Chinese already since a long time research and experimented with passive radar to counter US stealth planes since B-1 bomber was first deployed.
What you see today is an on going development and their products at current stage
In 1999 the downing for F-117 during the NATO bombing of Yugoslavia, the Chinese radar devepment team were collborating with Yugoslavia anti-aircraft missile units to experiment with their radar against US stealth F-117. On 27 March 1999 F-117 was shot down.
http://en.wikipedia.org/wiki/1999_F-117A_shootdown
After 2 months. On May 7, 1999, the US bombed the Chinese embassy in Yugoslavia. I believe that the Chinese passive radar research team were the real target and they were hidden within the embassy. USA hope by bombing they could set back Chinese military technology progress to gain advantage in crippling their stealth technology.
http://en.wikipedia.org/wiki/U.S._bombing_of_the_Chinese_embassy_in_Belgrade
I was told by Chinese friends that within the embassy the Chinese actually acquired some parts from the F-117 wreakage to help research of the passive radar. Whitehouse want to prevent Chinese from shipping back this sample. So they bombed embassy and later gave some stupid excuses.
Today it is 15 years after these histories. Chinese definitely have some completed products to shoot US stealth planes, Their continued development will bring out better versions and models.