I wish they went into more detail as to how they did that.
Well, you should expect practical information on beating stealth to be about as easy to come by as practical information on building nuclear weapons. That said, the wikipedia entry for Nighthawk has a little more information:
According to NATO Commander Wesley Clark and other NATO
generals, Yugoslav air defenses detected F-117s by
operating their radars on unusually long wavelengths,
making the aircraft visible to radar for brief periods.
It is also possible that the aircraft was visible due to
a disruption of its radar signature caused by open bomb-
bay doors. This was the justification given by Colonel
Dani in a 2007 interview.
Well, you should expect practical information on beating stealth to be about as easy to come by as practical information on building nuclear weapons. That said, the wikipedia entry for Nighthawk has a little more information:
http://en.wikipedia.org/wiki/F-117_Nighthawk#Combat_losses
And http://en.wikipedia.org/wiki/Stealth_technology#Radar_stealt... has information about stealth technology counters in general, the sort of thing you might find in a radar engineering handbook.