Siemens SIMATIC RF600 Series System Manual page 60

RF600 system planning
4.6 Planning and installation of UHF read points
Propagation of the antenna field
The waves do not propagate as a homogeneous field, there is superposition of the waves
that can cause the following effects:
● Overshoots and field gaps due to obliteration of two waves
These are caused by reflection and the resulting propagation on different paths
(comparable with fading effects on the car radio, e.g. noise when the vehicle is standing)
● Generation of overshoots due to reflecting objects and surfaces
This can be illustrated by comparing it with a "hall of mirrors". The signal transmitted by the
reader is reflected (several times) by metallic objects such as housings, steel supports or
grilles and this can lead to unwanted effects and read errors. Is also possible that a
transponder is not identified although it is located in the assumed direct identification range
of the reader. It can also happen that a transponder moving outside the antenna field is read
out due to overshoots.
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②
Figure 4-6
Properties of the transmitting antenna
Depending on their design, UHF RFID antennas provide different properties. They differ in
the polarization and antenna gain.
The direction of the electrical field component of an electromagnetic wave and the alignment
of the antenna decide the polarization of the radiation. A distinction is made between linear
and circular polarization of an antenna. With linear polarization you achieve the maximum
write/read distances when the polarization axes of the antenna and transponder are parallel
to each other. As the deviation increases, the received power deteriorates.
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Identification situation with two transponders in an ideal radio/antenna field
Identification situation with two transponders in a real radio/antenna field with reflections that can
lead to obliteration and overshoots
Propagation of UHF RFID antenna fields
System Manual, 10/2016, J31069-D0171-U001-A19-7618
SIMATIC RF600