ETSI TR 102 436 V1.2.1 (2008-02)

ETSI TR 102 436 V1.2.1 (2008-02)
Technical Report

Electromagnetic compatibility
and Radio spectrum Matters (ERM);
Short Range Devices (SRD) intended for operation
in the band 865 MHz to 868 MHz;
Guidelines for the installation and commissioning
of Radio Frequency Identification (RFID) equipment at UHF

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2 ETSI TR 102 436 V1.2.1 (2008-02)



Reference
RTR/ERM-TG34-005
Keywords
ID, radio, short range, terrestrial
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3 ETSI TR 102 436 V1.2.1 (2008-02)
Contents
Intellectual Property Rights.5
Foreword.5
1 Scope.6
2 References.6
2.1 Informative references.6
3 Definitions, symbols and abbreviations .7
3.1 Definitions.7
3.2 Symbols.7
3.3 Abbreviations.8
4 Principles of operation.8
4.1 Characteristics of RFID at UHF .9
4.1.1 Antennas.9
4.1.2 Data Rates.10
4.1.3 Intermodulation Products.10
4.1.4 De-tuning and absorption .10
4.1.5 Shielding.11
4.1.6 Transparent materials.12
4.2 Operation in the band 865 MHz to 868 MHz according to EN 302 208 .12
4.2.1 Dense interrogator mode.12
4.2.2 4 channel plan.13
4.2.3 Multiple interrogators.13
4.2.4 Sharing the spectrum with SRDs .13
4.2.5 Fixed and portable readers.14
4.2.6 Near field systems.14
4.3 Operation in the band 868 MHz to 870 MHz under EN 300 220 .14
4.3.1 Hand held readers .15
4.3.2 Vehicle mounted readers.15
4.3.3 Proximity printers.15
5 Preliminary considerations.16
5.1 Acceptance Tests.16
6 Site considerations.16
6.1 Site survey.16
6.2 Basic principles.17
6.3 Antenna configurations.17
6.4 Configurations for near field systems at UHF.18
6.5 Tags using E.M. transmissions.19
6.6 Near field tags .20
6.7 Sources of interference.20
7 Recommendations for installation.20
7.1 Antenna fixtures.20
7.2 Selection of antennas.21
7.3 Positioning of the antenna .21
7.4 Outside antennas .21
7.5 Cabling.21
7.6 Earthing (Fixed Interrogators).22
7.7 RFID and Short Range Devices operating within the same area.22
8 Commissioning.22
8.1 Setting to work.22
8.2 Site records.22
9 Maintenance .23
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4 ETSI TR 102 436 V1.2.1 (2008-02)
Annex A (informative): Conversion of units of measurement.24
A.1 Measurements of power .24
Annex B (informative): Earthing systems.25
B.1 Earth System Minimum Requirements .25
B.2 Typical electrode and array characteristics .25
B.2.1 Vertical rod.25
B.2.2 Buried ring.26
B.2.3 Buried grid.26
B.2.4 Measurement of soil resistivity .26
B.3 Earthing of support structures and buildings.28
B.3.1 Ancillary equipment external to buildings .28
B.3.2 Metal support poles on buildings .28
B.3.3 Metal security fences.28
B.4 Interconnection of lightning protection systems with power supply earthing arrangements .28
Annex C (informative): Prefabricated portals.29
Annex D (informative): Commissioning procedure .30
Annex E (informative): Bibliography.31
History .32

ETSI

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5 ETSI TR 102 436 V1.2.1 (2008-02)
Intellectual Property Rights
IPRs essential or potentially essential to the present document may have been declared to ETSI. The information
pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found
in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in
respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the ETSI Web
server (http://webapp.etsi.org/IPR/home.asp).
Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee
can be given as to the existence of other IPRs not referenced in ETSI SR 000 314 (or the updates on the ETSI Web
server) which are, or may be, or may become, essential to the present document.
Foreword
This Technical Report (TR) has been produced by ETSI Technical Committee Electromagnetic compatibility and Radio
spectrum Matters (ERM).
Every TR prepared by ETSI is voluntary. This text should be considered as guidance only and does not make the
present document mandatory.
The present document has been produced by ETSI in response to a perceived need by RFID manufacturers, installers
and end users for general guidance on the installation and commissioning of RFID systems operating at UHF.
ETSI

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6 ETSI TR 102 436 V1.2.1 (2008-02)
1 Scope
The present document provides recommendations to system integrators and installers on good practice for the
installation and commissioning of RFID systems operating at UHF at power levels up to 2 W e.r.p. Guidance is given
on making best use of the available spectrum as envisaged within the ETSI standard EN 302 208 [1]. In addition the
present document covers the use of reduced power RFID devices at UHF, such as hand held readers and proximity
printers, operating in accordance with EN 300 220 [2]. This includes operation in the sub-bands 869,40 MHz to
869,65 MHz at power levels of 500 mW and 869,7 MHz to 870,0 MHz at power levels of 5 mW. In particular the
present document considers the practices necessary to minimize interference in situations where multiple interrogators
are co-located in close proximity. Failure to take the necessary precautions could lead to degradation in system
performance. The present document also endeavours to cover the approaches necessary to ensure that the operational
requirements of the end-user are met.
The present document concerns itself with radio matters only. It does not provide any guidance on computer hardware
and software that may be used to process the data recovered from tags.
Many of the techniques recommended in the present document have been subject to practical tests in a working
distribution centre. However each application is different and the techniques recommended in the present document
may not be applicable in all situations.
End users may wish to make use of the present document as a general guide.
The present document does not cover matters related to Health and Safety. End-users and system integrators should
familiarise themselves with the relevant national and international standards.
2 References
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific.
• For a specific reference, subsequent revisions do not apply.
• Non-specific reference may be made only to a complete document or a part thereof and only in the following
cases:
- if it is accepted that it will be possible to use all future changes of the referenced document for the
purposes of the referring document;
- for informative references.
Referenced documents which are not found to be publicly available in the expected location might be found at
http://docbox.etsi.org/Reference.
For online referenced documents, information sufficient to identify and locate the source shall be provided. Preferably,
the primary source of the referenced document should be cited, in order to ensure traceability. Furthermore, the
reference should, as far as possible, remain valid for the expected life of the document. The reference shall include the
method of access to the referenced document and the full network address, with the same punctuation and use of upper
case and lower case letters.
NOTE: While any hyperlinks included in this clause were valid at the time of publication ETSI cannot guarantee
their long term validity.
2.1 Informative references
[1] ETSI EN 302 208 (Parts 1 and 2): "Electromagnetic compatibility and Radio spectrum Matters
(ERM); Radio Frequency Identification Equipment operating in the band 865 MHz to 868 MHz
with power levels up to 2 W".
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7 ETSI TR 102 436 V1.2.1 (2008-02)
[2] ETSI EN 300 220 (Parts 1 and 2): " Electromagnetic compatibility and Radio spectrum Matters
(ERM); Technical characteristics and test methods for radio equipment to be used in the 25 MHz
to 1 000 MHz frequency range with power levels up to 500 mW".
[3] CEPT ERC/REC 70-03: "Relating to the use of Short Range Devices (SRD)".
[4] CEPT ECC Report 037: "Compatibility of planned SRD applications in 863 - 870 MHz".
[5] ISO 18000-6: "CD Information Technology RFI for item management Part 6 Parameters for air
interface communications at 860 - 960 MHz".
3 Definitions, symbols and abbreviations
3.1 Definitions
For the purposes of the present document, the following terms and definitions apply:
assigned frequency band: frequency band within which the device is authorized to operate
dense-interrogator mode: RFID operating mode in which multiple, nearby interrogators can transmit simultaneously
in a channel without incurring noticeable performance degradation
frequency agile technique: technique used to determine an unoccupied sub-band in order to minimize interference
with other users of the same band
interrogator: equipment that will activate an adjacent tag and read its data
NOTE: It may also enter or modify the information in a tag.
link frequency: frequency offset of the tag backscatter with respect to the centre frequency of the interrogating signal
load: collection of tagged items that are carried on a transportable device
listen before talk: action taken by an interrogator to detect an unoccupied sub-band prior to transmitting (also known
as "listen before transmit")
preferred channel: channel assigned to an interrogator which, provided it is available, is selected automatically as the
channel of first choice
radiated measurements: measurements which involve the absolute measurement of a radiated field
reading range: maximum range at which a tag may be read by an interrogator
secondary channel: channels assigned to an interrogator, which is selected in the event that use of the primary
preferred channel is not possible
tag: transponder that holds data and responds to an interrogation signal
3.2 Symbols
For the purposes of the present document, the following symbols apply:
dB decibel
dBm power in decibels relative to 1 mW
d distance
λ wavelength
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8 ETSI TR 102 436 V1.2.1 (2008-02)
3.3 Abbreviations
For the purposes of the present document, the following abbreviations apply:
AFA Adaptive Frequency Agility
AM Amplitude Modulated
CEPT European Conference of Postal and Telecommunications Administrations
E.M. ElectroMagnetic
e.r.p. effective radiated power
ECC Electronic Communications Committee
EMC ElectroMagnetic Compatibility
ERC European Radio communication Committee
FM Frequency Modulated
LBT Listen Before Talk
PIB PolyIsoButylene
PM Phase Modulated
R&TTE Radio and Telecommunications Terminal Equipment
RCD Residual Current Devices
RF Radio Frequency
RFID Radio Frequency IDentification
SRD Short Range Device
UHF Ultra High Frequency
4 Principles of operation
A basic RFID system comprises an interrogator with its associated antennas and a collection of tags. The antennas are
arranged to transmit their signal within an interrogation zone. Tags are attached to either animate or inanimate objects
that are to be identified. When a tag enters an interrogation zone, it is activated by the transmitted signal from the
interrogator. Typically the tag will respond by sending its identity and possibly some associated data. The identity and
data from the tag is validated by the receiver in the interrogator and passed to its host system. A block diagram of the
principle is shown in figure 1.
To Host
To Host
Tag Interrogator
Tag Interrogator
System
System

Figure 1: Principle of RFID
A sophisticated protocol is used to handle the transfer of data between the interrogator and tags. This ensures the
integrity of data transfer and may include error checking and correction techniques. In addition the protocol handles the
process for writing data to the tag and controls the procedure for reading multiple tags that may be present
simultaneously within the same interrogation zone.
Across the whole of the radio spectrum three different forms of communication are used for the transfer of information
between interrogators and tags. These are:
• Electrostatic.
• Inductive.
• Electromagnetic waves.
The present document confines itself solely to electromagnetic waves and near field techniques since they are the only
forms of communication that are relevant for RFID at UHF.
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9 ETSI TR 102 436 V1.2.1 (2008-02)
To transfer information between an interrogator and a tag it is necessary to superimpose the data on a carrier wave. This
technique is known as modulation. Various schemes are available to perform this function. They each depend on
changing one of the primary features of an alternating sinusoidal source in accordance with the transmitted data. The
most frequent choices of modulation are amplitude (AM), frequency (FM) and phase (PM).
Tags exist in a range of shapes and sizes to satisfy the particular needs of their intended application. Many tags are
passive and derive the power for their operation from the field generated by the interrogator. However some tags are
fitted with batteries, which may provide additional features (e.g. sensors) and may enable them to operate at
significantly greater ranges.
4.1 Characteristics of RFID at UHF
UHF transmission takes place by means of electromagnetic (E.M.) waves. At these frequencies E.M. waves have
properties that have many similarities to light. Transmissions travel in a straight line and the power of the received
signal is a function of the inverse square of the distance from its source. For example if the distance from a transmit
antenna is doubled the received power drops to one quarter. This property means that it is possible with UHF systems to
achieve significant reading ranges. Operation in the UHF band also makes it possible to transfer information at high
data rates. Both of these characteristics make UHF systems well suited for use in applications where tags are moving at
speed or in which there are multiple tags present in an interrogation zone.
UHF can present the installer with a number of challenges. Electromagnetic transmissions at UHF are readily reflected
from many surfaces. The reflections can cause the activation of unwanted tags and can also give rise to an effect known
as standing wave nulls. These can produce points within the interrogation zone where there are very low levels of
signal. UHF signals also experience significant levels of attenuation in the presence of water. In applications where
water may be present, system integrators must therefore make suitable provision for a reduction in reading range during
the design and configuration of the installation.
Operation is also possible using near field coupling between an interrogator and tags. This technique is useful in
situations where there are many tags in a confined area and it is necessary to control the transmitted field. Near field
systems generate magnetic fields that attenuate in accordance with the inverse cube of distance. Their properties
therefore make them useful for reading tags at close range while avoiding activation of tags outside the area of interest.
Near field techniques require the use of special antennas that are configured in the shape of a loop. Some tags have
antennas that are capable of operating with both E.M. transmissions and near field coupling.
4.1.1 Antennas
At UHF the shape of the interrogation field generated by the E.M. antennas of an interrogator will typically be in the
form of a cone. The angle subtended between the half power (or 3 dB) points of this cone is known as the beamwidth.
Often beamwidth is specified in both horizontal and vertical values, which need not necessarily be the same. In many
installations the long reading ranges possible at UHF mean that tags outside the wanted interrogation zone are
inadvertently activated. The use of antennas with a narrow beamwidth provides one means by which it is possible to
limit the area where tags may be read.
The most common type of antenna used at UHF is the patch antenna. This typically has a beamwidth of the order of
70 degrees. The patch antenna is fully satisfactory for many short to medium range applications where there are no
other interrogators and unwanted tags in the immediate vicinity. In applications where longer reading ranges are
required it may be necessary to control the extent of the interrogation zone more precisely. A first order of improvement
may be achieved by using a variant of the standard patch antenna that is physically larger. This makes it possible to
produce antennas with a horizontal beamwidth down to 30 degrees. Other types of antenna exist with narrower
beamwidths. One of these is the helical antenna, which can have a beamwidth of as little as 10 degrees. This narrow
beamwidth makes it possible to generate an interrogation zone that is very directional.
As the beamwidth of an antenna is reduced the transmitted power is compressed into a smaller volume, which produces
increased field intensity. This effect is quantified by the term "antenna gain". Since the radio regulations limit the
maximum field level that is permitted, it is necessary to reduce the level of power generated by the interrogator to
compensate for the increased gain of the antenna. Where the use of different antennas is allowed by the manufacturer,
details of how this adjustment should be carried out should be included within the product manual for the interrogator.
Generally transmissions from the antenna of the interrogator will be circularly polarized. This eliminates differences in
the reading range of tags caused by their orientation in the x and y planes (but not the z plane, which is the direction of
travel of the radio wave). The variation of reading range with orientation in the z plane is considered under
"Recommendations for mounting tags" in clause 6.5.
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10 ETSI TR 102 436 V1.2.1 (2008-02)
4.1.2 Data Rates
The maximum data rate of the communication link from the interrogator to the tag (sometimes called the downlink) is
determined by the size of the permitted channel of operation of the interrogator. The size of the channel is specified in
ERC/CEPT 70-03 [3] and is effectively a fixed parameter. For channels of 200 kHz channel spacing as defined in
annex 11 of ERC/CEPT 70-03 [3] the maximum possible data rate is of the order of 40 kbits per second. However the
protocol used for transferring the information includes error checking and other features, which reduce the effective
speed of information transfer. Details of the agreed standard data rates are included in ISO 18000-6 [5].
In most situations the response from the tag (sometimes called the uplink) will lie in the same, or adjacent channels as
the downlink. This will place a practical limit on the achievable data rate. Where interrogators operate in accordance
with the 4 channel plan as specified in EN 302 208 [1], the tag may be set to operate at link frequencies of
approximately 300 kHz. In such circumstances data rates of 75 kbits per second are achievable.
However EN 302 208 [1] also permits the wanted signal from the tag to occupy the entire designated band from
865 MHz to 868 MHz provided that the levels specified in the spectrum mask are met. For some applications this
provides scope for manufacturers to create systems with substantially faster uplinks, which could provide significant
benefits. Where this technique is used, system designers m
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