Direction of Arrival Estimation Using Amplitude and Phase Information in Low-Profile MIMO Arrays

Accurate direction of arrival (DOA) estimation in compact terminal devices using small antenna arrays is challenging due to their limited radiating apertures. In this communication, we employ both the amplitude and the phase information to improve the estimation accuracy and eliminate phase ambiguity without increasing the size of the antenna array. The optimal amplitude ratio between the antenna patterns is theoretically studied using the theories of the Fisher information, Cramér-Rao bound, and ambiguity function. Criteria of proper amplitude ratio are summarized from the theoretical investigations. Following the guidelines, two antenna arrays are modified to build effective antenna patterns and improve the estimation accuracy. Specifically, the compact monopole-patch array and the dual-monopole array reduce the DOA estimation errors by over 60% and 20%-40%, respectively, under a medium SNR of 10 dB. The phase ambiguity has been eliminated in both arrays as well. The monopole-patch array requires phase calibration in the measurement, whereas the dual-monopole array does not. Experiments were carried out for the dual-monopole array in the anechoic chamber, achieving the estimation accuracy of 0.67° averaged over 360°.