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Design and Analysis using theAnsoft Product Suite

Richard Remski, Brian Gray, Liza Ma Ansoft Application Engineering Staff

Frequency Selective Surfaces

Presentation #4

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Outline

w Introductionw FSS applicationsw Definition, types, and characteristicsw Traditional analysis techniques

w Planar FSS Analysisw Ansoft Designer™ EMw Ansoft HFSS™w Optimization/Parameterization

w 3D FSS Analysis Using Ansoft HFSS™w Non-planar FSSs

w System Simulation Using FSSsw References

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What is an FSS?w A Frequency Selective Surface (FSS) is any

surface construction designed as a ‘filter’ for plane waves

w Evolution from Radar Cross Section (RCS)w Angular/frequency dependencew Band pass/band stop behavior

w FSS Characteristicsw Typically narrow bandw Periodic, typically in two dimensions

w FSS Degrees of Freedom w Element type: dielectric or metallic/circuitw Element shape, size, loadingw Element spacing and orientation

Some different types of planar FSS circuit elements. Source: Reference [1]

Some different types of planar FSS circuit elements. Source: Reference [1]

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FSS Applications

w Traditional Applicationsw Radomesw “Dichroic” subreflectorsw Reflect array lenses

w More Recent Applicationsw RFID tagsw Collision avoidancew RCS augmentationw Robotic guided pathsw EMI protectionw Photonic bandgap structuresw Waveguide or cavity controlled

couplingw Low-probability of intercept

systems (e.g. “stealth”)

The Ohio State University Center for Intelligent Transportation Research (CITR) used an FSS embedded in a road stripe as a lane locator for a autonomous vehicle

demonstration system. (pictures: Reference [2])

The Ohio State University Center for Intelligent Transportation Research (CITR) used an FSS embedded in a road stripe as a lane locator for a autonomous vehicle

demonstration system. (pictures: Reference [2])

FSS are used in dish antenna dichroic feeds & avionics antenna applications

FSS are used in dish antenna dichroic feeds & avionics antenna applications

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FSS Definitions and Types

w Planar FSSsw Printed circuits on substratesw Loaded or unloaded elementsw Single or multi-layer

w Non-Planar FSSsw Periodic dielectric shapesw Cross-layer connected

elementsw Photonic bandgap (PBG)

structuresw Circuit-equivalent effects

w Band passw Band stop

Unloaded (left) and Loaded (right) FSS circuit elements. Loading is also accomplished in some cases by element

packing. (Reference [1])

Unloaded (left) and Loaded (right) FSS circuit elements. Loading is also accomplished in some cases by element

packing. (Reference [1])

Dielectric Grid FSS (left) and Hexagonal ‘mushroom’ Sievenpiper PBG (right, design from Reference [3])

Dielectric Grid FSS (left) and Hexagonal ‘mushroom’ Sievenpiper PBG (right, design from Reference [3])

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Cost of Traditional FSS Design

w Periodic Moment Method (PMM)w Method-of-Moments in combination

with array theoryw “Plane Wave Expansion” techniquew Specific MoM code limitations

w Substratesw Element type/shapew Incidence angle

w Waveguide Simulation Limitationsw Unit cell analysisw Discrete incidence anglesw Enforced polarizations

w Fabrication & Measurementw Difficultw Expensive

w Costw Time

“Waveguide” simulation limits analysis of behavior vs. incidence angle, which is a major design challenge for most

FSS types.

“Waveguide” simulation limits analysis of behavior vs. incidence angle, which is a major design challenge for most

FSS types.

Anechoic Chamber testing, even in small-scale near field ranges, is time consuming and costly

Anechoic Chamber testing, even in small-scale near field ranges, is time consuming and costly

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Ansoft DesignerTM Planar EM - FSS Analysis Made Easy

Ansoft Designer™w Automates planar FSS analysisw Ansoft Designer™ Planar EM –

formerly Ansoft EnsembleTM

w Feature Highlightsw Integrated PMM solverw Full model parameterizationw Automated parameter sweepsw Mixed-meshing capabilitiesw Automated transmission and

reflection calculationw Circuit and EM Integrationw Variable source angle

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Ansoft DesignerTM Planar EM FSS Setup Procedure

w Define Design Parametersw Create stackup layers

w Ground planesw Tracesw Dielectrics

w Draw FSS element(s)w Slotsw Traces

w Define unit cellw Sizew Skew

w Define plane wave incidencew Thetaw Phi

w Discretize geometryw Setup solution information

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Drawing FSS Element/Unit Cell

w Dynamic Drawing Interfacew Slot FSS Elements

w Slots drawn/meshed on ground plane layers

w Magnetic currents calculatedw Efficient compared to

meshing metal

w Metallic FSS Elementsw Elements drawn/meshed on

signal layersw Electric current calculated

w Use Most Efficient Element Type

Cross slot drawn on ground layer becomes hole in solid plane

Cross slot drawn on ground layer becomes hole in solid plane

“Crow’s Foot” Tripole Drawn on Trace Layer becomes Band-reject trace

element (easily drawn as one rectangle, rotated and copied twice, then united).

“Crow’s Foot” Tripole Drawn on Trace Layer becomes Band-reject trace

element (easily drawn as one rectangle, rotated and copied twice, then united).

Inductive grid with central ring resonator

(For Ground layer drawing, mesh shows where metal should be omitted. Outer red

outline indicates Array unit cell size.)

Inductive grid with central ring resonator

(For Ground layer drawing, mesh shows where metal should be omitted. Outer red

outline indicates Array unit cell size.)

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Full Model Parameterization

w Ansoft Designer™ Project Variables

w Full model parameterizationw Sweep:

w Incidence anglew Scan anglew Frequency, …

w Define variables for:w Parameterizationw Optimizationw Sensitivity Analysis

Project Variables are assigned via right-click from the Design Tree, and afterwards are visible in the Properties window anytime the Project Name is highlighted.

Project Variables are assigned via right-click from the Design Tree, and afterwards are visible in the Properties window anytime the Project Name is highlighted.

Once created, variables can be assigned to array setup, layer

stackup, plane wave angles, as well as more ‘traditional’ parametrical

features like materials and geometric objects.

Once created, variables can be assigned to array setup, layer

stackup, plane wave angles, as well as more ‘traditional’ parametrical

features like materials and geometric objects.

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Axial versus Skewed FSSs

Axial

Skewed

Ansoft DesignerTM Planar EM allows axial and skewed arrays to be easily defined.

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Define Unit Cell & Plane Wave Excitation

w Define Incident Wavew Plane of incidence phi, thetaw TE and TM polarizations

computed automatically

w Define Rectangular Unit Cellw Center locationw Cell sizew Lattice skew anglew Scan angle

w Infinite Arraysw FSSs

Plane Wave Excitation

Plane Wave Excitation Dialog (Note: Variable Friendly!)Plane Wave Excitation Dialog (Note: Variable Friendly!)

Infinite Array Setup Dialog, permitting skewed as well as

rectangular lattices (Also Variable Friendly!)

Infinite Array Setup Dialog, permitting skewed as well as

rectangular lattices (Also Variable Friendly!)

Infinite Array and Plane Wave Excitation Settings available right from the Toolbar

Infinite Array and Plane Wave Excitation Settings available right from the Toolbar

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Planar FSS Case 1: Gangbuster Array

w Gangbusterw Linear dipole arrayw Band-pass surfacew Parameterize Dx, Dz, order n,

and dipole width w

Dx Dz lattice provides the basis for the Gangbuster ElementDx Dz lattice provides the basis for the Gangbuster Element

By setting the start point of an element at (x,z) and the endpoint at (x+Dx,z+nDz), many different element lengths

and packings are possible with the same overall lattice repeat.

By setting the start point of an element at (x,z) and the endpoint at (x+Dx,z+nDz), many different element lengths

and packings are possible with the same overall lattice repeat.

All drawings adapted from Figures in Reference [1]All drawings adapted from Figures in Reference [1]

Dx

n=1 n=2

n=3

DxDz

Dx

2Dz

3Dz

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Planar FSS Case 1: Parameterized Gangbuster

w Fully Parameterized Ansoft Designer™ EM circuit

w Parametric solution vs. frequency shown for one design

w Library of possible configurations using a single model

w Response for n=2 Gangbuster shown

w Results match published expectations

w Reference [1] identical results plotted, Fig 2.3

The lattice, order, and line width can all be varied with a few central Project Variables to permit analysis of any

similar Gangbuster element. Or, a parametric sweep can generate and maintain results for many variations at once.

The lattice, order, and line width can all be varied with a few central Project Variables to permit analysis of any

similar Gangbuster element. Or, a parametric sweep can generate and maintain results for many variations at once.

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Planar FSS Case 1: Additional Gangbusters

n=3 Gangbuster results (Compare to Reference [1], Figure

2.5)

n=3 Gangbuster results (Compare to Reference [1], Figure

2.5)

n=4 Gangbuster results (Compare to Reference [1], Figure

2.6)

n=4 Gangbuster results (Compare to Reference [1], Figure

2.6)

Raising the order (n) of the Gangbuster decreases resonance frequency and

sharpens the response

Raising the order (n) of the Gangbuster decreases resonance frequency and

sharpens the response

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Planar FSS Case 2: Double-Ring FSS

w Skewed FSS grid, analyzed for transmission VS frequency, off-normal incidence

w Fixed angle of incidence

w Compares well to literature [2]

w Metal extends beyond ‘unit cell’ outline

w Legal provided metal does not overlap when arrayed

Measured and Analytical Results from Reference [4]

Measured and Analytical Results from Reference [4]

Double Ring FSS, showing Ensemble Solver mesh in Ansoft Designer

Double Ring FSS, showing Ensemble Solver mesh in Ansoft Designer

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Planar FSS Case 3: Sievenpiper PBG

w Ansoft HFSS FSS simulation capability documented during 2000 Ansoft Roadshow

w Analysis using Ansoft Designer™ Planar EM

w Efficient results compared to measurements [3]

w Automated reflection-phase calculation

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Who put the “FSS” in HFSS?w Planar FSS structures may be

solved in HFSSw Incident waves, periodic

boundaries are features present since 2000

w Ansoft’s phased-periodic boundaries permit off-normal analysis, unlike less general “wraparound” boundaries

w Different PBG and FSS structures analyzed successfully since Version 7

w Ansoft technical staff have published papers on these applications

w References at right may be obtained from our website or applications staff Reference [6]Reference [6]

Reference [5]Reference [5]

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Planar FSS in HFSS: Ring FSS

w Planar ring resonator FSS modeled using HFSS

w HFSS unit cell model requires air above/below the cell, as well as a terminating layer

w Standard radiation boundary acceptable for normal incidence

w Perfectly Matched Layer for off-normal incidence studies

w Transmission and Reflection Coefficients calculated using Field Post-processing

w Results Plotted via Macro and compared to reference

Single Screen Rings. TE Case, Theta = 45 Deg

-35

-30

-25

-20

-15

-10

-5

0

0 2 4 6 8 10 12 14

Frequency/GHz

Tra

nsm

issi

on L

oss/

dB

MeasuredHFSS 8

Single Screen Rings. TE Case, Theta = 45 Deg

-35

-30

-25

-20

-15

-10

-5

0

0 2 4 6 8 10 12 14

Frequency/GHz

Tra

nsm

issi

on L

oss/

dB

MeasuredHFSS 8

Ring Inner Diameter: 5.6 mm

Ring Outer Diameter: 6.1 mm

Dielectric Thickness: 0.64 mm

Cell Size 7.24 mm

Dielectric Constant: εr = 11

FSS Design and Measured Results from Reference [7]

Ring Inner Diameter: 5.6 mm

Ring Outer Diameter: 6.1 mm

Dielectric Thickness: 0.64 mm

Cell Size 7.24 mm

Dielectric Constant: εr = 11

FSS Design and Measured Results from Reference [7]

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Non-Planar FSS Structures

w Some FSS or PBG structures are constructed of periodic-defect or ‘woodpile’ dielectrics

w Ansoft Designer™ Planar EM no longer appropriate due to 3D dielectric properties

w HFSS 3D analysis required

w Solve with dispersion curve analysis, direct-transmission with waveguide simulations, or reflection analysis, as described in [5] and [6].

w Planar FSSs used in 3D applications may also require HFSS

Deformed dielectric lattices at top (Reference [8] FSS, left and Reference

[9] PBG, right) and a ‘woodpile’ dielectric stackup PBG at bottom (Reference [10])

Deformed dielectric lattices at top (Reference [8] FSS, left and Reference

[9] PBG, right) and a ‘woodpile’ dielectric stackup PBG at bottom (Reference [10])

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FSS in HFSS: 3D FSS Applications

w Analysis of an FSS used as one wall of a dual-band waveguide structure is only possible in full 3D Field Solvers

w Design per Reference [11]

w An FSS curled around a dielectric rod forms this conceptual wireless application antenna

w Design per Reference [12]

The FSS layer behaves as a ‘transparent’ wall at the frequency of

the overall WG, allowing a TE01 mode, while providing a conductive

wall for higher-frequency propagation of an orthogonal WG mode in the

isolated rectangular section.

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w This periodic dielectric lattice FSS is solved for normal and oblique incidence using a unit-cell approach in HFSS

w Results matched well with the data in reference [8], as shown.

HFSS Case 1: Periodic Dielectric Example

Dielectric blocks are 1 x 1 x 0.2 cm, spaced 2 cm apart. Blocks have εr=10,

surrounding layer εr=4. Tested for normal and 30 degree incidence angles

from 10 – 12 GHz.

Dielectric blocks are 1 x 1 x 0.2 cm, spaced 2 cm apart. Blocks have εr=10,

surrounding layer εr=4. Tested for normal and 30 degree incidence angles

from 10 – 12 GHz.

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w Another form of FSS used in avionics applications due to higher strength is the perforated metal plate [13]

w The holes are loaded with a dielectric, which also provides a pressure seal

w Material choice, hole diameter and spacing, and metal thickness all influence transmission.

HFSS Case 2: Loaded, Perforated Metal FSS

A solid metal plate perforated with holes filled (incompletely) with a

dielectric filler having εr=11. Green slabs top and bottom of image are perfectly matched layers (PMLs) while gray planes are for data

extraction.

A solid metal plate perforated with holes filled (incompletely) with a

dielectric filler having εr=11. Green slabs top and bottom of image are perfectly matched layers (PMLs) while gray planes are for data

extraction.

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w Dielectric rod antenna[12] analyzed using HFSS

w Match to circular waveguide input port shown.

w Antenna patterns conform to reference expectations, showing that the FSS will squint the main lobe from the vertical

HFSS Case 3: Square-loop FSS on Rod Antenna

Dielectric rod εr=2, radius 7.5 mm. Square-loop patches are 9 mm

outer length with 0.6 mm widths, spaced 3.5 mm apart in both the

circumferential and axial directions.

Dielectric rod εr=2, radius 7.5 mm. Square-loop patches are 9 mm

outer length with 0.6 mm widths, spaced 3.5 mm apart in both the

circumferential and axial directions.

9 GHz Antenna Gain, showing pattern squinted

toward FSS elements (only 2 columns)

9 GHz Antenna Gain, showing pattern squinted

toward FSS elements (only 2 columns)

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w Anisotropic substrates require HFSS

w Design contains loaded tripoles in a triangular array, arranged on both isotropic and anisotropic layers [14]

w Hexagonal unit-cell design created using HFSS.

w Sides are linked boundaries

w Top and bottom terminated with PML surfaces

HFSS Case 3: Anisotropic Substrate FSS

Tripoles have arm lengths of 9 mm, trace widths of 0.5 mm, with inner spacing (opening width) of 3 mm. The are arranged in an equilateral-triangle periodicity with period of

16.5 mm. Substrate thickness is 6 mm, material characteristics to

follow.

Tripoles have arm lengths of 9 mm, trace widths of 0.5 mm, with inner spacing (opening width) of 3 mm. The are arranged in an equilateral-triangle periodicity with period of

16.5 mm. Substrate thickness is 6 mm, material characteristics to

follow.

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HFSS Case 3: Aniso Substrate FSS Results

Theoretical

Single Freq Adapt

Adapt at each Frequency

Theoretical

Adapt at each Freq

=

300030003

rε

=

3000100003

rε

Theoretical curves extracted from Reference [14].

Theoretical curves extracted from Reference [14].

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System-Level Impact of FSS

w FSS transmission and reflection coefficients incorporated directly into communication system analysis

w Ansoft Designer™ system simulation

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FSS Reflection & Transmission Analogous toTwo Port Scattering Matrix

w Generate Data Tablew Select reflection &

transmission coefficients for desired polarization

w ‘Copy to file’ saves resulting data table

w Modify to create S2P file format

Plane Wave Excitations don’t provide “port” information for black

boxes!

Plane Wave Excitations don’t provide “port” information for black

boxes!

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System-level FSS:Create a circuit parameter file

w With some edits to the line-feed format and the header, you can re-save this data table as a S2P file

Original Data Table output shown in back, with modified file format shown

in Front. Only the header and linefeed formatting are different.

Original Data Table output shown in back, with modified file format shown

in Front. Only the header and linefeed formatting are different.

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System-level FSS: Create FSS Circuit Element

w Create FSS circuit element using:

w Ansoft DesignerTM

w EMw Circuitw System

w N-port circuit element referenced to *.s2p data file

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System-level FSS: Solve!

w System-level simulation including FSS impacts

w Example at right shows FSS added in the link path between two parabolic dish antennas

FSS Black Box, containing full

complex reflection and transmission coefficients

FSS Black Box, containing full

complex reflection and transmission coefficients

AntennaAntenna AntennaAntenna

Propagation Distance

Propagation Distance

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Conclusionw Historical FSS Analysis

w Much theoretical/measurement expertise requiredw Long and costly build/test cycle

w Modern FSS Designw Commercial Design Tools Availablew Planar and 3D EM, circuit/system capabilities

w Fully paramaterizable geometries, materials, analysesw Automated analyses, sweeps, optimization, postprocessingw Integrated design environment with EM, circuit and system analysesw Flexible geometry types/shapes and array configurationw Efficient design flow

w Ansoft Products applied in this presentationw Ansoft DesignerTM Planar EMw Ansoft HFSSw Ansoft DesignerTM circuit/system

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References1. Ben A. Munk, Frequency Selective Surfaces: Theory and Design, John Wiley & Sons,

Inc., 2000, ISBN 0-471-37047-9 2. The OSU Autonomous Vehicle Website, Ohio State University Center for Intelligent Traffic

Research (CITR), http://eewww.eng.ohio-state.edu/citr/Demo97/osu-av.html3. D. Sievenpiper, L. Zhang, R. F. J. Broas, N. G. Alexópolous, and E. Yablanovitch, “High-

Impedance Electromagnetic Surfaces with a Forbidden Frequency Band,” IEEE Transactions on Microwave Theory and Techniques, Vol 47, Number 11, November 1999, pp. 2059-2074.

4. T. K. Wu and S. W. Lee, “Multiband Frequency Selective Surface with Multiring Patch Elements,” IEEE Transations on Antennas and Propagation, Vol 42, Number 11, November 1994, pp. 1484-1490

5. I. Bardi, R. Remski, D. Perry and Z. Cendes, "Plane Wave Scattering from Frequency Selective Surfaces by the Finite Element Method", COMPUMAG Conference Proceedings, Evian France, July 2001

6. R. Remski, “Analysis of Photonic Bandgap Surfaces using Ansoft HFSS”, Microwave Journal, September, 2000

7. J. Huang, Te-Kao Wu and Shun-Wu Lee, “Tri-Band Frequency Selective Surface with Circular Ring Elements,” IEEE Trans A&P, Vol. 42 No. 2, Feb, 1994, pp. 166-175

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References8. T. F. Eibert, J. L. Volakis, D.R. Wilton and D.R. Jackson, “Hybrid FE/BI Modeling of 3-D

Doubly Periodic Structures Utilizing Triangular Prismatic Elements and an MPIE Formulation Accelerated by the Ewald Transformation,” IEEE Trans. On Ant. Propagat.,Vol. 47, May 1999, pp 843-850

9. John D. Shumpert, William J. Chappell, and Linda P. B. Katehi, “Parallel-Plate Mode Reduction in Conductor-Backed Slots Using Electromagnetic Bandgap Substrates,” IEEE Transactions on Microwave Theory and Techniques, Vol 47, Number 11, November 1999, pp. 2099-2104

10. R. Gonzalo, C. Sagaseta, I. Ederra, B. Martinez, H.P.M. Pellemans, P. Haring-Bolivar, C. Mann, and P. deMaagt, “The Effect of a Woodpile Photonic Crystal at Sub-millimetreWave Frequencies used as Substrate in a Dipole Configuration,” Proceedings of 24th ESTEC Antenna Workshop on Innovative Periodic Antennas, June 2001

11. R. J. Langley, “A Dual-Frequency Band Waveguide Using FSS”, IEEE Microwave and Guided Wave Letters, Vol 3, Number 1, January 1993, pp 9 - 10

12. Cox, G.J.; Zorzos, K.; Seager, R.D.; Vardaxoglou, J.C., “Study of frequency selective surface (FSS) resonator elements on a circular dielectric rod antenna for mobile communications,” Antennas and Propagation, 2001. Eleventh International Conference on(IEE Conf. Publ. No. 480) , Volume: 2 , 2001, pp. 758 -761

13. FSS Geometry provided to Ansoft by Dr. Youseff Kalatisadeh, ERA Technology Ltd., Surrey, UK. (Prior text source not known to presentation authors.)

14. G. Kristensson, M. Akerberg, and S. Poulsen, “Scattering from a Frequency Selective Surface supported by a Bianisotropic Substrate,” Publication of the Dept. of Electroscience and Electromagnetic Theory, Lund Institute of Technology, Sweden, Code LUTEDX/(TEAT-7085)/1-28/(2000), Revision 1, Jan 2001