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AN/FPS-117 “Seek Igloo” (RRP-117)

Description of the radar set, tactical-technical characteristics

Figure 1: RRP-117 antenna
© Lockheed Martin

Figure 1: RRP-117 antenna
© Lockheed Martin

frequency: 1215 - 1400 MHz
pulse repetition time (PRT): 0.9 - 4 ms
pulse repetition frequency (PRF): 250 / 1100 Hz
pulsewidth (τ): 100 / 800 µs
receiving time: 0,6 / 3 ms
dead time: ca 200 µs
peak power: 20 kW
average power:
instrumented range: bis 463 km
range resolution:
beamwidth: β:3,4°, ε:2,7°
hits per scan: 1 … 3
antenna rotation: 12 s or 10 s

AN/FPS-117 “Seek Igloo” (RRP-117)

The air-defense radar AN/FPS-117 (in Germany: RRP-117; Remote Radar Post) is an L band (IEEE designation) or D band (NATO designation) radar system in solid-state technology. It consists of a primary radar, a secondary radar and a subsystem for simulation. The AN/FPS-117 provides 3D- target information in real time over the whole range of detection correlated with the replies of the secondary radar. It uses a phased array antenna turning within 5 rpm (in Germany: 6 rpm) and an electronically steared beam in elevation.

In condition of the using of solid-state transmitter modules the radar works with the pulse compression to get a better range resolution nevertheless the relatively long pulsewidth.

But that is only half the truth: during the transmitting time the antenna is busy and the receiver cannot work! If the pulse width of the transmitter is e.g. 800 microseconds then the receiver can work from 800 µs ·150 m= 120 km. The possible pulse width is limited therefore and the most radar sets use alternating a shorter pulse as the so-called “short range mode”. The peak power is the same as by the long-range mode. The shorter pulse make the energy balance weaker and so the radar set reaches a lower maximum range as by the long-range mode.

AN/TPS-77 (formerly known as the AN/TPS-117) and AN/TPS-59 are mobile variants of Lockheed Martin’s “117” radar family.

Picture gallery of RRP-117

Figure 2: Antenna pattern of a 3D-radar

Figure 3: Animation AN/TPS-59

Figure 4: Maintenance-shelter with the control processing group