In total I used 3 square feet (1 foot x 3 feet or 12 inches x 36 inches) of aluminum sheet. Two squares were cut to 12" x 12". The 3rd 12" x 12" square was then cut diagonally in half. I believe the video will show you how they all go together. The remaining pieces weren't at all precise and I just them as I thought they should be to hold hangers to be mounted to the front side of the mast. I hope this helps.
RADAR (radio detection and ranging) sends out a signal and listens for an echo in order to plot the range and bearing of anything solid, like land or other vessels. A radar reflector, such as the one I built in this video, when attached to a high-point on an object such as a small boat like mine, is good at returning the radar signals and helps other boats "see" me. This is especially useful during times of diminished visibility (e.g., fog, storms, night).
To keep your high priced military asset from getting hit. Whether that asset is a formation of tanks or a SAM battery. You stick these on some poles a safe distance away and radar guided missiles will be drawn to the reflector rather than your assets. Missiles are kinda stupid, so they will usually go after the biggest return their seeker sees and these reflectors are designed to stand out as much as possible.