"In December 2011, Japan picked Lockheed Martin’s new F-35A stealth fighter as its next fighter aircraft, to replace its aging F-4 “Kai” Phantom fleet. The F-35 was actually their 2nd choice.
Back in February 2006, Inside The Air Force (ITAF) reported that momentum was building within the USAF to sell the ultra-advanced F-22A Raptor abroad to trusted US allies, as a way of increasing numbers and production. Japan clearly wanted them, and the Raptor was a topic of diplomatic discussions in several venues, including a 2007 summit meeting. In the end, however, US politics denied export permission for downgraded export variants of the F-22, and its production line was terminated. That left Japan looking at other foreign “F-X” fighter options in the short term, while they considered a domestic stealth fighter design as their long-term project.
In the ensuing F-X competition, the F-35 Lightning II beat BAE’s Eurofighter Typhoon, as well as an upgraded F/A-18E Super Hornet from Boeing."
Interesting article from Defense Industry Daily going over the choice of different fighters and the reason behind the eventual selection of the notorious F-35.
On the ATD-X, "Japan hopes the Advanced Technology Demonstrator eXperimental (ATD-X) will lead to a larger high-performance production aircraft with low-observable (stealthy) qualities, designed and built indigenously sometime in the next decade. New technologies that the ATD-X will test include a second generation AESA radar, advanced "fly-by-fiber-optic" flight control system that can compensate for battle damage and control surface failures, an advanced ESM and ECM suite, thrust vectoring and locally developed high-thrust turbofan engines to name a few."
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The single ATD-X aircraft, about the size of a Saab Gripen, is undergoing ground tests, says the defense ministry’s Technical Research and Development Institute (TRDI), the sponsor of the program. TRDI is due to fly the ATD-X this year, beginning an evaluation program that will run until 2016. The aircraft has been built to demonstrate technologies—including stealth shaping, skin sensors and fly-by-light controls—that the ministry hopes to apply in its next fighter development program (AW&ST Aug. 6, 2007, p. 26).