Doppler Signature Analysis and Separation of Mixed O/X-Mode in HF Hybrid Sky-Surface Wave Radar

The High-frequency hybrid sky-surface wave radar (HSSWR) working with frequency modulated continuous wave (FMCW) has great potential for large-scale monitoring targets and ocean environment. HF signal propagating through the ionosphere split into the ordinary (O) and extraordinary (X) waves due to the influence of the geomagnetic field. In this paper, the computational formula of the Doppler signatures is derived in the case of a mixed O/X-mode signal model and analyze the results in Range-Doppler spectrum. It is shown that the Doppler components cannot be separated using matched filtering. The fractional Fourier transform (FRFT) for separating two O/X mode Doppler components is proposed according to the derived Doppler signature expression. The simulation results illustrate that the proposed scheme is an effective solution for O/X mode Doppler separation.