Siemens SIMATIC RF600 System Manual page 161

Selection of linear polarized antenna
When using linear polarized antennas, you must always make sure that the transmitter
antenna, receiver antenna and transponder have identical polarizations (vertical or
horizontal). As a result of the principle used, no special requirements need be observed to
suppress the orthogonal components (cross-polarization).
①
②
③
Figure 6-7
Front-to-back ratio
Definition
As a result of their design, directional antennas not only transmit electromagnetic waves in
the main beam direction but also in other directions, particularly in the reverse direction. The
largest possible suppression of these spurious lobes is expected in order to reduce faults
and to keep the influence on other radio fields low. This attenuation of spurious lobes in the
opposite direction to the main beam is called the front-to-back ratio.
Specifications
Requirement: The front-to-back ratio must be ≥ 10 dB. This requirement also applies to
spurious lobes illustrated by the following graphics in Section Beam width (Page 162).
SIMATIC RF600
System Manual, 10/2009, J31069-D0171-U001-A8-7618
Transmitter antenna, vertical polarization
Receiver antenna, vertical polarization
Transponder dipole
Homogenous vertical polarization of antenna system and transponder
6.2 Guidelines for selecting RFID UHF antennas
Antennas
161