APESARS

An aspect of this radar is phased array antenna technology which is now common in defence applications. This system differs from a mechanical radar, which must be physically aimed at an object in space to detect and/or track it. The phased array antenna is in a fixed position and can be part of the building wall. Phased array antenna aiming, or 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.

Construction period(1992-2001)
A phased array antenna, as with any other directional antenna, will receive 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. 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.

Performance
The primary radars of RAF Fylingdales are Active Electronically Scanned Array (AESA) (phased array) radars, mounted on each face of a truncated tetrahedron, typically referred to as the "pyramid". This makes Fylingdales unique amongst its peers in that it covers a full 360 degrees. Each of the three arrays contains around 8,560 transmit/receive modules; total peak power output equates to some 7.5MW, with a tracking range of 6,000+ miles.

In wave theory, a phased array is a group of antennas in which the relative phases of the respective signals feeding the antennas are varied in such a way that the effective radiation pattern of the array is reinforced in a desired direction and suppressed in undesired directions.[1] Phased array transmission was originally developed in 1905 by Nobel  Laureate Karl Ferdinand Braun who demonstrated enhanced transmission of radio waves in one direction.[2]  During World War II, Nobel  Laureate Luis Alvarez used phased array transmission in a rapidly-steerable radar system for "ground-controlled approach", a system to aid in the landing of airplanes in England. At the same time GEMA in Germany built the PESA Mammut 1.[3] It was later adapted for radio astronomy leading to Nobel Prizes for Physics for Antony Hewish and Martin Ryle after several large phased arrays were developed at the University of Cambridge. The design is also used in radar, and is generalized in interferometric radio antennas. DARPA researchers recently announced a 16 element phased array integrated with all necessary circuits to send at 30–50 GHz on a single silicon chip for military purposes.[4]

An antenna array is a multiple of active antennas coupled to a common source or load to produce a directive radiation pattern. Usually the spatial relationship also contributes to the directivity of the antenna. Use of the term "active antennas" is intended to describe elements whose energy output is modified due to the presence of a source of energy in the element (other than the mere signal energy which passes through the circuit) or an element in which the energy output from a source of energy is controlled by the signal input. One common application of this is with a standard multiband television antenna, which has multiple elements coupled together.