GPS Signal for Sufficient Coherence with Multiple SDR Receivers System for Antenna Array Applications

This paper explores the requirements for phase stability of two or multiple software-defined radio (SDR) receivers using the global positioning system (GPS) signal. The illustration relies on a technique that features the benefits of combining the use of injection-locking techniques with GPS signals as a common clock source when applied to a low-cost software-defined radio to improve the accuracy of coherent multiple receivers. This is because coherent systems impose severe requirements on the frequency stability of the signal source at the receiver. This paper shows the benefits of using the highly stable GPS signal, experimentally illustrates the applicability of GPS signal as a common source to multiple SDR receivers, the implications to achieve sufficient coherence with multiple SDRs and its impact to increase the beam directivity precision. The beamforming demonstrated in the results proves the advantages of higher signal-to-noise ratio, interference prevention and rejection over co-channel interference. The phase stability to achieve sufficient coherence proves the feasibility of use for many applications, which include radio astronomy, radio frequency (RF) emitter detection and geo-localization, and beamforming.