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1S91 “Straight Flush”

Description of the radar set, tactical-technical characteristics

Figure 1: 1S91 “Straight Flush”

Figure 1: 1S91 “Straight Flush”

frequency: C-Band I-Band
pulse repetition time (PRT):
pulse repetition frequency (PRF):
pulsewidth (τ):
receive time:
dead time:
peak power: 600 kW
average power: 25 kW
instrumented range: 75 km
range resolution:
hits per scan:
antenna rotation: 15 or 20 min-1

1S91 “Straight Flush”

The 1S91 (Cyrillic: 1С91; NATO designation: Straight Flush) is a missile guidance radar for the surface-to-air missile system “Kub” (Cyrillic: Куб, NATO designation: SA-5 Gammon). With the built-in high-resolution TV camera, the target can also be tracked visually. The radar system operates in C-band and the target tracking radar and target illumination transmitter in I-Band. The secondary radar method with “active response” is used for target tracking of the anti-aircraft missile.

The “Kub” anti-aircraft missile complex was included in the armament of the armed forces of the Soviet Union in 1967 and was in the service of many states of the former Warsaw Treaty. Mistakenly believing that it was targeting a Ukrainian transport aircraft, the Malaysia Airlines MH17 plane was shot down over Ukrainian territory with the help of this radar.

Surveillance radar 1S11

The antenna of the 1S11 surveillance radar is a rectangular parabolic cutout and is mounted on the turret of the tracked vehicle. The search radar can be moved independently of the target tracking radar.

Target tracking radar 1S31

The antenna of the 1S31 fine search and target tracking radar is a solid circular parabolic reflector with a small planar reflector for target illumination suspended in front of the feed. The entire antenna unit can be rotated horizontally 360° independently of the search radar. The target illumination transmitter is integrated into the antenna of the 1S31.

Picture gallery of “Straight Flush”

Figure 2: Surface-to-air missile system “Kub”, SA-5 Gammon