It was effectively invisible to the radars that existed when it was made.

High frequency radars are more accurate than low frequency, nobody used low frequency at the time. They're also smaller, I don't think you could use a low frequency radar with a missile's seeker. Low frequency is good enough to throw up flak, though--and that's how the one that was lost got hit.

It was also vulnerable to bistatic radar--but I don't believe a bistatic radar could even have been built back then.

It was basically a one-trick wonder that got counterdesigned.