CONGAFLOCK is a general purpose RF retroreflector intended for experimentation.
A fully functional prototype was presented at DEF CON 22: https://www.defcon.org/html/defcon-22/dc-22-speakers.html#Ossmann
step 1: Assemble PCB
step 2: Connect two wires to PCB to serve as a dipole antenna (2.45 GHz recommended).
step 3: Connect PCB to ground and target signal.
Basic Usage Instructions
step 1: Transmit CW signal at frequency of installed antenna toward CONGAFLOCK with directional antenna.
step 2: Simultaneously receive reflected signal with another directional antenna.
step 3: AM demodulate the received signal to recover the target signal.
Michael Ossmann (@michaelossmann)