How do you build a radar reflector?

[PilotSmith]

I just got for my b-day a radar gun. I believe it operates on "K" band. I saw last year a post with specifications for building a small reflector so you can clock the planes easier. Anyone have the link to that post or know the dimensions / specs to build a small reflector?

[Sparky Paul]

A "corner reflector" will send the incoming beam directly back to the source.
http://www.exploratorium.edu/snacks/corner_reflector.html