The Erieye described:
The Erieye is an active phased-array radar, operating in the S-band (3.1 to 3.3 Ghz). Its solid state hardware uses 192 transmitter/receiver (T/R) units, that are arranged in a row at the centre of a carbon fibre antenna unit that is mounted above the carrier aircraft. The antenna plates for the radar run along both sides of the housing. Two cooling ducts run above and below the radar modules, and between the antenna plates, fed by a ram air inlet at the front of the antenna unit. The radar is a multi-mode pulse-Doppler system that has a high bandwith and a flexible waveform. The beamwidth (in azimuth and elevation) is 0.7 degrees and 9 degrees. It has a selected 3-D capability and uses an adaptive sidelobe cancelling technique to improve the performance of what is already a low sidelobe antenna design.
The Erieye radar has an instrumented range of around 450km (279 miles). It can detect a (high- altitude) fighter-sized target at around 350km (186 miles), a surface ship at around 300km (186 miles) and a low-flying cruise missile-type target at about 150km (93 miles). The ESM system has a detection range of 450km (279 miles) against a fighter radar.
The Erieye surveillance search area is defined by the operator and can be concentrated across a broad front or in a constant, specific area. The search pattern can be aircraft-stabilised, to search along the track flown by the aircraft, or ground-stabilised; i.e. always fixed on a particular area of interest no matter where the aircraft goes.
Radar modes include: (air target surveillance) air target track-while-search, support air surveillance, helicopter surveillance, high-performance air tracking, extended early warning, primary air surveillance, secondary air surveillance; (sea target surveillance) sea search.
Erieye's active phased-array radar uses a technique known as adaptive radar control. This allows for the intelligent uses of radar energy that can be concentrated on specific targets or areas of interest. Unlike a rotating radar antenna, the Erieye is not limited to scanning a fixed volume of airspace over a fixed period of time. As soon as a target of interest is detected one of the radar's multiple beams (generated by the multiple T/R modules) can be allocated to lock on to that target, with tracking initiated immediately after first detection. By concentrating on a specific area the Erieye delivers a high update rate that can be prioritised as ore information on the likely threat emerges. The first radar 'hit', or target detection, in a surveillance scan is followed immediately by a higher-energy, shaped radar beam that establishes a track confirmation far faster than a conventional radar - mini ising the time in which a target can be lost switching from detection to tracking. Any target that begins to manouvre will immediately attract a higher measurement and update rate. The rapid updating allows for effective tracking of a target that is manoeuvring hard, perhaps in an attempt to evade radar detection or ti gain an advantageous position fro weapons release.
The Erieye can track several targets, or groups of targets, in its surveillance area using individual radar beams - while all the time maintaining an ongoing search scan. At the same time the radar operations can be interleaved to offer simultaneous air priority, air surveillance and sea surveillance modes.
The onboard mission system , as selected by all customers outside Sweden, uses an open architecture system design with COTS (commercial off the shelf) hardware and operating systems. A MIL-STD 1553B databus connects the Erieye radar, its IFF/SSR and ESM subsystems plus the navigation system, to the main command and control and data management computers. These computers are tied into datalink and other tactical communications equipment and drive the aircraft's onboard workstations.
The aircraft can be equipped with the NATO-standard MK XII IFF/SSR (Identification Friend or Foe/Secondary Surveillance Radar) that offers Mode 1, 2, 3/A, C and secure Mode 4 operations. The (optional) ESM system provides coverage in the 2-18 Ghz range. This system is designed to operate in a dense RF (radio frequency) environment with an automatic analysis and identification process, correlated with an onboard threat library. The system will deliver high DF (direction-finding) accuracy for localisation and targeting, with high sensitivity for long-range detection. For ELINT tasks target tracks and pulse descriptions canbe recorded, and exploited on the onboard consoles. A self-protection suite with an integrated threat warning system and countermeasures dispenser can be fitted.
Phased-Array Radars:
A new breed of antennas are at the cutting edge of today's radar technology. Instead of the familiar dish or flatplate antenna, they incorporate arrays of individual transmitter/receiver (T/R) modules, that can be independently controlled.
Each T/R module operates as a separate 'mini radar'.
The modules can be grouped together to operate as one large radar or several smaller radars - all looking in different directions and at different targets. These groups are controlled in phase, to either transmit or receive. Therefore, they can be actively 'looking' for targets like a normal radar, or passively 'listening' to detect the emissions from other, hostile, electronic emitters.
Because the T/R modules are arranged in rows these radars are often referred to as planar arrays, but because of the way they operate (using several simultaneous phases instead of just one) they are most commonly referred to as phased-arrays.
The first generation of phased-array radars were largely passive phased-arrays. Examples include the B-2s APQ-181 (developed by Hughes), the Rafale's RBE (developed by Thomson-CSF) and the Mig-31's Zaslon (developed by Phazotron). Passive arrays are essentially single arrays, with one transmitter driving all the elements of the array. The phase of the transmissions from each element is then delayed through a beam-forming computer to switch the radio frequency (RF) energy along different delay paths, producing the required phase changes in each module.
In an active phased-array, the mass of smaller, individual T/R modules (typically in their hundreds) does away with the need to manipulate a single radar beam. As in a passive array the electronic scanning in the horizontal and vertical planes is controlled by the phase of the individual radiating elements. However, in the active array, each of these has its own transmitter, receiver and antenna. Each module transmits radar pulses individually, controlled in phase so that the complete array will produce a beam of transmitted energy or a receive beam of the required shape, all directed in the desired direction.
Electronic scanning allows the user to look in any direction at any time, to acquire near-simultaneous target updates from several different directions. The Erieye's S-band radar offers extremely sharp and narrow main beams, with low sidelobes, compared to the UHF wavelenght of other phased-arrays.
Source: International Air Power Review, Volume 11
Argus in Operation
The Swedish Air Force conducted its first full sclae exercise with the Gripen and Argus (Saab 340AEW&C) early in 1999. The FSR 890 (Argus S 100B) is an integral part of Flygvapnet's FV2000 (Air Force 2000) plan for a fully-integrated network-centric warfighting capability.
Under the Swedish concept of operations , the S 100B is controlled by the national network of underground StriC (Stridsledningscentral) control and reporting centres. Data is transmitted from the air using the secure high-speed datalink element of the TARAS digital tactical radio system.
The StriC operators fuse the information from the FSR 890 with that from the rest of the national radar and sensor network to build a complete picture of the battlespace. From the StriC, FSR 890 data can be uplinked to other aircraft, such as the JAS 39 Gripen, or across to the Navy's own command centres for transmission to ships at sea.
The six S 100Bs represented maximum value at minimum cost. By eliminating onboard operators from the equation, Sweden also did away with the need to recruit, train and mantain a corps of personnel to operate the aircraft. Sweden already had a highly integrated C2 system - and the air force was entering a period of heavy cutbacks when every resource had to be maximized.
In Flygvapnet service the Erieye has demosntrated an instrumented range of 450km (280 miles) - and Ericsson points out that this figure is a software limit set by the Swedish customer. Some company demonstrations have indicated an actual detection range of 500km (310 miles). There is an unspoken acknowledgement that, in some areas, the Erieye's ground functions were deliberately limited to dissuade army and navy access to the system. Patrolling at around 160 kt (296 km/h) the S 100B has an on-station endurance of six hours.
Sweden has examined the possibility of adding operator stations to its S 100Bs, to support possible deployed operations. The aircraft already has a 'technical operator's station' in the main cabin (used largely for flight test purposes) but there is an acknowledgement that 2 or 3 Argus plus a squadron of Gripens could function like a small independent air force, if Flygvapnet chose to do so.
When Ericsson started to develop the Erieye there was no other phased-array AEW radar available - or even a plan for one. Since then the Israeli-developed Phalcon system has come to the market. There is only one user of a single system (Chile's Condor aircraft) althoug a deal has now been struck to supply the Phalcon to India, using an Il-76 platform (US pressure on Israel blocked an earlier Phalcon deal with China). The Phalcon uses a 1-Ghz L-band transmitter. This has a direct effect on the size of the platform aircraft, because longer wavelength radars need a corresponding larger antenna to produce their given beamwidth.
One assessment of this is that longer wavelength radars benefit from an uncomplicated design but are very easy to jam.
Higher frequency radars, such as the 3-Ghz S-band Erieye, have a narrower beam-width. Using a 8-m (26-ft 2-in) antenna, for example, an L-band radar will have three times the beamwidth of an equivalent S-band transmitter. The wider a radar's beam, the easier it is for hostile jamming to isolate it and crack it open. The Erieye produces a 1 degree beam that is very narrow, focused and hard to jam. By way of comparison, a typical UHF beamwidth could be around 10 times that.
The Swedish version of the Erieye covers an arc of 120 degrees on either side of the aircraft. Fro Brazil's R 99As this coverage was increased to a 150 degrees arc (still maintaining the 1 degree beamwidth). While Ericsson has always been dismissive of the criticism that its radar's basic design does not afford a full 360 degrees coverage, it has quietly moved to provide just that. The radar fitted to Greece's EMB 145 AEW&Cs delivers (compensated) 360 degrees coverage. Sweden's FSR 890 system can track 300 air targets and 300 maritime targets. For export customers that capability has been significantly expanded. The Greek aircraft, for example, are capable of tracking 1,000 air targets and 1,000 sea targets.
Ericsson says that the Erieye costs between one eigth and one tenth of an E-3 Sentry to operate and has quoted a cost of USD500 per flight hour for the Erieye, compared to USD 2,700 for an E-2C Hawkeye and USD 8,300 for an E-3 Sentry.
Brazilians R 99As and R99Bs are based at Anapolis AB in the state of Goias, central Brazil. They are flown by the 2nd/6th GAV (Grupo de Aviacao, aviation group). When in the air their call sing is 'Guardiao' (guardian). The FAB appears to be very pleased with their performance so far. Towards the end of 2003, the Brazilian press reported that an R 99A had played a crucial role in the rescue of 70 Argentinean captives that were being held by Peruvian Guerrillas. There are no official details of the mission but it is understood that R 99As were used to locate suspicious air traffic that pin-pointed the group's location.
Source: International Air Power Review, Volume 11