The Serbs were using a new radar that looks for “holes” in the electromagnetic field transmitted by TV and radio towers. That radar was used to find and track and shoot down an F-117. China provided that radar to the Serbs. The bombing of the Chinese embassy was a warning. I have no proof of this but you can look up all the individual events and draw your own conclusion.
Stories about mystery radars using civilian TV and radio repeaters were spread to justify destruction of TV station in Belgrade and TV towers. In other words, to justify war crimes.
If such radars existed, Serbian air defense would shoot down hundreds of U.S. and NATO jets, and that did not happen.
What existed was the "lightshow" - numerous radars were operated from the same centre, each illuminating sky for less than 2 seconds and then powering off.
Radar antennas were directed toward ground and reflected beam was still strong enough to illuminate. Ground around radar stations was plowed by HARMs beyond recognition while radars remained unscathed.
Low tech and know how vs. high-tech.