A very interesting episode of the bombing deserves to be mentioned in detail. On March 27, 1999, Serbian Colonel László Dani, a member of the Hungarian minority, leader of the 3rd Division of the 250th Anti-Aircraft Brigade, succeeded in destroying an F-117A Nighthawk Nr. 82-0806 (stealthy American aircraft) detectable by radar or rather only detectable from a very short distance.)
How did he achieve this goal?
Dani's unit was equipped with the S-125M Neva / Pectora anti-aircraft missile (operating at lower altitude, at lower speeds, and with a more efficient system against electronic countermeasures, commissioned in 1961) whose old radar was the Soviet P-18. This radar is the successor of the P-12 radar developed in the USSR in the 1970s.
Technologically it is very simple, because 16 antennas YAGI (for TVs) consists of its base, installed on a turntable over a heavy weight URAL 4320. Basically, new radar technology is advancing to higher frequencies (with the wavelength becoming shorter, S, X and K band). In the United States the old units were dismantled, however in the USSR and in its former allies several units, in principle obsolete, remained in service.
That's why Dani was able to reveal the secret that the F-117A is perhaps few detectable or undetectable by US high-frequency radars in service, but not by the old Russian low-frequency radars. He also tinkered (despite the order and prohibition of his superiors) a little, to lower the frequency and thus increase the wavelength of the radar (able to detect the F-117A in 25 km), and he changed some capacitors.
What did Dani do to destroy the planes of NATO?
In Budanovci (Vojvodina, Serbia) he climbed a hill and studied the flight direction of the aircraft for several days in order to be able to target his radar as well as possible for detection in a very short time. It was a viable question to detect the aircraft and to trigger the anti-aircraft missiles as quickly as possible (start, capture and turn off the radar in 21 seconds and move after, in 1.5 hours) because also the aircraft could detect the waves of his radar and react by firing air-to-ground missiles (especially: AGM-88 HARM) to destroy his unit. (To deceive the HARMs when needed, they used several older MIG-21 radars.)
One of NATO's largest defenses that its jamming and target-sensing radio devices were not working against old VHF systems at short range. The pilots communicated on non-coded frequencies so that radio amateurs in Serbia were able to catch it and inform the military (on the landline), as well as those who saw the take-off of aircraft near military airports in Italy. The four F-117A returned their tracks after the mission and (for the third test) the Neva managed to capture one of 13 km in 8 km of the altitude and destroy it by one of the two missiles fired.
That is, technology and the time factor were the two keys to success.