The AN/FPS-126 is a solid-state, space tracking, phased array radar which belongs to the US Air Force Space Command PAVE PAWS radar system. This system is under the control of three 21st Space Wing squadrons for missile warning and space surveillance. The AN/FPS-126 operates at a frequency of 420 to 450 MHz and has the ability to track thousands of satellites orbiting the earth. Developed by Raytheon in the 1980s, the PAVE PAWS radar system is used mainly to detect and track sea-launched (SLBM) and intercontinental ballistic missiles (ICBMs). The radar system is capable of detecting and monitoring a great number of targets that would be consistent with a massive SLBM attack. The system must rapidly discriminate between vehicle types, calculating their launch and impact points in addition to the scheduling, data processing and communications requirements. The operation is entirely automatic, requiring people only for monitoring, maintenance and as a final check of the validity of warnings. Three different computers communicate with each other from the heart of the system, which relays the information to Cheyenne Mountain AS.
The AN/FPS-126 phased array antenna beam steering is done rapidly by electronically controlling the timing (the phase) of the incoming and outgoing signals. Controlling the phase through the many segments of the antenna system allows the beam to be quickly projected in different directions. This greatly reduces the time necessary to change the beam direction from one point to another, allowing almost simultaneous tracking of multiple targets while maintaining the surveillance responsibility. This ability is known as "track while scan". The large fixed antenna array through its better beam focusing, improves system sensitivity and tracking accuracy. A phased array antenna receives signals from space only in the direction in which the beam is aimed. The maximum practical deflection on either side of antenna center of the phased array beam is 60 degrees. This limits the coverage from a single antenna face to 120 degrees. To provide surveillance across the horizon, the building housing the entire system and supporting the antenna arrays is constructed in the shape of a triangle. The two building faces supporting the arrays, each covering 120 degrees, will monitor 240 degrees of azimuth. The array faces are also tilted back 20 degrees to allow for an elevations deflection from three to 85 degrees above horizontal.