"stealth" is such fuzzy Term
The Frist stealth system were build to mask of frequency of Soviet Radar system
That stealth system was beaten by weather radar or Euro fighter two band radar system.
because those work of much different frequency as Soviet Radar system
and Russians made hell of upgrades on there Radar system since 1991.
In end of 1980s, France military look into ways to trace and pinpoint such "stealth" aircraft in,
magazine "Science & Vie" publish interesting article about such detector system,
They would equip every french household has TV antenna & Phone
With a Module connected to Phone line in case of crisis the System is activated
turing the TV antenna into Dipol transmitter and Module to receiver
If a F-117 fly true this field of TV antennas, it disrupt the Transmission field of each antenna it past.
That Information is transmit over phone to Military base and Interceptors attack the F-117.
In theory it worked, in realty you had to turn every french House hold into Radarstation.
What's a logistic and budgetary nightmare, if you need maintain 25 million Radar stations...
And now comes artificial Terahertz radiation in 2004.
First application start in 2013 with scanner for Airports and Medical use
it was matter of time some one put Terahertz equipment into Radar system.
This case it's China
Now what US has to do is overworked the "stealth" on F-35 and F-22 to deal with this matter
what could increase the Program cost on F-35 again...