1、 International Telecommunication Union ITU-T K.70TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (06/2007) SERIES K: PROTECTION AGAINST INTERFERENCE Mitigation techniques to limit human exposure to EMFs in the vicinity of radiocommunication stations ITU-T Recommendation K.70 ITU-T Rec. K.70 (06/2007
2、) i ITU-T Recommendation K.70 Mitigation techniques to limit human exposure to EMFs in the vicinity of radiocommunication stations Summary ITU-T Recommendation K.70 defines techniques which may be used by telecommunication operators to evaluate the cumulative (total) exposure ratio in the vicinity o
3、f transmitting antennas and to identify the main source of radiation. It offers guidance on mitigation methods which allow reduction of radiation level in order to comply with exposure limits. It also provides guidance on procedures necessary in the environment (on site) in which, in most cases, the
4、re is a simultaneous exposure to multiple frequencies from many different sources. Radiating sources may belong to many operators and may represent different radiocommunication services (e.g., cellular systems, trunking systems, broadcasting, radio relays, wireless access, etc.). Source ITU-T Recomm
5、endation K.70 was approved on 29 June 2007 by ITU-T Study Group 5 (2005-2008) under the ITU-T Recommendation A.8 procedure. Keywords EMF, exposure limits, intentional radiator, multiple sources environment, transmitting antenna. ii ITU-T Rec. K.70 (06/2007) FOREWORD The International Telecommunicati
6、on Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a vie
7、w 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 which, in turn, produce Recommendations on these topics. The approval of ITU-T Recommendat
8、ions 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 and IEC. NOTE In this Recommendation, the expression “Administration“ is used for concisen
9、ess to indicate both a telecommunication administration and a recognized operating agency. Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure e.g., interoperability or applicability) and compliance with the Recommendation
10、 is achieved when all of these mandatory provisions are met. The words “shall“ or some other obligatory language such as “must“ and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party. INTE
11、LLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, w
12、hether asserted by ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementers are
13、 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 2008 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permissio
14、n of ITU. ITU-T Rec. K.70 (06/2007) iii CONTENTS Page 1 Scope 1 2 References. 1 3 Terms and definitions . 3 4 Abbreviations and acronyms 5 5 Evaluation of exposure levels. 6 5.1 Full-wave methods . 7 5.2 Synthetic model 8 5.3 Point source model . 8 5.4 Influence of the reflections. 8 5.5 Uncertainty
15、 . 8 6 The EIRP and other parameters for the radiocommunication transmitting stations. 9 7 Evaluation of the cumulative exposure ratio in multiple sources environment . 9 8 Identification of the main source of radiation. 10 9 Compliance distances . 11 10 Description of the mitigation techniques 11 1
16、1 Conclusion 12 Annex A Radiation pattern of the transmitting antenna . 13 A.1 Horizontal and vertical radiation patterns 13 A.2 HRP and VRP for typical radiocommunication and broadcasting antennas 14 A.3 Two levels approach. 14 Annex B The point source model . 15 B.1 Description of the point source
17、 model 15 B.2 Applicability of the point source model . 17 Annex C Simplified method for the calculation of the compliance distances 21 Annex D Examples of mitigation techniques . 22 D.1 Decrease in the transmitter power 22 D.2 Increase in the antenna height 22 D.3 Decrease in the VRP downtilt 23 D.
18、4 Increase in the antenna gain . 25 D.5 Changes in the VRP 27 D.6 Changes in the HRP 29 D.7 Multiple methods applied simultaneously 31 Appendix I Software EMF-estimator 32 I.1 Applicability of the EMF-estimator . 32 I.2 Typical situation . 33 I.3 Software description. 33 I.4 Compliance distances . 3
19、7 iv ITU-T Rec. K.70 (06/2007) Page I.5 Coefficient concerning transmitter power 37 I.6 Library radiation patterns of the antenna systems. 38 I.7 Examples of calculations 38 I.8 Additional comments 38 I.9 System requirements 38 Appendix II Parameters of typical radiocommunication systems 39 II.1 Mob
20、ile base stations . 39 II.2 Trunked radio and wireless access systems 41 II.3 TV and DVB-T transmitting stations . 41 II.4 FM and T-DAB transmitting stations. 42 II.5 AM and DRM transmitting stations . 44 II.6 Radio relay links. 45 ITU-T Rec. K.70 (06/2007) v Introduction The real sources of intenti
21、onal EMFs are transmitting antennas not transmitters themselves because the radiation patterns of the transmitting antennas determine EMF distribution in the vicinity of a transmitting station. The compliance with unintentional radiation of the radiocommunication or broadcasting transmitters, such a
22、s around their enclosure (or in the case of an open enclosure for maintenance or tuning purposes), is not under the scope of this Recommendation. The accuracy of calculations during the exposure assessment depends on the methodology used and on the information concerning radiating source. In this Re
23、commendation, particular stress is laid on the guidance referring to radiating source characteristics, mainly the most important parameters, i.e., transmitting antenna radiation patterns. This Recommendation offers information on radiation patterns for a wide range of typical transmitting antennas u
24、sed in radiocommunication and broadcasting. It also gives guidance on how to organize calculations, depending on accessible data. This Recommendation presents the possible technical solutions to the problem when the reference levels are exceeded in the multiple sources environment. In the case when
25、many operators have radiating sources in the considered area, the proper solution has to be found on the basis of an agreement between all parties. In the case when such an agreement is not possible, the operator who introduces the last change in the installations will be responsible for the appropr
26、iate limitation of the exposure level from his source of radiation so as not to exceed the allowed global limit. ITU-T Rec. K.70 (06/2007) 1ITU-T Recommendation K.70 Mitigation techniques to limit human exposure to EMFs in the vicinity of radiocommunication stations 1 Scope This Recommendation provi
27、des guidance on mitigation techniques for limiting the exposure from radiocommunication installations, especially in the multiple sources environment. This guidance presents methods for field strength distribution evaluation, cumulative exposure ratio evaluation, identification of the main source of
28、 radiation, and offers mitigation techniques methods for reducing the levels of electromagnetic fields during simultaneous exposure in the multiple sources environment. In this Recommendation, the following reference limits are used: electric field strength, magnetic field strength and power density
29、. Since compliance with the reference limits guarantees the compliance with basic restrictions, this is a conservative approach. In the far-field region the use of the reference levels gives results which are very close to real radiation levels. In the near-field region the obtained results will ove
30、restimate or underestimate real radiation levels. Moreover, this Recommendation deals with reference levels calculated in free space, so EMF influence on human tissues or human body is not considered. This Recommendation also gives guidance on identifying those areas in which the highest radiation l
31、evels should be expected. This piece of information may be helpful to define the area for measurements. The guidance given in this Recommendation applies to any exposure limits; however, in the examples of calculations, the ICNIRP exposure limits are taken. A software EMF-estimator (see Appendix I)
32、is attached to this Recommendation in order to support its application. The software implements the methodology described in this Recommendation and gives the possibility to calculate the cumulative exposure for the reference levels. It also contains the library of the radiation patterns of transmit
33、ting antennas for a wide range of radiocommunication and broadcast services. The EMF-estimator is not appropriate for the equipment certification in order to put it on the market. This Recommendation is intended for use when considering the EMFs in areas around transmitting stations, e.g., around tr
34、ansmitting antennas in their places of installation. 2 References The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recomm
35、endations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly
36、published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. ITU-T K.52 ITU-T Recommendation K.52 (2004), Guidance on complying with limits for human exposure to electromagnetic fields. ITU-T K.61 ITU-T Recommendation
37、K.61 (2003), Guidance to measurement and numerical prediction of electromagnetic fields for compliance with human exposure limits for telecommunication installations. ITU-T Rec. K.70 (06/2007) 2 ITU-R BS.80-3 ITU-R Recommendation BS.80-3 (1990), Transmitting antennas in HF broadcasting. ITU-R BS 705
38、-1 ITU-R Recommendation BS.705-1 (1995), HF transmitting and receiving antennas characteristics and diagrams. ITU-R BS.1195 ITU-R Recommendation BS.1195 (1995), Transmitting antenna characteristics at VHF and UHF. ITU-R BS.1386-1 ITU-R Recommendation BS.1386-1 (2001), LF and MF transmitting antennas
39、 characteristics and diagrams. ITU-R BS.1698 ITU-R Recommendation BS.1698 (2005), Evaluating fields from terrestrial broadcasting transmitting systems operating in any frequency band for assessing exposure to non-ionizing radiation. ITU-R F.1245-1 ITU-R Recommendation F.1245-1 (2000), Mathematical m
40、odel of related radiation patterns for line-of-sight point-to-point radio-relay system antennas for use in certain coordination studies and interference assessment in the frequency range from 1 GHz to about 70 GHz. ITU-R F.1336-1 ITU-R Recommendation F.1336-1 (2007), Reference radiation patterns of
41、omnidirectional, sectoral and other antennas in point-to-multipoint systems for use in sharing studies in the frequency range from 1 GHz to about 70 GHz. EN 50383 CENELEC EN 50383:2002, Basic standard for the calculation and measurement of electromagnetic field strength and SAR related to human expo
42、sure from radio base stations and fixed terminal stations for wireless telecommunication systems (110 MHz 40 GHz). EN 50400 CENELEC EN 50400:2006, Basic standard to demonstrate the compliance of fixed equipment for radio transmission (110 MHz 40 GHz) intended for use in wireless telecommunication ne
43、tworks with the basic restrictions or the reference levels related to general public exposure to radio frequency electromagnetic fields, when put into service. EN 50413 CENELEC 50413:2007, Basic standard on measurement and calculation procedures for human exposure to electric, magnetic and electroma
44、gnetic fields (0 Hz 300 GHz). EN 50492 CENELEC 50492 (draft), Basic standard for in-situ measurement of electromagnetic field strength related to human exposure in the vicinity of base stations. ICNIRP ICNIRP Guidelines (1998), Guidelines for limiting exposure to time-varying electric, magnetic and
45、electromagnetic fields (up to 300 GHz). IEC/EN 62311 IEC/CENELEC 62311:2007, Assessment of electronic and electrical equipment related to human exposure restrictions for electromagnetic fields (0 Hz 300 Hz). IEEE P1597.1 IEEE P1597.1 (draft), Draft Standard for Validation of Computational Electromag
46、netics (CEM) Computer Modelling and Simulation. UNCERT ISO/IEC MISC UNCERT (1995), Guide to the expression of uncertainty in measurement. ITU-T Rec. K.70 (06/2007) 33 Terms and definitions This Recommendation defines the following terms: 3.1 antenna: Device that serves as a transducer between a guid
47、ed wave (e.g., coaxial cable) and a free space wave, or vice versa. It can be used to emit or receive a radio signal. In this Recommendation the term antenna is used only for emitting antenna(s). 3.2 antenna gain: The antenna gain Gi(, ) is the ratio of power radiated per unit solid angle multiplied
48、 by 4 to the total input power. The gain is frequently expressed in decibels with respect to an isotropic antenna (dBi). The formula defining the gain is: =dd4),(riniPPG (3-2) where: , are the angles in a polar coordinate system Pris the radiated power in the (, ) direction inis the total input powe
49、r an elementary solid angle in the direction of observation. NOTE In manufacturers catalogues, the antenna gain is understood as a maximum value of the antenna gain. 3.3 basic restrictions: Restrictions on exposure to time-varying electric, magnetic and electromagnetic fields that are based directly on established health effects. Depending upon the frequency of the field, the physical quantities used to specify these restrictions are: current density (J), specific absorption rate (SAR) and power dens
