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TECHNICAL IEC
REPORT
TR 62064
First edition
1999-07
Radio-frequency cables –
Relationship between surface transfer
impedance and screening attenuation
(A background to the recommended limits
contained in IEC 61196-1, clause 14)
Câblages pour fréquences radioélectriques –
Relation entre l'impédance de transfert en surface
et l'affaiblissement d'écran
Reference number
IEC/TR 62064:1999(E)
Numbering
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•
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Terminology, graphical and letter symbols
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used in electrical technology, IEC 60417: Graphical symbols for use on equipment.
Index, survey and compilation of the single sheets and IEC 60617: Graphical symbols
for diagrams.
* See web site address on title page.
TECHNICAL IEC
REPORT
TR 62064
First edition
1999-07
Radio-frequency cables –
Relationship between surface transfer
impedance and screening attenuation
(A background to the recommended limits
contained in IEC 61196-1, clause 14)
Câblages pour fréquences radioélectriques –
Relation entre l'impédance de transfert en surface
et l'affaiblissement d'écran
IEC 1999 Copyright - all rights reserved
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mechanical, including photocopying and microfilm, without permission in writing from the publisher.
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Telefax: +41 22 919 0300 e-mail: [email protected] IEC web site http://
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International Electrotechnical Commission
For price, see current catalogue
– 2 – TR 62064 © IEC:1999(E)
CONTENTS
Page
FOREWORD . 3
Clause
1 Scope . 4
2 General. 4
3 Correlation between measured screening attenuation a and measured surface transfer
s
impedances at 30 MHz and 300 MHz. 6
4 Recommended limits for surface transfer impedance and screening attenuation . 6
5 Reference documents . 14
TR 62064 © IEC:1999(E) – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
___________
RADIO-FREQUENCY CABLES – RELATIONSHIP BETWEEN SURFACE
TRANSFER IMPEDANCE AND SCREENING ATTENUATION
(A background to the recommended limits contained
in IEC 61196-1, clause 14)
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 reports, technical specifications 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 technical report may be the subject of
patent rights. The IEC shall not be held responsible for identifying any or all such patent rights.
The main task of IEC technical committees is to prepare International Standards. However, a
technical committee may propose the publication of a technical report when it has collected
data of a different kind from that which is normally published as an International Standard, for
example "state of the art".
Technical reports do not necessarily have to be reviewed until the data they provide are
considered to be no longer valid or useful by the maintenance team.
IEC 62064, which is a technical report, 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.
The text of this technical report is based on the following documents:
Enquiry draft Report on voting
46A/330/CDV 46A/348/RVC
Full information on the voting for the approval of this technical report 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.
This document which is purely informative is not to be regarded as an International Standard.
A bilingual version of this technical report may be issued at a later date.
– 4 – TR 62064 © IEC:1999(E)
RADIO-FREQUENCY CABLES – RELATIONSHIP BETWEEN SURFACE
TRANSFER IMPEDANCE AND SCREENING ATTENUATION
(A background to the recommended limits contained
in IEC 61196-1, clause 14)
1 Scope
This technical report describes the valuable background material used during the revision of
IEC 61196-1, clause 14, guidance for surface transfer impedance and screening attenuation
limits for flexible r.f. cables.
In this report the relationship between surface transfer impedance (Z ) and screening
T
attenuation (a ) is given, also measurements of Z and a are provided to show the correlation
s T s
of mean scanning attenuation between 200 MHz and 500 MHz and Z at both 30 MHz and
T
300 MHz.
The sensitivity of a and the relative velocity difference between the inner and outer system is
s
shown, also the need for the cable data sheet to show the a values in a standardized form –
s
Δv/v = 10 % and the characteristic impedance of the outer system is 150 Ω. It is also shown
that a relative velocity difference change from 10 % to 40 % gives an improvement of 12 dB in
screening attenuation.
2 General
At high frequencies when the surface transfer impedance Z and effective transfer
T
impedance Z = Z ±Z , and increases 6 dB per octave, its relation to the screening
TE F T
n, f
attenuation a is frequency independent and can be written as (see also figure 1):
s
a = −20 × log T (1)
n
s 10
n
f
f
Z Z c
T T o
= −20 × log = −20 × log (2)
10 10
l l
Z Z ω ε ± ε
1 2 r2 r1
Z Z ω ±
1 2
v v
2 1
U / Z
2n
f
and T =
n
f
U / Z
1 1
where
l is the length of the cable under test;
T are the coupling transfer functions;
n,f
‘n’ for the near end and ‘f’ for the far end;
Z is the characteristic impedance of the cable;
Z is the impedance of the outer circuit;
ε is the cable dielectric permittivity;
r1
ε is the permittivity of the outer circuit;
r2
c is the velocity of light in vacuum;
o
v is the propagation velocity of the inner circuit;
TR 62064 © IEC:1999(E) – 5 –
v is the propagation velocity of the outer circuit;
Z is the capacitive coupling impedance;
F
Z is the surface transfer impedance;
T
Z is the effective transfer impedance.
TE
n, f
l
+
E
Z
Z 2
U
2f
U
2n
Z
U Z
(2) 1f
U
1n
D
(1) 1
Z
v
Z
v
2 2
IEC 884/99
(1) The inner circuit, cable under test.
(2) The outer circuit, formed by test line or cylinder or the outer environment as in the absorbing clamp method.
Figure 1 – Concept of screening measurement set-ups
When the capacitive coupling impedance Z is present (spaces in the outer conductor), Z
F T
shall be substituted by Z .
TE
"+" sign is for the near end and "–" sign for the far end. Z and Z are the impedances of the
1 2
inner and outer system and v and v the corresponding velocities.
1 2
Screening attenuation a is a reliable measure of screening efficiency when the frequency is
s
constant. This is true when Z or Z increases 6 dB/octave a
...