NaB, from your link,
The design comprises of a single mechanically scanned radar head which uses an innovative system to provide 360o visibility from the underside of the helicopter, and which folds up to the side of the aircraft when not in operation.
Who the hell writes stuff for the Government websites?
Seriously, though,
Originally Posted by Philip Dunne, Minister of State for Defence Procurement
It is essential that our ships and particularly our future aircraft carriers will have the best possible protection. The Crowsnest system onboard our new Merlin Mk2 helicopter will deliver an essential surveillance and intelligence capability, providing early warnings to our personnel of any potential threats.
He means it's the only option. Having taken the cats away, it pretty much has to be a helo-based system. Only the best for the Navy, eh?
I know it should be a good system, but...