Siemens SIMATIC RF600 System Manual page 71

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.
①
②
③
Figure 4-16
Linear antennas can only be used if the alignment of the transponder is defined. On the
other hand, one advantage of linear antennas is that they react less sensitively to reflections.
This restriction does not apply with circular polarization. Circular antennas can also be used
with differing alignments of the transponder and achieve constant results (e.g. RF680A or
RF685R). It has been shown that with a defined transponder alignment, the linear antenna
normally produces the best results.
SIMATIC RF600
System Manual, 06/2019, J31069-D0171-U001-A22-7618
Polarization axes parallel: approx. 100 % range
Polarization axis turned through 45°: approx. 50% range
Polarization axis turned through 90°: approx. 10% range
Effect of the polarization axes on the write/read distance with linear antennas
4.7 Planning and installation of UHF read points
RF600 system planning
71