I have worked on the specifications for advanced radars, and yes, we do take very effective measures to protect against passive detection.
the "Passive Radar" approach has been known since WWII, when the German "Metax" radar detection device was used to locate German Submarines.
NNUS: Nothing New Under the Sun
NNUS: Nothing New Under the Sun.
Actually, yes there is, the introduction of computing power to radar has revived the concept. From Lockheed-Martin's early-version Silent Sentry onto today's classified R&D projects, we are ourselves pushing to make stealth aircraft visible for detection and tracking. Although fire-control targetting may still be proving elusive.
Anyways, our letting Chinese espionage successfully glean the science behind this was simply criminal. As for counter-measures, perhaps decoys could work, and perhaps an ECM package can be devised. But the viability thereto probably depends on knowing where the Chinese detection systems are. All of them. And to revert back to dependence on ECM, when our stealth approach was based on low observability and close-to-zero EM emissions...seems rather contradictory.