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Antenna Manual
ID RW24
FEIG ELECTRONIC GmbH
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h80391-1e-ID.doc
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.
