High-frequency (HF) signals reflected from different points within each ionospheric layer may have slightly different Doppler frequencies and angles of arrival. The superposition of these signals leads to time varying and nonplanar wavefronts. Investigation of temporal and spatial characteristics of the ionospherically propagated HF signals plays an important role in designing the signal processing algorithms for the HF over-the-horizon radar (OTHR). A cost-efficient superresolution algorithm for simultaneously estimating the Doppler frequencies and angles of arrival of the ionospherically propagated HF signals is proposed in this paper. The effectiveness of the proposed algorithm is verified by the experimental data from a trial HF OTHR. Furthermore, the superposition model with the HF signal reflected by a smooth ionospheric layer consisting of a number of submode signals is also confirmed by the experimental data processing results.