91N6

The 91N6 (NATO designation “Big Bird”) is an S-band surveillance and tracking radar operating at 2.9–3.3 GHz, developed for the SA-21 “Growler” (S-400 “Triumf”) surface-to-air missile system. The 91N6E variant is an upgraded version of the 64N6E radar (NATO designation “Tombstone”), featuring the same antenna design but increased transmitter power. Its digital signal processing enables detection of up to 300 targets, with an instrumented range of 600 km and an accuracy of 200 meters and 0.5 degrees. The radar system is housed in two containers: one for radar electronics and indicators, and the other for transmitters, receivers, and antennas. It utilizes two back-to-back, space-fed phased-array antennas of reflection type, each with 2,700 phase shifters, allowing beam scanning in two planes and antenna rotation at 5 or 10 revolutions per minute. The radar offers various operating modes, including continuous antenna rotation, sector view, stopped antenna drive, and additional antenna tilt, and incorporates an IFF system and auxiliary antenna/receiver channels for sidelobe jammer suppression.

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