Radar systems use a variety of different radar frequencies; higher frequency radar tend to have finer resolution than lower frequency radar for a given aperture size; and this results in increased detection range; if an aircraft is modeled by the equivalent of one pixel on the data system half the time, it is hard to distinguish it from noise, but if it is rendered by a consistent 20 pixel object you can be relatively certain it's an aircraft.
However, stealth aircraft tend to be optimized for absorption performance against high-frequency radars; while a stealth aircraft may be mostly invisible to an X-band high-resolution fighter AESA, an L-band AWACs AESA will still see it, albeit likely in low resolution and low range due to the radar frequency.
"Second-generation" Chinese electronic radars probably refer to first-generation GaAs AESA, with the first generation referring to PESA systems. If they're expected to be roughly comparable to American AESAs of the same generation and have 450km range against m^2, they are probably X-band systems.
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The comment I made was that for a F-22 RCS, you can get a .4m^2 RCS one of two ways. The first is if you go down to L-band, which has an inherently limited radar range, or you could average the X-band RCS of the entire aircraft from all angles together. Even with radar absorbing materials, a .4m^2 RCS as an all-aspect average is believable.
