 Bendix AN/FPS-20 radar | |
| Country of origin | United States |
|---|---|
| Type | General Surveillance Radar |
| Frequency | L band |
| PRF | 440 |
| Pulsewidth | 4 μS |
| RPM | 3.3, 5, 10 RPM |
| Power | 750 kW x 2 |
| Other Names | AN/FPS-3, AN/MPS-7, AN/FPS-64, AN/FPS-65, AN/FPS-66, AN/FPS-67, AN/FPS-91, AN/FPS-93, AN/FPS-100, AN/FPS-113, AN/GPS-4, AN/FPS-508 |
TheAN/FPS-20 was a widely usedL bandearly warning andground-controlled interception radar system employed by theUnited States Air ForceAir Defense Command, theNORADPinetree Line inCanada, the USAFCONAD in the continental United States, and a variety of other users. The design started life as theBendixAN/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 earlyCold War 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 theFAA, modified forair traffic control use, and becameARSR-60s.
The first AN/FPS-3 arrived in December 1950, slated for installation atEniwetok Atoll to control aircraft involved in the atomic bomb tests of early 1951.[1] Over the next few years, 48 FPS-3s were installed to replace older systems in theLashup Radar Network. The FPS-3 and was also produced as theAN/MPS-7, a mobile version.[2][a] The system used two 5J26magnetrons at 750 kW peak power, operating at 1300 MHz a 400 Hzpulse repetition frequency (prf) and 2 microsecond pulse width.[4] 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 55,000 feet (17 km) 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 theAN/GPA-27 add-on unit, increasing the altitude to 65,000 feet (20 km).[N 1] Installations began in 1956.[2][N 2] New-build units from Bendix with this equipment pre-installed became the AN/FPS-20 in 1957.[N 3] 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.[N 4]
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.[5] Similar upgrades using a Canadian OA-4831 system produced theAN/FPS-87 and AN/FPS-87A. The BADGE 412-L upgrade of the FPS-20A created theAN/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 theAN/FPS-91 and 91A. The similar MK-748 applied to the -60 series resulted in theAN/FPS-64A,AN/FPS-65A,AN/FPS-66A andAN/FPS-67A. Canadian AN/FPS-87s were also converted, becomingAN/FPS-93 and 93A. These units were used with theSAGE system.[6]
The FPS-20 was widely used in Japan. They produced their own series of modifications, including atunnel diode 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 digitalmoving target indicator (MTI) system from Bendix to create theAN/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 later produced a similar digital MTI system, theAN/FPS-113.
In accordance with theJoint Electronics Type Designation System, the radar's "AN/FPS-20" designation represents the 20th design of an Army-Navy fixed radar(pulsed) electronic device for searching.[7][8]
