Radar detection of very small RCS objects, eg. F-35s?

Here is another thought provoking article from the Asia-Pacific Defence Reporter, July 29, 2020, at
 https://asiapacificdefencereporter.com/thales-ground-fire-radar-production-gets-underway/

"Thales Ground Fire radar production gets underway"

"The first Ground Fire radar is now in production at the Thales Limours site in Essonne to equip, among others, the French Air Force’s New Generation Medium Range Surface-to-Air System (SAMP/T NG). The fully digital multifunction radar, equipped with advanced anti-air and anti-missile capabilities, is capable of countering a wide range of threats, including ballistic missiles. Highly mobile, tactical and air transportable, the radar can be deployed in less than 15 minutes, a major advantage in the theatres of operation. It can handle 360° coverage in azimuth, up to 90° in elevation, and a 400km range.

"Ground Fire: Production of the latest generation radar for air and ballistic missile defence, Thales, [Uploaded by Thales July 28, 2020]"

Designed to simultaneously detect and track a wide range of stealth targets, drone swarms and to prevent coordinated saturation  attacks, the Ground Fire has an air defence missile guidance capability to intercept high-manoeuvring or ballistic targets. Multi-mission, it can be used in various contexts, such as air defence, air surveillance, counter-battery or trajectography.

Ordered in 2019 by the French Procurement Agency, the radar draws on years of engineering and manufacturing development for the Sea Fire, the naval version of the radar selected to equip the Defence and Intervention Frigates of the French Navy. The Ground Fire benefits from Thales’ technological advances in artificial intelligence and cyber security, enabling it to respond perfectly to the fast evolving needs and threats faced by the armed forces..." 

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PETE COMMENT

For the most modern radars capable of counter-battery mode (like Thales' Ground Fire) Wikipedia reports https://en.wikipedia.org/wiki/Counter-battery_radar#Description :

"The basic technique is to track a projectile for sufficient time to record a segment of the trajectory... done automatically...Projectile detection ranges are governed by the radar cross section (RCS) of the projectiles. Typical RCS are:

·      -  Mortar bomb 0.01 m²

·      -  Artillery shell 0.001 m²

·       -  Light rocket (e.g., 122 mm) 0.009 m²

·       -  Heavy rocket (e.g., 227 mm) 0.018 m²

The best modern radars can detect howitzer shells at around 30 km and rockets/mortars at 50+ km." 

So counter-battery Radar detection of an Artillery shell with an RCS of "0.001 m²" can be achieved.

Then, in anti-aircraft mode, can detection of the latest F-35s and future B-21 bombers be achieved (albeit with widely distributed sensors eg. other radars and IRST)?

The Russian and Chinese could get hold of such Western radars through third party countries - then incorporate the technology into S-400 radar-missile systems.