This doesn't mean they don't have anything of their own. In logic, as long as you can demonstrate an exception to a rule, the rule is proven false. The rule you are suggesting is the assumption that Japanese ALWAYS rely on west since WW2 on everything military, and therefore they cannot independently have military research. This logic is so wrong I don't even know how to start fixing it.
I will demonstrate exception instead.
1. Type 10 tank. Independently developed. Different structure and chasis with Type 90 which is based off Leopard design philosophy only smaller and lighter for island fighting. Type 10 has extreme high tensile strength steel armour and laminate ceramics different. Gun based off Rheinmetal like all western tanks except english and french but because it is a fantastic gun and they want to use same 120mm types of rounds.
2. ASM-3 missile. Totally different design and Japanese exclusive. Again self developed.
3. Type 88 missiles. Again I don't see a direct US link.
4. Type 12 missiles. Again I don't see a direct US link.
5. Type 96 multipurpose missile.
6. Type 11 SAM
7. Type 03 SAM
8. AAM 3
9. AAM 5
10. Izumo class VTOL carrier
Just some examples to prove they do develop some equipment and definitely build and design most sub-components but many things are obviously common. Just like UK and US have many common things shared too. They are allies.
This proves they can and do have the infrastructure to do these things and radar is included.
https://asia.nikkei.com/Politics/In...an-radar-tech-to-double-missile-defense-range
They have good semiconductor industries and only one of two countries in the world other one being netherlands that have lithography technique for semiconductor fabrication. Very technologically advanced country with very small military budget. They can become very serious big player if they wanted to.
It is Japan who doesn't want to with article 9 but USA beginning to wish Japan does build military industry. Right now, Japanese military industry doesn't get serioius funding like for example China's. If they decide to, they will come out with some amazing terrifying things and world becomes more dangerous because everyone has big military technologies and before when war mostly is shooting at each other, now some bombs can destroy entire countries. Neutron bomb will clean out entire region. So too dangerous to play war nowadays. Better find economic and diplomatic ways to get along and spend more effort that direction which Japan sometimes tries. They are not a really bad guy anymore so don't blame them for no military power because they are very very capable of it. Just restraining themselves a bit because they are wise enough to understand there is no win anymore better to look after non-military power and Japan is ffantastic in those areas.
Most Japanese military stuff is really US that is true. Almost all of it. But you are thinkng just because majority is, therefore all of it is and Japanese are not able to do any independently more or less. But truth is not like that. They have small parts that they do play around with in niche technology areas and they are definitely very innovative and capable. So it is very possible that radar is totally Japanese and facts are USA started developing fighter AESA after and fielded them after J/APG-1. They also bought this radar to analyse. Any Japanese equipment is usually shared and Japan is usually happy to share with US. So the english name for this radar system is J/APG-1 because it is a common system that USA can get hands on anytime. If you believe otherwise, please share proof this system was developed by US and given to Japan. I haven't found any.
Original poster is wrong. US didn't take AESA technology from Japan. AESA technology was quite widely understood then and many phased arrays already exist all over the world but it is first fighter sized and can track target and shoot at small fast targets and doing this has diferent challenges to the very large phased radars for ballistic missile detection. USA may have gotten this and studied it and find ways to develop this type of technology for fighters. I think USA already had projects to do this because it makes sense to have them and obvious direction for development. But please don't suggest JApann 100% incapable and must have this given from USA. This isn't true until proven so and there is no proof and everything suggest the opposite.