The 64N6E Big Bird is the key to the improved engagement capability, and ballistic missile intercept capability in the later S-300P variants. This system operates in the 2 GHz band and is a phased array with a 30% larger aperture than the US Navy SPY-1 Aegis radar, even accounting for its slightly larger wavelength it amounts to a mobile land based Aegis class package. It has no direct equivalent in the West.
Like other components of the S-300PM system, the 64N6E has a number of unique and lateral design features. The radar antenna is mounted on a cabin, in turn mounted on a turntable permitting 360 degree rotation. Unlike Western phased arrays in this class, the 64N6 uses a reflective phased array with a front face horn feed, the horn placed at the end of the long boom which protects the waveguides to the transmitters and receivers in the cabin. The beam steering electronics are embedded inside the antenna array, which has around 2700 phase elements on either face. This Janus faced arrangement permits the Big Bird to concurrently search two 90 degree sectors, in opposite directions, using mechanical rotation to position the antenna and electronic beam steering in azimuth and elevation. This design technique permits incremental growth in output power as the only components of the system which have to handle high microwave power levels are the waveguide and feed horn.