WAPJ Volume 31 (Winter 1997): Panavia Tornado Variant Briefing: Part Two by John Lake
Again, here's the relevant bits on Foxhunter:
From page 118-120:
"The first and most critical change to the basic Tornado was the provision of a new dedicated fighter radar. This was the newly developed GEC Marconi AI-24 Foxhunter, a frequency-modulated interrupted continuous wave (FMICW) set operating in the 3-cm I-band. Marconi-Elliott (with Ferranti as a major subcontractor) received a contract to develop the radar in 1976, building on existing radars which had been flying in experimental and trials aircraft for years. The radar consisted of eight (not 12, as often stated) liquid-cooled LRUs clustered around a central transmitter. The front-end was predominantly analog, with a coherent travelling wave tube transmitter giving high power over a range of bandwidths. The conventional twist-cassegrain antenna was light and simple, and gave greater consistency and lower sidelobes than the new planar arrays which were in vogue with the latest teen-series US fighters. The radar incorporated a J-band illuminator for SkyFlash or similar semi-active radar homing missiles. A modern pulse-Doppler radar was not used, the choice being a compromise based on the performance required.
High PRFs were used to maximise detection range, while low PRFs were used against targets with little Doppler shift (e.g. tailchase targets). The radar incorporated sophisticated track-while-scan capabilities, and was extremely user-friendly, with its synthetic symbiology clearly displayed and easy to manipulate. A built-in processor suppressed ground clutter and the radar also incorporated an integrated Cossor IFF-3500 interrogator, whose dipole antennas were mounted on the surface of the main reflector. The new radar necessitated the provision of a new cold air unit to cool it, and a pop-up ram air turbine (RAT) was provided to power essential emergency systems for use in the event of a high-altitude engine flameout, in place of the one-shot battery fitted to the IDS.
The Tornado ADV was originally envisaged as having an electro-optical Visual Augmentation System, which would have given the crew a TV picture of the target sufficient for positive identification in time to allow a front-hemisphere missile shot by day, or in a starlight-only night. The equipment would also permit an interceptor to safely shadow a target by night, or to make passive, emission-free intercepts in some circumstances. In late 1978 Marconi Avionics received a contract to develop the equipment, which was to be expanded from existing low-light-level TV systems. The VAS was to have been carried on a retractable mounting just in front of the cockpit, and was intended to be steerable. Quite what happened to the VAS (which never reached service) remains a mystery. The deletion of this feature was reportedly more due to cost than technical performance. At around the same time, the RAF was officially optimistic that Tornado ADV crews would have a helmet-mounted sight, but this optimism proved sadly misplaced, and RAF fighter pilots will have to wait for Eurofighter before they gain a piece of equipment which their Russian counterparts (and even Israeli and South African pilots) take for granted. The non-appearance of a helmet sight was due to the importance placed on BVR operations, and the relative unimportance of short-range capability in the ADV."
...some BS about SkyFlash...Sidewinder...drop tanks...
From page 121-122:
"The figher variant had a very different avionics and instrument fit to that of the IDS. The Tornado ADV was given double the original IDS's computer power, going from 32k to 64k, and also introduced a GEC-Marconi TACAN, Cossor ILS and IFF, though these were also being incorporated in IDS aircraft, as was the revised communications suite. The latter consisted of a GEC-Plessey VHF/UHF, Rhode and Schwarz HF/SSB, and SIT emergency UHF, with a Comms COntrol Unit by Ultra and an Epsylon CVR. As well as lacking the IDS's Texas Instruments TFR, GEC-Marconi LRMTS and Lital Secondary Attitude and heading Reference System, the Tornado ADV also lacked the Decca 72 Doppler of the bomber. The provision of IFF was essential, of course, but caused delays, since NATO was then caught in a major impasse over what the next-generation IFF should be. The US wanted to stick with a D-band (1-2 GHz) system (since it already operated a large number of D-band IFF equipped aircraft), while most European nations favored an E/F-band (2-4 GHz) system. Eventually, the participating nations agreed on a D-band IFF system which incorporated a radar mode, allowing a radar pulse to interrogate the IFF transponder, and not just a dedicated interrogator."
From page 124:
"The ADV's Foxhunter radar was delayed by a multitude of technical problems, and by the RAF 'moving the goalposts', demanding progressive improvements in capability beyond that detailed in the initial contract and specification (such as a tailchase capability). Shortcomings from the original specification included unacceptably large sidelobes (which brought increased detectability, and vulnerability to countermeasures) and a severe shortfall in multi-target tracking capability. Technical problems with the AI.24 were unexpected and unwelcome. The radar had been flying in an MoD(PE) Canberra since 1975, and had proved reliable and impressive in that (somewhat limited) environment.
It was not until June 1981 that ZA283 became the first Tornado to fly with the new radar. Test versions of the radar had flown previously in Canberra and Buccaneer testbeds. ZA283 (the third of the three F.Mk 2 prototypes) remained the only radar-equipped Tornado ADV for some time, flying with B series radar (the third incarnation flown on ZA283) in March 1983. The first of 20 pre-production radar sets was delivered in July 1983, but radars were not fitted on the Warton production line until mid-1985, by which time the radar was four eyars late and more than 50 percent over budget. Tornado F.Mk 2s were delivered to No. 229 OCU at Conningsby between 5 November 1984 and October 1985.
All F.Mk 2s are understood to have eventually flown with PP radar fitted, allowing a limited degree of realistic role training. Few aircraft arrived on the unit with radar, however. The aircraft had sufficient combat capability to allow the unit to be declared to NATO as an emergency air defense unit in May 1985. In December 1986 the declaration was increased in scope and the unit took up the shadow squadron identity of No. 65 Squadron."
From page 125:
"The single crucial difference between aircraft from differrent blocks lies in radar standard although, as earlier radars have been upgraded, the differences have reduced or in some cases disappeared.
The first AI24 Foxhunter radar sets delivered were well below even the RAF's original specification, and were known as Type W (or W standard) radars. Although the W standard radar was below specification, early Tornado F.Mk 3 crews were publicly enthusiastic about the new radar's resistance to jamming, its look-down performance and multi-target track-while-scan abilities.
Seventy Type W radars were produced for the first 62 ADVs (those from batch 4 and some of those from Batch 5, which is to say all of the 18 production F.Mk 2s and the first 44 F.Mk 3s). Forty-four of the Type W radars (presumably those fitted to the F.Mk 3s) were subsequently upgraded to Type Z standards, in a programme which began in 1988.
The next 80 RAF Tornado ADVs received Type Z (or Z standard) radars, which had increased tracking capability and increased range, and effectively met the RAF's original specification before additional levels of capability were requested. Most of the original Type W radars were brought up to Z standard from 1988, and all the Z standard sets (including those which had begun life as Type W radars) were themselves subsequently brought up to Stage One standard.
The last 46 RAF Tornado F.Mk 3s and the 24 aircraft delivered to Saudi Arabia were fitted with the new Stage One radar, manufactured from September 1988, with revised cooling and new software."
Whew! More of this one later.