Texas Instruments 2000 LF Series Installation and operating instructions

11-06-21-068, March 2003
Radio Frequency Identification Systems
Series 2000 LF Antenna Design Guide
Application Note

Lit Number: 11-06-21-068
Contents
Contents ................................................................................................................................ i
Edition 1 – March 2003 ........................................................................................................ i
About this Manual................................................................................................................ii
Abstract ................................................................................................................................ 1
1Why Custom Antennas may be Required.................................................................... 2
2Standard Antennas........................................................................................................ 3
2.1 27 µH Inductance Antennas...................................................................................... 3
2.2 47 µH Inductance Antenna........................................................................................ 4
2.3 116 µH Inductance Antenna...................................................................................... 5
3Fine Tuning Antennas................................................................................................... 5
3.1 Tuning to Resonance @ 134.2 kHz........................................................................... 5
3.1.1 The RFM-104B Module ......................................................................................................6
3.1.2 RFM-003B and RFM-007B Modules ..................................................................................7
3.1.3 The RFM-008B Tuning Board.............................................................................................7
3.1.4 The STU-MRD1 MicroReader. ...........................................................................................8
4Antenna Design ............................................................................................................. 8
4.1 Determining Self Inductance ..................................................................................... 9
4.1.1 By Calculation .....................................................................................................................9
4.1.2 By Measurement...............................................................................................................10
4.2 Antenna Q............................................................................................................... 11
4.2.1 Determing the Antenna’s Q Value ....................................................................................12
4.2.1.1 By Measurement........................................................................................................................ 12
4.2.1.2 By Calculation ............................................................................................................................ 12
4.3 Controlling the Antenna’s Q .................................................................................... 13
4.3.1 Wire Selection...................................................................................................................13
4.3.1.1 Skin Effect.................................................................................................................................. 13
4.3.1.2 Litze Wire ................................................................................................................................... 14
4.3.1.3 Other Wires Used in Antenna Construction ............................................................................... 15
4.4 Antenna Size........................................................................................................... 16
4.4.1 Antenna Size vs. Inductance ............................................................................................17
4.4.2 Adapting a non 27µH Antenna .........................................................................................18
4.4.2.1 Using External Capacitance....................................................................................................... 18
4.5 Antenna Tails.......................................................................................................... 21
4.5.1 Tail Construction...............................................................................................................21
4.6 Ferrite Cored Antennas........................................................................................... 22
5Other Antennas ........................................................................................................... 22
5.1 Field Lines .............................................................................................................. 22
5.2 Opposing Antennas (In-Phase) ............................................................................... 23
5.3 Opposing Antennas (out-of-phase) ......................................................................... 24
5.4 Noise Canceling Antennas..................................................................................... 26
Appendix A – MicroReader Antenna Designs.................................................................. 27
Appendix B. Contacts........................................................................................................ 32
Figures
Figure 1. Standard Antennas............................................................................................. 3

Lit Number: 11-06-21-068
Figure 2. MicroReader Antenna (47 µH)............................................................................ 4
Figure 3. Mini-RFM Antenna (116 µH) ............................................................................... 5
Figure 4. The RFM-104B RF Module.................................................................................. 6
Figure 5. Inductance Fine-Tuning ..................................................................................... 6
Figure 6. RFM-003B and RFM-007B Modules ................................................................... 7
Figure 7. Capacitance Fine-Tuning ................................................................................... 7
Figure 8. RFM-008B RF Module and ACC-008A Tuning Board ....................................... 8
Figure 9. The MicroReader ................................................................................................ 8
Figure 10. “ADU.EXE” Screen .......................................................................................... 10
Figure 11. LCR Meter ........................................................................................................ 10
Figure 12. High Q Vs. Low Q ............................................................................................ 11
Figure 13. LF System Spectrum....................................................................................... 11
Figure 14. Spectrum Analyzer Screen ............................................................................. 12
Figure 15. Litze Wire (3 sizes) .......................................................................................... 14
Figure 16. ‘Jumbo’ Oxygen Free Hi-Fi Wire..................................................................... 15
Figure 17. Road Loop Wire............................................................................................... 15
Figure 18. Transformer Wire ............................................................................................ 16
Figure 19. Reading Range Reduction due to Noise........................................................ 16
Figure 20. Windings Vs. Inductance ................................................................................ 17
Figure 21. Single Loop Vs. 27 µH Inductance ................................................................. 17
Figure 22. Out of Tune Conditions................................................................................... 18
Figure 23. Polypropylene Capacitor De-rating................................................................ 20
Figure 24. Polypropylene capacitors (0.01 µF & 0.47 µF) ............................................... 20
Figure 25. Antenna Tail Construction.............................................................................. 21
Figure 26. Ferrite Cored Antenna..................................................................................... 22
Figure 27. Field Lines ....................................................................................................... 23
Figure 28. Antenna Field patterns.................................................................................... 23
Figure 29. Opposing Antennas (In-phase)....................................................................... 24
Figure 30. Two 54 µH Antennas Connected in Parallel (In-Phase) ................................ 24
Figure 31. Opposing Antennas (out-of-phase)............................................................... 25
Figure 32. Two 54 µH Antennas connected in Parallel (out-of-phase) .......................... 25
Figure 33. Noise Canceling Antenna ............................................................................... 26
Figure 34. MicroReader Antenna 1 .................................................................................. 28
Figure 35. MicroReader Antenna 2 .................................................................................. 28
Figure 36. MicroReader Antenna 3 .................................................................................. 29
Figure 37. MicroReader Antenna 4 .................................................................................. 30
Tables
Table 1. RF Module Antenna Characteristics.................................................................. 9
Table 2. External Capacitance Values ............................................................................. 19
Table 3. MicroReader Antenna Designs.......................................................................... 27

Lit Number: 11-06-21-068
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Edition 1 – March 2003
This is the first edition of this LF Antenna Design Guide
It contains details on how to develop custom antennas for use with the following
products:
RFM-003B, RFM-104B, RFM-007B, RFM-008B RF Modules and the MicroReader
(Note: The S2510 reader incorporates the RFM-007B)
This document has been created to help support Texas Instruments’
Customers in designing in and /or using TI*RFID products for their
chosen application. Texas Instruments does not warrant that its
products will be suitable for the application and it is the responsibility of
the Customer to ensure that these products meet their needs, including
conformance to any relevant regulatory requirements.
Texas Instruments (TI) reserves the right to make changes to its
products or services or to discontinue any product or service at any time
without notice. TI provides customer assistance in various technical
areas, but does not have full access to data concerning the use and
applications of customers’ products.
Therefore, TI assumes no liability and is not responsible for Customer
applications or product or software design or performance relating to
systems or applications incorporating TI products. In addition, TI
assumes no liability and is not responsible for infringement of patents
and / or any other intellectual or industrial property rights of third parties,
which may result from assistance provided by TI.
TI products are not designed, intended, authorized or warranted to be
suitable for life support applications or any other life critical applications
which could involve potential risk of death, personal injury or severe
property or environmental damage.
TIRIS and TI*RFID logos, the words TI*RFID™ and Tag-it™ are trademarks or
registered trademarks of Texas Instruments Incorporated (TI).
Copyright (C) 2001 Texas Instruments Incorporated (TI)
This document may be downloaded onto a computer, stored and duplicated as
necessary to support the use of the related TI products. Any other type of duplication,
circulation or storage on data carriers in any manner not authorized by TI represents a
violation of the applicable copyright laws and shall be prosecuted.

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PREFACE
Read This First
About this Manual
This LF Antenna Design Guide Application Note (11-06-21-068} is written for the
sole use by TI*RFID Customers who are engineers experienced with TI*RFID and
Radio Frequency Identification Devices (RFID).
Regulatory and safety notes that need to be followed are given Section XX.
Conventions
Certain conventions are used in order to display important information in this manual,
these conventions are:
WARNING:
A warning is used where care must be taken or a certain
procedure must be followed, in order to prevent injury or
harm to your health.
CAUTION:
This indicates information on conditions, which must be met,
or a procedure, which must be followed, which if not heeded
could cause permanent damage to the system.
Note:
Indicates conditions, which must be met, or procedures, which
must be followed, to ensure proper functioning of any hardware or
software.
Information:
Indicates conditions, which must be met, or procedures, which
must be followed, to ensure proper functioning of any hardware or
software.
If You Need Assistance
For more information, please contact the sales office or distributor nearest you. This
contact information can be found on our web site at: http://www.ti-rfid.com.

Lit Number 11-03-21-004
Page (1)
LF Antenna Design Guide
J.A.Goulbourne
Abstract
This document describes how to design and develop custom antennas suitable
for attaching to Texas Instruments’ Low Frequency (LF) Radio Frequency (RF)
modules and readers. It looks at the matching circuits of the standard RFMs
and details the antenna requirements for each one.
The issues of reader inductance and Q are examined, together with wire
selection, tail construction and the use of external capacitance in bringing an
antenna to resonance.

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1 Why Custom Antennas may be Required
There are many reasons why custom built antennas may be required:
•special sized antennas are needed
•the antennas have to be built into structures/ equipment e.g. doors
•very large antenna are required e.g. road loops
•small antennas are needed (for localized reading).
•the antenna is for the microreader
A further reason may be to get increased read distance but the reader antenna
is just one factor amongst many that dictates reading distance. In order of
importance these factors are:
•The size and shape of the transponder’s antenna.
•The size and shape of the reader’s antenna
•The electrical noise in the environment
•The transmitter power (limited by legislation)
•Metal in the environment
Warning:
Increasing the antenna size doesn’t automatically lead to an
increase in a tag’s reading performance – it may reduce.
The tag’s signal must always be 6 dB stronger than any
electrical noise to ensure a successful read.
As an reader’s antenna size increases, more ambient noise
is picked up and a tag may have to move closer to the
antenna to make sure its signal is still the strongest.
Result – shorter reading distance
Texas Instrument’ antennas are optimized and, size for size, a custom antenna design
is unlikely to give a greater read range.

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2 Standard Antennas
Because different RF Modules require antennas with different inductances, Texas
Instruments have three categories of antennas available:
2.1 27 µH Inductance Antennas
These antennas are used with the RFM-104B, RFM-007B and RFM-008B RF
modules.
Figure 1. Standard Antennas
RI-ANT-G02E
RI-ANT-G02E
RI-ANT-S02C
RI-ANT-G04E

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The RI-ANT-G01E, RI-ANT-G02E antennas have 1m tails and are nominally 27 µH
and when connected to the appropriate RF Module can be tuned to resonate at 134.2
kHz. The RI-ANT-G04C antenna is provided with no tail and is nominally 26 µH. If
2.5 mm2(14 SWG) wire is used, a 4m (12’) tail can be added and still be capable of
being tuned to resonance.
Information:
The antenna tail is an integral part of the RF Module’s matching
circuit. Changing the length of the tail changes the performance.
This topic is dealt with in a later section
2.2 47 µH Inductance Antenna
The MicroReader requires an antenna with a self inductance of 47 µH. The following
antenna is available:
Figure 2. MicroReader Antenna (47 µH)
RE-LNA-DLXK-NO

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2.3 116 µH Inductance Antenna
The RFM-003B module requires an antenna with a self inductance of 116 µH and the
following antenna is available:
Figure 3. Mini-RFM Antenna (116 µH)
Historically, the Mini-RF Module was intended for hand-held readers and so the
antenna is supplied with a 100 mm (5”) tails.
3 Fine Tuning Antennas.
The antenna and feed cable are all part of an LC antenna matching circuit on Series
2000 readers. Changing any part has an impact on the total system, e.g. lengthening
the feeder cable. Each module requires antennas of a certain Inductance to ensure
the matching circuit is correct and, because of manufacturing tolerances, each
antenna must be fine tuned in its final positions before a system is commissioned,.
Each module has provision for this tuning.
3.1 Tuning to Resonance @ 134.2 kHz
Texas Instrument’s LF RFID system operates at 134.2 kHz and any antenna must be
fine-tuned to resonate at that frequency for optimum performance.
ƒ(134.2 kHz) = 1
2π LC [1]
RI-ANT-P02A

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Equation [1] is the formula that determines at what frequency the antenna circuit
resonates and you can see how either the Capacitance (C) or the Inductance (L) can
be varied to arrive at the required frequency (ƒ). Some RF modules tune to resonance
by varying the capacitance, whilst the RFM-104B and the Remote Antenna Tuning
Boards both vary the inductance.
3.1.1 The RFM-104B Module
The RFM-104B (standard) RF module is shown in Figure 4
Figure 4. The RFM-104B RF Module
RFM-104B modules use a variable inductor to fine tune antennas. A representation of
the circuit is shown in Figure 5.
Figure 5. Inductance Fine-Tuning
Ca
p
acitance
(
C
)
Variable
Inductance
(
L
)
Antenna
Inductance
(
L
)
Variable
Inductor

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3.1.2 RFM-003B and RFM-007B Modules
The RFM-003B (Mini-RFM) and the RFM-007B (Power RFM) are shown in Figure 6
Figure 6. RFM-003B and RFM-007B Modules
The RFM-003B and RFM-007B modules both use capacitance tuning (using jumpers)
for the fine tuning. This circuit is represented in Figure 7.
Figure 7. Capacitance Fine-Tuning
3.1.3 The RFM-008B Tuning Board
The RFM-008B (Remote Antenna) Module’s resonant components have been taken
off the RF Module and attached to a separate tuning board. In this way it is possible
to have cable runs of up to 120 m (400’) between the RF Module and the tuning board.
Capacitance (C) Antenna
Inductance (L)
Capacitance
Jumpers

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Figure 8. RFM-008B RF Module and ACC-008A Tuning Board
The board has a wide range of capacitance, which can be selected using on-board
jumpers. This arrangement allows for antennas with inductances from 12 to 80 µH to
be connected and fine tuned by a variable inductor.
3.1.4 The STU-MRD1 MicroReader.
This reader is shown in Figure 9.
Figure 9. The MicroReader
Unlike the other RF modules already described which need high Q antennas for
optimum performance; the MicroReader is designed for low Q antennas. Antenna Q
is described in more detail in later sections but in general, low Q antennas are more
tolerant of miss-tuning and the presence of metal. If MicroReader antennas have an
inductance close to 47 µH, then fine tuning is rarely necessary.
4 Antenna Design
Making antennas for S2000 Series readers is straight-forward. Only two
characteristics need to be controlled - Inductance and antenna Q

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For an antenna to function correctly with a particular RF Module, the parameters must
match those in Table 1
RF Module Inductance
(µH)
Inductance
Range (µH)
Q
RI-RFM-104B 27 26 ~ 28 100
RI-RFM-007B 27 25.5 ~ 28.5 100
RI-ACC-008B 27 12 ~ 80 60 ~ 120
RI-STU-MRD1 47 46 ~ 48 20
RI-RFM-003B 116 115 ~ 117 200
RI-STU-S251B 27 26 ~ 27.9 100
Table 1. RF Module Antenna Characteristics
4.1 Determining Self Inductance
The unit of measurement for inductance is the Henry (H). The values for Series 2000
antennas are in the micro-Henry (µH) range
4.1.1 By Calculation
For S2000 Series readers, antenna inductance can be calculated using the software
utility “ADU.exe” (Antenna Design Utility). This program is available from your local
Texas Instruments RFID representative and is shown in Figure 10.
Note:
Because of the different characteristics of various wire types,
some experience with this program is required. By modelling and
then constructing different sized loops, you can determine what
offsets are required for the wire you are using, to get the exact
inductance

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.
Figure 10. “ADU.EXE” Screen
The length and width of an antenna and the wire size can be specified and by
adjusting the number of windings (or the size) you can decide what size antenna will
give you the correct inductance.
4.1.2 By Measurement
Relatively low cost LCR (Inductance, Capacitance and Resistance) meters are
available that will measure the inductance of a loop accurately enough for our
purposes.
Figure 11. LCR Meter

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These meters normally measure the inductance at 1 kHz (not 134.2 kHz) but providing
that the meter has a resolution of 0.1 µH, they can be used
4.2 Antenna Q
The Q value of an antenna is a measure of the efficiency. For the same input power,
high Q antennas have a much greater RF output than lower Q antennas.
Figure 12. High Q Vs. Low Q
A high Q antenna also serves as a filter ignoring signals outside its bandwidth but high
Q antennas are more effected by the presence of metal than low Q ones.
Figure 13. LF System Spectrum
CENTRE 134 400.0 H SPAN 200 000.0
RBW 1 KHZ VBW 3 KHZ ST .4 SEC
10 DB/DIV RANGE .0 DBM -20.1 DBM
REF .0 DBM MARKER 134 400.0 H
B = 12 kHz
60 dB
High "Q"
Low "Q"
Frequenc
y
ƒ0

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Which is why the MicroReader, which was designed for applications such as vehicle
immobilizer systems (where the antenna is around the lock barrel) and hotel door
locks, requires low Q antennas.
4.2.1 Determing the Antenna’s Q Value
4.2.1.1 By Measurement
Q values are normally measured using a signal generator and a spectrum analyzer. A
signal is fed into the antenna circuit and the peak amplitude of the resulting output is
detected by a spectrum analyzer.[ƒ0] (this should be around 134.2 kHz). The
frequency of the input signal is then raised until a 3 dB drop in the amplitude of the
spectrum analyzer signal is detected [ƒ2]. The frequency of the input signal is then
reduced until the signal is at the -3 dB point on the low side [ƒ1]. Then using formula
[2] the Q can be determined
Figure 14. Spectrum Analyzer Screen
Q = ƒ0[2]
ƒ1- ƒ2
4.2.1.2 By Calculation
This is method depends on the accurate measure of the series resistance of the
antenna but even when read by an LCR meter will give an adequate approximate
value.
Q = 2πƒL
R[3]
-3dB
ƒ0
ƒ1ƒ2

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Example 1. RI-ANT-G01E antenna,
Where:
ƒ = 134200 Hz (134.2 kHz)
L = 0.000027 H (27 µH)
R = 0.2 Ohms
Q = (2 * 3.142 * 134200 * 0.000027)/ 0.2 = 114
Example 2. MicroReader antenna,
Where:
ƒ = 134200 Hz (134.2 kHz)
L = 0.000047 H (47 µH)
R = 2.4 Ohms
Q = (2 * 3.142 * 134200 * 0.000027)/ 2.4 = 16.5
4.3 Controlling the Antenna’s Q
We have seen from Equation [3] that the resistance (R) controls the Q. When R is
low, an antenna has a high Q and when R is high, the Q is low.
By selecting the correct wire type we can vary the Q.
4.3.1 Wire Selection.
At RF frequencies, the behavior of an AC current through a wire is different from the
flow through a DC circuit. What might be considered a low resistance wire in a DC
circuit can become high impedance when in an AC circuit because of the ‘Skin Effect’.
4.3.1.1 Skin Effect
At RF frequencies e.g. 134 kHz, when a signal passes through a wire, eddy currents at
the centre of the wire inhibit flow and the current tends to flow close to the
circumference (skin) of the wire. This is the ‘Skin Effect’ and the higher the frequency,
the thinner the depth of the skin through which the current flows.
ƒ
2
1000
[4]
Skin depth(mm) =
So, at 134.2 kHz, we get a skin depth of:
Depth = 2 / (sq root (134200/1000)) = 0.173 mm (0.007”)

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4.3.1.2 Litze Wire
Because a low resistance is required for high Q antennas, Texas Instruments use
Litze Wire in their antennas. Litze wire uses multiple (e.g. 120) individually insulated
(lacquered) wire stands, covered in silk to make up the wire. As each strand is twice
the skin depth, total current flow occurs in each strand and for a particular wire size,
eddy currents are eliminated. Result – low impedance wire and, because there is only
a thin silk outer layer, multiple windings are kept as close together as possible.
Figure 15. Litze Wire (3 sizes)
Litze wire has its disadvantages though:
•It is expensive
•It is more brittle and liable to break if vibration is present.
•It is more difficult to work
One re-occurring issue is when a standard antenna connector breaks off. The
temptation is to strip off the silk and crimp a new connector onto the copper wire.
Unfortunately, you are crimping onto the insulating lacquer, and the antenna will no
longer work effectively. When using Litze wire, the insulating lacquer has to be burnt
off in a solder pot.
Tip 1:
If just the wire is put into the solder pot, solder flows up the wire by
capillary action and the wire swells at the end and is too large for the
connector. Always lightly crimp the terminating connectors onto the wire
before putting into the pot.
Tip 2:
Commercially available solder pots are rated at 320 ºC (608 ºF) but
struggle to reach that temperature. Some have space for an additional
heating element. Buy a spare set and add the extra element.