OVERVIEW: The AN/FPS-23 “Fluttar” (Flutter Radar) was continuous wave (CW), short-range gap filler radar system to fill the low-altitude gaps between AN/FPS-19 radars in the Distant Early Warning (DEW) line. It operated in the UHF Band.

DETAILS:  AN/FPS-23 radars were continuous wave (CW) systems composed of geographically-separated AN/FPT-4 Fluttar Transmitters and AN/FPR-2 Fluttar Receivers. AN/FPT-4 Fluttar Transmitters were located only at Intermediate ("I") Sites, while AN/FPR-2 Fluttar Receivers were located only at Main and Auxiliary Sites. The transmitters and receivers were typically about fifty miles apart. 

Designed to detect aircraft crossing at low altitude (50 feet over water, 200 feet over land), The FPS-23 fluttar system differed markedly from conventional pulse-generating radars. The transmitter antenna generated a steady stream  of continuous wave beams which were picked up by a receiver at the next DEW station. A target penetrating the electronic field created Doppler-induced frequency changes in the field, which triggered an alert.

Specifications:

Frequency: 		475 … 525 MHz (UHF Band)
Power output: 		1 KW (average);  2 MW (peak)
PRF:			  300-500 Hz	
Range Resolution:	 				
On/Off time:		unknown
Deploy/Stow Time	unknown
Max Range:		approx. 50 miles

		

NOTES: IOC 1952.  An ineffective system, the USAF evaluated the the AN/FPS as having "demonstrated virtually no operational usefulness." Hisorically, the system reported only 79 percent of known penetrations of the system, and generated more false alarms than actual alarms.  Decommissioned in 1963.

SOURCES:    
"AN/FPS-23 - Radartutorial." Grundlagen Der Radartechnik. Accessed April 27, 2020. https://www.radartutorial.eu/19.kartei/11.ancient2/karte042.en.html.
"AN/FPS-23." Accessed April 27, 2020. https://www.radomes.org/museum/parseequip.php?html=fps-23.html&type=equip_html ; "AN/FPS-23." Military Wiki. Accessed April 27, 2020. https://military.wikia.org/wiki/AN/FPS-23 ; "Technical Info." DEWLine Adventures. Accessed April 27, 2020. https://www.dewlineadventures.com/technical-info/; Ray, Thomas W.,  ADC Historical Study No. 31: "A History of the DEW line, 1946-1964", (June 1965) located at https://www.northcom.mil/Portals/28/Paper%20No%2031%20A%20History%20of%20the%20Dew%20Line,%201946-1964%20Full%20Release.pdf?ver=2017-03-16-115749-817;