"modern" long wavelength radar?
Here's an article a quick Google search brought up about the F-117 and British radar... from the Los Angeles Times... from 1991. http://articles.latimes.com/19... - and this was using radar considered then to be obsolete, having been "new" in the 1970s. Basically, during Gulf War One, British warships were detecting the location of these stealth fighters at about 40 miles away. From 40 miles out, it is enough time to get your fighter planes in the air to combat the stealth planes. L-band radar may not be precise enough for anti-aircraft weapons on the ground but in combination with air-to-air combat it is good enough - your response just needs to be super fast.