSv12

• Distributes a model’s mesh/solution across several computers distributing the RAM

• Solves a model’s full behavior as if run on a single computer

Domain Decomposition Overview

Generalized DDM

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1. RAM limitations?

2. Long meshing and solve times?

3. Working with geometry with thousands of parts?

– Takes manual setup time

– Leads to large file sizes

– Is more intensive on the UI

What Challenges Exist for Large Finite Array Modeling that DDM Could Solve?

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• Utilizes Replicated DDM Unit Cell to Address Array Concerns

• Geometry and Mesh copied directly from Unit Cell Model

• Unit Cell geometry expanded to finite array through a simple GUI

• Adaptive Meshing Process imported from Unit Cell Simulation

– Dramatically reduces the meshing time associated with finite array analyses.

– Mesh periodicity reinforces array’s periodicity.

Solution: Finite Array Domain Decomposition

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Advantages of the new finite array tool in V14 of HFSS:

1. Solves much BIGGER arrays on the same hardware

2. Obtains ACCURATE results that match HFSS explicit simulations

3. Enables EFFICIENT simulation of large finite arrays utilizing domain decomposition (DDM)

4. Makes it EASY to transform a master/slave unit cell into a finite array

Finite Array Tool Advantages

256 element Vivaldi with metal thickness, under 32GB of RAM!

Embedded element pattern: array tool vs. explicit

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• Start off with a Unit Cell Model to create the Unit Cell Mesh

• Accounts for infinite array behavior

• Unit Cell Simulation is Fast

• Unit Cell Simulation is Memory Efficient

• May use radiation boundary or PML capped unit cell

How It Works!!!

Master / Slave Boundary Pairs Mimic Array’s Periodicity

Radiation Boundary Absorbs Radiated Fields

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• Construct the Finite Array

• Simple GUI based creation

• Reduces model complexity

• Reduces display issues

• Creates 1 unit cell of additional space around the array edge elements to terminate the array fields in vacuum or infinite ground plane.

How It Works!!!

Defines directions of periodicity based on Master / Slave Boundaries

Defines number of elements in each direction

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• Pull the mesh from the unit cell

• Set HFSS so it doesn't perform any additional meshing

How It Works!!!

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• Define a set of computers

• Run the Analysis

• Final results is a full solution to the entire finite array

• RAM was distributed across many computers

• Mesh was created efficiently through Unit Cell Simulation

• All Mutual Coupling between elements included

• Edge affect included

How It Works!!!

© 2011 ANSYS, Inc. May 24, 2012 11

How It Works!!! - Video Demonstration of Finite Array DDM Setup

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Examples 1) Vivaldi Array

2) Probe Fed Patch Array

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Example #1: Vivaldi Antenna Array

256 element slant polarized Vivaldi array

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Vivaldi Unit Cell Setup

PML

Master/slave boundaries on all outer walls

• Unit Cell consists of 4 Vivaldi elements, 2 in each polarization

• Modeling an 8x8 array of the unit cell yields 256 elements

• Realistic 35um metal thickness for grounds; 18um for striplines

4 wave port excitations 2 for each polarization

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• Can solve large arrays with few cores. Here solved with 3 (minimum) and 13 cores.

• Solving > 11 million tets, using most accurate pattern settings, and with standard hardware!

• Fewer cores means less RAM, but more solve time. User can choose tradeoff.

Vivaldi Finite Array Using DDM Simulation Statistics

Model #

Sources #

Cores Mesh Time

Solve Time

# Tets Array

Array Total RAM

Max Domain

RAM

Avg. Domain

RAM

8x8 DDM Array 256 3 0h:7m 76h:18m 11,242,700 30.7GB 15.37GB 15.36GB

8x8 DDM Array 256 13 0h:7m 30h:30m 11,242,700 48.2GB 6.0GB 4.0GB

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Mutual Coupling

P1

Element A2

Element A1

Master/slave B direction

Master/slave A direction P2

P3 P4 1,1

2,1

1,2

1,1

1,3

3,1 1,2

2,3

3,3

Mutual coupling can be displayed in Designer’s Network Data Explorer in tabular or graphical format

Element B1 Element B2

P1 P2

P3 P4

P1 P2

P3 P4

P1 P2

P3 P4

P1 P2

P3 P4

P1 P2

P3 P4

P1 P2

P3 P4

P1 P2

P3 P4

P1 P2

P3 P4

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Mutual Coupling with Network Data Explorer in Designer

0dB

-5dB

-10dB

-15dB

-20dB

-25dB

-30dB

-35dB

-40dB

• Simultaneous graphical RL and mutual coupling values • Set thresholds for coupling value range visualization • Quick identification of coupling ranges for large data sets

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Vivaldi Array Pattern Data

• Feeding only P1 element in each of four test cells.

• The center element has a more even pattern as might be expected

P1 P1

P1

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Explicitly Solved Finite Vivaldi Array vs. DDM Comparison

Vacuum buffer region mimics DDM

Model #

Sources #

Cores Mesh Time

Solve Time

# Tets Array

Array Total RAM

Max Domain

RAM

Avg. Domain

RAM

8x8 DDM Array 256 13 0h:7m 30h:30m 11,242,700 48.2GB 6.0GB 4.0GB

256 Element Explicit Array

256 12 Total = 122h:18m 5,881,409 211GB N/A N/A

Radiation boundary on sides

PML

Explicit 256 element slant polarized array

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Inphi LRDIMM test machine – 284GB RAM

Special Thanks to Inphi

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Example #2: Probe Fed Patch Array

A. K. Skrivervik and J. R. Mosig, “Analysis of Finite Phased Arrays of Microstrip Patches,” IEEE Trans. Antennas Propagat., vol. 41, pp. 1105-1114, 1993.

Model a simple 9x5 probe-fed patch array from a reference

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Center Element Embedded Element Pattern Comparison with Reference

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Probe Fed Patch Array with Feed Network

Add complexity to the design to make it more realistic:

-7x7 = 49 elements

-Wilkinson power divider on stripline layer

-Via cage isolation on stripline layers

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• Unit cell is analyzed to create mesh

• Unit cell mesh is then replicated to form remaining elements in the array

Finite Phased Array Setup Using DDM

Unit Cell Simulation Creates Mesh

Master / Slave Boundaries

Radiation Boundary

7x7 Finite Array

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• All mutual coupling terms are reported

• Here the coupling is reported from the center element to every other element in the array.

• Symmetry maintained down to the tenths of a dB level.

Mutual Coupling Data

-37dB

-34dB

-33dB

-31dB

-33dB

-34dB

-37dB

-33dB

-30dB

-29dB

-27dB

-29dB

-30dB

-33dB

-30dB

-24dB

-22dB

-26dB

-22dB

-24dB

-30dB

-33dB

-21dB

-13dB

-13dB

-13dB

-21dB

-33dB

-30dB

-24dB

-22dB

-26dB

-22dB

-24dB

-30dB

-33dB

-30dB

-29dB

-27dB

-29dB

-30dB

-33dB

-37dB

-34dB

-33dB

-31dB

-33dB

-34dB

-37dB

* Note: Mutual coupling terms does not show overlaid on top of geometry

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• Active return loss is calculated by setting the desired excitations in the Edit Sources dialog

• Vertical symmetry maintained when array is scanned toward the left.

Active Return Loss with Phase Taper

-12dB

-9dB

-8dB

-10dB

-8dB

-9dB

-12dB

-12dB

-11dB

-9dB

-11dB

-9dB

-11dB

-12dB

-11dB

-11dB

-9dB

-10dB

-9dB

-11dB

-11dB

-10dB

-10dB

-8dB

-8dB

-8dB

-10dB

-10dB

-12dB

-10dB

-8dB

-9dB

-8dB

-10dB

-12dB

-15dB

-14dB

-12dB

-13dB

-12dB

-14dB

-15dB

-13dB

-18dB

-16dB

-16dB

-16dB

-18dB

-13dB

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• The embedded element patterns predict expected behavior based on their location in the array.

Embedded Element Patterns

E-Plane Cut

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• Array has no phase shift taper so the beam is pointed toward boresite

• Sidelobe Levels are -10.86dB and -13.23 dB in the E & H Planes.

Array Pattern in the E-Plane

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• Array has a progressive phase shift applied to the edit sources to scan the main beam to 45o in E-plane

• Actual beam steered to 43o due to the finite nature of the array

• Sidelobe Levels are -10.86dB and -13.23 dB in the E & H Planes.

Array Pattern Scanned to 45o in the E-Plane

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Explicitly Solved Finite Patch Array vs. DDM Comparison

Vacuum buffer region mimics DDM

Model #

Sources #

Cores Mesh Time

Solve Time

# Tets Array

Array Total RAM

Max Domain

RAM

Avg. Domain

RAM

7x7 DDM Array 49 33 0h:14m 8h:27m 6,540,912 111.1GB 3.526GB 3.471GB

7x7 Array 49 8 Days ? ? ? N/A N/A

DDM Explicit finite array

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• Instead of saving fields in the entire 3D volume, HFSS has a new option to save fields only on radiation surfaces.

• This drastically reduces disk space usage for problems such as large antenna arrays.

Efficiency Enhancements: Save Radiated Fields Only Option

Model Disk

Space

Default: “Save Fields” (in 3D

Volume) 15.6GB

With New “Save Radiated Fields Only” Option

0.66GB

9x5 patch array with 90 excitations

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Efficiency Enhancements to Edit Sources Dialogue

• The Edit Sources setup can now be saved to a file or loaded from a file in V14 • The 256 excitation Vivaldi array is shown here with only P1 excited for each element. This was done using a .csv file that was quickly edited in excel.

The excitation setup can be changed arbitrarily in post-processing.

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• Large finite antenna arrays are solved efficiently and quickly with the new array tool + DDM in HFSS V14

• The most accurate solution possible is achieved through mesh re-use of a well converged unit cell

• Setup of finite arrays is easier than ever, only requiring drawing of a single unit cell.

• The “Save Radiated Fields Only” option, and file based Edit Sources settings help to save substantial amounts of time and disk space

Conclusions