2-D Direction-of-Arrival Estimation System Using Circular Array With Mutually Coupled Reference Signal

Direction-of-arrival (DOA) systems rely on proper phase measurements acquired from receiving antennas for optimal performance. Unfortunately, imperfections in any antenna and receiver system may present false phase measurements, the major cause of DOA estimation error. This paper discusses experimental results from an actual implementation of synchronizing a DOA circular array receiver system to mitigate these imperfections. A reference signal located at the center of the DOA array was coupled to array elements such that both the coupled reference signals and signals from a target were captured simultaneously in the receiver. This coupled reference signal was used to compensate for any phase error offsets produced by receiver system imperfections on cable length, phase of local oscillators, and phase delays in active devices. Furthermore, this approach did not necessitate an off-line calibration process of each receiver channel requiring accurate measurements. We implemented a 16-element circular array DOA estimation system using the Universal Software Radio Peripheral platform operating in the Sand C-bands. Results show that this implementation was able to combat receiver phase offset errors and estimated the DOA angles with an rms error of 0.92°.