FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1989
1989 - 0572.PDF
and ECR.90 reinforces the company's claim that Blue Vixen's performance is not compromised significantly by the power, weight, and space limitations imposed by the Sea Harrier. If ECR.90 can meet the EFA requirement, Blue Vixen must be a state-of- the-art design, offering good target resolu tion in the most difficult modes. Ferranti maintains that the sidelobe clutter with which Blue Vixen must contend over moderate seas is not significantly different to that which EFA would encounter over land. Processing power Central to the design of Blue Vixen is fully programmable signal processing, claimed to be an order of magnitude more powerful than that of the Hughes APG-65 fitted to the F-18. With so much processing power available, the transmission characteristics of the radar can be optimised for maximum target-return quality and ECM resistance, even if this is best achieved at pulse-repetition frequencies (PRFs) which generate ambiguities in range and velocity. Blue Vixen automatically selects the best combination of pulse-repetition frequencies throughout a mission to achieve maximum target definition, depending on background clutter and target density, while minimising pilot workload during what Ferranti describes as "sensor inundation". Recent trials aboard the BAe 125 have demonstrated successful implementation of Blue Vixen's four main air-to-air modes: low, medium, and high pulse-repetition frequencies, plus high-PRF velocity search. Theoretically, the lower the PRF the better the quality, but, although low PRF gives high clarity at long range, it will not yield velocity information on the target and This BAe 125 is about to start flight trials with a Blue Vixen integrated into a Sea Harrier FRS.2 weapons system is ineffective against clutter. It can be used to good effect in look-up engagements, how ever. If mainbeam clutter returns are expected from the surface, high PRF can provide good velocity (speed and direction) information at long range; the range is ambigu ous, however. Velocity search mode maxi mises detection range by forgoing any attempt to place numerical values on the range. Once a detection is made in a high-PRF mode, and signal strength is high enough, medium PRF should then be selected. This generates inherent ambiguities in both range and velocity (and early implementations were poor in head-on engagements), but these problems can be rectified by modern signal processing. In medium-PRF mode, Blue Vixen is capable of all-aspect air-to-air engagements, against surface clutter, at considerable range, although Ferranti says that it is worth retaining a high-PRF mode as a long-range alerter to closing targets. The recent success ful Blue Vixen trials are said to have included the most difficult mode against a high-clutter background. Ferranti stresses that, despite its small size, Blue Vixen "fully implements and exploits" AMRAAM because of its mix of PRFs and the quality of signal processing. Ferranti maintains that the keys to modern fighter radar performance are enhanced digi tal processing and the maintenance of high mean power in all modes. Early pulse- Doppler radars had to use quite high PRFs so as to place as much energy as possible on a long-range airborne target. Not only did this reduce peak-power demands, but also such transmissions reduced the need for signal processing. Now, however, signal processing can easily cope with the range and velocity ambiguities inherent with medium PRFs, making it possible to "customise" waveforms for greater air-to-air definition while retaining high mean power in air-to-surface modes. Modern signal processing can also minimise the chances of alerting a target by interleaving enough different medium PRFs to decode all velocity and range ambiguities on a single "dwell" on the target in track- while-scan mode. *J Technology plateau Ferranti believes there is little scope to advance beyond the technology employed in Blue Vixen and its ECR.90 contender for the European Fighter Aircraft without employing active electronic scanning with a fixed antenna. This is useless beyond 40° off boresight, and generates a disadvan tageous wide beam, but it offers unprece dented tactical agility with the prospect of "graceful degradation" after failure or combat damage. Conformal radar, using elements of the aircraft structure rather than discrete aerials to focus signals, is regarded as so elegant that it must eventually be used. The precision with which slots would have to be cut in the structure puts the tech nology 20 years into the future, however. Ferranti's studies suggest that even a 2°C ambient temperature change could cause sufficient structural distortion to render the system unworkable. Solid-state amplifiers are unable to generate high peak power, so, if they are to replace travelling wave tubes, they will need high pulse-repetition rates. This brings back the problems which modern digital processing has enabled medium- PRF radars to circumvent. Although Ferranti radars have not been incorporated into "cutting edge" avionics suites aboard fighters for three decades, the company has a strong pedigree in airborne radar. Its 1950s-technology AI.23 gave the Lightning the world's first high-power monopulse unit. Some 420 were sold, alongside 220 of the company's Blue Parrots, which provided long-range search and mapping for the Buccaneer. Nevertheless, Blue Fox for the current operational Sea Harrier FRS.l had to bridge a 20-year technology gap to incorpo rate a planar array antenna and frequency agility, for good electronic counter- countermeasures performance and clutter rejection in both air-to-air and air-to- surface modes. Despite this, it had to be a low-risk programme because Sea Harrier represented the Royal Navy's last chance to stay in the fixed-wing business, and it could not be allowed to run away with the budget. Accordingly, the limitations of a non-Doppler radar were accepted, but this left an embarrassingly serious lookdown/shootdown capability gap— hence the subsequent development of Blue Vixen. Ferranti also holds design authority for updating the Westinghouse radars of RAF Phantoms, but claims to have taken five years to understand them. (Whether such an admission would have been forth coming if the company's competitors for the EFA radar had not been proposing a development of an American unit is a moot point.) Ferranti also participates in production of Texas Instruments radars for the interdictor strike version of the Tornado, and has a 35 per cent subcontract on the Foxhunter radar for the Air Defence Variant. 50 FLIGHT INTERNATIONAL, 4 March 1989
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
