1、 I n t e r n a t i o n a l T e l e c o m m u n i c a t i o n U n i o n ITU-T Series K TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU Supplement 6 (10/2016) SERIES K: PROTECTION AGAINST INTERFERENCE ITU-T K.115 Measuring shielding effectiveness using normalized site attenuation in free space ITU-T K
2、-series Recommendations Supplement 6 K series Supplement 6 (10/2016) i Supplement 6 to ITU-T K-series Recommendations ITU-T K.115 Measuring shielding effectiveness using normalized site attenuation in free space Summary When estimating the effectiveness of the countermeasures described in Recommenda
3、tion ITU-T K.115 against high altitude electromagnetic pulse (HEMP) or high power electromagnetic (HPEM) attacks, the actual shielding effectiveness of buildings or structures must be taken into account. The methods for measuring shielding effectiveness are defined by IEEE Std. 299 as the transmissi
4、on loss method or IEC 61587-3 as the insertion loss method. These methods need to use the reference value measurements that are the standards for calculating shielding effectiveness. However, the in-situ measurement of reference values is affected by surrounding structures such as walls, floors, cei
5、lings, and so on. Therefore, the measured shielding effectiveness may be overestimated or underestimated when the affected references are used. Also, the measurements are very time consuming because measurements both with and without shielding are needed, and so in-situ measurements need specific kn
6、ow-how and techniques for reproducibility. In order to solve these problems, improve reproducibility and reduce measurement time, this supplement introduces a measurement method for shielding effectiveness using normalized site attenuation (NSA) in free space. Because the NSA method obtains the refe
7、rence values by calculation, it is possible to measure the shielding effectiveness continuously at any frequency, unlike the present situation where the reference values are unobtainable by conventional methods due to the effects of reflecting objects. An example of measurement using this method is
8、given in this supplement. History Edition Recommendation Approval Study Group Unique ID* 1.0 ITU-T K Suppl. 6 2016-10-14 5 11.1002/1000/13141 Keywords Electromagnetic security, high altitude electromagnetic pulse (HEMP), high power electromagnetic (HPEM), intentional electromagnetic interference, no
9、rmalized site attenuation, shielding effectiveness. * To access the Recommendation, type the URL http:/handle.itu.int/ in the address field of your web browser, followed by the Recommendations unique ID. For example, http:/handle.itu.int/11.1002/1000/11830-en. ii K series Supplement 6 (10/2016) FORE
10、WORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying
11、 technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups w
12、hich, in turn, produce Recommendations on these topics. The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with ISO a
13、nd IEC. NOTE In this publication, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. Compliance with this publication is voluntary. However, the publication may contain certain mandatory provisions (to ensure
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17、uired to implement this publication. However, implementers are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database at http:/www.itu.int/ITU-T/ipr/. ITU 2017 All rights reserved. No part of this publication may be reproduced
18、, by any means whatsoever, without the prior written permission of ITU. K series Supplement 6 (10/2016) iii Table of Contents Page 1 Scope . 1 2 References . 1 3 Definitions 1 3.1 Terms defined elsewhere 1 3.2 Terms defined in this Supplement 1 4 Abbreviations and acronyms 1 5 Conventions 2 6 Shield
19、ing effectiveness using NSA in free space . 2 6.1 Calculating shielding effectiveness using NSA (NSA method) . 2 6.2 Measurement example 3 K series Supplement 6 (10/2016) 1 Supplement 6 to ITU-T K-series Recommendations ITU-T K.115 Measuring shielding effectiveness using normalized site attenuation
20、in free space 1 Scope This document is a supplement to ITU-T K.115, dealing with the measurement of shielding effectiveness that also considers the mitigation of intentional high altitude electromagnetic pulse (HEMP) or high power electromagnetic (HPEM) attacks. Also, this Supplement can provide an
21、alternative measurement method when the application of IEEE 299 or IEC 61587-3 is difficult. 2 References ITU-T K.34 Recommendation ITU-T K.34 (2003), Classification of electromagnetic environmental conditions for telecommunication equipment Basic EMC Recommendation. ITU-T K.115 Recommendation ITU-T
22、 K.115 (2015), Mitigation methods against electromagnetic security threats. CISPR 16-1-4 CISPR 16-1-4 (2010), Specification for radio disturbance and immunity measuring apparatus and methods Part 1-4: Radio disturbance and immunity measuring apparatus Antennas and test sites for radiated disturbance
23、 measurements. IEC 61587 IEC 61587-3 (2013), Mechanical structures for electronic equipment Tests for IEC 60917 and IEC 60297 Part 3: Electromagnetic shielding performance tests for cabinets and subracks. IEEE 299 IEEE 299-2006, IEEE Standard Method for Measuring the Effectiveness of Electromagnetic
24、 Shielding Enclosures. 3 Definitions 3.1 Terms defined elsewhere This Supplement uses the following term defined elsewhere: 3.1.1 shielding effectiveness ITU-T K.34: For a given external source, the ratio (usually expressed in dB) of electric or magnetic field strength at a point before and after th
25、e placement of the shield in question. 3.2 Terms defined in this Supplement This Supplement defines the following terms: 3.2.1 normalized site attenuation (NSA): NSA refers to site attenuation after subtraction of the antenna factors and any mutual coupling effects. 3.2.2 reference value: This is si
26、te attenuation without shielding enclosures and reference for the calculation of shielding effectiveness. 4 Abbreviations and acronyms This Supplement uses the following abbreviations and acronyms: AF Antenna Factor 2 K series Supplement 6 (10/2016) CF Correction Factor NSA Normalized Site Attenuati
27、on SE Shielding Effectiveness TL Transmission Loss 5 Conventions None. 6 Shielding effectiveness using NSA in free space 6.1 Calculating shielding effectiveness using NSA (NSA method) The NSA is defined as the site attenuation divided by the factors of the two measuring antennas. Therefore, the meas
28、ured NSA with shielding enclosures is expressed in Equation (1); all terms are in dB. = (1) where received voltage when both transmitting and receiving coaxial cables are connected directly received voltage at the receiving antenna transmitting antenna factor receiving antenna factor mutual impedanc
29、e correction factor. Note that theoretical values for are given in CISPR 16-1-4. NSA in free space (NSAFREE) is given by Equation (2); all terms are in dB. = 20log10 (502)( 1 1()2+ 1()4)20log10 (2) where distance between the phase centres of the antennas in metres 0 reference impedance (i.e., 50 ) i
30、s defined as 2/ frequency in MHz. From the above, the shielding effectiveness (SE) using the NSA method as a reference is defined by Equation (3); all terms are in dB. SE + (3) NSAFREE is obtained by calculation. CF is the correction factor considering the antenna factor in the measurement site. The
31、refore, the time required to measure shielding effectiveness will be dramatically reduced compared to the conventional method due to the elimination of the unnecessary reference measurement. Improved reproducibility can also be expected when the measurement locale is surrounded by reflecting objects
32、. K series Supplement 6 (10/2016) 3 6.2 Measurement example This clause presents an example of the measurement of shielding effectiveness using the NSA method. For comparison, the measurement is conducted in accordance with IEEE 299 as the conventional method. In this measurement, a shielded room is
33、 used with metallic walls 2.5 mm thick, and measuring 1.8 m 1.8 m 2.5 m. First, the measurement system for the reference is shown in Figure 1. The transmitting (Tx) and receiving (Rx) antennas are located outside the shielded room. Their measured frequency ranges from 30 MHz to 1 GHz, a biconical an
34、tenna is used for 30 MHz to 300 MHz, and a log-periodic dipole antenna for 300 MHz to 1 GHz. A signal generator and spectrum analyser are used as measurement instruments. Each reference value in the NSA method and the conventional method is obtained from the following equations; all terms are in dB.
35、 (NSA method) = + + + (4) (Conventional method) = + (5) where RNSA reference value obtained by the NSA method RCONV reference value obtained by the conventional method VR received voltage without the shielding structures. RNSA is obtained by the calculation of NSAFREE from Equation (2). Figure 1 Mea
36、surement system for reference The measurements and calculated resulting reference values are shown in Figure 2 (horizontal polarization) and Figure 3 (vertical polarization). 4 K series Supplement 6 (10/2016) Figure 2 Measured and calculated reference values (horizontal polarization) Figure 3 Measur
37、ed and calculated reference values (vertical polarization) As seen in Figures 2 and 3, the reference value of the conventional method has some deviations at frequencies of 250 MHz, 550 MHz and 800 MHz in Figure 2 and 220 MHz in Figure 3. This is believed to be due to reflections from the floor and/o
38、r surrounding structures. In contrast, the reference value of the NSA method shows no abrupt deviations and varies smoothly. Therefore, the conventional method may cause overestimation or underestimation relative to the actual shielding effectiveness. In contrast, the NSA method can provide an appro
39、priate evaluation even if the reference values at specific measurement frequencies are affected by reflecting objects. Next, the transmission loss with a shielded room is measured, using the system in Figure 4. The transmitting (Tx) and receiving (Rx) antennas are placed on either side of the wall.
40、The signal generator and spectrum analyser are used for measurements, and the VSITE is measured. The transmission loss (TL) with the shielded room is calculated by the following equation; all terms are in dB. K series Supplement 6 (10/2016) 5 = + (6) The SE is calculated by subtracting RNSA or RCONV
41、 from TL. Figure 4 Measurement system for shielding effectiveness The measured results for shielding effectiveness using the NSA method and the conventional method are shown in Figure 5 (horizontal polarization) and Figure 6 (vertical polarization). Figure 5 Shielding effectiveness for horizontal po
42、larization 6 K series Supplement 6 (10/2016) Figure 6 Shielding effectiveness for vertical polarization These figures indicate that the NSA method can avoid overestimation and underestimation, compared with the conventional method. Based on the above, the NSA method can evaluate the actual shielding
43、 effectiveness. Also, this method can be used to confirm the accuracy of shielding effectiveness as measured by the conventional method. Printed in Switzerland Geneva, 2017 SERIES OF ITU-T RECOMMENDATIONS Series A Organization of the work of ITU-T Series D General tariff principles Series E Overall
44、network operation, telephone service, service operation and human factors Series F Non-telephone telecommunication services Series G Transmission systems and media, digital systems and networks Series H Audiovisual and multimedia systems Series I Integrated services digital network Series J Cable ne
45、tworks and transmission of television, sound programme and other multimedia signals Series K Protection against interference Series L Environment and ICTs, climate change, e-waste, energy efficiency; construction, installation and protection of cables and other elements of outside plant Series M Tel
46、ecommunication management, including TMN and network maintenance Series N Maintenance: international sound programme and television transmission circuits Series O Specifications of measuring equipment Series P Terminals and subjective and objective assessment methods Series Q Switching and signallin
47、g Series R Telegraph transmission Series S Telegraph services terminal equipment Series T Terminals for telematic services Series U Telegraph switching Series V Data communication over the telephone network Series X Data networks, open system communications and security Series Y Global information infrastructure, Internet protocol aspects and next-generation networks, Internet of Things and smart cities Series Z Languages and general software aspects for telecommunication systems
