Retrodirective airborne radar for urban surveillance

Urban surveillance with airborne radar systems is very challenging due to blockage of line-of-sight caused by buildings. To overcome this limitation, it is very likely that the radar will be mounted on a small, inexpensive unmanned aerial vehicle (UAV) that can fly directly over an urban area of interest. Unfortunately, such systems provide very little power to their payloads, frequently less than 100 W. Despite recent advances in high-performance computing, it is extremely doubtful that such a limited power budget will be sufficient to both provide persistent illumination of the region of interest, and implement the very sophisticated radar processing that will be required for urban operation. In this paper, we propose a means of overcoming this power deficit by off loading nearly all of the required processing to a ground station. This is accomplished by a strategy we call ldquoretrodirective airborne radarrdquo. In essence, the waveform used for transmit at a particular pulse time corresponds to a coded version of the signal received during the previous receive interval. A ground station is used to demodulate the signals (originally received at the UAV) and process them.