English: A secondary surveillance radar (SSR) near the military airport "Neubrandenburg" (ETNU) in Germany/Western-Pommerania. SSRs interrogate the transponders on civilian craft and the IFF (Identification Friend or Foe) units on military craft. These units transmit a coded signal back to the SSR identifying the aircraft and giving its altitude, so this information appears on the radar screen of the air traffic controller. This SSR uses an LVA (large vertical array) antenna. It consists of a series of vertical waveguides with slots cut in them which act as radiators. This type of phased array antenna has better control of energy radiated at low angles, preventing ground reflections that cause nulls in the radiation pattern which can result in an aircraft not being detected.