The Network consists of U.S. Army, Navy and Air Force operated, ground-based radars and optical sensors at 25 sites worldwide.
"The AN/FPS-133 Air Force Space Surveillance System, colloquially known as the Space Fence, was a U.S. government multistatic radarsystem built to detect orbital objects passing over America. It is a component of the US space surveillance network, and according to the US Navy was able to detect basketball sized (29.5 inches (75 cm)) objects at heights up to 30,000 km (15,000 nautical miles.)
The system ceased operation in September 2013. Plans for a new space fence are underway with sites at the Kwajalein Atoll in the Marshall Islands, along with an option for another radar site in Western Australia.
*or "new/2nd generation Space Fence"
Known previously as "BMEWS radar network" (Ballistic Missile Early Warning System)
It consists of five phased arrays located in four U.S. Air Force Bases/Stations and one UK Royal Air Force (RAF) Base: Beale (California), Cape Cod (Massachusetts), Clear (Alaska), RAF Fylingdales (UK), and Thule (Greenland).
The two East-West Coast RADARs - AN/FPS-123 PAVE PAWS (Beale and Cape Cod):
When in the early 1970s certain limitations occurred concerning the detection of Soviet missiles by the East and West Coast Radars 474N, two new radars of the phased-array type were proposed.
Phased arrays were selected because mechanically-rotated RADAR could not rotate fast enough to track many missiles. The beam of a phased array is steered electronically within milliseconds.
The two proposed Radars would constitute the PAVE PAWS (PAVE: Precision Acquisition Vehicle Entry) (PAWS: Phased Array Warning System) and would be of the type "AN/FPS-115" (cf. below). One would be installed in the East Coast at the Otis Air Force Base in Cape Cod, Massachusetts and another at the Beale Air Force Base in California (near Sacramento). These reached initial operating capability in 1981. The two new Radars marked the initiation of the "Solid State Phased Array Radar System" (SSPARS). The term "solid state" refers to the generation of transmitters that followed those with vacuum tube electronic devices (VEDs) e.g. klystrons and magnetrons.
"The AN/FPS-115 radar consists of two phased arrays of antenna elements mounted on two sloping sides of the 105 ft high transmitter building". "The radar operates in the UHF band between 420 - 450 MHz, just below the UHF television broadcast band, that is a wavelength of 71–67 cm, with circular polarization."
Eventually an upgrade was conducted to AN/FPS-123 (Raytheon).
It is noted that Radar names use prefix "AN/" for "Army-Navy" followed by a three-letter code e.g. AN/FPS stands for: F = Fire control radar, P = Automatic transmitting and receiving, S = Search (https://en.wikipedia.org/wiki/List_of_radars#United_States)
The entire SSPARS as of January 31, 2001 consisted of the following (image): https://en.wikipedia.org/wiki/Solid_State_Phased_Array_Radar_System
1) AN/FPS-123 PAVE PAWS Radar at Beale (FPS-115 IOC 1980) and Cape Cod (FPS-115 IOC 1980)
2) AN/FPS-120 Solid State Phased Array Radar at Thule with greater Radar capabilities than the FPS-115 PAVE PAWS radars
3) AN/FPS-126 Solid State Phased Array Radar at Fylingdales with three faces for 360 degree coverage
4) AN/FPS-120 Solid State Phased Array at Clear (using an older antenna from the 1987 PAVE PAWS EWR in Texas for the "Clear Radar Upgrade") - "upgraded to the AN/FPS-123 model" SSPA Radar
Note that Raytheon was the prime contractor for all.
"The US approved sale of an AN/FPS-115 to Taiwan in 2000 and it was introduced in 2006."
Environmental and health concerns
"USAF environmental assessments in August 1975 and March 1976 for PAVE PAWS were followed by the EPA's Environmental Impact Analysis in December 1977. Environmental impacts were litigated in U.S. District Court in Boston. The government asserted the position that Pave Paws would protect the American coastline (...)"
Figure 4: VLF/LF submarine communication system (From https://fas.org/nuke/guide/usa/c3i/vlf.htm)