CLC/TR 50485:2010
(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
Standards Content (Sample)
SLOVENSKI STANDARD
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
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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
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.
– 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
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
– 5 – CLC/TR 50485:2010
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.
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
– 7 – CLC/TR 50485:2010
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.
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);
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
– 9 – CLC/TR 50485:2010
-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]
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.
– 11 – CLC/TR 50485:2010
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.
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;
2) the transmission loss (M ) is measured in dB with the cables connected to the antennas;
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 distances equal to or greater than 5 m. The free space antenna
factors of the transmit and receive antenna are required for this procedure. The theoretical NSA is a
simple calculation between point sources, and therefore does not account for the radiation patterns of the
actual antennas used. As the transmit antenna is moved throughout the volume it will be slightly off the
boresight direction of the receive antenna. The effects of the radiation pattern are small and can be
corrected for assuming the pattern is that of a Hertzian dipole, or cos θ. The phase-centre variation of
log.-periodic and bicon-log-periodic antennas have also to be taken into account (see 6.1).
– 13 – CLC/TR 50485:2010
The site validation for each measurement point is performed in four steps:
1) the insertion loss (M ) is measured in dB with the cables connected together;
2) the transmission loss (M ) is measured in dB with the cables connected to the antennas;
3) the measured NSA (NSA ) is calculated in dB according to Equation (5):
m
NSA = M − M − AF − AF in dB
(5)
m 0 1 T R
where
AF and AF are free space antenna factors in dB/m.
T R
4) the deviation of the measured NSA (Equation (5)) from the theoretical NSA (Equation (2)) is
calculated according to Equation (6). NSA is given by Equation (2) in 5.1.
calc
NOTE The real distance d between the reference points of the transmit and receive antenna has to be used in Equation (2),
not the nominal test distance d . i.e. if the LPDA antenna has been calibrated at its true phase centre at each frequency, a
nominal
phase centre correction must be included if a fixed distance (to the reference point on the LPDA) is used.
Dev = NSA − NSA in dB
(6)
calc m
5.3 Anechoic room requirements
A measurement site shall comply with the two following requirements.
1) The room validation procedure shall provide deviations which are within ± 4 dB of the site reference
values (or the theoretical NSA values for the NSA method) for both horizontal and vertical polarisation
and for the test volume intended to be occupied by the EUT.
2) The maximum diameter and height of the EUT is equal or less than the test distance divided by 2.
This requirement ensures acceptable uncertainties in EUT emission testing. These include distance
variation to the emission source, antenna directivity and near field effects. The maximum diameter as
a function of 3 test distances is given in Table 2.
Table 2 – Relation between maximum diameter of EUT and test distance
Maximum diameter Test distance
and height of EUT
1,5 m 3,0 m
2,5 m 5,0 m
5,0 m 10,0 m
The uncertainty budget of the site evaluation measurement shall be available.
6 Emission measurement
6.1 Test set up
The same type of antenna shall be used for EUT emission testing as the receive antenna used for room
validation testing. The antenna height is fixed at the geometrical centre height of the test volume. The test
distance is measured from the reference point of the antenna to the boundary of the EUT. In the case of a
difference between the reference point on an antenna and the phase centre, a correction factor, C dB,
R
shall be applied to obtain the field strength at the test distance (see Annex E).
C = 20log[(d + P − R) d]
R f (7)
E-field strength is given by Equation (8)
E = V + AF + C
(8)
f f FS( f ) R
where
= frequency (MHz);
f
d = the required separation from the source to the reference point (m);
= phase centre position as a function of frequency (m from tip of the LPDA);
P
f
R = distance of the LPDA reference point from the antenna tip (m);
= E-field at distance R from source (dBµV/m);
E
f
= voltage at output of antenna at frequency f (dBµV);
V
f
AF = antenna factor (free space) for E-field at the phase centre (dB/m);
FS(f)
C
= phase centre correction factor.
R
The correction factor C is only applicable if the calibration distance is different from the measurement
R
distance.
Figure 3 illustrates a typical test set up.
a
Test volume
b X
EUT volume
80 cm
Antenna X
EUT
box EUT cabling
1)
80 cm
X
A
h d
m
e
Ferrite
c
clamp 2)
Key
A turntable and EUT-support
2X 1,5 m; 2,5 m; 5 m
h middle level of the test volume
m
d 3 m; 5 m or 10 m
a, b, c and e
≥ 0,5 m recommended (≥ 1 is discretionary)
1) The antenna cable layout shall be the same as in the validation procedure
2) Ferrite clamp under consideration
Figure 3 – Typical test set-up in FAR, where a, b, c and e depend on the room performance
– 15 – CLC/TR 50485:2010
The EUT shall be placed on a turntable to enhance the emission testing procedure. The turntable can be
arranged above the floor absorbers. The turntable, antenna mast and any supporting floor material shall
be transparent to electromagnetic waves (relative permittivity, є , as near to one as practicable).
r
6.2 EUT position
The EUT shall be configured, installed, arranged and operated in a manner consistent with typical
applications. Interface cables shall be connected to each type of interface port of the EUT.
If the EUT consists of separate devices the space between the devices shall be in normal configuration
but with 10 cm separation if possible. Interconnecting cables shall be bundled and separated from each
other. The bundle shall be around 30 cm to 40 cm long and longitudinal to the cable.
Ancillary equipment, which is required to exercise the EUT but does not form part of the EUT, shall be
located outside the screened room.
The entire EUT shall fit in the test volume.
To improve the measurement repeatability, the following guidelines shall be taken into account:
1) smaller table-top equipment (including cabling) will be placed in the geometrical centre (horizontally
and vertically) of the calibrated volume (see Figure 4);
2) the bottom of larger table-top equipment (Figure 5) and floor standing equipment will coincide with the
bottom of the test volume.
Figure 4 and Figure 5 illustrate the set up of several types of EUTs in the Fully Anechoic Room. Work is
in progress to decide the appropriate termination condition for cables exiting the volume. Ferrite clamps
are shown here for purposes of illustration.
Test volume
X
EUT volume
80 cm
X
Antenna
EUT
EUT cabling
1) box
80 cm
X A
d
Ferrite
clamp 2)
Key
A turntable and EUT-support
2X 1,5 m; 2,5 m; 5 m
d 3 m; 5 m or 10 m
1) The antenna cable layout shall be the same as in the validation procedure
2) Ferrite clamp under consideration
Figure 4 – Typical test set-up for table top equipment within the test volume of a FAR
Test volume
X
80 cm
EUT
box
X
1)
1)
EUT
X
cabling
80 cm
Pallet
12 cm
d
Ferrite
A
clamp 3)
Key
A turntable and EUT-support
2X 1,5 m; 2,5 m, 5 m
d 3 m; 5 m or 10 m
1) The antenna cable layout shall be the same as in the validation procedure
2) The cable layout depends on the location of the cable outlets and shall be close to the surface of the housing
3) Ferrite clamp under consideration
Pallet of 12 cm (10 cm to 14 cm) is a compromise between metal- and wooden ground (see EN 55022:1998, 8.1.2).
Figure 5 – Typical test set-up for floor standing equipment within the test volume of a FAR
6.3 Cable layout and termination
In EMC testing the reproducibility of measurement results is often poor owing to differences in cable
layout and termination, when one single EUT is measured at various Test-Sites.
The following listed items are general conditions of the test set up in order to provide good reproducibility
(see Figure 4 and Figure 5). Ideally all radiation to be measured should only be emitted from the
evaluated test volume. The cables used during the test shall be in accordance with manufacturers'
specifications. If such specifications are not available, the specifications of the used cables used during
testing shall be clearly described in the test report. Also Annex H can serve as a reference.
1) The cables, that are connected to the EUT and auxiliary equipment or power supply, shall be
arranged with a length of 0,8 m horizontally and 0,8 m vertically (without any bundling) inside the test
volume. Floor standing EUT shall be arranged in the same manner (cable outlet of the EUT at 80 cm
height, as shown in Figure 5). If the manufacturer specifies a shorter length than 1,6 m, then this full
length shall be oriented in horizontal and/or vertical direction within the test volume.
– 17 – CLC/TR 50485:2010
2) Cables, that are not exercised through auxiliary equipment during the test must be appropriately
terminated:
i) coaxial (shielded) cables with coaxial terminator with correct impedance (50 Ω or 75 Ω);
ii) shielded cables with more than one inner wire must have common mode (line to reference
earth/ground) and differential-mode (line to line) termination in accordance with EUT
manufacturers' specifications;
iii) unshielded cables must have differential mode termination in accordance with manufacturers'
specifications.
3) If the EUT needs auxiliary equipment to be operated properly, special care has to be taken that no
emission of that equipment can influence the radiation measurement. Preferably, auxiliary equipment
should be operated outside the Fully Anechoic Room. The measures against RF-leakage into the
FAR through the interconnection cables must be taken.
The test set up including cable layout, specifications of attached cables and termination, ferrite clamps
and other measures taken to suppress emission outside the test volume must be clearly described in the
test report.
Due to the large variety of EUTs a generally valid definition of the cable layout cannot be given in this
Technical Report. Corresponding product standards may require special set up conditions.
7 Test procedure
The test set up, EUT and cable layout and termination shall be in accordance with 6.3.
The EUT shall operate within its intended climatic conditions.
The temperature and relative humidity shall be recorded in the test report.
The normal mode(s) of operation of the EUT shall be used. If necessary all of the modes of operation
shall be examined to record the highest amount of disturbance. All units of the EUT capable of generating
disturbances shall be operating in the mode that gives that highest amount of disturbance.
During the measurement the EUT shall be rotated to find the direction of the maximum field strength. The
direction may vary for different frequencies. Measurements shall be made with both vertically and
horizontally polarised antennas.
The need for measurements at one or more heights at frequencies above 400 MHz for products
exceeding 0,5 m in height should be investigated.
If the reading fluctuates the value shall be observed for at least 15 s at each measured frequency. The
highest reading shall be recorded with the exception of any brief isolated clicks (high reading) that shall
be ignored.
8 Test plan
It is a recommended practice that EMC tests are performed according to an EMC test plan provided by
the laboratory and/or the customer and agreed upon by both parties. Guidance is given in
EN ISO/IEC 17025.
An EMC test plan is a document setting out the specific practices, resources and sequences of activity
relevant to a particular product, service, contract or project.
The configuration, operation and performance of the EUT and auxiliary equipment are essential
information for planning and carrying out EMC tests. Furthermore, the laboratory's and customer's
responsibilities for operating the EUT shall be established before the tests commence.
An EMC test plan may include the following:
1) EUT description;
2) description of peripherals (included in EUT/auxiliary equipment);
3) EUT configuration (hardware and software);
4) EUT operating instructions;
5) test sequence;
6) the customer's role during the tests;
7) criteria for terminating the test.
9 Test report
The following information should be addressed in the test report:
1) environmental conditions in the room (temperature and humidity);
2) a list of instrumentation used including the room;
3) test distance, position and reference point of antenna;
4) a description of the test set up (photo);
5) a description of the EUT, cables (type, length) and auxiliary equipment;
6) operating mode(s) of the EUT.
– 19 – CLC/TR 50485:2010
Annex A
(informative)
Determining the Site Reference
For accurate site validations at distances less than 5 m it is recommended to determine the Site
Reference of the antenna pair (transmit and receive antenna). Therefore, a quasi free space test site is
required. It consists of 2 non-metallic antenna masts which allows the placement of antennas at a certain
height above ground level. Care shall be taken to avoid reflections from the ground. The height (h) above
the ground level of the antennas (centre) shall satisfy Equation (A.1):
h ≥ d ∗ 5 3
(A.1)
where
d is the antenna separation.
This distance shall be equal to the actual distance between the antennas in the room. The antennas are
operated vertically polarised (horizontal polarisation shall not be used because of stronger interference
with the ground-reflected signal). This setup is called "quasi free space test site". It ensures good
approximations of free space (which can never be realized). A quasi free space test setup has a
transmission loss between a receiving and a transmitting antenna in accordance with true free space
transmission loss within ± 1 dB.
CISPR 16-1:1999, 5.13 gives details of the method to evaluate a ground plane site (10 m OATS) using a
pair of calculable dipole antennas. CISPR 16-1:1999, 5.13.5.3.1 sets a tolerance of ± 1 dB for agreement
between the measured transmission loss with the calculated value. The same principles can be used
here.
Care has to be taken that the antenna feed cables do not affect the test result. This is best avoided by
arranging the cable as shown in Figure A.1 and putting ferrite rings around the cable.
ct d cr
transmit receive
antenna
h vertically polarised h
non metallic masts
network analyser
Key
d calibration distance
h height of the antennas above soil
ct, cr coaxial feed cables for transmit and receive antenna ori
...
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