Julian Moxon/PARIS
The Rafale's RBE2 (radar à balayage electronique/2) multirole electronic scanning radar is the first of its type to be developed in Europe and will be one of the first in the world to enter service.
The RBE2 was developed jointly between Thomson RCM and Dassault Electronique, the two having been merged in 1998 and renamed Thomson-CSF Detexis. The former was responsible for the RDI and RDY radars developed for the air defence/interceptor Mirage 2000C and 2000-5, while Dassault Electronique developed the Antilope radar for the ground attack Mirage 2000N and 2000D. "Combining the expertise of the two companies therefore bought together the abilities needed to develop a true air-to-air, air-to-ground and air-to-sea multimode radar," says Jacques Mijonnet, vice-president and chief operating officer of Thomson Detexis.
Development of the initial version of the radar started in mid-1989, and series production is about to begin. This will be mainly capable of air-to-air operations, but will have some air-ground capability. Funding for development of the more advanced standard that will be applied to F2 Rafales was approved at the beginning of this year, with first deliveries set for 2003. This version will have full air-ground capability, including "some terrain following" ability, and enhancements to the air-to-air mode. The F3 version, still unfunded, will provide improved terrain following at lower altitude, along with air-to-surface and nuclear warfare functions.
The RBE2 development challenge, recalls Mijonnet, "was to develop an electronically scanned antenna at an acceptable cost". This meant using solid state technology that was both affordable and met the extremely demanding performance specifications. Besides the multimode capability this included ensuring the radar was resistant to electromagnetic spikes from nuclear blasts as well as being able to withstand the shock of a carrier landing. The radar also had to be 30% lighter than that of the Mirage 2000-5 and occupy half the volume. "We have achieved this," says Mijonnet.
The RBE2 consists of six line-replaceable subassemblies: frequency generator/receiver, responsible for microwave emission and signal reception and for converting analogue signals to digital; amplifier; signal and data processor (responsible also for real-time management of functions and dialogue with the Rafale armaments system); the support structure; the scanning electronic antenna, plus microwave receptor and, finally, the radome.
The heart of the radar is the passive, phased array antenna which uses Thomson-CSF Detexis' RADANT design featuring two solid state electronically controlled "lenses" working in the vertical and horizontal planes, each containing around 25,000 diodes. In between the lenses is a polarising filter, enabling extremely accurate, instantaneous vertical or horizontal beam shifting within a 60í cone. The company says the RBE2 can therefore effectively carry out several tasks simultaneously, with "very low losses through secondary lobes and therefore excellent performance in low altitude detection, as well as higher efficiency in clutter". The antenna is cooled cryogenically, reducing noise and increasing range.
RBE2 modes
•Air-to-air: the RBE2 is designed to support semi-active, active and passive air-to-air missiles, including datalinks. It can detect and track several dozen targets automatically providing initial co-ordinates and target priority for the fire-and-forget Matra Bae Dynamics Mica air-to-air missiles. Electronic scanning enables evaluation of the target selected while the sky is searched for other targets.
Threats are automatically labelled as targets and are displayed to the pilot with symbols indicating ranges as well as speed. "The independence of detection and pursuit modes, not possible with a mechanically-steered radar, has meant the RBE2 has real multi-targeting capability," says Mijonnet.
In combat mode, the RBE2 enables automatic tracking and pursuit of up to four targets at once, providing input on which weapon - Mica, Magic 2 or cannon - is appropriate.
• Air-to-ground: the RBE2 provides air-to-ground telemetry and ground mapping to recalibrate the Rafale's navigation system for launching precision air-to-ground weapons. In modes such as this, the radar works together with the infrared/TV Front Sector Optronics system. In very low altitude mode, the RBE2 provides three-dimensional mapping of the terrain ahead to enable automatic terrain following, terrain avoidance and threat avoidance. Tall vertical obstacles can be identified by the radar with, says Thomson-CSF Detexis, "a very high degree of security". In its most developed state, the radar will provide terrain-following function simultaneously with air-to-air search, prioritising on the latter if a threat is identified, for example, by the self-defence system.
• Air-to-surface: detection and pursuit of ships at long range to enable firing of Exocet and supersonic anti-ship missiles. Optimised to be able to operated in clutter.
Development of the RBE2 is being carried out progressively, with airborne testing aboard a pair of Dassault Mystere 20s and a Mirage 2000. Mijonnet says results from the 3,000 flights carried out to-date indicate the radar is "meeting all of its performance targets and is also proving to be extremely reliable". Multiple target detection has been carried out, along with radar-directed firings of the Mica missile. Range specifications have been met (the radar has a similar air-air range to that of the Mirage 2000-5, its main advance being in its multimode capability) while initial tests of the terrain mapping mode, which he says will provide resolution "down to a few metres" are under way.
Spectra system
Perhaps even more than the radar, the Rafale's Spectra (Système de Protection et d'Evitement des Conduites de Tire du Rafale) electronic self-defence system highlights the need for a system that is totally integrated with all of the other surveillance, detection, weapons and equipment in the aircraft.
The principal functions of the Spectra are:
• integrated electromagnetic detection and jamming;
• laser detection and alert;
• decoy, including ejection of active and passive electromagnetic, infrared or electro-optical decoys;
• compatibility management, to provide general processing for the system and its interfaces with the weapons system.
"We used exactly the same planning system for the Spectra as for the radar," says Mijonnet (who headed the radar, seekers and systems division of Dassault Electronique in the early 1980s). "We had to know very early on, for example, where the various Spectra antennae should be located around the aircraft. Because every location is in a different environment, this meant working closely with virtually every supplier on the aircraft."
There are more than 1 million lines of software code in the Spectra, handling several hundred megabits of information each second, making it one of the most challenging electronic systems ever developed for a French combat aircraft. Thomson-CSF Detexis was responsible for all electromagnetic functions of the Spectra, Matra being in charge of the infrared and decoy components.
Development began in 1989, with first delivery of a prototype system in 1993 and launch of industrialisation and production in 1995. It has been cleared for operational use in the F1 version of the Rafale, with the F2 and F3 software under progressive development and integration with the radar and optronics systems. Series production of initial systems has begun for F1 standard Rafales.
The main functions of the Spectra are to detect and counter all types of weapons, using electromagnetic, infrared and laser detection, jamming and decoy elements. Coverage is omnidirectional, with detectors and jammers located all over the Rafale, providing the basic data for input to the air-to-air tactical situation and fire control system. It also provides extremely accurate location of hostile threats, to within 1í, using the data to help the pilot select the best weapons, depending on the threat picture and mission phase. Transmission and reception of data to and from the relevant jamming systems and is then managed in real time.
For low observability, the various sensors, chaff launchers and jammers are made to conform as much as possible with the Rafale airframe, presenting the further challenge of protection from local interference from heat (in the engine area), electromagnetic energy (in the radar area) and so on. As with the radar, mechanical protection from carrier landing shock - which is more severe in the Rafale than the Super Etendard because of its higher landing speeds - had to be provided.
Source: Flight International
