In this paper, we have proposed an improved direction-of-arrival (DoA) estimation algorithm, which uses the power pattern cross-correlation (PPCC) estimator and received signal strength (RSS) values recorded at electronically steerable parasitic array radiator (ESPAR) antenna's output port, providing more accurate DoA results for unknown signals impinging the antenna. The PPCC estimator in its original form provides accurate DoA estimation results for directions lying within the horizontal plane. However, the estimation accuracy drops for other elevation angles as the estimator relies on ESPAR antenna's radiation patterns measurements in the horizontal plane only. Our proposed modification allows one to measure ESPAR antenna's radiation patterns in two different elevation planes during the calibration phase, which improves PPCC-based DoA estimation algorithm's overall accuracy for signals impinging the antenna from arbitrary elevation angles. The proposed algorithm has been verified during anechoic chamber measurements using our ESPAR antenna prototype.