2D Direction of Arrival Estimation Using Uniform Circular Arrays With Radiation Pattern Reconfigurable Antennas

This paper focuses on direction of arrival (DoA) estimation using adaptive arrays that consist of radiation pattern reconfigurable antenna (RPRA) elements for 2D direction finding (i.e., azimuth and elevation DoA estimation). In particular, uniform circular arrays (UCAs) are explored that use RPRA elements with two different elevation radiation pattern states to achieve unambiguous estimates over all possible incident angles. Theoretical cardioid-type directional patterns are investigated to determine the pattern states that minimize overall DoA estimation error, and the performance of 3-, 4-, and 5-element RPRA UCAs is compared with baseline theoretical arrays composed of isotropic elements. The results demonstrate that RPRA UCAs with optimized cardioid patterns can achieve similar accuracy to the baseline arrays, but with fewer antennas/front-ends. For example, a 4-element RPRA UCA can achieve approximately the same root mean square error (RMSE) as a 6-element uniform spherical array composed of isotropic elements. Furthermore, unambiguous estimates can be achieved over all incident angles with electrically large UCA radii using optimized RPRA elements, which can further improve accuracy and increase bandwidth. To demonstrate the feasibility of the technique, a practical RPRA was designed at 6 GHz with a pattern that approximates the optimized cardioid, and the performance meets or exceeds the theoretical pattern performance for RMSEs less than 3°.