SIST-TP CLC/TR 50485:2011
(Main)Electromagnetic compatibility - Emission measurements in fully anechoic chambers
Electromagnetic compatibility - Emission measurements in fully anechoic chambers
This Technical Report applies to emission measurements of radiated electromagnetic fields in Fully
Anechoic Rooms (FAR) in the frequency range from 30 MHz to 18 GHz. This Technical Report covers the
frequency range from 30 MHz – 1 000 MHz. The frequency range above 1 GHz is under consideration,
due to the absence of practical experience.
This Technical Report describes the validation procedure for the Fully Anechoic Room for radiated
emission tests and the procedures to carry out the tests (e.g. test set up, EUT position, cable layout and
termination, test procedures). Recommendations for the relation between FAR emission limits and
common Open Area Test Site (OATS) emission limits given in standards such as EN 55011 and
EN 55022 are given in Annex B.
This FAR emission method may be chosen by product committees as an alternative method to emission
measurement on an Open Area Test Site (OATS) as described in CISPR 16 series. In such cases, the
product committee should also define the appropriate limits. Typical measurement uncertainty values for
FARs and OATS are given in Annex C.
Elektromagnetische Verträglichkeit - Störaussendung in Absorberräumen
Compatibilité électromagnétique - Emission en chambres anéchoïques entiers
Elektromagnetna združljivost - Meritve oddajanja v popolnoma neodbojnih sobah
To tehnično poročilo velja za meritve oddajanja sevanih radiomagnetnih polj v popolnoma neodbojnih sobah (FAR) v frekvenčnem razponu med 30 MHz in 18 GHz. To tehnično poročilo zajema frekvenčni razpon med 30 MHz in 1 000 MHz. Frekvenčni razpon nad 1 GHz se obravnava, ker praktičnih izkušenj ni.
To tehnično poročilo opisuje postopek validacije za popolnoma neodbojne sobe za preskuse sevanega oddajanja in postopek za izvedbo preskusov (npr. nastavitev preskusa, položaj EUT, postavitev in zaključevanje kablov, preskusni postopki). V dodatku B so podana priporočila za razmerje med mejnimi vrednostmi oddajanja v FAR in splošnimi mejnimi vrednostmi oddajanja za merilni poligon na prostem (OATS), podanimi v standardih, kot sta EN 55011 in EN 55022.
Metodo za oddajanje v FAR lahko izberejo odbori za proizvode kot alternativno metodo merjenju oddajanja na merilnem poligonu na prostem (OATS), kot je opisano v seriji CISPR 16. V takih primerih mora odbor za proizvode opredeliti tudi ustrezne mejne vrednosti. Tipične vrednosti negotovosti merjenja za FAR in OATS so navedene v dodatku C.
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
SIST-TP CLC/TR 50485:2011
01-december-2011
1DGRPHãþD
SIST R210-010:2003
Elektromagnetna združljivost - Meritve oddajanja v popolnoma neodbojnih sobah
Electromagnetic compatibility - Emission measurements in fully anechoic chambers
Elektromagnetische Verträglichkeit - Störaussendung in Absorberräumen
Compatibilité électromagnétique - Emission en chambres anéchoïques entiers
Ta slovenski standard je istoveten z: CLC/TR 50485:2010
ICS:
33.100.10 Emisija Emission
SIST-TP CLC/TR 50485:2011 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST-TP CLC/TR 50485:2011
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SIST-TP CLC/TR 50485:2011
TECHNICAL REPORT
CLC/TR 50485
RAPPORT TECHNIQUE
March 2010
TECHNISCHER BERICHT
ICS 33.100.10 Supersedes R210-010:2002
English version
Electromagnetic compatibility -
Emission measurements in fully anechoic chambers
Compatibilité électromagnétique - Elektromagnetische Verträglichkeit -
Emission en chambres Störaussendung in Absorberräumen
anéchoïques entiers
This Technical Report was approved by CENELEC on 2009-12-17.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia,
Cyprus, the Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania,
Slovakia, Slovenia, Spain, Sweden, Switzerland and the United Kingdom.
CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
Central Secretariat: Avenue Marnix 17, B - 1000 Brussels
© 2010 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. CLC/TR 50485:2010 E
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CLC/TR 50485:2010 – 2 –
Foreword
This Technical Report was prepared by the Technical Committee CENELEC TC 210, Electromagnetic
Compatibility (EMC).
This document supersedes R210-010:2002.
In order not to loose the information provided in R210-010:2002, CENELEC TC 210 decided to transfer
the content of that document unchanged into a Technical Report. It should be noted that CISPR
incorporated a major part of the document R210-010:2002 into the CISPR 16 series and the references to
standards were not updated.
The document still provides a comprehensive overview and describes some fundamental items of interest
for the appropriate use of fully anechoic chambers. The main reason for keeping the document in the
public domain in this new form is that it contains background information that has not been included in
EN 55016-1-4.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN and CENELEC shall not be held responsible for identifying any or all such patent
rights.
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– 3 – CLC/TR 50485:2010
Contents
1 Scope .5
2 References .5
3 Definitions and abbreviations .6
3.1 Definitions .6
3.2 Abbreviations .7
4 Test and measurement equipment .7
4.1 Fully Anechoic Rooms (FARs) .7
4.2 Antenna .7
5 Anechoic room performance .8
5.1 Theoretical normalised site attenuation .8
5.2 Room validation procedure . 10
5.3 Anechoic room requirements . 13
6 Emission measurement . 13
6.1 Test set up . 13
6.2 EUT position . 15
6.3 Cable layout and termination . 16
7 Test procedure . 17
8 Test plan . 17
9 Test report . 18
Annex A (informative) Determining the Site Reference . 19
Annex B (informative) Limit values . 21
Annex C (informative) Comparison of measurement uncertainties for 3 m OATS and 3 m FAR . 27
C.1 Introduction . 27
C.2 Uncertainty budgets for 3 m OATS and 3 m FAR . 28
C.3 Comments on uncertainty budgets . 30
Annex D (informative) Derivation of free space NSA formula . 32
D.1 Theoretical free space Normalised Site Attenuation . 32
D.2 NSA formula for near-field separations . 35
Annex E (informative) Corrections of field strength for test distance . 36
E.1 Introduction . 36
E.2 Field strength correction factor for LPDAs . 37
Annex F (informative) NSA measurements with biconical antennas . 38
F.1 Background . 38
F.2 ANSI method . 39
F.3 Conclusion . 39
Annex G (informative) Measurement of Balun imbalance . 40
Annex H (informative) FAR project . 41
H.1 Description of the FAR project . 41
H.2 Rationale of the FAR project . 41
Bibliography . 43
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CLC/TR 50485:2010 – 4 –
Figures
Figure 1 – Theoretical NSA .9
Figure 2 – Measurement points in room validation procedure . 11
Figure 3 – Typical test set-up in FAR, where a, b, c and e depend on the room performance . 14
Figure 4 – Typical test set-up for table top equipment within the test volume of a FAR . 15
Figure 5 – Typical test set-up for floor standing equipment within the test volume of a FAR . 16
Figure A.1 – Free space site reference measurement set up . 20
Figure B.1 – Differences in emission measurement results between OATS and FAR . 22
Figure B.2 – Geometrical optics model for OATS measurements . 23
Figure B.3 – Field attenuation between two half-wave dipoles above ground plane with fixed transmit
antenna height and variable receive antenna height . 23
Figure B.4 – Equivalent circuit diagram of a typical Equipment Under Test (EUT) . 24
Figure B.5 – Differences in the received field strength of an electrically short straight wire on an ideal
OATS (1 m – 4 m scan of the receive antenna), and in a FAR (E – E ) . 25
OATS FAR
Figure B.6 – Differences in the received field strength of an electrically short straight wire on an ideal
OATS (1 m – 4 m scan of the receive antenna), and in a FAR (E – E ) . 26
OATS FAR
Figure F.1 – NSA values for free space, calculated for a small and a large biconical antenna
separated by 3 m . 38
Tables
Table 1 – Frequency ranges and step sizes . 11
Table 2 – Relation between maximum diameter of EUT and test distance . 13
Table B.1 – Preferred limits . 21
Table C.1 – Uncertainty budget for emission measurements on 3 m open area test site . 28
Table C.2 – Uncertainty budget for emission measurements in 3 m FAR . 29
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1 Scope
This Technical Report applies to emission measurements of radiated electromagnetic fields in Fully
Anechoic Rooms (FAR) in the frequency range from 30 MHz to 18 GHz. This Technical Report covers the
frequency range from 30 MHz – 1 000 MHz. The frequency range above 1 GHz is under consideration,
due to the absence of practical experience.
This Technical Report describes the validation procedure for the Fully Anechoic Room for radiated
emission tests and the procedures to carry out the tests (e.g. test set up, EUT position, cable layout and
termination, test procedures). Recommendations for the relation between FAR emission limits and
common Open Area Test Site (OATS) emission limits given in standards such as EN 55011 and
EN 55022 are given in Annex B.
This FAR emission method may be chosen by product committees as an alternative method to emission
measurement on an Open Area Test Site (OATS) as described in CISPR 16 series. In such cases, the
product committee should also define the appropriate limits. Typical measurement uncertainty values for
FARs and OATS are given in Annex C.
2 References
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
EN 50147-1, Anechoic chambers – Part 1: Shield attenuation measurement
EN 55011, Industrial, scientific and medical (ISM) radio-frequency equipment – Electromagnetic
disturbance characteristics – Limits and methods of measurement (CISPR 11, mod.)
1)
EN 55022:1998 , Information technology equipment – Radio disturbance characteristics – Limits and
methods of measurement (CISPR 22:1997, mod.)
2)
CISPR 16-1:1999 , Specification for radio disturbance and immunity measuring apparatus and methods
– Part 1: Radio disturbance and immunity measuring apparatus
3)
CISPR 16-2 , Specification for radio disturbance and immunity measuring apparatus and methods –
Part 2: Methods of measurement of disturbance and immunity
4)
CISPR 16-3:2000 , Specification for radio disturbance and immunity measuring apparatus and methods
– Part 3: Reports and recommendations of CISPR
CISPR 16-4 series, Specification for radio disturbance and immunity measuring apparatus and methods –
Part 4: Uncertainties, statistics and limit modelling
IEC 60050-161, International Electrotechnical Vocabulary (IEV) – Chapter 161: Electromagnetic
compatibility
———————
1)
Superseded by EN 55022:2006, Information technology equipment – Radio disturbance characteristics – Limits and methods of
measurement (CISPR 22:2005, mod.).
2)
Superseded by CISPR 16-1 series, harmonized as EN 55016-1 series, Specification for radio disturbance and immunity
measuring apparatus and methods – Part 1: Radio disturbance and immunity measuring apparatus.
3)
Superseded by CISPR 16-2 series, harmonized as EN 55016-2 series, Specification for radio disturbance and immunity
measuring apparatus and methods – Part 2: Methods of measurement of disturbance and immunity.
4)
Superseded by CISPR 16-3:2003, Specification for radio disturbance and immunity measuring apparatus and methods – Part 3:
CISPR technical reports.
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CLC/TR 50485:2010 – 6 –
3 Definitions and abbreviations
3.1 Definitions
For the purposes of this document, the terms and definitions given in IEC 60050-161 and the following
apply.
3.1.1
Fully Anechoic Room (FAR)
shielded enclosure whose internal surfaces are lined with radio frequency absorbing material (i.e. RAM),
that absorbs electromagnetic energy in the frequency range of interest
NOTE The fully Absorber-Lined Room is intended to simulate free space environment.
3.1.2
Equipment Under Test (EUT)
test sample including connected cables
NOTE The EUT may consist of one or several pieces of equipment.
3.1.3
test volume
region of the room that meets the NSA requirements of this Technical Report and which contains the EUT
as fully set up
3.1.4
free space antenna factor (AF )
FS
antenna factor of an antenna which is not affected by mutual coupling to conducting bodies in the
environment of the antenna
NOTE It is also the antenna factor measured when the antenna under test is illuminated by a plane wave, which implies that the
source antenna is in the far-field of the antenna under test. Antenna factor is defined as the ratio of the magnitude of the E-field in
which the antenna is immersed to the voltage at the antenna output of a given transmission line impedance, usually 50 Ω.
3.1.5
antenna reference point
physical position on the antenna from which the separation distance to the defined reference plane on the
EUT is measured
NOTE For dipole and biconical antennas this will be the centre of the antenna in line with the central antenna elements. For an
LPDA antenna and a hybrid antenna, the reference point is the mark on the antenna provided by the manufacturer for this purpose.
The reference point is approximately at the mid-way point between the array elements that are active at the top and bottom
frequencies at which the measurements are being made. Hybrid antenna is here defined as a combination of a biconical and LPDA
antenna which has a frequency range including 30 MHz to 1 GHz.
3.1.6
Normalised Site Attenuation (NSA)
site attenuation obtained from the ratio of the source voltage connected to a transmitting antenna and the
received voltage as measured on the receiving antenna terminals
NOTE Normalised site attenuation is site attenuation in decibels minus the antenna factors of the transmit and receive antenna
factors. NSA was first introduced for evaluation of open area test sites with ground planes and was measured by height scanning
the receive antenna. In this Technical Report, NSA is measured in a quasi-free space environment, and because there is no
deliberate ground plane, height scanning is not required.
3.1.7
test distance (d )
t
distance measured from the reference point of the antenna to the front of the boundary of the EUT
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3.2 Abbreviations
For the purposes of this document, the following abbreviations apply.
EUT Equipment Under Test
FAR Fully Anechoic Room
NSA Normalised Site Attenuation
AF Antenna Factor (free space)
FS
LPDA Log-Periodic Dipole Array
OATS Open Area Test Site
RS Reference Site
SA Site Attenuation
SA measurement of SA made on RS
R
NEC Numerical Electromagnetic Code
4 Test and measurement equipment
Equipment in accordance with CISPR 16 series shall be used.
4.1 Fully Anechoic Rooms (FARs)
A Fully Anechoic Room is required for the emission testing in which the radiated electromagnetic waves
propagate as in free space and only the direct ray from the transmitting antenna reaches the receiving
antenna. All indirect and reflected waves shall be minimised with the use of proper absorbing material on
all walls, the ceiling and the floor of the FAR.
The screening of the FAR shall have an adequate attenuation level to avoid outside electromagnetic
radiation entering the room and influencing the measurement results. The shield attenuation is measured
in accordance with EN 50147-1. Shielding recommendations are given in CLC/TR 50484.
4.2 Antenna
Linear polarised antennas shall be used to measure the emitted electromagnetic field of the EUT.
Biconical or log-periodic antennas and hybrid antennas are typical antennas used. The free space
antenna factor shall be used. CISPR 16-3:2000, 4.7 gives parameters of broadband antennas. However
no length limitation on LPDA or hybrid antennas is given. CISPR 16-1:1999, 5.5.4 and 5.5.5 give
information on antennas. CISPR 16-1:1999, 5.5.5.2 b) states “it is essential that the variation of the
effective distance of the antenna from the source and its gain with frequency be taken into account”.
Antennas over 1,5 m in length could increase the uncertainties of emission testing using a separation of
3 m between the reference point of the antenna and the front of the EUT.
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CLC/TR 50485:2010 – 8 –
5 Anechoic room performance
5.1 Theoretical normalised site attenuation
The Site Attenuation (SA) is the loss measured between the connectors of two antennas on a particular
site. For a free space environment the SA (in dB) can be defined by Equation (1) (see Annex D):
5Z d
O
SA = 20log − 20log f + AF + AF []dB
(1)
10 10 m R T
2π
1 1
1− +
2 4
()βd ()βd
where
AF is the antenna factor of the receive antenna in dB/m;
R
AF is the antenna factor of the transmit antenna in dB/m;
T
d is the distance between the reference points of both antennas in meters;
Z is the reference impedance (i.e. 50 Ω);
0
ß is defined as 2π/λ;
f is the frequency in MHz.
m
The theoretical Normalised Site Attenuation (NSA) in dB is defined as site attenuation with respective
antenna factors subtracted, thus:
5Z
d
O
NSA = 20log − 20log f
(2)
calc 10 10 m
2π
1 1
1− +
2 4
()βd ()βd
In far-field conditions Equation (2) simplifies to Equation (3) by omitting the near field terms:
5Z d
O
NSA = 20log − 20log f
calc 10 10 m
(3)
2π
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SIST-TP CLC/TR 50485:2011
– 9 – CLC/TR 50485:2010
40
30
20
10
0
-10
-20
30 m
-30
10 m
5 m
-40
3 m
-50
10 100 1000 10000 100000
Frequency [MHz]
1a) Plot of theoretical NSA values in free space for far field conditions (Equation (3))
0.2
0.0
-0.2
-0.4
-0.6
-0.8
-1.0
-1.2
2.3
-1.4
0 2 4 6 8 10 12 14 16
Separation, m
Distances relate to a frequency of 30 MHz.
1b) Difference in theoretical NSA between Equation (2) and Equation (3)
Figure 1 – Theoretical NSA
Using the simplified Equation (3) the error is less than 0,1 dB at frequencies above 60 MHz for 5 m
distance and above 110 MHz for 3 m distance. Figure 1b shows the worst case near-field error which is at
30 MHz. However at higher frequencies there are Fresnel zone errors for large antennas which are
treated in Annex F.
Difference, dB
NSA [dB]
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CLC/TR 50485:2010 – 10 –
Equation (1) and Equation (2) account for near field effects of small antennas. In this context, using a
transmit antenna less than 40 cm long, near-field effects become significant (> 0,2 dB) where the receive
antenna length is greater than a quarter of the separation distance. This assumes the use of a 1,4 m long
biconical antenna at 300 MHz. Figure F.1 shows that the error is less than 0,2 dB for a separation of 3 m
and a maximum frequency of 200 MHz (it is common to change to a log antenna above 200 MHz). To
cater for the general use of antennas (biconicals up to 300 MHz, or bilogs), the site reference method
(6.2.1 and Annex A) shall be used for chamber validation at distances up to 5 m. In this method the site
attenuation measured in the FAR are compared to those measured on a free space reference site.
5.2 Room validation procedure
The test volume must meet the room requirements given in 5.3. The shape of the test volume will be a
cylinder, due to the rotation of the EUT on a turntable. The minimum height and diameter of the test
volume shall be 1 m. The height and diameter do not have to be equal between the maximum and
minimum values.
A single SA measurement is insufficient to pick up possible reflections from the construction and/or
absorbing material comprising the walls, the floor and the ceiling of the Fully Anechoic Room.
In validating the Fully Anechoic Room SA measurements shall be performed at 15 measurement points
for horizontal and vertical polarisation of the antennas:
1) at three heights of the test volume: bottom, middle and top of test volume;
2) at five positions in all three horizontal planes: the centre, left, right, front and back position of the
horizontal plane.
For SA measurements, two broadband antennas shall be used: one transmit antenna at the
measurement points of the test volume and one receive antenna outside this test volume at a prescribed
orientation and position. The transmit antenna shall approximate an omnidirectional antenna pattern and
shall have a maximum dimension of 40 cm. Typical antennas are biconical antennas. The receive
antenna used during the room validation shall be of the same type as the receive antenna used during
radiated emission testing of the EUT.
The frequency range 30 MHz to 1 GHz can be covered with one antenna, a hybrid antenna. The
measurement results may be different if separate biconical and LPDA antennas are used.
For FAR validation the receive antenna shall be in the position of the middle level of the test volume as
shown in Figure 2 and operated in horizontal and vertical polarisation. The distance between reference
points of the receive and transmit antennas shall be d . The height of the measurement volume is
nominal
less than the height of the test volume by the height of the transmit antenna. This is in order that the tip of
the vertically polarised transmit antenna does not protrude above the top plane or below the top plane of
the test volume. This treatment has not been applied, by reducing the diameter, to the horizontally aligned
antenna, because it is room height rather than width which is at issue.
When varying the transmit antenna to the other positions of the test volume the receive antenna shall be
moved to d . In all positions and polarisation the antennas shall face each other (receive antenna
nominal
tilted). When the transmit antenna is placed in the upper and bottom level, the receive antenna remains in
the middle level. The transmit antenna is moved to all 15 positions, and the 30 site validation
measurements are performed. Tilting of the antennas implies that only one site reference measurement is
needed to cover all 15 positions.
The back-position does not need to be taken into account if the distance between the boundary of the test
volume and tips of the absorber is more than 1 m. Experiments and modelling have shown that this
distance could be reduced to 0,5 m and further work may be needed to confirm this.
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Figure 2 – Measurement points in room validation procedure
For each measurement the frequency range is incrementally swept. The frequency step size shall not
exceed 1 % and need not be less than 1 MHz as given in Table 1.
Table 1 – Frequency ranges and step sizes
Frequency range Maximum frequency step
MHz MHz
30 – 100 1
100 – 500 5
500 – 1 000 10
For validating the room performance, two methods exist:
1) the site-reference method, preferred for a test distance up to 5 m;
2) the NSA-method, preferred for test distances larger than 5 m.
NOTE With reference to the site reference method, achieving quasi-free space conditions requires expertise. The problem is in
sufficiently eliminating reflections from the ground. In practice this probably confines the site reference method as described in
Annex A to distances of less than 5 m. On the other hand there are also limitations with the NSA method in that the free space
antenna factor is used. At 3 m distance the antenna coupling is not negligible and expertise is required to correct the free space
antenna factor for coupling. A practical solution is to confine the NSA method to distances greater than 5 m. Corrections, such as to
phase centre, are required, but this can be done precisely.
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CLC/TR 50485:2010 – 12 –
The intention of the SA measurement is to give "0 dB" deviation on an ideal site. Any measure can be
taken to improve the measurement accuracy as long as it is not contradictory to the described setup and
procedure and does not hide any bad room performance (e.g. smoothing).
The accuracy in the validation procedure can be improved by the following measures.
1) The cables are extended by at least 2 m behind each antenna before dropping the cable to the
ground for a vertically polarised antenna. The cables will - if possible - extend straight back to the
bulkhead connectors in the wall of the room. Additional possibilities are ferrite rings around cables.
2) Any bad match of the antennas is padded out by use of attenuators at the antenna connectors (e.g.
6 dB or 10 dB).
3) Antennas with a good balance of the balun shall be used, giving a change in receiver reading of less
than ± 0,5 dB when the illuminated antenna is inverted with respect to its input cable (see Annex G).
4) The directional pattern of the receive antenna can be accounted for on site validations with the NSA
method.
The room validation procedure shall be applied at a regular interval (to detect long-term changes in room
characteristics) and when changes in the Fully Anechoic Room are implemented or occurred, that might
influence the electromagnetic wave transmission characteristics of the room.
5.2.1 Site reference method
The SA measurement of the antenna pair (transmit and receive antenna) on a quasi free space test site is
required as reference. The antenna pair that is used for site validation is calibrated as a pair on a
reference site. In Annex A the procedure of determining this Site Reference (SR) is described. This
method accounts for coupling of the antennas and near field effects which can have a significant
influence at a 3 m test distance, reducing as the distance increases to 5 m.
The site validation for each measurement point is performed in three steps:
1) the insertion loss (M ) is measured in dB with the cables connected together;
0
2) the transmission loss (M ) is measured in dB with the cables connected to the antennas;
1
3) the deviation of the measured site attenuation from site reference is calculated according
Equation (4).
Dev = M − M − SR()d
(4)
0 1
5.2.2 NSA method
The NSA method is recommended for d
...
SLOVENSKI STANDARD
oSIST-TP CLC/prTR 50485:2008
01-oktober-2008
Elektromagnetna združljivost - Meritve oddajanja v popolnoma neodbojnih sobah
Electromagnetic compatibility - Emission measurements in fully anechoic chambers
Elektromagnetische Verträglichkeit - Störaussendung in Absorberräumen
Compatibilité électromagnétique - Emission en chambres anéchoïques entiers
Ta slovenski standard je istoveten z: CLC/prTR 50485:2008
ICS:
33.100.10 Emisija Emission
oSIST-TP CLC/prTR 50485:2008 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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oSIST-TP CLC/prTR 50485:2008
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oSIST-TP CLC/prTR 50485:2008
DRAFT
TECHNICAL REPORT
CLC/prTR 50485
RAPPORT TECHNIQUE
August 2008
TECHNISCHER BERICHT
ICS 33.100.10 Will supersede R210-010:2002
English version
Electromagnetic compatibility -
Emission measurements in fully anechoic chambers
Compatibilité électromagnétique - Elektromagnetische Verträglichkeit -
Emission en chambres anéchoïques Störaussendung in Absorberräumen
entiers
This draft Technical Report is submitted to CENELEC members for comments prior to the voting meeting.
Deadline for CENELEC: 2008-11-07.
It has been drawn up by CLC/TC 210.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Cyprus, the
Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.
Warning : This document is not a Technical Report. It is distributed for review and comments. It is subject to
change without notice and shall not be referred to as a Technical Report.
CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
Central Secretariat: rue de Stassart 35, B - 1050 Brussels
© 2008 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Project: 17074 Ref. No. CLC/prTR 50485:2008 E
Draft for Enquiry
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oSIST-TP CLC/prTR 50485:2008
CLC/prTR 50485:2008 – 2 –
1 Foreword
2 This draft Technical Report was prepared by the Technical Committee CENELEC TC 210,
3 Electromagnetic compatibility (EMC).
4 It is circulated for comments prior to the voting meeting foreseen on 2008-12-11 in accordance with
5 the Internal Regulations, Part 2, Subclause 11.4.3.2 (simple majority).
6 This document will supersede R210-010:2002.
7 ________________
8
9 CLC/TC 210 Secretariat’s note:
10 National Committes are invited to comment on whether Annex H should be removed.
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11 Contents
12 1 Scope .5
13 2 References .5
14 3 Definitions and abbreviations .6
15 3.1 Definitions .6
16 3.2 Abbreviations .7
17 4 Test and measurement equipment .7
18 4.1 Fully Anechoic Rooms (FARs) .7
19 4.2 Antenna .7
20 5 Anechoic room performance .8
21 5.1 Theoretical normalised site attenuation .8
22 5.2 Room validation procedure . 10
23 5.3 Anechoic room requirements . 13
24 6 Emission measurement . 13
25 6.1 Test set up . 13
26 6.2 EUT position . 15
27 6.3 Cable layout and termination . 16
28 7 Test procedure . 17
29 8 Test plan . 17
30 9 Test report . 18
31 Annex A (informative) Determining the Site Reference . 19
32 Annex B (informative) Limit values . 21
33 Annex C (informative) Comparison of measurement uncertainties for 3 m OATS and 3 m FAR . 27
34 C.1 Introduction . 27
35 C.2 Uncertainty budgets for 3 m OATS and 3 m FAR . 28
36 C.3 Comments on uncertainty budgets . 30
37 Annex D (informative) Derivation of free space NSA formula . 32
38 D.1 Theoretical free space Normalised Site Attenuation . 32
39 D.2 NSA formula for near-field separations . 35
40 Annex E (informative) Corrections of field strength for test distance . 36
41 E.1 Introduction . 36
42 E.2 Field strength correction factor for LPDAs . 37
43 Annex F (informative) NSA measurements with biconical antennas . 38
44 Background . 38
F.1
45 F.2 ANSI method . 39
46 F.3 Conclusion . 39
47 Annex G (informative) Measurement of Balun imbalance . 40
48 Annex H (informative) FAR project . 41
49 H.1 Description of the FAR project . 41
50 H.2 Rationale of the FAR project . 41
51 Bibliography . 43
52
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53 Figures
54 Figure 1 – Theoretical NSA .9
55 Figure 2 – Measurement points in room validation procedure . 11
56 Figure 3 – Typical test set-up in FAR, where a, b, c and e depend on the room performance . 14
57 Figure 4 – Typical test set-up for table top equipment within the test volume of a FAR . 15
58 Figure 5 – Typical test set-up for floor standing equipment within the test volume of a FAR . 16
59 Figure A.1 – Free space site reference measurement set up . 20
60 Figure B.1 – Differences in emission measurement results between OATS and FAR . 22
61 Figure B.2 – Geometrical optics model for OATS measurements . 23
62 Figure B.3 – Field attenuation between two half-wave dipoles above ground plane with fixed
63 transmit antenna height and variable receive antenna height . 23
64 Figure B.4 – Equivalent circuit diagram of a typical Equipment Under Test (EUT) . 24
65 Figure B.5 – Differences in the received field strength of an electrically short straight wire on an
66 ideal OATS (1 m – 4 m scan of the receive antenna), and in a FAR (E – E ). 25
OATS FAR
67 Figure B.6 – Differences in the received field strength of an electrically short straight wire on an
68 ideal OATS (1 m – 4 m scan of the receive antenna), and in a FAR (E – E ). 26
OATS FAR
69 Figure F.1 – NSA values for free space, calculated for a small and a large biconical antenna
70 separated by 3 m . 38
71
72 Tables
73 Table 1 – Frequency ranges and step sizes . 11
74 Table 2 – Relation between maximum diameter of EUT and test distance . 13
75 Table B.1 – Preferred limits . 21
76 Table C.1 – Uncertainty budget for emission measurements on 3 m open area test site . 28
77 Table C.2 – Uncertainty budget for emission measurements in 3 m FAR . 29
78
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79 1 Scope
80 This Technical Report applies to emission measurements of radiated electromagnetic fields in Fully
81 Anechoic Rooms (FAR) in the frequency range from 30 MHz to 18 GHz. This Technical Report covers
82 the frequency range from 30 MHz – 1 000 MHz. The frequency range above 1 GHz is under
83 consideration, due to the absence of practical experience.
84 This Technical Report describes the validation procedure for the Fully Anechoic Room for radiated
85 emission tests and the procedures to carry out the tests (e.g. test set up, EUT position, cable layout
86 and termination, test procedures). Recommendations for the relation between FAR emission limits and
87 common Open Area Test Site (OATS) emission limits given in standards such as EN 55011 and
88 EN 55022 are given in Annex B.
89 This FAR emission method may be chosen by product committees as an alternative method to
90 emission measurement on an Open Area Test Site (OATS) as described in CISPR 16 series. In such
91 cases, the product committee should also define the appropriate limits. Typical measurement
92 uncertainty values for FARs and OATS are given in Annex C.
93 2 References
94 The following referenced documents are indispensable for the application of this document. For dated
95 references, only the edition cited applies. For undated references, the latest edition of the referenced
96 document (including any amendments) applies.
97 EN 50147-1, Anechoic chambers – Part 1: Shield attenuation measurement
98 EN 55011, Industrial, scientific and medical (ISM) radio-frequency equipment – Electromagnetic
99 disturbance characteristics – Limits and methods of measurement (CISPR 11, mod.)
1)
100 EN 55022:1998 , Information technology equipment – Radio disturbance characteristics – Limits and
101 methods of measurement (CISPR 22:1997, mod.)
2)
102 CISPR 16-1:1999 , Specification for radio disturbance and immunity measuring apparatus and
103 methods – Part 1: Radio disturbance and immunity measuring apparatus
3)
104 CISPR 16-2 , Specification for radio disturbance and immunity measuring apparatus and methods –
105 Part 2: Methods of measurement of disturbance and immunity
4)
106 CISPR 16-3:2000 , Specification for radio disturbance and immunity measuring apparatus and
107 methods – Part 3: Reports and recommendations of CISPR
108 CISPR 16-4 series, Specification for radio disturbance and immunity measuring apparatus and
109 methods – Part 4: Uncertainties, statistics and limit modelling
110 IEC 60050-161, International Electrotechnical Vocabulary (IEV) – Chapter 161: Electromagnetic
111 compatibility
———————
1)
Will be superseded by EN 55022:2006, Information technology equipment – Radio disturbance characteristics – Limits and
methods of measurement (CISPR 22:2005, mod.) at the dow of the latter, i.e. 2009-10-01.
2)
Superseded by CISPR 16-1 series, harmonized as EN 55016-1 series, Specification for radio disturbance and immunity
measuring apparatus and methods – Part 1: Radio disturbance and immunity measuring apparatus.
3)
Superseded by CISPR 16-2 series, harmonized as EN 55016-2 series, Specification for radio disturbance and immunity
measuring apparatus and methods – Part 2: Methods of measurement of disturbance and immunity.
4)
Superseded by CISPR 16-3:2003, Specification for radio disturbance and immunity measuring apparatus and methods –
Part 3: CISPR technical reports.
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112 3 Definitions and abbreviations
113 3.1 Definitions
114 For the purposes of this document, the terms and definitions given in IEC 60050-161 and the following
115 apply.
116 3.1.1
117 Fully Anechoic Room (FAR)
118 shielded enclosure whose internal surfaces are lined with radio frequency absorbing material (i.e.
119 RAM), that absorbs electromagnetic energy in the frequency range of interest
120 NOTE The fully Absorber-Lined Room is intended to simulate free space environment.
121 3.1.2
122 Equipment Under Test (EUT)
123 test sample including connected cables
124 NOTE The EUT may consist of one or several pieces of equipment.
125 3.1.3
126 test volume
127 region of the room that meets the NSA requirements of this Technical Report and which contains the
128 EUT as fully set up
129 3.1.4
130 free space antenna factor (AF )
FS
131 antenna factor of an antenna which is not affected by mutual coupling to conducting bodies in the
132 environment of the antenna
133 NOTE It is also the antenna factor measured when the antenna under test is illuminated by a plane wave, which implies
134 that the source antenna is in the far-field of the antenna under test. Antenna factor is defined as the ratio of the magnitude of
135 the E-field in which the antenna is immersed to the voltage at the antenna output of a given transmission line impedance,
136 usually 50 Ω.
137 3.1.5
138 antenna reference point
139 physical position on the antenna from which the separation distance to the defined reference plane on
140 the EUT is measured
141 NOTE For dipole and biconical antennas this will be the centre of the antenna in line with the central antenna elements. For an
142 LPDA antenna and a hybrid antenna, the reference point is the mark on the antenna provided by the manufacturer for this
143 purpose. The reference point is approximately at the mid-way point between the array elements that are active at the top and
144 bottom frequencies at which the measurements are being made. Hybrid antenna is here defined as a combination of a biconical
145 and LPDA antenna which has a frequency range including 30 MHz to 1 GHz.
146 3.1.6
147 Normalised Site Attenuation (NSA)
148 site attenuation obtained from the ratio of the source voltage connected to a transmitting antenna and
149 the received voltage as measured on the receiving antenna terminals
150 NOTE Normalised site attenuation is site attenuation in decibels minus the antenna factors of the transmit and receive
151 antenna factors. NSA was first introduced for evaluation of open area test sites with ground planes and was measured by height
152 scanning the receive antenna. In this Technical Report, NSA is measured in a quasi-free space environment, and because there
153 is no deliberate ground plane height scanning is not required.
154 3.1.7
155 test distance (d )
t
156 distance measured from the reference point of the antenna to the front of the boundary of the EUT
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157 3.2 Abbreviations
158 For the purposes of this document, the following abbreviations apply.
EUT Equipment Under Test
FAR Fully Anechoic Room
NSA Normalised Site Attenuation
AF Antenna Factor (free space)
FS
LPDA Log-Periodic Dipole Array
OATS Open Area Test Site
RS Reference Site
SA Site Attenuation
SA measurement of SA made on RS
R
NEC Numerical Electromagnetic Code
159 4 Test and measurement equipment
160 Equipment in accordance with CISPR 16 series shall be used.
161 4.1 Fully Anechoic Rooms (FARs)
162 A Fully Anechoic Room is required for the emission testing in which the radiated electromagnetic
163 waves propagate as in free space and only the direct ray from the transmitting antenna reaches the
164 receiving antenna. All indirect and reflected waves shall be minimised with the use of proper absorbing
165 material on all walls, the ceiling and the floor of the FAR.
166 The screening of the FAR shall have an adequate attenuation level to avoid outside electromagnetic
167 radiation entering the room and influencing the measurement results. The shield attenuation is
168 measured in accordance with EN 50147-1. Shielding recommendations are given in CLC/TR 50484.
169 4.2 Antenna
170 Linear polarised antennas shall be used to measure the emitted electromagnetic field of the EUT.
171 Biconical or log-periodic antennas and hybrid antennas are typical antennas used. The free space
172 antenna factor shall be used. CISPR 16-3:2000, 4.7 gives parameters of broadband antennas.
173 However no length limitation on LPDA or hybrid antennas is given. CISPR 16-1:1999, 5.5.4 and 5.5.5
174 give information on antennas. CISPR 16-1:1999, 5.5.5.2 b) states “it is essential that the variation of
175 the effective distance of the antenna from the source and its gain with frequency be taken into
176 account”. Antennas over 1,5 m in length could increase the uncertainties of emission testing using a
177 separation of 3 m between the reference point of the antenna and the front of the EUT.
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178 5 Anechoic room performance
179 5.1 Theoretical normalised site attenuation
180 The Site Attenuation (SA) is the loss measured between the connectors of two antennas on a
181 particular site. For a free space environment the SA (in dB) can be defined by Equation (1) (see
182 Annex D):
5Z d
O
SA = 20log − 20log f + AF + AF []dB
(1)
10 10 m R T
2π
1 1
1− +
2 4
()βd ()βd
183 where
184 AF is the antenna factor of the receive antenna in dB/m;
R
185 AF is the antenna factor of the transmit antenna in dB/m;
T
186 d is the distance between the reference points of both antennas in meters;
187 Z is the reference impedance (i.e. 50 Ω);
0
188 ß is defined as 2π/λ;
189 f is the frequency in MHz.
m
190 The theoretical Normalised Site Attenuation (NSA) in dB is defined as site attenuation with respective
191 antenna factors subtracted, thus:
5Z d
O
NSA = 20log − 20log f
(2)
calc 10 10 m
2π
1 1
1− +
2 4
()βd ()βd
192 In far-field conditions Equation (2) simplifies to Equation (3) by omitting the near field terms:
5Z d
O
NSA = 20log − 20log f
calc 10 10 m
(3)
2π
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40
30
20
10
0
-10
-20
30 m
-30
10 m
5 m
-40
3 m
-50
10 100 1000 10000 100000
Frequency [MHz]
193
194 1a) Plot of theoretical NSA values in free space for far field conditions (Equation (3))
0.2
0.0
-0.2
-0.4
-0.6
-0.8
-1.0
-1.2
2.3
-1.4
0 2 4 6 8 10 12 14 16
Separation, m
195
196 Distances relate to a frequency of 30 MHz.
197 1b) Difference in theoretical NSA between Equation (2) and Equation (3)
198 Figure 1 – Theoretical NSA
199 Using the simplified Equation (3) the error is less than 0,1 dB at frequencies above 60 MHz for 5 m
200 distance and above 110 MHz for 3 m distance. Figure 1b shows the worst case near-field error which
201 is at 30 MHz. However at higher frequencies there are Fresnel zone errors for large antennas which is
202 treated in Annex F.
203 Equation (1) and Equation (2) account for near field effects of small antennas. In this context, using a
204 transmit antenna less than 40 cm long, near-field effects become significant (> 0,2 dB) where the
205 receive antenna length is greater than a quarter of the separation distance. This assumes the use of a
206 1,4 m long biconical antenna at 300 MHz. Figure F.1 shows that the error is less than 0,2 dB for a
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Difference, dB
NSA [dB]
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207 separation of 3 m and a maximum frequency of 200 MHz (it is common to change to a log antenna
208 above 200 MHz). To cater for the general use of antennas (biconicals up to 300 MHz, or bilogs), the
209 site reference method (6.2.1 and Annex A) shall be used for chamber validation at distances up to
210 5 m. In this method the site attenuation measured in the FAR are compared to those measured on a
211 free space reference site.
212 5.2 Room validation procedure
213 The test volume must meet the room requirements given in 5.3. The shape of the test volume will be a
214 cylinder, due to the rotation of the EUT on a turntable. The minimum height and diameter of the test
215 volume shall be 1 m. The height and diameter do not have to be equal between the maximum and
216 minimum values.
217 A single SA measurement is insufficient to pick up possible reflections from the construction and/or
218 absorbing material comprising the walls, the floor and the ceiling of the Fully Anechoic Room.
219 In validating the Fully Anechoic Room SA measurements shall be performed at 15 measurement
220 points for horizontal and vertical polarisation of the antennas:
221 1) at three heights of the test volume: bottom, middle and top of test volume;
222 2) at five positions in all three horizontal planes: the centre, left, right, front and back position of the
223 horizontal plane.
224 For SA measurements, two broadband antennas shall be used: one transmit antenna at the
225 measurement points of the test volume and one receive antenna outside this test volume at a
226 prescribed orientation and position. The transmit antenna shall approximate an omnidirectional
227 antenna pattern and shall have a maximum dimension of 40 cm. Typical antennas are biconical
228 antennas. The receive antenna used during the room validation shall be of the same type as the
229 receive antenna used during radiated emission testing of the EUT.
230 The frequency range 30 MHz to 1 GHz can be covered with one antenna, a hybrid antenna. The
231 measurement results may be different if separate biconical and LPDA antennas are used.
232 For FAR validation the receive antenna shall be in the position of the middle level of the test volume
233 as shown in Figure 2 and operated in horizontal and vertical polarisation. The distance between
234 reference points of the receive and transmit antenna shall be d . The height of the measurement
nominal
235 volume is less than the height of the test volume by the height of the transmit antenna. This is in order
236 that the tip of the vertically polarised transmit antenna does not protrude above the top plane or below
237 the top plane of the test volume. This treatment has not been applied, by reducing the diameter, to the
238 horizontally aligned antenna, because it is room height rather than width which is at issue.
239 When varying the transmit antenna to the other positions of the test volume the receive antenna shall
240 be moved to d . In all positions and polarisation the antennas shall face each other (receive
nominal
241 antenna tilted). When the transmit antenna is placed in the upper and bottom level, the receive
242 antenna remains in the middle level. The transmit antenna is moved to all 15 positions, the 30 site
243 validation measurements are performed. Tilting of the antennas implies that only one site reference
244 measurement is needed to cover all 15 positions.
245 The back-position does not need to be taken into account if the distance between the boundary of the
246 test volume and tips of the absorber is more than 1 m. Experiments and modelling have shown that
247 this distance could be reduced to 0,5 m and further work may be needed to confirm this.
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248
249 Figure 2 – Measurement points in room validation procedure
250 For each measurement the frequency range is incrementally swept. The frequency step size shall not
251 exceed 1 % and need not be less than 1 MHz as given in Table 1.
252 Table 1 – Frequency ranges and step sizes
Frequency range Maximum frequency step
MHz MHz
30 – 100 1
100 – 500 5
500 – 1 000 10
253
254 For validating the room performance, two methods exist:
255 1) the site-reference method, preferred for a test distance up to 5 m;
256 2) the NSA-method, preferred for test distances larger than 5 m.
257 NOTE With reference to the site reference method, achieving quasi-free space conditions requires expertise. The problem is
258 in sufficiently eliminating reflections from the ground. In practice this probably confines the site reference method as described
259 in Annex A to distances of less than 5 m. On the other hand there are also limitations with the NSA method in that the free
260 space antenna factor is used. At 3 m distance the antenna coupling is not negligible and expertise is required to correct the free
261 space antenna factor for coupling. A practical solution is to confine the NSA method to distances greater than 5 m. Corrections,
262 such as to phase centre, are required, but this can be done precisely.
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263 The intention of the SA measurement is to give "0 dB" deviation on an ideal site. Any measure can be
264 taken to improve the measurement accuracy as long as it is not contradictory to the described setup
265 and procedure and does not hide any bad room performance (e.g. smoothing).
266 The accuracy in the validation procedure can be improved by the following measures.
267 1) The cables are extended by at least 2 m behind each antenna before dropping the cable to the
268 ground for a vertically polarised antenna. The cables will - if possible - extend straight back to the
269 bulkhead connectors in the wall of the room. Additional possibilities are ferrite rings around cables.
270 2) Any bad match of the antennas is padded out by use of attenuators at the antenna connectors
271 (e.g. 6 dB or 10 dB).
272 3) Antennas with a good balance of the balun shall be used, giving a change in receiver reading of
273 less than ± 0,5 dB when the illuminated antenna is inverted with respect to its input cable
274 (see Annex G).
275 4) The directional pattern of the receive antenna can be accounted for on site validations with the
276 NSA method.
277 The room validation procedure shall be applied at a regular interval (to detect long-term changes in
278 room characteristics) and when changes in the Fully Anechoic Room
...
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