Alim is the first Iranianpassive radar. Passive radars do not transmit waves and instead, detect and track objects by processing reflections from non-cooperative sources of illumination in the environment, such as commercial broadcast and communications signals.
Alim is cheaper and has less maintenance cost than normal radars because it doesn't have transmitter and movable mechanical parts. Although it needs high processing power because it has to do six levels of processing to track a target. Other advantages include the ability to detect low RCS targets in low altitudes. Also as it doesn't transmit anything, it is not possible to destroy it using anti radiation missiles such as American AGM-88 HARM thus it can be deployed near the enemy lines.
It was first seen in 2011 during the parade of Iranian armed forces. The radar has a range of between 250-300 km and is able to detect slow, low flying targets with relative ease.