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Description of the radar set, tactical-technical characteristics

Figure 1: AN/CPS-4 at Keesler Air Force Base (AFB) in 1950

frequency: 2 700 … 2 900 MHz
pulse repetition time (PRT): 1 575 µs
pulse repetition frequency (PRF): 635 Hz
pulsewidth (τ): 2 µs
receiving time:
dead time:
peak power: 750 kW
average power:
instrumented range: 90 NM
range resolution:
beamwidth: β= 4.7°; ε= 1.2°
hits per scan:
antenna rotation:

AN/CPS-4 height-finding radar

AN/CPS-4 “Beaver Tail” was a medium range S band nodding height-finding radar developed by MIT’s Radiation Laboratory used by the United States Air Force Air Defense Command. The radar was designed to be used in conjunction with the SCR-270 and SCR-271 search sets.

The CPS-4 required six operators. This S-band radar could detect targets at a distance of ninety miles. It showed these targets on an RHI-scope. The AN/CPS-4 antenna was horn fed with a reflector 20 x 5 ft shaped as an elliptical section of a paraboloid. The antenna gave a beam 1.2° wide in the vertical plane, and to pick up the targets in altitude this was raised and lowered 25 cycles per minute by nodding the antenna structure between −2° and 32°. The radars accuracy was 1000 ft in absolute altitude and 500 ft in relative altitude at 45 miles range, preferably 90 miles.[1] This radar was often paired with the AN/FPS-3 search radar during the early 1950s at permanent network radar sites.

The first production model AN/CPS-4 came out in June 1945. The AN/CPS-4 was installed e.g. in der Keesler AFB, in US Omaha Air Force Station (AFS) and Belleville AFS,[2] as well as in Germany on the Erbeskopf-Site. The AN/CPS-4 was also used in meteorology, to explore the structure of the “Bright Band”.[3]

Sources and ressorces:

  1. Chas. R. Burrows, Stephen S. Attwood: “Radio Wave Propagation, Consolidated Summary Technical Report of the Committee on Propagation of the National Defense Research Committee”, Academic Press Inc. New York, 1949, p. 65 (online preview)
  2. Mark L. Morgan, Mark A. Berhow: “Rings of Supersonic Steel. Air Defenses of the United States Army 1950-1979: an Introductory History and Site Guide” Hole In The Head Press, 2002, ISBN 0615120121, p. 135, 175 (online preview)
  3. L Brown: “Technical and Military Imperatives. A Radar History of World War 2” CRC Press, 1999, ISBN 0750306599, p. 443 (online preview)