Long-Range Wireless Frequency Synchronization for Distributed Phased Arrays

We demonstrate wireless frequency synchronization of separate wireless systems over a 90 m distance using a microwave system supporting joint frequency transfer and localization. Wireless frequency synchronization represents one of the basic coordination requirements in coherent distributed phased arrays. When combined with inter-node ranging, frequency synchronization enables separate nodes to implement distributed beamforming for various applications. We build on a novel spectrally-sparse two-tone ranging waveform combined with a self-mixing receiver circuit that demodulates a frequency reference from the two-tone separation and is used to synchronize the local oscillator. Measurements conducted outdoors demonstrate basic synchronization between two wireless systems, providing a framework for future distributed beamforming with widely separated nodes.