Chambers Absorber

7/29/2019 Chambers Absorber

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Copyright 2003, ETS-Lindgren, L.P.

An Introduction to RFAnechoic Chamber

Technology

Vicente Rodriguez, Ph.D.

ETS-Lindgren

1301 Arrow Point Dr.

Cedar Park, TX, 78613

[email protected]


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SUMMARY

The Chamber Family

Absorber Materials

The EMC Chamber The antenna Chamber

Tapered and Rectangular.

RCS chambers References


3/81


Chamber Types: Two Main Families

EMC testing Properties: Semi-free space or

half free space

Absorber: FS-1500,1000,600,400

(polyurethane) and FS-

1250,600,400 PS and EMC-24,(for High frequency applications

other absorber may be used).

Design tools: In-House Software

Std. Doc: ANSI C63.4-1992/1998;

EN50147-2 (semi-anechoic),-

3(fully anechoic),-1(shielding

test); VCCI V98.3 (Japanese);

RCS and Antenna. Properties: Fully anechoic.

Absorber: EHP series absorbers

RCS: mostly military

applications, is a chamber to

measure radar cross section of atarget

Antenna: military and

commercial, these are chambers

to measure the radiation pattern

of a radiator, could be an

antenna or an antenna plus other

system.


4/81


The Absorber Family 1

Microwave

Pyramidal absorber.

EMC and EHP series

Electric Losses

Preferred technology

for High frequencies

It can be used for low

frequencies if size(length) is increased


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Ferrite Tile .

Magnetic Losses

Preferred technology

for Low frequencies (up

to 1GHz), it has lowprofile.

It cannot be used for

high frequencies


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Hybrid Absorber .

Electric and Magnetic Losses

Preferred technology for EMC

Applications. foam has to havespecial formula for good

matching with ferrite tile at the

bottom. At High frequencies its

performance is not as good as

MW pyramid of equal size. Flattop causes undesired reflections

at MW range.


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Flat laminate .

Electric Losses

Preferred technology for

laboratory set ups. It is asandwich of different foams.

About 20dB absorption as

frequency increases.


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Wedge and pyramid

Electric Losses

A variant of pyramidal

absorber wedge does not showbackscattering. Preferred

technology for QZ treatment

and for RCS chambers.


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Popular types of absorber have constitutive parameters of:

12

1

jr

r

Non magnetic material

Low permittivity with losses

We will study how the electromagnetic wave behaves as isincident on to a wall of this type of absorber.

This material isvolumetrically

loaded having

the same

constitutive

parameters

through the

volume of the

pyramid

Pyramidal Absorber Theory (Example)


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At the tip of theabsorber

The wave

impedance is that

of air

At the base of the pyramidThe wave impedance becomes

oZ 0377

o

jZ 3.1325212

377

Along the length of thepyramid the waveimpedance falls betweenthose two values.



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12/81


dBee

jjjj

x

m

Np

o

380123.02235.0

35.046.1"'

1.022221.0

2

1.022

Letsassume a

length of

30cm

The

wavelength

at 3GHz is

10cmAnd at

10GHz is

30mm

Lets approximate by saying that the

pyramid is equivalent to a solid mediumof 1/3 the height

For 3GHz

Wavelength

at 3GHz

Approximate thickness of

equivalent solid material


C i h 2003 ETS Li d L P


13/81


dBee

jjjj

x

m

Np

o

1271029.4

7335.0

35.046.1"'

71.07322

03.02

03.0

22

Lets approximate by saying that the

pyramid is equivalent to a solid mediumof 1/3 the height

For 10GHz

Wavelength

at 3GHz

Approximate thicknessof equivalent solid

material

In practice the reflection coefficient may not be as small as this but it will be significantly

Smaller than at 3GHz


C i ht 2003 ETS Li d L P


14/81


EMC Chamber

Design is guided by thestandards and the test that thecustomer is going to perform.Frequency range is from 30 to1000MHz

At what distance is themeasurement (3m, 5m,10m)?Are we testing immunity oremissions?

The chamber must perform asif it was an infinite groundplane in an infinite open space

NSA is a measurement of howclose we are to this goal.

Std.Docs call for NSA beingwithin +- 4dB of the theoretical.

4m

1m

1,3,5,10m

C i ht 2003 ETS Li d L P


15/81


EMC Chamber

A

B

D Tx1

Tx2

QzdQzs

abs

abs

abs

Rx2

Rx1

Dsin()

mQzsmRxwhereabsQzsRxQzdDA

1,21:212

Rx1 can be a minimum of 1.5m

It is desirable that > 0 so that

reflections from the side walls

Do not arrive in phase to the test

area.

There are some rules that can be

applied when sizing an EMC

Chamber once the test distance

and the quiet zone size are

known

Copyright 2003 ETS Lindgren L P


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EMC Chamber

The FCC asks that the

performance of that anechoic

chamber matches that of an out

door range.

The Normalize Site Attenuation

(NSA) is measured.

Another common measurement

for qualification is the field

uniformity measurement

A

H

D

Tx1

1m

abs

abs

14 meter scan

1.5m

2m


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EMC Chamber

A typical standard will have wording similar to this:

ANSI C 63.4-1992 5.4.2, Alternate test Sites: Measurements can be

made at a location other than an OATS, ... Provided that the alternate site

meets the site attenuation requirements of 5.4.6 over the volume occupied

by the EUT, and the ground plane requirements of 5.4.3

What this means is that it must be shown that the

chamber performs like an infinite ground planewith no obstructions anywhere.

Chamber Validation Requirements


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Vertical Polarization VNSA

EMC Chamber


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Horizontal Polarization HNSA

EMC Chamber


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Testing the Uniform Area according EN 61000-4-3. For chambers where immunity measurements will

be performed it may be required to test the FU according to a given standard. this will show that thereflections from the wall do not affect the field.

0.5 m

0.5 m

0.8 m

This plane includes the uniform area, 12 from 16 points of E-Field are within +6/-0 dB.

EMC Chamber



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Copyright 2003, ETS Lindgren, L.P.

EMC Chamber: Partially linedchambers

Mil Std chambers and some other aircraft

and SAE EMC standard documents call for

partial absorber treatment chambers. Frequencies for use start in the 100 of

MHz.

Not looking for a half free space.

Absorber is loading the cavity (chamber) to

reduce any resonant behavior. EMC24 absorber is enough for these

applications.(A pyramidal specially loaded

absorber)

EUT Bench

1m



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Copyright 2003, ETS Lindgren, L.P.

EMC Chamber: Mil Std Chamber Mil Std 461 Defines the size of the chamber in terms if the EUT being measured,

EUT size determines the size of the chamber. The sketches bellow show the

standard MIL-STD chamber offered by ETS-Lindgren.



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py g , g ,

Mil Std 461E

What is it? Department of Defense: Requirementsfor the control of electromagneticinterference characteristics of

subsystems and equipment So it is a complete Standard for all

different EMC measurements



24/81

py g , g ,

Mil Std 461E

Mil Std 461 E came to be inAugust 20 1999

It superseding bothMil Std 461D and Mil Std 462DWhich passed away(rest in peace)



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py g g

Mil Std 461E

Mil Std 461EIs made ofmany parts(which one

are YOUinterestedin)

Conducted

Radiated

Emissions

Susceptibility

Emissions

Susceptibility



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Mil Std 461E Conducted

Conducted

Emissions

Susceptibility

CE 101

CE 102

CE 106

CS 101

CS 103

CS 104

CS 105

CS 109

CS 114

CS 115

CS 116




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Mil Std 461E ConductedEmissions

CE

CE 101

CE 102

CE 106

Conducted Emissions, power leads 30HZ-10KHz

Conducted Emissions, power leads 10KHz-10MHz

Conducted Emissions, Antenna terminal, 10KHz to40GHz

No chamber requiredShielded roomrecommended.

LISN, receivers,Ocope, data

recorders, sig gens,Current probe, etcare part of therequired Equipment




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Mil Std 461E ConductedSusceptibility (Immunity)

CS

CS 101CS 103

CS 104

CS 105CS 109

CS 114

CS 115CS 116

Conducted Susceptibility, Power leads, 30Hz, to 150KHz

Conducted Susceptibility, Antenna Port, Intermodulation, 15KHz to10GHz

Conducted Susceptibility, Antenna Port, rejection of Undesiredsignals, 30Hz to 20GHz

Conducted Susceptibility, Antenna Port, Cross-modulation, 30Hz to20GHz

Conducted Susceptibility, Structure Current, 60Hz to 100KHz

Conducted Susceptibility, Bulk Cable Injection, 10kHz to 200Mhz

Conducted Susceptibility, Bulk Cable Injection, Impulse excitation

Conducted Susceptibility,Damped Sinusoidal transients, cables andpower leads, 10KHz to 100MHz



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Mil Std 461E Radiated

Radiated

Emissions

Susceptibility

RE 101

RE 103

RE 105

RS 101

RS 103

RS 105




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Mil Std 461E RadiatedEmissions

RE

RE 101

RE 102

RE 105

Radiated Emissions, Magnetic Field, 30Hz to 100KHz

Radiated Emissions, Electric Field, 10KHz to 18GHz

Radiated Emissions, Antenna Spurious andharmonic Outputs, 10KHz to 40GHz




31/81

Mil Std 461E RadiatedSusceptibility (Immunity)

RE

RS 101

RS 103

RS 105

Radiated Susceptibility, Magnetic Field, 30Hz to 100KHz

Radiated Susceptibility, Electric Field, 2MHz to 18GHz

Radiated Susceptibility, Transient Electromagneticfield


Mil Std 461E Where do we


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Mil Std 461E Where do wetest?

Paragraph 4.3.2

Paragraph 4.3.2.1

To prevent interaction between the EUT and the outsideenvironment, SHIELDED ENCLOSURES will be usuallyrequired for testing

RF absorber material shall be used when performing

RE and RS testing inside a shielded enclosureThe RF absorber shall be placed above, behind and onboth sides of the EUT, and behind the radiating orreceiving antenna



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The Absorber Family

EMC-24

Mil Std 461E requirementsTABLE I page 10

6dB absorption 80Mhz to 250Mhz10dB absorption 250Mhz and above



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Mil Std Chamber side view Mil Std 461 Defines the size of the chamber in terms if the EUT being measured,





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Mil Std Chamber Side View Mil Std 461 Defines the size of the chamber in terms if the EUT being measured,




Mil Std Chamber RE and RS


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Mil Std Chamber RE and RSEquipment

RE101

RECOMMENDED REQUIRED

CHAMBER

EMCO 3725-2MCurrent Probe

EMCO 4-TR

EMCO 7604




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RE103

REQUIRED

CHAMBER

EMCO 3725-2M

EMCO 4-TREMCO 7-TR

EMCO 3301BEMCO 3110B

EMCO 3106

EMCO 3115

MIL STD 461E does not longer accept Log Periodic and spiral Logs onlydouble ridge horns above 200MHz




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RS101

RECOMMENDED REQUIRED

CHAMBER

EMCO 3725-2MCurrent Probe

EMCO 4-TR

EMCO 7605/7606




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RS103

REQUIRED

CHAMBER

EMCO 3725-2M

EMCO 4-TREMCO 7-TR

EMCO 3301BEMCO 3109

EMCO 3106

EMCO 3115

MIL STD 461E does not longer accept Log Periodic and spiral Logs onlydouble ridge horns above 200MHz




40/81


RS103

paragraph 5.19.4, states that an accepted method is the mode tunedreberveration chamber, the range is 200MHz to 40GHz, for the reverb logperiodics can be used since pattern is no longer an issue


CISPR 25


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CISPR 25

Limits and methods of measurement of radio

disturbance characteristics for the protection ofreceivers used on board vehicles

This means that we measure the emissions that would

affect any receiver in the vehicle. Is another self

immunity standard, of how vehicle receivers areimmune to radiated emissions from its own systems

SAE J 551-4 and SAE J 1113-41 are equivalent

standards


CISPR 25


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CISPR 25

Covers the frequency range from 150KHz- 1000MHz

When an absorber lined chamber is used theabsorption of the material has to be better than 6dB for

the range 70MHz and up.

For the chamber testing of subsystems a monopole is

used for the range 150KHz to 30MHz, for 30MHz to200MHz a biconical antenna is used, the log periodic is

used for the range 200MHz-1000MHz. For equipment

testing a TEM cell can be used.


EMC Chamber: CISPR 25 Chamber


43/81

EMC Chamber: CISPR 25 Chamber The CISPR-25 calls for reflectivity in the EUT area to be better

than 6dB.

There is no method for testing this.

Normal incidence performance of absorber is the best way todetermine the reflectivity in the area given the test geometry




44/81

EMC Chamber: CISPR 25 Chamber A recommended practice is to map the field along the cable

harness although the standard does not mentions anythingabout any chamber validation method. This method can helpcompare the results in two different chambers.


CISPR 25 Chamber Side View (Bicon)


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46/81



CISPR 25 Chamber Monopole Testing


47/81

CISPR 25 Chamber Monopole Testing



48/81


Apart from component testing the CISPR 25 rooms could

accommodate some vehicle testing if the floor is reinforced.



49/81

CISPR 25 TEM Cells

Additionally CISPR 25 allows for testing ofequipment in TEM cells and other TEM likedevices


Automotive Testing:


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Automotive Testing:A Short Introduction 50

Every manufacturer has its ownrequirements (usually very difficult to

meet).

Automotive standards are actually

rather simple.

The most common are SAE, ISO and95/54 EC. These usually are copies of

each other with small difference.

The previous slides look at the FACT

25 chamber which can be used for

automotive component testing for allthese standards.

A short introduction to emission testing

of whole vehicles is presented now



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Automotive Testing:A Short Introduction

51

The 10m emission testing

locates the antenna 10m from

the outer shell of the vehicle

The antenna is not scan but

located at 3m height. (For 3m

testing the antenna is located at1.8meters.

Both sides of the vehicle and

both polarizations are tested

10 meters

LPDA

BICONICAL

HORN

10 meters

10 meters


Automotive Testing:


52/81

Automotive Testing:A Short Introduction 52

The antenna is to be

in line with the

middle point of the

engine compartment.

A two antenna

position chamber

makes the test much

easier

Plane of longitudinal symmetry

10 meters

mid point of engine

compartment

Antenna in line with

mid point of engine

compartment

10 meters

The antenna not in use is set

At a different polarization to

reduce coupling between antennas

10 meters


EMC Ch b


53/81

EMC Chamber

There are a lot of different Standards in EMC. When a

different standard request appears the RF engineer mustanalyze the requirements of the standard and

recommend a proper solution.

Also customers may have their own special requirements.

Their company may have internal requirements fortesting. RF engineering analysis must be conducted to see

how to meet these requirements (or if is even possible to

meet them.

Most chambers are required to meet several standards.


A Ch b R i


54/81

The purpose of these chambers is to measure the radiation

pattern and characteristics of a radiator

Antenna Chamber: Requirements

Requirements

1. Frequency range:

2. Far field Requirement:

3. Quiet Zone Size:

This may determine if a tapered or

rectangular chamber should be used

Directly related to the previous

requirement since is related to the

wavelength at the lowest frequency:

The far field distance will determine

the path length and hence the

chamber length.

freq.lowest

22

dSd


A t Ch b R i t


55/81


Requirements

3. Quiet Zone Size:

4. Source Antenna Selection:

Test region where the level of

reflected energy is equal or smallerthan certain specified value

Must be large enough to encompass

the largest antenna being measured:

It also determines the size of the

chamber, the rule of thumb is that

width and height of chamber be at

least 3 times the Qz diameter or side.

Can be:

SphericalCubical volume

Cylindrical


A t Ch b R i t


56/81


Requirements

4. Source Antenna Selection:

5. Back wall

Considerations:

Rectangular chamber: the source antennamust have a pattern that illuminates the whole

Qz while avoiding the side walls.

Tapered chambers: Small antennas better.

15dB gain at least. No LPDA as phase center

moves.

Absorber normal incidence must be at least

equal to Qz level, avoid lights, cameras and

doors, ( for both rectangular and tapered.)


Antenna Chambers: Rectangular and


57/81

Rectangular Free Space condition

What Antennas can be

measured? Omni-directional

and directional.

Tapered Quasi-free Space.

Absorber treatment is used to create a

far field free space behavior of the

waves at the location of the antenna

under test.

Lower frequency antenna patterns can

be measured

It can be used for High frequency

testing but positioning of the source

antenna is critical

Antenna Chambers: Rectangular andTapered


Antenna Chambers: Rectangular and


58/81

Antenna Chambers: Rectangular andTapered

CRITERIA RECTANGULAR TAPERED

Antenna Patterns Poor at LF, good at

mid and HF

Good at Low Mid and

High F

Source placement Not critical Critical at HF

Source antenna Limited by Far field 15dB directivity

Axial ratio 25dB

Swept frequency

measurements

Ideal configuration Not recommended

Amplitude taper (Qz) Freq. independent Freq. Dependent

Phase deviation (Qz) Freq. independent Freq. Dependent

Boresite error low Potentially high


A t Ch b R t l I


59/81

Antenna Chamber Rectangular I

Pyramid

Top (or side view)

Pyramid

Pyramid

A

B

Pyramid

Qz

2

Path length

depthabsorber24

yaccuratellmoreor3

depthabsorber2

freq.lowest

2freq.lowest

2

QzB

QzB

PL

QzPLAd


A t Ch b R t l II


60/81

Antenna Chamber Rectangular II

QzPath length

Design of Rectangular chambers:

The application of the chamber will determine the Qz size and the Path length and

with it the size of the chamber

Determining the specular performance:

Based on the thickness of absorber the

behavior at different incident angles can be

computed.

Assume a chamber with: width B; pathlength L; Qz radius r, then

rBd

Ld

dL

)(tan

)(tan

1

1

d

Br

It is desirable to have


61/81

Antenna Chamber Rectangular III

QzPath length

With the value of it is possible (based on the thickness of the absorber in terms of

wavelengths) to determine the expected reflectivity.

With the known directivity of the antenna and

The knowledge of it is possible to compute

The gain of the antenna in that direction

The reflection at the edge of the quiet zone

Is given by:

Where R is the absorber reflectivity and G is the gain of the source antenna

atat GRQz tyreflectivi


Antenna Chamber: The Absorber


62/81

Treatment

Back wall(receive end wall)

Side wall

Normal Reflectivity better than QZ level

Oblique incidence Reflectivity with off

main beam gain better than QZ level




63/81

Treatment

Side wall absorber is only needed on those areas

where a specular reflection exists between thesource and the QZ

Everywhere elseshorter absorber canbe used




64/81

Treatment

Transmit end wall absorber can have a reflectivity

that when added to the front to back ratio of thesource antenna it meets the required QZ level




65/81

Antenna Chamber: The AbsorberTreatment

1. For a given pyramid element size chosen there is no expected backscattering

component. The scattered field is a sum of all the possible grating lobe waveswhich propagate in different directions, Only those where the following conditionis satisfied contribute to the scattering at a distance [*]

2. For m=0 and n=0 we have specular reflection only. For higher order modes topropagate we see that the period of the structure has to be larger than thewavelength

3. [*] W. Sun, C. BalanisAnalysis and Design of Periodic Absorbers by Finite-DifferenceFrequency-Domain Method report No. TRC-EM-WS-9301 TelecommunicationsResearch Center, Arizona State University, Tempe, AZ 1993.

2

22

22k

D

nk

D

mk

x

i

x

y

i

y

DD

22




66/81

Treatment

At high frequencies the antenna under test may re-

scattered the backscattered energy from thepyramidal absorber surrounding it




67/81

Antenna Chamber: The AbsorberTreatment

1. Traditionally in RCS chambers the backscatter of the side walls

(and ceiling/floor pair) is to be reduced using Wedge. By usingwedge around the QZ section of the chamber we can improvethe quality of the measurements at high frequencies




68/81

Treatment

Pyramid

Top (or side view)

Pyramid

Pyramid

A

B

Pyramid

Qz

2Wedge

Wedge


Far Field and QZ


69/81

Far Field and QZ

QZ )(xf Absorber reflectivity, chamber size,Gain of source antenna

FF )(xf Antenna size and frequency of operation


Far Field and QZ


70/81

Far Field and QZ

QZ reflectivity can be found. For any frequency.But that does not imply that the whole QZ is in the FF

)(xf

Knowing the chamber size, absorber layout,Gain of source antenna, and QZ diameter


Far Field and QZ


71/81

Far Field and QZ

If the path length is fixedThat it is possible todetermine what is the QZdiameter that will be in thefar field assuming

illumination by sphericalwaves from a point sourceat the location of thesource antenna


Far Field and QZ


72/81

Far Field and QZ

ANECHOIC CHAMBER DESIGN SUMMARY

Job # : 0 Customer: XXXXXXXXXXXXXX

19-Aug-03 Location: XXXXXXXXXXXXXX

SPHERICAL Quiet Zone 2 ft. dia.

Receive Endwall Abs Size = EHP-24 EHP- 24 CL

Specular Region Abs Size = EHP-18 EHP- 18 CL

Dimensions are (LxWxH)= 20 x 10 x 10

Path Length (ft) = 13

RCV Ant. Discrimination added

Angle of Incidence = 57.3 Degrees

SIDE WALLS, FLOOR/CEILING CALCULATIONS FOR

ANECHOIC CHAMBER QUIET ZONE PERFORMANCE

WORST CASE

Frequency Wavelength Thickness/ Absorber Spec 5 10 15 18

(MHz) (inches) Reflectivity (-DB)

1000 11.82 1.52 24 25 25 27 35 38

2000 5.91 3.05 33 34 36 43 452500 4.73 3.81 35 35 37 39 47 51

7000 1.69 10.66 48 50 49 51 55 55

8000 1.48 12.18 50 50 52 55 55

9000 1.31 13.71 52 50 51 53 55 55

14000 0.84 21.32 53 52 53 55 55

18000 0.66 27.41 53 50 52 53 55 55

Source Antenna Gain (DB)

GUARANTEED PERFORMANCE

So for a given size

Chamber we canprovide the QZreflectivity for a set offrequencies anddifferent sourceantenna gains.

The example shows a

20ft by 10ft by 10 ftchamber with 18 and

24 absorber and a 2ft

diameter QZ.


Far Field and QZ


73/81

Far Field and QZ

But of the given 2ft ofQZ and for a fixed 13ftpath length onlysmaller spheres are inthe FF of the sourceantenna

freq (MHz) c lambda QZ ft QZ m PL m PL ft

1000 3.00E+08 0.3 2.5 0.762 3.87096 132000 3.00E+08 0.15 1.8 0.54864 4.013411 13

3000 3.00E+08 0.1 1.45 0.44196 3.906573 13

4000 3.00E+08 0.075 1.25 0.381 3.87096 13

6000 3.00E+08 0.05 1.05 0.32004 4.097024 13

8000 3.00E+08 0.0375 0.9 0.27432 4.013411 13

10000 3.00E+08 0.03 0.8 0.24384 3.963863 13

18000 3.00E+08 0.016667 0.6 0.18288 4.013411 1340000 3.00E+08 0.0075 0.4 0.12192 3.963863 13


Antenna Chamber Tapered I


74/81

Antenna Chamber Tapered I

Top (or side view)

Pyramid

Pyramid

Pyramid

Qz

2

Wedge

Wedge

Wedge

Pyramid

Tapered chamber concept was develop to avoid the deficiencies of the Rectangular

chambers at low frequencies

At frequencies below 500MHz: Horns are no longer an option (very large).Less efficient antennas must be used.

The thickness of the side wall absorber has to be

increased to allow for good

performance (and the chamber size

increases to accommodate absorber).

Tapered chambers do not eliminate the specular reflection. The specular region is locatedclose to the aperture of the source antenna.

The resulting Quiet Zone amplitude

and phase tapers approach those

Expected in free-space hence the term

QUASI-FREE-SPACE


Antenna Chamber Tapered II


75/81

Antenna Chamber Tapered II

Top (or side view)

Pyramid

Pyramid

Pyramid

Qz

2

Testing antenna

Std Horn or ridge horn dipole minimum, No Log Periodic (phase center moves

away from the side walls)

Wedge

Wedge

Wedge

Pyramid

This area absorber is critical

This areaabsorber is less

than

thickness


Antenna Chamber Tapered III


76/81

Antenna Chamber Tapered III

Top (or side view)

Pyramid

Pyramid

Pyramid

Qz

2

Wedge

Wedge

Wedge

Pyramid

1. Qz needs to be 1/3w clear from the sides

2. half wavelength clear from absorber tips

3. Apex angle less than 28 deg. Hence length

depthabsorber24

yaccuratellmoreor3

freq.lowest

QzB

QzB

o

LF

B

Length

28

2width)(absorber2

tan

2


RCS Chambers I


77/81

RCS Chambers I To measure Radar cross

section

We only want reflection

from the target

Wedge is used on part of

the walls, ceiling and floor

to reduce reflections from

incidence on the flat part

of the pyramids.

The target illumination

mechanism changes

depending on frequency

and type of radar.

Pyramid

Pyramid

Top (or side view)

Wedge

Wedge

Pyramid

Pyramid

A/3A

B



78/81

The RCS Chamber

To measure Radar cross section (That is, the energy that bounces back froma target to the source of the original incident signalMONOSTATIC, or to a

receiver located at a different pointBISTATIC)

We only want reflection from the target coming back

Wedge is used on part of the walls, ceiling and floor to reduce reflections

from incidence on the flat part of the pyramids.


RCS Chambers II


79/81

RCS Chambers II

Reflection of the back wall willlimit how small of a RCS can be

measured in the chamber.

Assuming a good targetillumination system is used theRCS of the back wall can begiven by the RCS of an infinite

reflective wall

Minus the normal incidencereflectivity of the absorberplaced on the back wall.

2DRCS

D


RCS Chamber: Target Illumination


80/81

RCS Chamber: Target Illumination

Always try to reduce the any energy going to

the side walls.

Two antennas (one receive one transmit)

One antenna (receive and transmit)

Compact range reflector

Top (or side view)

Pyramid

Wedge

Wedge

Pyramid

Pyramid

A/3

A

B

Pyramid

Top (or side view)

Pyramid

Wedge

Wedge

Pyramid

Pyramid

A/3

A

B

Pyramid

Top (or side view)

Pyramid

Wedge

Wedge

Pyramid

Pyramid

A/3A

B

Pyramid


References


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References

Brownell F. P. Radio Frequency Anechoic

Chambers lecture materials, Microwave AntennaMeasurement short Course, fb ConsultantsCamarillo,California.

Kraus J. D.Antennas, 2d Ed. McGraw Hill:

Boston, Ma, 1988.

Balanis C. A.Antenna Theory: Analysis anddesign, 2d Ed, Wiley: New York, NY, 1997.

Liu K. Private Communication

Chambers Absorber

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