Paris Air Show

Europe scrambles to fit fighters with AESA kits

 - June 11, 2007, 5:33 AM

As the U.S. equips its fighter aircraft with active electronically scanned array (aesa) radars, Europe’s avionics industry is working hard to put similar technology into its three “Euro-canard” fighters–the Gripen, Rafale and Eurofighter Typhoon. This effort was highlighted last month by the first flight of a Typhoon with an AESA radar installed.

Fifth-generation aesa radars dispense with the traditional mechanically scanned antenna and replace it with approximately 1,000 individual transmit/receive (T/R) modules in a flat array. The T/R array can be tasked to operate collectively to form a high-powered beam, or can be divided into groups so that several functions can be undertaken concurrently. The nature of the array allows it to form very narrow beams, and for power to be applied adaptively, using only sufficient power to perform the task. Both factors give the aesa an excellent low-probability of intercept rating.

The versatility of the aesa allows it not only to perform many traditional radar tasks at the same time, but also to potentially undertake other nontraditional tasks, such as passive surveillance and communications. Its performance is limited only by array size and the computational power of the processors in the “back end” behind the array.

In 1993 an Anglo-French project (with German technology input) was launched in the form of AMSAR, which sought to examine the technologies necessary to provide AESA radars for both the Rafale and Typhoon. In mid-1998, a 144-module array was tested successfully, laying the groundwork for later projects.

Workable, affordable aesa technology was still a dream when the Rafale was first planned, but the French elected to take an interim step by fitting the aircraft with a passive electronically steered array (pesa) radar in the form of the Thales RBE2 (radar à bayalage electronique deux plans). While the RBE2 uses electronic steering of the beam, it retains a single transmitter source. Some analysts have written off PESA as a “technological deadend,” but it nevertheless provided Thales with good experience in electronic beam shaping and forming as a stepping-stone to aesa.

The Rafale was always destined to receive an Aesa radar as part of its development road-map, and Thales has been working on this technology for some years. A technology demonstrator–DRAA–first flew in 2003 in a Mystère XX testbed, and was subsequently flown in Rafale B301. The DRAA used an antenna array imported from the U.S. Development then switched to the dramaa with Thales-developed array; it took to the air earlier this year in a modified Mirage 2000.

In October 2006 the French government ordered full development of an operational aesa for the Rafale. The Rafale radar is due to enter production in late 2011 for operational fielding in 2012. Installation of an aesa version of the RBE2 will allow the Rafale to exploit the range capabilities of the Meteor missile, something that the current pesa RBE2 is unable to do.

The Typhoon developers faced a similar problem to those of the Rafale: aesa was on the horizon, but was not initially feasible. Rather than take the interim pesa step, the program’s European partners chose a more conservative approach by installing the Captor-M mechanically scanned antenna radar. This has proven in service to be an excellent sensor with superb range characteristics. Although the Captor-M retained a traditional scanner, its back end was designed to be compatible with e-scan antennas when they became available, and work continued behind the scenes as an outgrowth of the AMSAR program.

For the Typhoon, the Euroradar consortium (Selex Sensors & Airborne Systems, EADS Defence Electronics, Galileo Avionica and Indra) is working on caesar (captor active electronically scanned array radar, originally known as Captor-E). This is based on the back end of the Captor-M currently installed in Typhoons.

CAESAR first flew in a BAC 111 testbed on Feb. 24, 2006. Just over a month ago, on May 8, a caesar development radar flew in a Typhoon for the first time, installed in aircraft DA5 which was flown from Manching, Germany.

At the heart of the caesar and French efforts is United Monolithic Semiconductors (UMS), a specialist in micro-components jointly owned by Thales and EADS, with facilities at Orsay, France, and Ulm, Germany. UMS makes the transmit/receive modules for the CAESAR and dramaa. Output is currently based on gallium arsenide (GaAs) technology, but the company is working on gallium nitride (GaN) T/R modules for the future. GaN circuits can work at hotter temperatures and higher voltages than current GaAs MMICs.

M-AESA for the Gripen
In Sweden, aesa programs have been running for many years in the hands of Saab (formerly Ericsson) Microwave Systems at its Gothenburg facility. Early development was conducted under the nora (not only a radar) and eliNt (electronic signals intelligence) programs and involved development of X-band T/R modules and test arrays. Development aesa arrays have also been extensively trialed on the ground, and in a pod mounted on the ramp of a C-130 Hercules military transport.
In 2001 Ericsson won a development contract from FMV, the Swedish Defence Material Administration, and the same year it signed a deal with Raytheon under which the U.S. company would supply a complete aesa array for installation on the back end of the Gripen’s PS-05/A radar. Delivered in June 2004, it was due to be installed in a Viggen for trials in mid-2005, but the early retirement of the Viggen from service resulted in a delay to the trials and a switch to another platform.
Tests of the Raytheon scanner are being undertaken as part of the nora program, which aims to provide an aesa radar for the Gripen. As its name implies, nora is also investigating the use of the antenna for functions such as communications and jamming, as well as its radar tasks.

Saab is working toward a PS-05/A Mk 5 aesa radar that could be available for export around 2010. The Mk 5 would focus primarily on its radar functions. Beyond that the company is looking at more developments that tightly integrate the functions of active radar, passive surveillance, electronic warfare, jamming and communications into a single sensor. The sensor could be mounted on a single-axis pedestal that would increase its scan to around 200 degrees. Such a multifunction nora radar could be ready for installation in Gripen around 2018. In November 2006, Saab Microwave systems signed with Italian companies Selex and Elettronica to jointly develop an M-AESA multirole system concept. This will be used as a basis for the next family of radars for a wide range of applications, including combat aircraft.