... in case maximizing the RCS of a stealth fighter seems counter-intuitive TAHA21, the rationale is to have a detachable device which allows a stealthy aircraft to operate safely in civilian air space in peacetime. That way it is visible to air traffic control radars, but can quickly be returned to a stealthy configuration for combat missions by simply taking off the the luneburg lens.
That's right, also for example in the case of the Zhuhai Airshow, it does indeed "cloak" the actual RCS of the J-20, or any other airframe that it is attached to, as those numbers are top-secret in each of our Air Forces flying 5th Gen aircraft!