The AN/FPS-20 was a widely used

L band The L band is the Institute of Electrical and Electronics Engineers (IEEE) designation for the range of frequencies in the radio spectrum from 1 to 2 gigahertz (GHz). This is at the top end of the ultra high frequency (UHF) band, at the lower en ...

early warning and ground-controlled interception radar system employed by the

United States Air Force The United States Air Force (USAF) is the air service branch of the United States Armed Forces, and is one of the eight uniformed services of the United States. Originally created on 1 August 1907, as a part of the United States Army Si ...

Air Defense Command Aerospace Defense Command was a major command of the United States Air Force, responsible for continental air defense. It was activated in 1968 and disbanded in 1980. Its predecessor, Air Defense Command, was established in 1946, briefly inac ...

, the

NORAD North American Aerospace Defense Command (NORAD ), known until March 1981 as the North American Air Defense Command, is a combined organization of the United States and Canada that provides aerospace warning, air sovereignty, and protection ...

Pinetree Line in

Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by to ...

, the USAF

CONAD Conad ('), stylized CONAD, is an Italian retail store brand which operates one of the largest supermarket chains in Italy. Created in 1962, Conad is a cooperative A cooperative (also known as co-operative, co-op, or coop) is "an autono ...

in the continental United States, and a variety of other users. The design started life as the Bendix AN/FPS-3 in 1950, was upgraded to the FPS-20, then spawned over a dozen different variants as additional upgrades were applied. The FPS-20 formed the backbone of the US air defense network through the early

Cold War The Cold War is a term commonly used to refer to a period of geopolitical tension between the United States and the Soviet Union and their respective allies, the Western Bloc and the Eastern Bloc. The term '' cold war'' is used because t ...

with over 200 units deployed. Most FPS-20 sites were replaced by modern equipment in the late 1960s, although a number were turned over to the FAA, modified for

air traffic control Air traffic control (ATC) is a service provided by ground-based air traffic controllers who direct aircraft on the ground and through a given section of controlled airspace, and can provide advisory services to aircraft in non-controlled airsp ...

use, and became ARSR-60s. The first AN/FPS-3 arrived in December 1950, slated for installation at Eniwetok Atoll to control aircraft involved in the atomic bomb tests of early 1951. Over the next few years, 48 FPS-3s were installed to replace older systems in the Lashup Radar Network. The FPS-3 and was also produced as the AN/MPS-7, a mobile version. The system used two 5J26

magnetron The cavity magnetron is a high-power vacuum tube used in early radar systems and currently in microwave ovens and linear particle accelerators. It generates microwaves using the interaction of a stream of electrons with a magnetic field while ...

s at 750 kW peak power, operating at 1300 MHz a 400 Hz pulse repetition frequency (prf) and 2 microsecond pulse width. The antenna was driven at three fixed speeds of 3.3, 5 or 10 RPM, normally operating at 5. Many of the operating modules were mounted on the rotating platform, with the output signals fed via slip rings to amplifiers and displays at the base of the unit. The FPS-3 was limited to about altitude, which was seen as a limitation in light of new jet-powered bombers known to be in development in the USSR. This led to the development of the AN/GPA-27 add-on unit, increasing the altitude to .The GPA-27 may be the slotted waveguide mounted on the top of the main antenna seen in images of the FPS-20. However, some images show this on radars labeled FPS-3, although this may be before they were renamed. Installations began in 1956.Winkler refers to upgraded units as FPS-3B on page 76, but other sources agree with his own page 33 that these were actually called FPS-3A. New-build units from Bendix with this equipment pre-installed became the AN/FPS-20 in 1957.Winkler does not mention this directly, but notes on page 77 that -3A units were also renamed FPS-20 when receiving updates. Otherwise similar units with an antenna from General Electric were known as the AN/FPS-20B. The slotted-waveguide antenna pictured above the AN/FPS-20 is for the associated IFF system.A high-resolution Slotted-waveguide IFF antenna for the AN/FPS-3 radar by J.Y. Wong 1957 NRC Canada. The FPS-20s were simple pulse-radar systems and subject to jamming using basic techniques. This led to a second series of upgrades to provide anti-jamming capabilities starting in 1959. Among these were the GPA-102 (MK-448) which turned an FPS-20 into an FPS-64 and a FPS-20A to an FPS-66, and the GPA-103 (MK-447) which turned a FPS-20 into an FPS-65 and the FPS-20A into an FPS-67. Similar upgrades using a Canadian OA-4831 system produced the AN/FPS-87 and AN/FPS-87A. The BADGE 412-L upgrade of the FPS-20A created the AN/FPS-82. A more major update was the MK-747, which added a new antenna from Raytheon, the Diplex Gating Unit (DGU), a bandpass filter and other modifications, to produce the AN/FPS-91 and 91A. The similar MK-748 applied to the -60 series resulted in the AN/FPS-64A, -65A, -66A and -67A. Canadian AN/FPS-87s were also converted, becoming AN/FPS-93 and 93A. These units were used with the SAGE system. The FPS-20 was widely used in Japan. They produced their own series of modifications, including a

tunnel diode A tunnel diode or Esaki diode is a type of semiconductor diode that has effectively " negative resistance" due to the quantum mechanical effect called tunneling. It was invented in August 1957 by Leo Esaki, Yuriko Kurose, and Takashi Suz ...

based amplifier and a separate receiver for the Airborne Instruments Laboratories system, producing the AN/FPS-20/20A JAPAN, or -J. The Indian Air Force used the FPS-20 with a new digital

moving target indicator Moving target indication (MTI) is a mode of operation of a radar to discriminate a target against the clutter. It describes a variety of techniques used for finding moving objects, like an aircraft, and filter out unmoving ones, like hills or tre ...

(MTI) system from Bendix to create the AN/FPS-100 and 100A. These systems were known as the "Blue Pearl", or Bendix Radar Processor BRP-150. These were remanufactured units with a new antenna, and included a new low-noise front-end amplifier.

General Dynamics General Dynamics Corporation (GD) is an American publicly traded, aerospace and defense corporation headquartered in Reston, Virginia. As of 2020, it was the fifth-largest defense contractor in the world by arms sales, and 5th largest in the Uni ...

later produced a similar digital MTI system, the AN/FPS-113.

Notes

References

Citations

Bibliography

* * ;Further reading
AN/FPS-3, 3A, 3B; MPS-7
radomes.org

radomes.org

radomes.org

{{DEFAULTSORT:AN FPS-020 Ground radars Military radars of the United States Radars of the United States Air Force Military equipment introduced in the 1950s Bendix Corporation