Feig Electronic OBID ID RW24-A User manual

h80391-1e-ID.doc
ID RW24-A
Antenna Manual
Version 1.1

OBID®Antenna Manual ID RW24
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Important notice
Copyright 1997 by FEIG ELECTRONIC GmbH
Lange Straße 4
D-35781 Weilburg-Waldhausen
OBID®is a registered trademark of FEIG ELECTRONIC GmbH.
Edition: mr/99/09/21 - h80391-1e-id.doc
The details given in this manual may be altered without previous notice.
With the publication of this manual, all prevous editions become void.
The information contained in this manual has been compiled to the best of our knowledge. FEIG ELECTRONIC GmbH
does not guarantee for the correctness of the indications made in this manual. Furthermore, FEIG ELECTRONIC GmbH
may not be held liable for damages ensuing from faulty information.
Since errors may never be avoided completely, we are always grateful for any corrections.
The installation recommendations given in this manual are based on favourable marginal conditions. FEIG ELECTRONIC
GmbH will not guarantee the perfect operativeness of its OBID®-system in cross surroundings.

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Contents:
1. General............................................................................................................................... 4
1.1. Functional description of the OBID®-system........................................................................4
2. Basic factors...................................................................................................................... 5
2.1. Equivalent circuit diagram.....................................................................................................5
2.2. Admissible antenna parameters for reader model ID RW24...............................................5
2.3. Methods of manufacture........................................................................................................6
2.3.1. Coiled wire antenna .........................................................................................................6
2.3.2. Flat strip cable antenna....................................................................................................6
2.3.3. Transmission antenna......................................................................................................6
2.3.4. Comparison......................................................................................................................7
3. Elementary antennas ........................................................................................................ 8
3.1. Simple frame antenna............................................................................................................8
3.2. 8-loop used as frame antenna.............................................................................................10
4. Gate antennas.................................................................................................................. 11
4.1. Gate antenna in Helmholtz arrangement............................................................................11
4.2. Gate antenna in Anti-Helmholtz arrangement....................................................................12
4.3. Gate antenna in mixed arrangement ..................................................................................13
5. Influences on the ID RW24-systems.............................................................................. 14
5.1. Mutual influence of two ID RW24-systems.........................................................................14
5.1.1. Mutual influence by carrier frequencies..........................................................................14
5.1.2. Mutual influence by transmission logs............................................................................14

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1. General
1.1. Functional description of the OBID®-system
The OBID®identification system is an inductive transmission system for touchless identification (ID)
of objects. The components of its read/write system facilitate the inscription and reading of passive
transponders. It consists of a reader, an antenna and a transponder used as data storage medium.
The system works with a carrier frequency of 125 kHz and uses amplitude modulation to transmit the
data between reader and transponder.
As soon as the transponder gets into the local magnetic alternating field of the antenna, it is con-
nected to power supply and may be inscripted resp. read. Data are received by the same antenna,
which also produces the magnetic field and sends them to the transponder.
The magnetic field and the data received and sent from and to the transponder may penetrate all
dielectric materials, so that even masked reading and writing is possible.

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2. Basic factors
2.1. Equivalent circuit diagram
In general, each of the antennas listed in this manual may be illustrated by the equivalent circuit dia-
grams as shown in diagram 2.1-1.
R
Ohm
L
C
W
R
ESB
L
ESB
a)
b)
In this case, the equivalent circuit diagram a) for the actual frequency of 125 kHz may be converted
to the more simple equivalent circuit diagram b). By carrying out this conversion, the parallel capaci-
tor, which is part of a) and describes the external and internal capacitance, leads to an increase in
the resistive and inductive component in b).
As an example, this may lead to the fact that an antenna which is working at an actual frequency of
125 kHz has a higher resistance than at lower frequencies or direct current. Thus, measuring the
internal resistance of the antenna with a multi-meter is only partially useful, since the multi-meter
generally performs direct-current measurement.
The same applies to the equivalent circuit diagram inductance LESB. This value, too is increased by
the parallel capacity CW. However, this apparent inductance increase does not lead to a greater
reading range of the reader, since the inductance L, which is effective for communication, is not in-
fluenced. This inductance increase has a rather parasitic effect.
2.2. Admissible antenna parameters for reader model ID RW24
The IDRW 24 is suitable for antennas with an inductance LESB of 600 µH up to 1200 µH. For the
maximum reading range, you have to choose the highest possible inductance for antennas with the
same dimensions. However, 1200µH should not be exceeded. A value of 1100 µH has proven con-
venient.
As far as the resistance RESB is concerned, values between 5 Ωand 30 Ωare admissible. However,
the optimal working range lies between 10 Ωand 20 Ω. In case that the resistance of the antenna is
less than 5 Ωor more than 30 Ω, the output driver of the ID RW24 is working off-specification, which
may lead to a drastical reduction of the reading range.

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2.3. Methods of manufacture
In principle, several methods of manufacture may be used to produce an antenna. In the following,
we will present and compare three different methods.
2.3.1. Coiled wire antenna
The coiled wire antenna consists of one single lead resp. insulated wire, which is, according to the
necessary number of turns, wound around a frame or something similar .
This kind of antenna is easy to manufacture, but, due to the fact that the windings are situated di-
rectly side by side, the coil capacity is rather high. As mentioned before, this may lead to an appar-
ently higher inductance for the reader, but the parasitic portion does not make a contribution to
higher range.
In the case of manually wound antennas, the various winding layers may differ from antenna to an-
tenna, due to tight or loose winding. Thus, even antennas of the same size and number of windings,
may have different inductances.
2.3.2. Flat strip cable antenna
Depending on the necessary number of turns, one or more layers of a flat strip cable are put on a
carrier plate or wound around a frame. After that, the two ends of the cable are connected with each
other in a staggered arrangement, so that a conductor loop with the appropriate number of turns is
created. Connections are formed by the first lead of the one end and the last lead of the other.
In order to simplify manufacture, this interlaced connection does already exist on the board of the
automatic antenna tuner ID AT for 26-wire flat strip cable. Furthermore, there is a small connection
board ID ANT.AP, which has been especially designed for interlaced connection of 26-wire-flat strip
cable. For both boards, the desired number of turns may be selected by jumpers.
2.3.3. Transmission antenna
In principle, the transmission antenna consists of one conductor loop with only one turn. The induc-
tance of this turn, together with the appropriate capacitor, forms the 125 kHz-transmission resonant
circuit. The relatively low inductance of this transmission resonant circuit is then transformed by a
translator into the necessary inductance of the reader’s working range. Since the translator also
transforms the current in the transmission resonant circuit to a higher level according to its turn ratio,
the capacitors have to be suitable for stronger currents, such as 4A. The conductor loop should have
a minimum diameter of 16 mm² . We recommend a construction made of copper pipe.

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Figure 2.3.3-1 equivalent circuit diagram of a transmission antenna.
C
L
N1/N
2
Figure 2.3.3-1
Due to its complex manufacture and very difficult alignment, we will not go into the particulars of this
antenna type.
2.3.4. Comparison
Chart 2.3.4-1 : comparison between the three methods of manufacture:
Manufacture Price Expenditure of
manufacture Alignment Parasitic capacity
Coiled wire
antenna Low medium Easy (ID AT-A) High
Flat strip cable
antenna Low-medium Low Easy (ID AT-A) Medium
Transmission
antenna High High difficult (ID MTU-A) Low

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3. Elementary antennas
Elementary antennas are subdivided into simple frame antennas and 8-loops.
In the sector of access control for persons, the simple frame antenna is used, since it has a larger
range. 8-loops are more suitable for industrial applications, where the special field alignment of the 8-
loop is very advantageous.
3.1. Simple frame antenna
Figure 3.1-1.b illustrates the field alignment of a simple frame antenna. It is the most simple and most
customary antenna type and is mostly used for access control of persons. The size of this antenna
depends highly on the requirements regarding reading range and on the surroundings.
Figure 3.1-1
In order to maximize the reading range, we recommend dimensions of approx. 50 cm x 70 cm for 22
to 26 turns, when using flat strip cable.
Chart 3.1-1 indicates the expected inductance for the various antenna sizes and the number of turns
of flat strip cable antennas. The surface of the antenna is calculated by multiplying the middle edge
lengths (see also figure 3.1-2). Please notice that the relation of edge length a and b does not ex-
ceed a value of 2:1.
In order to reach a maximum reading range, the number of turns with the highest inductance has to
be choosen.

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Inductance [µH] for the corresponding number of turns
Surface A
[cm²] 18 turns 22 turns 26 turns 28 turns 36 turns
800 603 909
1000 700 1059
1200 790
1400 660 875
1600 720 955
1800 778 1032
2000 626 833 1105
2200 666 886
2400 704 937
2600 740 986
2800 776 1034
3000 811 1081
3200 844 1126
3400 619 877
3600 642 910
3800 664 941
4000 685 972
4200 706 1002
4400 727 1032
4600 747 1061
4800 767 1090
5000 787 1118
Chart 3.1-1
b
a
Figure 3.1-2
A = a •• b

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3.2. 8-loop used as frame antenna
Figure 3.2-1.b shows the field alignment of an 8-loop used as frame antenna.
Transponder
Figure 3.2-1
Due to its relatively high field alignment resp. field directionality between the loop halves, this loop
type is mostly used for the detection of vehicles and goods, for which the position of the transponder
can be fixed according to the field alignment of the antenna. The range of such an antenna is rather
low compared to a simple frame antenna, which makes it unsuitable for the recognition of persons.
In the given case, where the position of the transponder at the vehicles resp. goods may be adapted
to the field alignment of the antenna, this antenna reaches a very high consistency.
One further advantage of this antenna type is the compensation of a large part of malfunctions
caused by external sources of interference.

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4. Gate antennas
Gate antennas are used for the recognition of persons as well as of goods. In general, they consist
of two single antennas connected in series, which are arranged in a way that the person or object to
be recognized passes in between the two antennas.
In case of access control of persons, a person should be recognized, due to this antenna arrange-
ment, by a transponder which is carried along by this person without having to take it out of the
pocket and holding it in front of the antenna. As far as the recognition of goods is concerned, such
antenna arrangements are used in systems, where the position of the transponder at the object is
unknown.
Since there is at least one transponder alignment for all gate types listed, where the transponder
cannot be recognized by the antenna, a 100% recognition rate is impossible without carrying out
further measures in the system.
In the sector of personal recognition, we recommmend to use transponder cards or transponders with
an appropriately large coil. In order to reach acceptable recognition rates, the gate width for smaller
transponders generally has to be small enough so that a person cannot go through.
In the sector of recognition of goods, the use of smaller transponders may be considered, depending
on the other marginal conditions of the system, such as object size and transponder alignment.
When wiring the antenna, both gate sides are generally connected in series, in order to make sure
that the same current is flowing through both halves of the antenna in the appropriate phase position.
4.1. Gate antenna in Helmholtz arrangement
Figure 4.1-1.b shows the field distribution of a gate antenna in Helmholtz arrangement, as well as the
predominant direction of a transponder in this antenna arrangement.
b)a)
Transponder
Figure 4.1-1
This gate type is mainly used for personal identification. The predominant direction of a transponder
for safe recognition is parallel to the shield surface (figure 4.1-1.b). If this marginal condition is also
kept for an object identification device, then this arrangement is also suitable for such a system.

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The optimal shield size for transponders of the ID DTK.B-A –type (transponder card) is approx. 50
cm x 70 cm. In this case, the gate width should not exceed 1m. Generally, the recognition rate in-
creases if the gate width is reduced.
The inductance of a gate antenna in Helmholtz arrangement is slightly higher than the sum of all
single inductances of the two single antennas.
4.2. Gate antenna in Anti-Helmholtz arrangement
Figure 4.2-1.b shows the field distribution of a gate antenna in Anti-Helmholtz arrangement, as well
as the transponder’s predominant direction for this antenna.
a) b)
Transponder
Figure 4.2-1
This gate type as well is used mainly for personal identification. The predominant direction of a
transponder for safe recognition is vertical to the shield surface (Figure 4.2-1.b). If this marginal con-
dition is also kept for an object identification devvice, then this arrangement is also suitable for such
a system.
In general, this gate type has a so-called dead range, situated in the middle between the two anten-
nas. Irrespective of the transponder alignment, communication with the transponder is impossible in
this range.
For the dimensions of such a gate, the same conditions apply as for a gate in Helmholtz arrange-
ment. The optimal shield size for transponders of the ID DTK.B-A –type (transponder card) is 50 cm x
70 cm and the gate width should not exceed 1m.
The inductance of a gate antenna in Anti-Helmholtz arrangement is slightly smaller than the sum of
all inductances of the two single antennas.

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4.3. Gate antenna in mixed arrangement
Figure 4.3-1 shows the field distribution of a gate antenna in mixed arrangement. The left half of the
gate consists of a simple shield antenna and the right half of an 8-loop. This leads to different field
alignments on both sides of the gate and therefore increases the probability that a transponder is
recognized on one of the two sides.
a) b)
Figure 4.3-1
One disadvantage of this arrangement is that, due to the more diffuse field, antenna sizes as used
for Helmholtz- or Anti-Helmholtz arrangement are no longer suitable. Due to the lower maximum
gate width, this arrangement is not suitable for personal identification. In the object identification
sector , this arrangement is however advantageous for systems with lower gate widths, since here
the identification probability increases compared to the other two arrangements.

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5. Influences on the ID RW24-systems
There are two main kinds of environmental influences on an ID RW24-system. On the one hand,
there is the influence of metallic objects in close proximity to the antennas. On the other hand, the
system is influenced by electronic appliances, which impair the reception of the RW24-system by
irradation of magnetic fields into the antenna.
If metallic objects are situated close to the antenna, this will lead to a detuning of the antenna and to
a weakening resp. change in the antenna field intensity. Detuning of the antenna may be leveled out
by an automatic antenna tuner, but the weakening resp. change in the field intensity may lead to
substantial range losses. In order to avoid such effects, no metallic objects should be situated within
a distance of 30 cm around the antenna. The second type of disturbance are electronic appliances,
which produce magnetic fields in the frequency ranges of the carrier frequency (125 kHz) or the data
rate (2 - 8 kHz) of the reader. One extreme example are PC-monitors, who’s magnetic picture tube
units may produce substantial disturbances, depending on their resolution and display rate.
5.1. Mutual influence of two ID RW24-systems
If the antennas of two ID RW24-systems are mounted in close proximity to each other, which means
in a distance of only some meters, a mutual influence is very likely. We distinguish two kinds of influ-
ence:
•by carrier frequencies
•by transmission logs.
5.1.1. Mutual influence by carrier frequencies
An influence on two systems by carrier frequencies makes itself felt by an interference with the dif-
ference frequency of the two systems on the corresponding carrier. This influence may lead to the
situation that both readers are unable to communicate with transponders. One possible remedy for
this is to increase the distance between the two antennas or to protect the antennas with a metallic
shield (see also chapter 5.2.2).
The minimum distance between two gate antennas with a shield size of 50 cm x 70 cm should be at
least 2,5 m, so that the disturbances will not impair the recognition rate in a non-acceptible way.
5.1.2. Mutual influence by transmission logs
An even more serious kind of disturbance is caused by transmission logs of neighbouring antennas.
Depending on the antenna size, the minimum distance between two antennas of noughbouring sys-
tems may exceed 10 m.
A metallic shield for the protection against this kind of disturbance would, depending on the type and
size of the antenna, need dimensions, which cannot be realized in practical operation. For example,
a shroud with an acceptable disturbance supression would need a projecting end of 20 cm on all
sides, if located at a distance of approx. 15 cm from the antenna. However, these values depend
highly on the application and have to be detected by trial.

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This problem may only be solved by a systematically controlled log run for both systems between
antenna and transponder. In this case, we have two possible variants:
1. Communication of only one system resp. antenna with one transponder.
2. Synchronization of the transmission logs of both systems, which means that both readers send
their request protocols and switch on receive mode at the same time.