Siemens SIMATIC RF640A Operating Instructions Manual page 29

Interpretation of directional radiation patterns
The following overview table will help you with the interpretation of directional radiation patterns.
The table shows which dBi values correspond to which read/write ranges (in %): You can read the radiated power
depending on the reference angle from the directional radiation patterns, and thus obtain information on the read/write range
with this reference angle with regard to a transponder.
The dBr values correspond to the difference between the maximum dBi/dBic value and a second dBi/dBic value.
Deviation from maximum antenna gain [dBr]
0
-3
-6
-9
-12
-15
-18
Example
As can be seen in Directional radiation patterns in the ETSI frequency band (Page 8), the maximum antenna gain in the
vertical plane is 3.45 dBi (6.45 dBic). In this plane, and with the polarization axis of the transponder parallel to the axis of
symmetry of the antenna, the antenna gain drops to about 0.5 dBic at +50° or 310°. Therefore the dBr value is -6. The
antenna range is only 50% of the maximum range at + 50° or 310° from the Z axis within the vertical plane (see values
shown in blue in the directional radiation pattern: Characteristic of the vertical plane of the antenna (Page 8) and the
associated representation of the reference system (Page 7)).
SIMATIC RF640A
J31069-D0225-U001-A2-7618, 12/2010
Read/write range [%]
100
70
50
35
25
18
13
13