Time and phase RF synchronization using free space optical technology

Small unmanned aerial systems (UASs) have found many applications within both the defense and commercial sectors. [1] With the increasing use of small UASs, it is desired to equip them with RF sensors/payloads to permit them to work together to form a coherent beam on a target. [2] To do this, precise time synchronization among the UASs is essential. Current techniques rely on either the use of GPS or an embedded signal from the target to time synchronize multiple UASs. The goal is to obtain accuracy in timing (10 to 100 picoseconds) and phase coherence of about 1/10 of a relevant RF operating wavelength (UHF or higher band) between nodes. 4S Silversword Software and Services (4S) is using their Free Space Optical (FSO) system identified as Through-the- Air Link Optical Component (TALOC) in conjunction with 915 MHz RF emissions to obtain sub-nanosecond time of flight measurements, corresponding to fractional wavelength position precision, using free space optical measurements. In this paper, we show the calculations, technology background, and the results of system tests.