SSR SLS Polar Diagram RNAV
The side lobe suppression, or SLSSLS —Side Lobe Suppression, or P2 pulse, is an omnidirectional pulse. As such, it will not be as strong as the main beam of the directional P1/P3 pulses (the pulse that travels in the direction the aerial is facing) but it will be stronger than any sidelobes (P1/P3 pulses travelling in directions other than the way the aerial is facing).
The purpose of this is so the aircraft knows whether or not the interrogation was valid. If the P1/P3 pulses were stronger than the P2 pulse, the aircraft is along the main beam axis, the interrogation is valid, and the aircraft responds. If the P2 pulse was stronger than the P1/P3, however, that means that the P1/P3 pulses were from a sidelobe, and so that interrogation can be ignored.