ElectroScience Lab Compact and Spherical Range Design, Application and Evaluation Walter D. Burnside...

ElectroScience Lab

Compact and Spherical Range Design, Application and Evaluation

Walter D. Burnside and Inder J. Gupta

The Ohio State UniversityElectroScience Laboratory

1320 Kinnear RoadColumbus, Ohio 43212

(614) 292-5747 and (614) 292-5951

Presented on September 21-22, 2005 for Raytheon (Tucson, AZ).

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Course Outline

• Basic Range Design Guidelines (Burnside)

• Compact Range Reflector Design (Gupta)

• Absorber Design and Layout (Burnside)

• Critical Range Evaluation (Gupta)

Second Half Day

First Full Day

• R-Card Fences for Outdoor Ranges (Gupta)

• Summary of Range Design Issues (Burnside)

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Walter D. Burnside

You Want to Build a New or Refurbish an Existing Chamber:

How is That Done Correctly?

The Ohio State University ElectroScience Laboratory1320 Kinnear Road, Columbus, Ohio 43212

(TEL) (614) 292-7981 (FAX) (614) 292-7297http://esl.eng.ohio-state.edu

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What are the Important Issues? Commercial absorber vendors are not capable of

creating state-of-the-art ranges that provide the superior performance required by modern systems.

The problem is associated with 50 year old absorber and chamber designs versus modern proven concepts.

The finest chamber designs are presently performed at universities. Their significant achievements have not been successfully transferred to industry, even though numerous papers and presentations have been published that describe their important findings.

The major contributor to this problem has been that the RF industry, which has relied on traditional absorber companies to provide the

specified performance. Thus, they have not been forced to change or update their practices, which require investments that they do not want to

make.

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The RF Industry has Created RFQ’s that Require Improved Performance - How is that Performance Achieved or is it?

Along with the lack of modern chamber design concepts, commercial vendors use antiquated evaluation methods.

Thus, they respond to RFQ’s with traditional evaluation tests that do not have the dynamic range to expose their failure to meet the specifications.

The RF industry accepts these inferior evaluation approaches because they appear to be following accepted practices. “That is the way we have always done it”.

Industry must require proper evaluation methods that can provide the dynamic range necessary to verify that the desired performance has been

achieved. This requires the most advanced testing methods possible.

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How Does One Overcome This Very Unfortunate Situation?

1) One must first determine what it is that they want measured and what are the requirements for that measurement, insuring that the full radiating or scattering system performance is being truly and accurately evaluated in this new or modified chamber.

2) The chamber design should begin by examining what type of chamber and dimensions are needed by simply using absorber but including changing the normal doping concentrations and using modern curved shapes and applying Chebyshev layouts.

3) During the absorber design phase, the chamber dimensions must be examined to determine if it has become excessive because the absorber only works for normal or near normal incidence.

4) If the chamber dimensions were increased significantly to avoid grazing or near grazing incidence, R-Card fences should be designed to reduce the chamber size and enhance performance.

5) Once the chamber has been built or modified, it must be probed and the resulting data processed using modern transform techniques to ascertain whether or not the desired performance has been achieved. If not, the source of the errors must be identified and corrected or at least better understood so that it does not happen again.

This design approach was used to modify and evaluate SIMFAX. Thus, it will be used in the following slides to illustrate these principles.

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Anechoic Chamber Current Capability Upgrade Requirement

Chamber Length 48 ft. shield, 40 ft. anechoic

Chamber Width x Height

32 feet x 32 feet

Spherical Array Dish 37.67 ft. radius, 19 ft. chord

Array Antenna Spacing

2 ft. (3 deg.) nominal,

1 ft. (1.5 deg.) high resolution

Quiet Zone 6 ft. cube @ flight table

6’x6’ base, 8’ into chamber

Quiet zone Reflectivity Performance (dB)

-38 @ 4 GHz –45 @ 8 GHz –50 @ >10 GHz

-45 @ 2 GHz –50 @ 4 GHz –55 @ 9-18 GHz –50 @ 35 GHz

Specular Zone Absorber

36 inch pyramidal TBD

Walls, ceiling, floor absorber (non-specular)

8 inch wedge

Array (TX) wall absorber

5 inch pyramidal

Flight Table (RX) wall 8 inch pyramidal

SIMFAX Chamber Parameters

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Avery Davis at Raytheon did a Very Careful System Performance Study and Found these Chamber Stray Signal Level Requirements

FrequencyStray Signal Level Versus Desired Illumination

2 GHz

4 GHz

9-18 GHz

35 GHz

-45 dB

-50 dB

-55 dB

-50 dB

The absorber design must achieve these stray signal levels within this existing chamber. This must be true for all the SIMFAX

antennas, including the critical one’s near the sidewalls.

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SIMFAX Sidewall Illumination is Very Close to Grazing Incidence for First Few Antennas.

Absorber on Sidewall

Quiet Zone

Sidewall Scattering

Desired Illumination

Normal pyramidal absorber can not be used for this illumination angle of incidence,

which will be shown in the next few slides.

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Bistatic Reflection Coefficients for 8 in Straight Pyramid Absorber

BISTATIC ANGLE (DEG)

0 30 60 90 120 150 180

RE

FLE

CT

ION

CO

EF

FIC

IEN

T (

dB

)

-60

-50

-40

-30

-20

-10

0


0 30 60 90 120 150 180

RE

FLE

CT

ION

CO

EF

FIC

IEN

T (

dB

)

-60

-50

-40

-30

-20

-10

0


0 30 60 90 120 150 180

RE

FLE

CT

ION

CO

EF

FIC

IEN

T (

dB

)

-60

-50

-40

-30

-20

-10

0


0 30 60 90 120 150 180

RE

FLE

CT

ION

CO

EF

FIC

IEN

T (

dB

)

-60

-50

-40

-30

-20

-10

0

FREQUENCY=500MHz

FREQUENCY=1000MHz

FREQUENCY=2000MHz

FREQUENCY=4000MHz

Note that the reflection levels approach unity as the angle of incidence approaches grazing (180 degrees). At 2 GHz, 8”

pyramidal absorber can not be used even for normal incidence.

-45dB stray signal level

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0 30 60 90 120 150 180

RE

FLE

CT

ION

CO

EF

FIC

IEN

T (

dB

)

-60

-50

-40

-30

-20

-10

0


0 30 60 90 120 150 180

RE

FLE

CT

ION

CO

EF

FIC

IEN

T (

dB

)

-60

-50

-40

-30

-20

-10

0


0 30 60 90 120 150 180

RE

FLE

CT

ION

CO

EF

FIC

IEN

T (

dB

)

-60

-50

-40

-30

-20

-10

0


0 30 60 90 120 150 180

RE

FLE

CT

ION

CO

EF

FIC

IEN

T (

dB

)

-60

-50

-40

-30

-20

-10

0

FREQUENCY=500MHz

FREQUENCY=1000MHz

FREQUENCY=2000MHz

FREQUENCY=4000MHz

Note that the reflection levels approach unity as the angle of incidence approaches grazing (180 degrees). At 2 GHz, 12” pyramidal absorber could be used directly for angles incidence up to 35 degrees (70 degrees in plot).


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0 30 60 90 120 150 180

RE

FLE

CT

ION

CO

EF

FIC

IEN

T (

dB)

-60

-50

-40

-30

-20

-10

0


0 30 60 90 120 150 180

RE

FLE

CT

ION

CO

EF

FIC

IEN

T (

dB

)

-60

-50

-40

-30

-20

-10

0


0 30 60 90 120 150 180

RE

FLE

CT

ION

CO

EF

FIC

IEN

T (

dB)

-60

-50

-40

-30

-20

-10

0

REFLECTION COEFFICIENT18 IN PYRAMID

FREQUENCY=4000MHz


0 30 60 90 120 150 180

RE

FLE

CT

ION

CO

EF

FIC

IEN

T (

dB

)

-60

-50

-40

-30

-20

-10

0

FREQUENCY=500MHz

FREQUENCY=1000MHz

FREQUENCY=2000MHz

FREQUENCY=4000MHz

Note that the reflection levels approach unity as the angle of incidence approaches grazing (180 degrees). At 2 GHz, 18” pyramidal absorber could be used directly for angles incidence up to 53 degrees (106 degrees in plot).


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Pyramidal Absorber Issues and Limitations

The angle of incidence on absorber is relative to the plane containing the absorber tips. Thus, thicker absorber has to deal with wider illumination angles.

For the first several antennas, normal pyramidal absorber can not used because of its poor wide angle performance.

Since pyramidal absorber was designed for near normal incidence, one can change the doping to examine its impact for wide angle illumination.

The Chebyshev layout approach and curved pyramids can also be considered to improve the wide angle performance.

All of these potential options were considered for SIMFAX. They are not options that are normally considered by absorber and chamber designers.

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Pyramidal Absorber with 4-Step Chebyshev Along Cross Range and Uniform Along Down Range

Cross RangeCross Range

Down Range

Down Range

Pyramid

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Enhanced Reflection Coefficient Performance Using Chebyshev Absorber Layout

Reflection Coefficient of Chebyshev Distribution4-Layer Chebyshev

-30-40-20

-20

-30

-10

-20

-30-40-50

-20

-30-40

-10

-20-30

-20

-30-40

-20

-30-40

-20

-20

-20-30

-30-40

-30

-20-30-40-50

-30-40

-30

-10

-20-30

-20-30

-30

-30

-20-30-40-50

-20

-30

-30

-30-40

-20

-20-30-40

-20-30

-30

-30-40

-30

-40

-20

-30

-20

-30-40

-20-30-40

-30

-30

-40-50

-20

-30

-20-30

-30

-20-30

-30

-40

-40

-10 -20-30

-30-40

-20

-30-40

-30-40

-40

-20

-20

-30-40-50

-30-40

-30

-30

-40

-20

-30

-30-40

-30-40

-30

-40

-50

-30

-30-40

-30-40

-40

-50

-40

-30

-40

-40

-40-50

-40

-40

-40

-40

Angle of Incidence (Degrees)

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75

Fre

qu

en

cy (

GH

z)

1

2

3

4

5

6

7

8

9

10

Reflection Coefficient of Chebyshev Distribution7-Layer Chebyshev

-50-60-40

-30

-30

-40-50-60

-30 -20 -10

-30

-30

-40

-50-60

-40-50-60

-10

-20

-30-40-50-60

-40-50-60

-40

-50-60

-40

-30-40-50-60

-40-50-60

-50-60

-10

-30

-40-50-60

-40

-40

-50-60

-50-60

-30

-20

-30-40-50-60

-40-50-60

-50-60

-50

-60

-50

-30-40-50-60

-40-50-60

-50-60

-60

-30

-40-50-60

-30

-40-50-60

-40-50-60

-50-60

-60

-30

-30

-40-50-60

-40-50-60

-40

-50-60

-60

-60

-40

-30

-40-50-60

-40-50-60

-40-50-60

-50-60

-60

-20 -30 -40-50-60

-40-50-60

-40

-50-60

-50-60

-60

-40

-10

-40-50-60

-50-60

-50-60

-50-60

-40-5

0-60

-50-60

-50-60

-60

-50-60

-60

-60

-60


0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75

Fre

quen

cy (

GH

z)1

2

3

4

5

6

7

8

9

10

4-Layer Chebyshev 7-Layer Chebyshev

-60 -50 -40 -30 -20 -10 0

The Chebyshev layout can be applied using any absorber type. The improvement shown here is added to the performance of that material.

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Rantec 8” Pyramidal Absorber with 18CL Doping

Rantec 8" Pyramid with 18cl Dielectric ConstantReflection Coefficients, Polarization:

-20

-10

-30

-40

-50

-60

-40

-60

-50

-60

-60

-60

-40

-30

-50


0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75

Fre

qu

en

cy (

GH

z)

1

2

3

4

5

6

7

8

9

10

Rantec 8" Pyramid with 18cl Dielectric Constantand 4-Layer Chebyshev Distribution

Reflection Coefficients, Polarization:

-60

-50

-40

-40-5

0

-30-20

-10

-60

-40

-50-60

-40

-60 -50-60

-60

-50

-50

-60-50-60-60

-60

-60

-50


0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75F

req

ue

ncy

(G

Hz)

1

2

3

4

5

6

7

8

9

10

-60 -50 -40 -30 -20 -10 0

Without Chebyshev Layout With Chebyshev Layout

The doping and Chebyshev layout have greatly improved the stray signal performance but not sufficient to used alone for the first four antennas.

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-30

-20

-10

-40

-50

-60

-60

-40

-60

-50

-40-40

-60


0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75

Fre

qu

en

cy (

GH

z)

1

2

3

4

5

6

7

8

9

10



-60 -5

0

-60-50

-40

-30

-20

-10

-50

-60

-60

-60

-60

-60

-50


0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75

Fre

qu

en

cy (

GH

z)1

2

3

4

5

6

7

8

9

10

-60 -50 -40 -30 -20 -10 0



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-50

-40

-30

-20

-60

-60

-60

-50

-60

-60

-60

-60

-50

-60

-50

-40

-50

-50

-60

-60

-60

-60 -60

-50-50

-60

-50-50-50


0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75

Fre

qu

en

cy (

GH

z)

1

2

3

4

5

6

7

8

9

10



-60-50

-40

-30

-20

-50

-60

-60

-60 -60

-60

-60-60


0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75F

requ

ency

(G

Hz)

1

2

3

4

5

6

7

8

9

10

-60 -50 -40 -30 -20 -10 0



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Absorber Alone will not Meet SIMFAX Stray Signal Performance so Tapered R-Card Fences must be Used

The R-Card Fences block the near grazing signals and reflect that energy back toward the transmit wall. The fences do not diffract significantly. Note

that there is one fence for each of the four antennas nearest the sidewall.

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3D View of SIMFAX Chamber Sidewall

Chamber Wall

18”+3.6” Chebyshev Pyramid



Test Zone

Tapered R-Card Fences

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Tapered R-Card Fence Resistive Film Layups

12

34

5

78

6

910

R C ard W idth

Fence W idth

Fence H eight

Fence 1R Card Index R Card Width R Card Resistance

0 N/A N/A1 0.2023' 5.682 0.1555' 13.163 0.1618' 27.774 0.1623' 56.105 0.1609' 98.106 0.1618' 162.707 0.1614' 287.508 0.1978' 383.009 0.2273' 575.0010 0.2273' 1150.00

Width 7.0'Height 2.1284'Angle (, Degrees) 31.3044

12

34

57

8

6

910

R Card W idth

Fence W idth

Fence Height

0


0 0.4617' 3.001 0.3082' 5.682 0.2368' 13.163 0.2465' 27.774 0.2472' 56.105 0.2451' 98.106 0.2465' 162.707 0.2458' 287.508 0.2996' 383.009 0.3479' 575.0010 0.3462' 1150.00

Width 13.0'Height 3.7246'

1 2 34 5

78

6

910

Fence W idth

Fence H eight

0

R Card W idth


0 0.9620' 3.001 0.3211' 5.682 0.2468' 13.163 0.2569' 27.774 0.2576' 56.105 0.2554' 98.106 0.2569' 162.707 0.2561' 287.508 0.3139' 383.009 0.3608' 575.0010 0.3607' 1150.00


12 3

4 57

86

910

Fence W idth

Fence Height

0

R C ard W idth


0 0.9658' 3.001 0.4298' 5.682 0.3303' 13.163 0.3438' 27.774 0.3448' 56.105 0.3419' 98.106 0.3438' 162.707 0.3429' 287.508 0.4201' 383.009 0.4829' 575.0010 0.4829' 1150.00


Fence #1 Fence #2

Fence #3 Fence #4

The tapered R-Card fences have a triangular shape to reduce the small diffraction from the outer edge of the fence. These thin film layups are held in place and mounted on the wall using light weight foam sandwich structures.

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18” Pyramid with 4-Step Chebyshev



Final Chebyshev Pyramidal Absorber Layout Located Between Each of the Four R-Card Fences

Note that the R-Card fences and absorber are fully integrated together to completely cover the sidewalls.

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Probe Measurements of SIMFAX Chamber Horizontal Scan at Various Fixed Frequencies

This probe data was collected across a horizontal scan through the center of the test zone.

The data was collected every inch from -40” to 40”. The position data at fixed frequency can then be

transformed to the angle domain which indicates the source of chamber stray signals.

The following slides show the angle domain data on the top plot and raw probe data on the bottom one.

The angle domain results will show that the side wall scattering is minimal.

Finally, the angle domain results will show the angular scan direction associated with each of the feeds mounted on the source wall.

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Pre-Probe Measurements of SIMFAX Chamber Antenna #L7 Horizontal Scan at 2 GHz

Horizontal Polarization Vertical Polarization

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Pre-Probe Measurements of SIMFAX Chamber Antenna #L7 Horizontal Scan at 2.8 GHz


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ElectroScience Lab

Post-Probe Measurements of SIMFAX Chamber Antenna #L7 Horizontal Scan at 2 GHz


Minimal side wall scattering


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Post-Probe Measurements of SIMFAX Chamber Antenna #L7 Horizontal Scan at 2.8 GHz




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Post-Probe Measurements of SIMFAX Chamber Higher Resolution 2-18GHz Probe Data

In order to resolve scattering in the horizontal plane which includes the other feeds and R-Cards, only horizontal scan data was collected for this high resolution study.

The data was collected every inch from -40” to +40” and from 2 to 18 GHz every 80 MHz.

With an 80 MHz frequency step size, the unaliased down range time window is 12.5 nanoseconds.

It will be shown that this resolution will not be sufficient to resolve the undesired stray signal time delays as will be seen in the following TDOA results.

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Post-Probe Measurements of SIMFAX Chamber Raw Probe Data for L7 Antenna


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Post-Probe Measurements of SIMFAX Chamber Direction-of-Arrival for L7 Antenna


SmallError

SmallError

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Post-Probe Measurements of SIMFAX Chamber Time and Direction-of-Arrival for L7 Antenna


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Post-Probe Measurements of SIMFAX Chamber Higher Resolution 2-6 GHz Probe Data

In order to resolve scattering in the horizontal plane which includes the other feeds and R-Cards, only horizontal scan data was collected for this high resolution study.

The data was collected every inch from -40” to +40” and from 2 to 6 GHz every 20 Mhz. The error term is more significant in the 2-6 GHz frequency band.

With an 20 MHz frequency step size, the unaliased down range is 50 nanoseconds.

This resolution will be sufficient to resolve the undesired stray signal time delays as will be seen in the following TDOA results.

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Post-Probe Measurements of SIMFAX Chamber Raw Probe Data for L7 Antenna


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Post-Probe Measurements of SIMFAX Chamber Direction-of-Arrival for L7 Antenna


SmallError

SmallError

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Post-Probe Measurements of SIMFAX Chamber Time and Direction-of-Arrival for L7 Antenna


SmallError

SmallError

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Small Error Terms Caused by Scattering of the R-Card Fences Followed by Scattering from the Transmit Wall

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Post-Probe Measurements of SIMFAX Chamber Raw Probe Data for R7 Antenna


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Post-Probe Measurements of SIMFAX Chamber Direction-of-Arrival for R7 Antenna


VerySmallError

VerySmallError

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Post-Probe Measurements of SIMFAX Chamber Time and Direction-of-Arrival for R7 Antenna


VerySmallError

VerySmallError

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Final Post-Probing Conclusions The post-probe results look very good in terms of the data

collection, even for the high resolution scans. Also, the post-probe results look very good in terms of

performance for all antennas tested even for vertical polarization.

As stated earlier, the L7 and R7 have a small amount of attenuation near the sidewall caused by the R-Cards which was expected. Nevertheless, the beam is clearly positioned toward the antenna.

One should note that the processed beam results show that the sidewall scattering is extremely small.

The small remaining scattering occurs as a result of R-Card scattering bouncing off the source wall as shown by the high resolution data.

This small scattering term is noticeable from 2-6 GHz but becomes very small above 6 GHz.

In summary, Raytheon should be very pleased to see that the major error source in SIMFAX has been removed that being the sidewall

scattering. The remaining errors are very small and result from interaction between the R-Card fences and the transmit wall scattering.

ElectroScience Lab Compact and Spherical Range Design, Application and Evaluation Walter D. Burnside...

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