nam wrote:If they are using GaN, then may be, it might have reduced cooling needs. If that is the case, then it is a achievement to get a X band GaN, jet radar.
Regular AESA with air cooling method, is a downgraded AESA.
It depends upon performance requirements, and how exactly you define air-cooled. There are radars, like the F-16's APG-83, for example that primarily use air-cooling, have a local heat exchanger or other embedded cooling solution, but do not require any addition of liquid cooling plumbing on the aircraft. This was a design requirement, as the USAF did not want to go through the expensive modifications of introducing plumbing for liquid cooling and overhauling the F-16's unlike the UAE's blk'60 aircraft, where they had to basically create a bespoke system. Northrop and Lockheed have met all performance requirements with this approach but had to upgrade the radar to include the latest generation components to do so (it isn't a recycled AN/APG-80 from the UAE bid). I believe the APG-83's main rical from Raytheon (RACR) also is primarily air-cooled and does not require plumbing for liquid cooling to be provisioned. These sets were designed to be drop in replacements on the F-16 and F/A-18 aircraft.
nam wrote:For the same power rating , GaN are more power efficient ( reduced heating), hence will need lower cooling.
If for the same power rating, if GaN thermal properties are bad compared to GaAS, then no one will move towards GaN.
You switch to GaN in order to drive more power, get better performance (or overcome performance deficiency) and achieve performance not possible with GaAs devices. It is a major cost driver to do so both from industrial capability and capacity perspective and from a pure acquisition cost perspective so you do not make that decision lightly. While there are reliability advantages even without tapping into higher performance they do not really matter much when you are dealing with a 6-8,000 hr fighter. Case in point - ON the F-35, the radar aperture is sealed shut as the GaAs T/R modules have demonstrated reliability far exceeding the expected life of the aircraft.