A Faraday Cage will still reflect radar, but won't emit as much if it's grounded. So while YOU would be invisible, the cage itself would not be. Of course, because the cage is grounded, it would not be as visible as it would be if it were not grounded, but...
The only way to be truly invisible to radar is to be made out of something that doesn't conduct electricity. Even if most of you are made out of some such, if there is a part of you that conducts, it will still be visible.
Some radar-stealthy objects, like stealth aircraft, have their materials set at angles that reflect radar away from the typical transmitter, so the receiver must be in a specific place in order to see them. As a result, a radar would have to be specifically designed to look downward from above or at some other unexpected angle could still see such craft.
The other way to avoid being seen by radar is to be underground (or underwater). Both conduct electricity and absorb radar waves well enough that they will block out any signal from reaching you. This is the same principle as the aforementioned Faraday Cage - except that the Earth is your cage, and it doesn't really help somebody you are hiding from to know that you are somewhere on (or under) the Earth.