Its not. I don't know why some people in these Russian defense forums are so obsessed about PESA and why they, or some others, think it would be difficult to do AESA, even with Russian radar companies have been working on AESA designs and modules since the 2000s. That's a long time ago. Plus there are many smaller companies in Australia, Israel, India, Sweden, Italy, Netherlands, Turkey, and Spain that already have produced operational AESA designs for some years now or working on them.
This is the Zaslon MF radar in display, and you can see the back of it, you can see access panels and is divided into subassemblies.
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Now compare those with the Thales SeaFire 500.
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I can't read all the technical specifications posted by Snake, but definitely it's outlining Active functions for Zaslon MF on X, S bands, and different Passive functions on L, S, X, C, Ku, followed by another set of (passive) functions on S, C, X, Ku and finally one last set on just X and Ku.
Back on topic now...
If 2 face radar can continuously illuminate targets, is there any immediate need for active seeker missile?