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AN/FPS-115 “Pave Paws”

Description of the radar set, tactical-technical characteristics
AN/FPS-115 - Source: National Archive, Released to Public Domain

Figure 1: AN/FPS-123at Clear Air Base, Alaska (USA)
(64°18'00.93" N   149°11'27.91" W)

frequency: 420 … 450 MHz
pulse repetition time (PRT):
pulse repetition frequency (PRF): 0.02 … 20 Hz
pulsewidth (τ): 250 … 16 000 µs
receiving time: > 38 ms
dead time:
peak power: 600 kW (per face)
average power: 150 kW
instrumented range: 3 000 NM (4 800 km)
range resolution:
beamwidth: 2.2 degrees
hits per scan:

AN/FPS-115 “Pave Paws”

AN/FPS-115 “Pave Paws” is a long-range UHF Early Warning Radar for Sea-launched Launched Ballistic Missile (SLBM) detection and warning and satellite tracking system. It is a solid-state active aperture phased array radar that was built for the Electronic Systems Division of the U.S. Air Force by the Equipment Division of the Raytheon Company during the late 1970s.[1][4]

The two-faced radar uses 1792 active T/R modules per face, and each module interfaces with a dipole antenna element. The elements are bent dipoles, each supported by a two-post balun. Crossed dipoles are used, thus providing both vertical and horizontal polarization. Extra passive elements and a narrow beam are used on receive, and upgrade capability has been included for the future installation of up to 5354 T/R modules per array face.[2] Search pulse lengths are 0.3, 5 (typical) and 8 ms with a chirp bandwidth of 0.1 MHz. Track pulse length are 0.25, 0.5, 1, 2, 4, 8, and 16 ms with a bandwidth of 1 MHz.[3]

Pave Paws consists of a pair of circular planar phased-arrays about 30 m in diameter. The arrays are inclined from the vertical by 20º and mounted in adjacent sides of a building measuring about 32 m high, forming sloping walls on the seaward side of the structure. Combined coverage of the electronic beams of the two arrays is 85º in elevation and 240º in azimuth.

The AN/FPS-115 system being installed at Fylingdales Moor (UK) differs from the others in that it has three faces, which will provide warning and tracking capabilities over 360º in azimuth.

Raytheon builds the AN/FPS-115 “Pave Paws” phased-array missile-warning radars first deployed during the early 1980s. There were originally four continental United States (CONUS) sites. Two of the original CONUS sites – Cape Cod AFS, MA, and Beale AFB, CA – are still in operation, and their radars were recently upgraded to the higher-power, more-capable AN/FPS-123 model. The other two CONUS sites – Robins AFB, GA, and Eldorado AFS, TX – have now ceased operations. The radar from Eldorado AFS was relocated to Clear AFS, AK, replacing the older BMEWS radar there. The Clear AFS “Pave Paws” radar also has been upgraded to the AN/FPS-123 model. Similar “Pave Paws” radars replaced the BMEWS radars at Thule AB, Greenland, and at RAF Fylingdales, UK. Thule AB received an AN/FPS-120 model, while RAF Fylingdales received an AN/FPS-126 model. The AN/FPS-126 is unique, having three radar faces, while the AN/FPS-120 and AN/FPS-123 each have two radar faces.

The AN/FPS-120, AN/FPS-123, AN/FPS-126, and AN/FPS-132 are all upgraded versions of the original AN/FPS-115 “Pave Paws” phased-array radar.[4] The AN/FPS-132 Early Warning Radar is designed to detect missile launches that take place thousands of miles away, providing many minutes of warning time to alert command and control centers and cue fire control systems. In 2013 the United States sold an AN/FPS-132 radar to Qatar.

Sources and ressorces:

  1. D. Hoft, “Solid-state transmit/receive module for the PAVE PAWS phased array radar,” Microwave Journal, pp. 33-35, October 1978.
  2. Merrill Ivan Skolnik, “Radar Handbook,” McGraw-Hill Companies, 2008, 3. Edition, ISBN 978-0-07-148547-0, p. 11.31
  3. Jerry L Eaves; Edward K Reedy: “Principles of Modern Radar,” Boston, MA : Springer US, 1987., ISBN 978-1-4612-9170-1, p. 475
  4. Jane’s Radar and Electronic Warfare Systems
Picture gallery of AN/FPS-115 “Pave Paws”

Figure 2: The „Pave Paws“ uses a thinned array

Figure 3: The AN/FPS-132 Early Warning Radar provides early detection and precise tracking of ballistic missiles.