SIST EN IEC 61788-15:2026

SLOVENSKI STANDARD
01-junij-2026
Nadomešča:
SIST EN 61788-15:2012
Superprevodnost - 15. del: Meritve elektronskih karakteristik - Lastna površinska
impedanca superprevodnih plasti pri mikrovalovnih frekvencah (IEC 61788-
15:2026)
Superconductivity - Part 15: Electronic characteristic measurements - Intrinsic surface
impedance of superconductor films at microwave frequencies (IEC 61788-15:2026)
Supraleitfähigkeit - Teil 15: Messungen der elektronischen Charakteristik -
Oberflächenimpedanz von Supraleiterschichten bei Mikrowellenfrequenzen (IEC 61788-
15:2026)
Supraconductivité - Partie 15: Mesures de caractéristiques électroniques - Impédance de
surface intrinsèque de films supraconducteurs aux fréquences micro-ondes (IEC 61788-
15:2026)
Ta slovenski standard je istoveten z: EN IEC 61788-15:2026
ICS:
17.220.20 Merjenje električnih in Measurement of electrical
magnetnih veličin and magnetic quantities
29.050 Superprevodnost in prevodni Superconductivity and
materiali conducting materials
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN IEC 61788-15

NORME EUROPÉENNE
EUROPÄISCHE NORM May 2026
ICS 17.220.20; 29.050 Supersedes EN 61788-15:2011
English Version
Superconductivity - Part 15: Electronic characteristic
measurements - Intrinsic surface impedance of superconductor
films at microwave frequencies
(IEC 61788-15:2026)
Supraconductivité - Partie 15 : Mesurages des Supraleitfähigkeit - Teil 15: Messungen der elektronischen
caractéristiques électroniques - Impédance de surface Charakteristik - Oberflächenimpedanz von
intrinsèque de films supraconducteurs aux fréquences Supraleiterschichten bei Mikrowellenfrequenzen
micro-ondes (IEC 61788-15:2026)
(IEC 61788-15:2026)
This European Standard was approved by CENELEC on 2026-04-27. CENELEC members are bound to comply with the CEN/CENELEC
Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC
Management Centre or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the
same status as the official versions.
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, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Türkiye and the United Kingdom.

European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2026 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 61788-15:2026 E

European foreword
The text of document 90/550/FDIS, future edition 2 of IEC 61788-15, prepared by TC 90
"Superconductivity" was submitted to the IEC-CENELEC parallel vote and approved by CENELEC as
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2027-05-31
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2029-05-31
document have to be withdrawn
This document supersedes EN 61788-15:2011 and all of its amendments and corrigenda (if any).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national committee. A
complete listing of these bodies can be found on the CENELEC website.
Endorsement notice
The text of the International Standard IEC 61788-15:2026 was approved by CENELEC as a European
Standard without any modification.
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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.
NOTE 1  Where an International Publication has been modified by common modifications, indicated by (mod),
the relevant EN/HD applies.
NOTE 2  Up-to-date information on the latest versions of the European Standards listed in this annex is available
here: www.cencenelec.eu.
Publication Year Title EN/HD Year
IEC 60050-815 2024 International Electrotechnical Vocabulary - -
(IEV) – Part 815: Superconductivity

IEC 61788-15 ®
Edition 2.0 2026-03
INTERNATIONAL
STANDARD
Superconductivity -
Part 15: Electronic characteristic measurements - Intrinsic surface impedance of
superconductor films at microwave frequencies
ICS 17.220.20; 29.050 ISBN 978-2-8327-1113-2

IEC 61788-15:2026-03(en)
IEC 61788-15:2026 © IEC 2026
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 8
2 Normative references . 8
3 Terms and definitions . 8
4 Requirements . 9
5 Apparatus . 9
5.1 Measurement equipment . 9
5.2 Measurement apparatus . 10
5.3 Dielectric rods . 15
5.4 Superconductor films and copper cavity . 16
6 Measurement procedure . 16
6.1 Set-up . 16
6.2 Measurement of the reference level . 16
6.3 Measurement of the R of oxygen-free high conductivity copper . 17
S
6.4 Determination of the R of superconductor films and tan δ of standard
Se
dielectric rods . 20
6.5 Determination of the penetration depth . 22
6.6 Determination of the intrinsic surface impedance . 23
7 Uncertainty of the test method . 24
7.1 Measurement of unloaded quality factor . 24
7.2 Measurement of loss tangent . 24
7.3 Temperature . 25
7.4 Specimen and holder support structure . 25
7.5 Uncertainty in the intrinsic surface impedance . 25
8 Test Report . 25
8.1 Identification of test specimen . 25
8.2 Report of the Z values . 26
S
8.3 Report of the test conditions . 26
Annex A (informative) Detailed information relating to Clauses 1 to 8 . 27
A.1 General . 27
A.2 Requirements . 29
A.3 Theory and the measurement procedure for the intrinsic surface impedance . 30
A.3.1 Theoretical relation between the Z and the Z [14] . 30
S Se
A.3.2 Calculation of the geometrical factors [22] . 35
A.3.3 Procedures for determining the Z [14] [22] [23] . 37
S
A.4 Dimensions of the standard sapphire rod . 38
A.5 Dimensions of the closed type resonators . 39
A.6 Test results for type A and type B sapphire resonators . 40
A.6.1 Test results for type A resonator . 40
A.6.2 Test results for type B sapphire resonator . 43
A.7 Uncertainty of the test results . 47
Annex B (informative) Additional information relating to determination of the
penetration depth and the intrinsic surface impedance of superconductor films at
microwave frequencies . 48
IEC 61788-15:2026 © IEC 2026
B.1 General . 48
B.2 Experimental requirements for utilizing Formula (A.43) . 48
B.2.1 Requirements with regard to the temperature . 48
B.2.2 Requirements with regard to the electromagnetic radiation effects . 48
B.2.3 Requirements for suppressing mechanical vibrations of the cryocooler . 50
B.3 Procedures for determining the penetration depth and the intrinsic surface
impedance of YBCO films . 50
Annex C (informative) Standard uncertainty evaluation in the test method for the
intrinsic surface impedance of superconductor films at microwave frequencies . 52
C.1 General . 52
C.2 Assessment of combined uncertainty in the Z from uncertainties in the R
S Se
and λ . 52
C.3 Assessment of combined uncertainty in the Z from the measured complex
S
conductivity . 53
C.4 Results from the round robin test . 54
C.4.1 Uncertainties in the R and f . 54
Se 0
C.4.2 Uncertainty in the λ . 57
C.4.3 Uncertainties in the Z of the YBCO films from the round robin test . 58
S
C.4.4 Effects of uncertainty in temperature on u (R ) from the round robin
r Se
test . 59
Bibliography . 61

Figure 1 – Schematic diagram for the measurement equipment for the intrinsic Z of
S
HTS films at cryogenic temperatures . 11
Figure 2 – Schematic diagram of a dielectric resonator with a switch for thermal
connection . 12
Figure 3 – Typical dielectric resonator with a movable top plate . 13
Figure 4 – Switch block for thermal connection . 14
Figure 5 – Dielectric resonator assembled with a switch block for thermal connection . 15
Figure 6 – A typical resonance peak . 18
Figure 7 – Reflection scattering parameters S and S . 19
11 22
Figure 8 – Definitions for terms in Table 5 . 25
Figure A.1 – Schematic diagram for the measurement system . 28
Figure A.2 – A motion stage using step motors . 29
Figure A.3 – Cross-sectional view of a dielectric resonator . 30
Figure A.4 – A diagram for simplified cross-sectional view of a dielectric resonator . 35
Figure A.5 – Mode chart for type A sapphire resonator with a cavity diameter of 12 mm . 39
Figure A.6 – Frequency response of type A sapphire resonator . 40
Figure A.7 – Q versus temperature for the TE and the TE modes of type A
U 021 012
sapphire resonator with 360 nm-thick YBCO films . 40
Figure A.8 – The resonant frequency f versus temperature for the TE and TE
0 021 012
modes of type A sapphire resonator with 360 nm-thick YBCO films . 41
Figure A.9 – The temperature dependence of the R of YBCO films with the
Se
thicknesses of 70 nm to 360 nm measured at ~ 40 GHz . 41
Figure A.10 – The temperature dependence of ∆λ for the YBCO films with the
e
thicknesses of 70 nm and 360 nm measured at ~ 40 GHz . 42
IEC 61788-15:2026 © IEC 2026
Figure A.11 – The temperature dependence of the penetration depth λ of the 360 nm-
thick YBCO film measured at 10 kHz using the mutual inductance method and at
~ 40 GHz using type A sapphire resonator . 42
Figure A.12 – The temperature dependence of the R of YBCO films with the
S
thicknesses of 70 nm to 360 nm measured at ~ 40 GHz . 43
Figure A.13 – Mode chart used for type B sapphire resonator with a cavity diameter of
15,78 mm. 44
Figure A.14 – Frequency response of type B sapphire resonator . 45
Figure A.15 – The temperature dependence of the R for the 300 nm-thick YBCO
se
films measured at ~ 38 GHz . 45
Figure A.16 – The temperature dependence of ∆λ for the 300 nm-thick YBCO film
e
measured at ~ 38 GHz . 46
Figure A.17 – The temperature dependence of σ for the 300 nm-thick YBCO films
measured at ~ 38 GHz . 46
Figure A.18 – The temperature dependence of the R for the 300 nm-thick YBCO films
S
measured at ~ 38 GHz . 47
Figure B.1 – A comparison between variations in the temperature of the top plate and
the rest of the sapphire resonator over time . 49
Figure B.2 – The temperature dependence of the ratio of Δf to f for type A sapphire
0 0
resonator having YBCO endplates for the gap distances of 0 μm (filled) and 10 μm
(open) . 49
Figure B.3 – The temperature dependence of TE -mode Q of type A sapphire
021 U
resonator for the gap distances of 0 μm (filled) and 10 μm (open) . 50
Figure C.1 – The temperature dependence of the measured TE -mode Q vs.
021 U
temperature data from the round robin test . 55
Figure C.2 – The temperature dependence of the measured resonant frequencies of
the TE mode for the sapphire resonator under the round robin test . 55
Figure C.3 – The temperature dependence of the relative uncertainty in the TE
mode Q and the TE mode Q from the round robin test . 56
U 012 U
Figure C.4 – The temperature dependence of the relative uncertainty in the TE
mode f vs. temperature data from the round robin test . 56
Figure C.5 – Comparison of the temperature dependence of the measured R at
Se
~ 38 GHz for the YBCO films under the round robin test . 57
Figure C.6 – The temperature dependence of the relative uncertainties in the R
Se
(open circle) and R (filled circle) at ~ 38 GHz for the YBCO films under the round
S
robin test . 58
Figure C.7 – The temperature dependence of the relative uncertainties in the TE -
mode Q from the RRT (open circle) and that due to the presumed uncertainty of 0,5 K
U
in the temperature (cross) at ~ 38 GHz for type B sapphire resonator . 60

Table 1 – Typical dimensions of a sapphire rod . 16
Table 2 – Typical dimensions of OFHC cavities and HTS films . 16
Table 3 – Geometrical factors and filling factors calculated for the standard sapphire
resonators . 20
Table 4 – Specifications of Vector Network Analyser . 24
Table 5 – Type B uncertainty for the specifications on the sapphire rod . 24
IEC 61788-15:2026 © IEC 2026
Table C.1 – Values of ε , l, t, β , β , β , λ and coth(t/λ) at 30 K . 53
r4 4 z4 h
Table C.2 – The average values for the R and the R of the YBCO films from the
Se S
round robin test and the relative uncertainties in the R and the R . 59
Se S
IEC 61788-15:2026 © IEC 2026
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
Superconductivity -
Part 15: Electronic characteristic measurements - Intrinsic surface
impedance of superconductor films at microwave frequencies

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
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2) The formal decisions or agreements of 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
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3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
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6) All users should ensure that they have the latest edition of this publication.
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) IEC draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). IEC takes no position concerning the evidence, validity or applicability of any claimed patent rights in
respect thereof. As of the date of publication of this document, IEC had not received notice of (a) patent(s), which
may be required to implement this document. However, implementers are cautioned that this may not represent
the latest information, which may be obtained from the patent database available at https://patents.iec.ch. IEC
shall not be held responsible for identifying any or all such patent rights.
IEC 61788-15 has been prepared by IEC technical committee 90: Superconductivity. It is an
International Standard.
This second edition cancels and replaces the first edition published in 2011. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) informative Annex B, combined relative standard uncertainty in the intrinsic surface
impedance is added;
b) the terms, ‘precision and accuracy’, are replaced with uncertainty;
c) results from a round robin test are added.
IEC 61788-15:2026 © IEC 2026
The text of this International Standard is based on the following documents:
Draft Report on voting
90/550/FDIS 90/556/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
A list of all parts in the IEC 61788 series, published under the general title Superconductivity,
can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
– reconfirmed,
– withdrawn, or
– revised.
IEC 61788-15:2026 © IEC 2026
INTRODUCTION
Since the discovery of high T superconductors (HTS), extensive researches have been
C
performed worldwide on electronic applications and large-scale applications with HTS filter
subsystems based on YBa Cu O (YBCO) having already been commercialized [1] .
2 3 7-δ
Merits of using HTS films for microwave devices such as resonators, filters, antennas, delay
lines, etc., include i) microwave losses from HTS films could be extremely low and ii) no signal
dispersion on transmission lines made of HTS films due to extremely low intrinsic surface
resistance (R ) [2] and frequency-independent penetration depth (λ) of HTS films, respectively.
S
In this regard, when it comes to designing of HTS-based microwave devices, it is important to
measure the intrinsic surface impedance (Z ) of HTS films with Z = R + jX and X = ωμ λ
S S S S S 0
denote the angular frequency and the permeability of vacuum, respectively, X ,
(here ω and μ
0 S
the intrinsic surface reactance, and X = ωμ λ is valid at temperatures not too close to the
S 0
critical temperature T of HTS films).
C
Various reports have been made on measuring the R of HTS films at microwave frequencies
S
with the typical R of HTS films as low as 1/100 to 1/50 of that of oxygen-free high conductivity
S
copper (OFHC) at 77 K and 10 GHz. The R of conventional superconductors such as niobium
S
(Nb) could be easily measured by using Nb cavities by converting the resonator quality factor
of Nb. However, such conventional measurement method could no longer be
(Q) to the R
S
applied to HTS films grown on dielectric substrates, with which it is basically impossible to make
all-HTS cavities. Instead, for measuring the R of HTS films, several other methods have been
S
useful, which include microstrip resonator method [3], coplanar microstrip resonator method [4],
parallel plate resonator method [5] and dielectric resonator method ([6] to [11]). Among the
stated methods, the dielectric resonator method has been very useful due to the fact that the
method enables to measure the microwave surface resistance in a non-invasive way and with
accuracy. In 2002, the International Electrotechnical Commission (IEC) published the dielectric
resonator method as a measurement standard [12].
The test method given in this document enables to measure not only the R but also the X of
S S
HTS films regardless of the film’s thickness by using single sapphire resonator, which differs
from the existing IEC standard (IEC 61788-7) that is limited to measure the surface resistance
of superconductor films having the thicknesses of more than 3λ at the measured temperature
by using two sapphire resonators. In fact, the measured surface resistances of HTS films with
different thicknesses of less than 3λ mean effective values instead of intrinsic values, which
cannot be used for directly comparing the microwave properties of HTS films among one
another [13], [14]. Use of a single sapphire resonator as suggested in this document also
enables to reduce uncertainty in the measured surface resistance that can result from using
two sapphire resonators with sapphire rods of different quality.
The test method given in this document can also be applied to HTS coated conductors, HTS
bulks and other superconductors having established models for the penetration depth.
This document is intended to provide an appropriate and agreeable technical base for the time
being to engineers working in the fields of electronics and superconductivity technology.
The test method covered in this document has been discussed at the VAMAS (Versailles Project
on Advanced Materials and Standards) TWA-16 meeting.

___________
Numbers in square brackets refer to the Bibliography.
IEC 61788-15:2026 © IEC 2026
1 Scope
This part of IEC 61788 describes measurements of the intrinsic surface impedance (Z ) of HTS
S
films at microwave frequencies by a modified two-resonance mode dielectric resonator method
[14], [15]. The object of measurement is to obtain the temperature dependence of the intrinsic
surface impedance, Z , at the resonant frequency f .
S 0
The frequency and thickness range and the measurement resolution for the Z of HTS films are
S
as follows:
– frequency: up to 40 GHz;
– film thickness: greater than 50 nm;
– measurement resolution: 0,01 mΩ at 10 GHz.
It is crucial that the Z data at the measured frequency, and that scaled to 10 GHz be reported
S
for comparison, assuming the f rule for the intrinsic surface resistance, R (f < 40 GHz), and
S
the f rule for the intrinsic surface reactance, X .
S
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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.
IEC 60050-815:2024, International Electrotechnical Vocabulary - Part 815: Superconductivity
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60050-815 and the
following apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
– IEC Electropedia: available at https://www.electropedia.org/
– ISO Online browsing platform: available at https://www.iso.org/obp
3.1
surface impedance
impedance of a metallic material or a superconductor when a high-frequency electromagnetic
wave is constrained to the surface
Note 1 to entry: The surface impedance governs the thermal losses of superconducting RF cavities.
Note 2 to entry: This entry was numbered 815-13-60 in IEC 60050-815:2015.
[SOURCE: IEC 60050-815:2024, 815-22-33]
IEC 61788-15:2026 © IEC 2026
3.2
intrinsic surface impedance
impedance of conductors (or superconductors) having the thicknesses sufficiently greater than
the skin depth (or the penetration depth), with the intrinsic surface impedance Z defined as
S
the ratio of the tangential component of the electric field (E ) and that of the magnetic field (H )
t t
at a conductor or a superconductor surface:
Z =E/=H R+ jX
(1)
S tt S S
3.3
effective surface impedance
impedance of conductors (or superconductors) having the thicknesses not sufficiently greater
than the skin depth (or the penetration depth) as defined by
Z E / H R + jX
(2)
Se t t Se Se
with Z being significantly different from Z in Formula (1).
Se S
4 Requirements
The Z of HTS films shall be measured by applying a microwave signal to a dielectric resonator
S
with the superconductor specimen and then measuring the attenuation of the resonator at each
frequency. The frequency shall be swept around the resonant frequency as the centre, and the
attenuation – frequency characteristics as well as the scattering parameters shall be recorded
to obtain the Q-value, which corresponds to the loss.
The target relative uncertainty of this method is less than 20 % at temperatures of 30 K to 60 K.
It is the responsibility of the user of this document to consult and establish safety and health
practices and to determine the applicability of regulatory limitations prior to use.
Hazards exist in this type of measurement. The use of a cryogenic system is essential to cool
the superconductors to allow transition into the superconducting state. Direct contact of skin
with cold apparatus components can cause immediate freezing, as can direct contact with a
spilled cryogen. The use of an r.f.-generator is also essential to measure high-frequency
properties of materials. If its power is too high, direct exposure to human bodies can cause an
immediate burn.
5 Apparatus
5.1 Measurement equipment
Figure 1 shows a schematic diagram of the equipment required for the microwave measurement.
The equipment consists of a network analyser system for transmission measurements, a
measurement apparatus, and thermometers for monitoring the temperature of HTS films under
test.
An incident power generated from a suitable microwave source such as a synthesized sweeper
is applied to the dielectric resonator fixed in the measurement apparatus. The transmission
characteristics are shown on the display of the network analyser.
= =
IEC 61788-15:2026 © IEC 2026
The measurement apparatus is fixed in a temperature-controlled cryostat. The cryostat consists
of a vacuum chamber and a cryocooler, the cold finger of which the measurement apparatus is
connected to. For the penetration depth measurements, vibrations from the cryocooler should
be dampened by using dampers between the vacuum chamber and the cryocooler. During
collection of resonance data as a function of temperature, the resonance signal should remain
stable at each temperature.
For measuring the Z of HTS films, a vector network analyser is recommended because it has
S
better measurement accuracy than a scalar network analyser due to its wider dynamic range.
5.2 Measurement apparatus
Figure 2 shows a schematic diagram of a typical measurement apparatus for the Z of HTS
S
films deposited on a substrate with a flat surface. The lower HTS film is pressed down (by the
copper cavity) against a spring, which is made of beryllium copper. Use of a plate type spring
is recommended for the improvement of measurement uncertainty. This type of spring reduces
the friction between the spring and the other part of the apparatus and enables smooth motion
of HTS films in the course of thermal expansion/contraction of the dielectric-loaded cavity. The
upper HTS film is glued to the Cu plate at the top using adhesives with good thermal conductivity.
The R is measured with the upper HTS film being in contact with the top of the Cu cavity.
Se
During measurements of the R , the whole resonator is first cooled down to the lowest
Se
temperature with the cryocooler turned on and then warmed up to higher temperatures with the
cryocooler turned off. Meanwhile, the X is measured with a small gap between the upper HTS
Se
film and the top of the Cu cavity. The gap distance shall be set to a value predetermined at the
room temperature by using either a micrometre or a step motor connected to the upper
superconductor film through a polytetrafluoroethylene rod. The real gap distances would be a
little longer at cryogenic temperatures than the corresponding predetermined ones due to
thermal contraction of the polytetrafluoroethylene rod. The gap distance should be small enough
not to cause significant radiation loss and large enough to enable control of the temperature of
the upper superconductor film. More detailed descriptions on a dielectric resonator with a
movable top plate are given in Figure 3, with Figure 4 and Figure 5 displaying a switch block
for thermal connection and the dielectric resonator assembled with the switch block,
respectively. Procedures for controlling the temperature of the upper HTS film for
measurements of the X are described in 6.6.
S
Each of the two semi-rigid cables shall have a small loop at the end as shown in Figure 3. The
loop, shaped like a semicircle, is affixed to the cross-sectional part of the outer conductor via
soldering at its terminal point. The plane of the loop shall be set parallel to that of the HTS films
in order to suppress the unwanted TM modes. The coupling loops shall be carefully checked
mn0
prior to the measurements to keep the good coupling conditions. For measuring the Q values
as a function of temperature, these cables can be moved to the right or to the left to maintain
the insertion attenuation (IA) slightly higher than 20 dB at the lowest temperature, with the
vertical position of each loop fixed in the middle of the sapphire rod. The distance between the
loop and the sapphire rod should be adjusted to a smaller value if the resonant signal gets too
noisy at higher temperatures. In this adjustment, coupling of unwanted cavity modes to the
interested dielectric resonance mode shall be suppressed. Unwanted, parasitic coupling to the
other modes not only reduces the high-Q value of the TE mode resonator but also increases
uncertainty in the measured resonant frequency of the TE mode resonator, making it difficult to
measure changes in the resonant frequency vs. temperature data with accuracy. For collecting
the temperature dependence of the resonant frequency data, the distance between the loop
and the sapphire rod should not be changed during measurements. In this case, IA at the lowest
temperature can be lower than 20 dB.
IEC 61788-15:2026 © IEC 2026
For suppressing the parasitic coupling, dielectric resonators shall be designed in such a way
that the frequencies of the resonance modes of interest are well separated from those of nearby
parasitic modes. The dielectric rod should be fixed at the centre of the bottom superconductor
film by using low-loss glue. A small drop of glue applied to the surface of the bottom
superconductor is enough to attach the film to the dielectric rod. It is noted that effects of glue
on the measured Q-value should be negligible.

Figure 1 – Schematic diagram for the measurement equipment for the intrinsic Z of
S
HTS films at cryogenic temperatures
IEC 61788-15:2026 © IEC 2026
Key
1 polytetrafluoroethylene rod
2 Cu plate
3 superconductor (or metal) film
4 Cu wire
5 switch for thermal connection
6 Cu plate
7 superconductor (or metal) film
8 Be-Cu spring
9 cold finger
10 Cu cavity
11 dielectric rod
12 temperature sensor
Figure 2 – Schematic diagram of a dielectric resonator
with a switch for thermal connection
IEC 61788-15:2026 © IEC 2026
Key
1 acryl plate 6 dielectric rod 11 screw
2 z-axis stage 7 superconductor film 12 superconductor film
3 polytetrafluoroethylene screw 8 Cu plate 13 Cu plate
4 connector 9 Be-Cu spring 14 semi-rigid coaxial cable
5 screw 10 Cu plate
Figure 3 – Typical dielectric resonator with a movable top plate
IEC 61788-15:2026 © IEC 2026
Key
1 stainless steel rod
2 micrometre
3 Cu block
4 sliding guide
5 polytetrafluoroethylene plate
Figure 4 – Switch block for thermal connection
IEC 61788-15:2026 © IEC 2026
Key
1 screw 6 Cu braid 11 Cu block
2 Cu block 7 Cu plate 12 spring
3 Cu braid 8 screw 13 Cu cavity block
4 thermal switch block 9 Cu braid 14 Cu block
5 Cu block 10 screw 15 screw
Figure 5 – Dielectric resonator assembled with a switch block for thermal connection
5.3 Dielectric rods
Dielectric resonators shall be designed in such a way that the TE and the TE modes
021 012
appeared next to each other without being coupled to the other TM or HE modes. Furthermore,
the resonant frequencies of the two modes shall be close enough for reducing the measurement
uncertainty in Z and far enough not to cause any coupling between them. The difference
S
between the resonant frequencies of the TE and the TE modes shall be less than 400 MHz,
021 012
a value corresponding to ~ 1 % of each resonant frequency.
The dielectric rods shall have low tan δ and low temperature variation of the dielectric constants
to achieve the requisite measurement accuracy in R and X , respectively. In this regard, c-cut
S S
sapphire rods are recommended for measuring the Z with accuracy (the relative permittivity
S
along the a-b plane ε ’ = 9,28 at 77 K for sapphire).
a-b
IEC 61788-15:2026 © IEC 2026
Designing schemes for the standard sapphire rod are described in Annex A.4 and A.5. Table 1
shows typical dimensions of the standard sapphire rod used for type A 40 GHz TE -mode
sapphire resonator and type B 38 GHz TE -mode sapphire resonator, respectively. The
resonant frequencies become lower if the dimensions are greater, for which, however, larger
HTS films are to be used to maintain the requisite measurement uncertainty. The resonant
-mode for type A and type B resonators are provided in Table 1, which
frequencies of the TE
are used during test to see if the respective resonators are installed correctly.
Table 1 – Typical dimensions of a sapphire rod
(Unit: GHz)
Resonator diameter height TE -mode TE -mode TE -mode frequency
011 012 021
type
frequency frequency
(mm) (mm) (GHz) (GHz) (GHz)
A 5,00 2,86 25,27 40,06 39,97
B 5,26 2,99 24,10 38,23 38,05
5.4 Superconductor films and copper cavity
Oxygen-free high conductivity copper (OFHC) shall be used for the surrounding wall of the
dielectric resonator. The diameter of the OFHC cavity shall be determined in such a way that
the requisite measurement
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