SIST EN 61726:2004
(Main)Cable assemblies, cables, connectors and passive microwave components - Screening attenuation measurement by the reverberation chamber method
Cable assemblies, cables, connectors and passive microwave components - Screening attenuation measurement by the reverberation chamber method
Describes the measurement of screening attenuation by the reverberation, or stirred, chamber, suitable for virtually any type of microwave component and having no theoretical upper frequency limit. It is only limited toward low frequencies due to the size of the test equipment, which is frequency dependent and is only one of several methods of measuring sreening attenuation. For the purpose of this standard, examples of microwave components are waveguides, phase shifters, diplexers/multiplexers, power dividers/combiners, etc.
Konfektionierte Kabel, Kabel, Steckverbinder und passive Mikrowellenbauteile - Messung der Schirmdämpfung mit dem Strahlungskammerverfahren
Câbles, cordons, connecteurs et composants hyperfréquence passifs - Mesure de l'atténuation d'écran par la méthode de la chambre réverbérante
Describes the measurement of screening attenuation by the reverberation, or stirred, chamber, suitable for virtually any type of microwave component and having no theoretical upper frequency limit. It is only limited toward low frequencies due to the size of the test equipment, which is frequency dependent and is only one of several methods of measuring sreening attenuation. For the purpose of this standard, examples of microwave components are waveguides, phase shifters, diplexers/multiplexers, power dividers/combiners, etc.
Cable assemblies, cables, connectors and passive microwave components - Screening attenuation measurement by the reverberation chamber method (IEC 61726:1999)
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SLOVENSKI SIST EN 61726:2004
STANDARD
april 2004
Cable assemblies, cables, connectors and passive microwave components -
Screening attenuation measurement by the reverberation chamber method (IEC
61726:1999)
ICS 33.120.10; 33.120.30 Referenčna številka
SIST EN 61726:2004(en)
© Standard je založil in izdal Slovenski inštitut za standardizacijo. Razmnoževanje ali kopiranje celote ali delov tega dokumenta ni dovoljeno
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NORME CEI
INTERNATIONALE IEC
61726
INTERNATIONAL
Deuxième édition
STANDARD
Second edition
1999-11
Câbles, cordons, connecteurs
et composants hyperfréquence passifs –
Mesure de l'atténuation d'écran
par la méthode de la chambre réverbérante
Cable assemblies, cables, connectors and
passive microwave components –
Screening attenuation measurement by the
reverberation chamber method
© IEC 2001 Droits de reproduction réservés ⎯ Copyright - all rights reserved
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microfilms, sans l'accord écrit de l'éditeur. writing from the publisher.
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CODE PRIX
Commission Electrotechnique Internationale
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PRICE CODE
International Electrotechnical Commission
Pour prix, voir catalogue en vigueur
For price, see current catalogue
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61726 © IEC:2001 – 3 –
CONTENTS
Page
FOREWORD . 5
INTRODUCTION .9
Clause
1 Scope . 11
2 Basic description of the reverberation chamber method . 11
3 Measurement of the screening attenuation of the device under test (DUT) . 13
4 Description of the test set-up. 13
4.1 Reverberation chamber . 13
4.2 Mode stirrer . 13
4.3 Antennas . 13
4.4 Test equipment . 15
4.5 Device under test (DUT). 17
4.6 Linking devices . 17
5 Measurement procedure. 19
5.1 General. 19
5.2 Measurement of the DUT . 19
5.3 Measurement of the insertion loss of the cavity. 19
5.4 Control of the test set-up. 21
5.5 Revolution speed of the mode stirrer . 23
5.6 Test frequencies . 23
5.7 Voltage standing wave ratio (VSWR) . 23
6 Evaluation of the test results . 23
6.1 Screening attenuation . 23
6.2 Relationship between transfer impedance parameters and screening attenuation. 25
6.3 Electromagnetic field surrounding the DUT . 27
Annex A (informative) Design of the reverberation chamber . 29
Annex B (informative) Design of the mode stirrer . 31
Annex C (informative) Example of a calibrator. 35
Annex D (informative) Relationship between transfer impedance and screening attenuation. 39
Bibliography . 43
Figure 1 – Example of a test set-up . 15
Figure B.1 – Construction diagram for mode-stirrer . 33
Figure B.2 – Details of collet for mounting tuner shaft to drive motor through the
wall of the test chamber.33
Figure C.1 – Basic construction details . 35
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61726 © IEC:2001 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
CABLE ASSEMBLIES, CABLES, CONNECTORS AND
PASSIVE MICROWAVE COMPONENTS –
SCREENING ATTENUATION MEASUREMENT BY THE
REVERBERATION CHAMBER METHOD
FOREWORD
1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of the IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, the IEC publishes International Standards. Their preparation is
entrusted to technical committees; any IEC National Committee interested in the subject dealt with may
participate in this preparatory work. International, governmental and non-governmental organizations liaising
with the IEC also participate in this preparation. The IEC collaborates closely with the International Organization
for Standardization (ISO) in accordance with conditions determined by agreement between the two
organizations.
2) The formal decisions or agreements of the IEC on technical matters express, as nearly as possible, an
international consensus of opinion on the relevant subjects since each technical committee has representation
from all interested National Committees.
3) The documents produced have the form of recommendations for international use and are published in the form
of standards, technical specifications, technical reports or guides and they are accepted by the National
Committees in that sense.
4) In order to promote international unification, IEC National Committees undertake to apply IEC International
Standards transparently to the maximum extent possible in their national and regional standards. Any
divergence between the IEC Standard and the corresponding national or regional standard shall be clearly
indicated in the latter.
5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with one of its standards.
6) Attention is drawn to the possibility that some of the elements of this International Standard may be the subject
of patent rights. The IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61726 has been prepared by subcommittee 46A: Coaxial cables, of
IEC technical committee 46: Cables, wires, waveguides, r.f. connectors, and accessories for
communication and signalling.
This second edition cancels and replaces the first edition, which was issued as a type 3
technical report in 1995. It constitutes a technical revision and now has the status of an
International Standard.
This bilingual version (2001) replaces the English version.
The text of this standard is based on the following documents:
FDIS Report on voting
46A/356/FDIS 46A/359/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 3.
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61726 © IEC:2001 – 7 –
Annexes A, B, C and D are for information only.
The committee has decided that the contents of this publication will remain unchanged
until 2005. At this date, the publication will be
reconfirmed;
withdrawn;
replaced by a revised edition, or
amended.
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61726 © IEC:2001 – 9 –
INTRODUCTION
The requirements of modern electronic equipment have indicated a demand for a method of
testing screening attenuation of microwave components over their whole frequency range.
Convenient test methods exist for low frequencies and components of regular shape and these
test methods are described in the relevant IEC product specifications.
For higher frequencies and for components of irregular shape a new test method has become
necessary and such a test method is described in this International Standard.
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61726 © IEC:2001 – 11 –
CABLE ASSEMBLIES, CABLES, CONNECTORS AND
PASSIVE MICROWAVE COMPONENTS –
SCREENING ATTENUATION MEASUREMENT BY THE
REVERBERATION CHAMBER METHOD
1 Scope
This International Standard describes the measurement of screening attenuation by the
reverberation chamber test method, sometimes named mode stirred chamber, suitable for
virtually any type of microwave component and having no theoretical upper frequency limit. It is
only limited toward low frequencies due to the size of the test equipment, which is frequency
dependent and is only one of several methods of measuring screening attenuation.
For the purpose of this standard, examples of microwave components are waveguides, phase
shifters, diplexers/multiplexers, power dividers/combiners etc.
2 Basic description of the reverberation chamber method
The reverberation chamber method for measurement of the screening attenuation of
microwave components consists of exposing the device under test (DUT) to an almost
homogeneous and isotropic electromagnetic field and then measuring the signal level induced
into the device.
These conditions are achieved by the use of a shielded enclosure, which acts as an oversized
cavity (in terms of wavelength), with a high quality factor. Its boundary conditions are
continuously agitated by a rotating reflective surface (mode stirrer), mounted within the
chamber, which enables the field to approach homogeneous and isotropic conditions during
one revolution.
Electromagnetic power is fed to the chamber by means of an input or transmitting antenna.
The strength of the field inside the chamber is measured through a reference antenna. The
ratio of the injected power (input antenna) to the received power (reference antenna) is the
insertion loss of the cavity. The insertion loss is strongly frequency dependent and is also
dependent on the quality factor of the cavity.
It has been shown that, due to the isotropic field, any antenna placed inside the cavity behaves
1)
as if its gain was unity [1] , therefore no directional effect is to be expected. If the device
under test is electrically short, its screening attenuation will be directly related to usual transfer
parameters (Z and Z). If the device under test is not electrically short the screening
t f
attenuation may still be related to Z and Z in some simple cases (evenly distributed leakage,
t f
periodically distributed leakage) using summing functions derived from antenna network theory.
___________
1)
Figures in square brackets refer to the Bibliography.
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61726 © IEC:2001 – 13 –
3 Measurement of the screening attenuation of the device under test (DUT)
The measurement of screening attenuation is based on the comparison of the electromagnetic
field power outside the DUT to the electromagnetic field power induced into the DUT. The
screening attenuation is then defined as:
⎛ P ⎞
DUT
⎜ ⎟
a = −10 log (1)
s 10
⎜ ⎟
P
⎝ REF ⎠
or
⎛ ⎞
P
DUT
a = −10 log ⎜ ⎟ − ∆ (2)
s 10 ins
⎜ ⎟
P
⎝ INJ ⎠
where
P is the power coupled to the device under test (W);
DUT
P is the power coupled to the reference antenna (W);
REF
P is the power injected into the chamber (W);
INJ
∆ is the insertion loss of the chamber in decibels (dB).
ins
4 Description of the test set-up
4.1 Reverberation chamber
The reverberation chamber is a shielded enclosure having any shape, provided that its smallest
dimension exceeds three wavelengths at the lowest test frequency. A perfect cubic shape
should be avoided for optimum performance at lower frequencies. It shall be made of
conductive materials (copper, aluminium or steel) and shall not contain lossy materials.
The upper frequency limit depends only on the screening attenuation, which shall exceed 60 dB
for the whole frequency range. However, this value is not critical if the spectrum analyzer and
the connecting devices of the test set-up are sufficiently screened and if the quality factor of
the cavity remains sufficiently high. The quality factor shall be checked to verify that during one
revolution of the mode stirrer the ratio between the maximum and the minimum power at the
output of the reference antenna exceeds 20 dB. As a minimum, the test chamber and the test
instrumentation shall have a combined screening attenuation at each test frequency that is
10 dB greater than the screening requirement of the DUT.
The shielded enclosure is drilled with four coaxial feed-throughs: two for the output of the
antennas and two for the output of the measuring loop. For further details see annex A.
4.2 Mode stirrer
The mode stirrer shall be large with respect to wavelength and be bent at angles to the walls of
the chamber. The mode stirrer shall be at least two wavelengths from tip to tip at the lowest
test frequency. An example of a mode stirrer is described in annex B.
4.3 Antennas
The reverberation chamber is equipped with input and reference antennas. Both antennas shall
present limited resonances in the frequency range and shall not introduce losses; their return
loss shall be better than 6 dB.
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61726 © IEC:2001 – 15 –
For convenience, the same antenna should be kept for the whole frequency range. However,
strongly polarized and directional antennas may disturb measurements due to lack of isotropic
field state. This may be checked by modifying the location and orientation of the antennas. It
should have no noticeable effect on the insertion loss of the cavity.
A wire antenna can be used between 10 GHz and 20 GHz. Its length shall be greater than five
wavelengths at the lowest test frequency. It shall be matched at both ends in order to avoid
resonances. It shall travel along two sides of the chamber, at such a distance that its input
impedance remains superior to 300 Ω. To avoid direct coupling between antennas, they shall
neither be installed on the same panels nor be at the same level and orientation.
Horn antennas may also be used, especially for higher frequencies, provided that direct path
coupling between antennas is avoided. If horns are used, they should be placed in different
corners of the chamber and located so that they face into the corner.
4.4 Test equipment
The essential test equipment and components required for an automated screening attenuation
measurement are shown in figure 1. Preamplifiers, amplifiers and other control equipment may
also be included in order to improve performance.
The generator and the spectrum analyzer shall have a common, highly stable frequency
reference.
Reverberation chambre
P
INJ
Input
antenna
Mode-
Stepper
stirrer
motor
P
DU
Frequency
Spectrum
synthesizer
analyzer
Reference
antenna
P
REF
Insertion loss measurement
(calibration) otherwise 50 Ω load
Motor
Computer
control
IEC 108/01
Figure 1 – Example of a test set-up
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61726 © IEC:2001 – 17 –
4.5 Device under test (DUT)
To avoid resonances, the DUT is inserted into a loop (made of semi-rigid coaxial cable) having
a length of more than four wavelengths at minimum frequency. The other ports of the DUT
should be terminated with matched loads having a screening attenuation at least 10 dB better
than the DUT. The assembly is then placed inside the chamber in any orientation and location,
the coupling zone being at a minimum distance from the chamber panels of one wavelength at
lower frequency. If the DUT is a cable, it shall be ensured that the connectors used are those
recommended for the particular type of cable, in order to minimize interface losses. If the cable
is to be used in a bent form, than it shall be tested as such within the limitations imposed by a
relevant standard or the manufacturer.
Both ends of the loop are connected to the outputs from the chamber. One end is terminated
with a matched load and the other end is connected to the spectrum analyzer. It is also
acceptable to terminate the DUT inside the chamber, in which case, the second leg of the loop
shall be replaced by a single wire, one end being electrically linked to the DUT, the other end to
a panel of the chamber.
For the purpose of this method of measurement, waveguides and waveguide accessories
(WUT) are not coaxial devices. Therefore, they require to be connected to the appropriate
waveguide to coaxial transition(s) in order to be tested in the reverberation chamber.
The measurement of the dynamic range, insertion loss and coaxial calibrator shall be carried
out with the waveguide to coaxial transition assembled in the test circuit in the same manner as
for the testing of the WUT.
The design of the waveguide to coaxial transitions shall be such that their input and output
return loss shall be better than 15 dB. Their design shall ensure that when they are assembled
into the test circuit, with a highly screened waveguide in place of the WUT, the total screening
effectiveness (dynamic range) shall be at least 10 dB better than the specification for the WUT.
4.6 Linking devices
Linking devices are normally 50 Ω coaxial lines having a screening attenuation at least 10 dB
better than the DUT. Depending on practical considerations, semi-rigid or semi-flexible cables
may be used.
All linking lines shall be characterized for attenuation at all test frequencies prior to starting the
test (attenuators, cable assemblies, etc.).
Equation (2) shall be corrected, taking into account the insertion losses of linking devices:
⎛ P ⎞
DUT
a = −10log ⎜ ⎟ −− X (3)
s 10 ins L
⎜ ⎟
P
⎝ INJ ⎠
where X is the insertion loss of all linking devices inside or outside the chamber and is
L
expressed in decibels (dB).
These corrections may be included as part of the test programme for an automated test
system. They shall be checked periodically and, at least, during calibration of the test system.
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61726 © IEC:2001 – 19 –
5 Measurement procedure
5.1 General
Different approaches are acceptable depending on the performance of the equipment:
– discrete tuning (step positioning of the mode stirrer);
– continuous tuning (constant rotation of the stirrer);
– peak power acquisition on one revolution of the mode stirrer;
– averaged power calculation on one rotation of the mode stirrer.
When deciding on a measurement procedure it shall be recognized that:
– discrete tuning is slow and requires a large number of sample measurements to be taken
per revolution of the mode stirrer (200 is a usual value up to 20 GHz). This does, however,
result in the acq
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