Side Lobe Suppression
In secondary surveillance radar technology the sidelobes of the antennas affect particularly unfavourably. Transponders also can be interrogated over the sidelobes and then answer about these, too and a response telegram can be received also over the sidelobes. This circumstance results from the fundamentally better transmitting- and reception conditions for secondary radar units.
Such answers cannot be assigned obviously on the radar screen. They rather appear as several targets in the same range but in different directions. In the extreme case an airplane can be interrogated permanently during a turn of the antenna. Such an reply then appears on the PPI-scope as a „ring around”.
There are two principles of Side Lobe Suppression (SLS)
- Interrogation Path Side Lobe Suppression (ISLS), and
- Reply Path Side Lobe Suppression (RSLS)
The techniques for ISLS are very similar to those for RSLS.
A supplementary so-called
method uses the techniques of ISLS to reduce the influence of false replays caused by reflection.