Japanese MOD and UK MOD have started a cooperative research on the technology demonstrator of a Japan and Great Britain Universal Advanced RF system (JAGUAR).

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JAGUAR universal radio-frequency system (Picture source: Acquisition Technology & Logistics Agency)

The JAGUAR, a state-of-the-art radio-frequency (RF) sensor system, enables us to instantly observe a wider area than before with digitally computed multiple receiving beams. Japanese MOD expects that the outcomes of this cooperative research will be utilized to enhance the capability of  RF sensor for a fighter in the future.  

It would presumably be intended for the Japanese F-X and UK-led Tempest fighter programs.

Last December, the UK and Japan announced plans to develop a future fighter aircraft engine demonstrator and agreed to explore further combat air technologies.