I think the usual contractors involved in these fighter projects have developed stealth "surfaces" (whatever you want to include in that) for 6th gen fighters and want to upgrade 5th gens with, if not the same tech, tech based on similar principles. Makes some logical sense right?
If it's applied on the sides, bottom and top, it could be due to new stealth tech being capable of reducing RCS from side profiles... this of course includes all the angles where the emitter is directed at the major surfaces exposed - looking directly downwards, upwards, from the side, as opposed to front on or mostly frontal.
J-20 uses some secretive metamaterials. Since F-35, plenty of online literature and forumners suspected metamaterials being the latest stealth tech. Only J-20 and F-35 used some form of it where the F-22 is suspected to use some other form of stealth materials and coating. Maybe F-35 didn't even reach the metamaterials level of J-20 until these new upgrades lol or maybe they've gone to the next and while all the 6th gen projects in both countries are hidden tightly still, contractors are applying upgrades to existing 5th gen or at least testing them out, quite publicly too.
If it's applied on the sides, bottom and top, it could be due to new stealth tech being capable of reducing RCS from side profiles... this of course includes all the angles where the emitter is directed at the major surfaces exposed - looking directly downwards, upwards, from the side, as opposed to front on or mostly frontal.
J-20 uses some secretive metamaterials. Since F-35, plenty of online literature and forumners suspected metamaterials being the latest stealth tech. Only J-20 and F-35 used some form of it where the F-22 is suspected to use some other form of stealth materials and coating. Maybe F-35 didn't even reach the metamaterials level of J-20 until these new upgrades lol or maybe they've gone to the next and while all the 6th gen projects in both countries are hidden tightly still, contractors are applying upgrades to existing 5th gen or at least testing them out, quite publicly too.