Experimental Study on Effects of Ionospheric Multi-path on Echo Spectra in HF Hybrid Sky-surface Wave System

In high-frequency (HF) hybrid sky-surface wave system, owing to the ionosphere propagation mode, the echo spectrum of hybrid sky-surface wave propagation channel are extremely complex in spatial, time, and frequency domains, which seriously affect radar performance. Using the newly-developed hybrid sky-surface wave experimental system and the oblique incidence sounders (OIS), the echo spectra for hybrid sky-surface wave propagation channel and the ionospheric propagation paths are obtained separately. The typical examples of echo spectra via the different propagation paths are analyzed. For ionospheric one-path propagation, the Range-Doppler spectra include sea clutter and ionospheric direct wave via one mode, which is conductive for target detection and location. For ionospheric multi-path propagation, the echoes via multi-path interact with each other, and the qualities of spectra reduce, which would seriously affect ship target detection. It is found that the propagation mode of echo spectra vary complicatedly with frequency and ionosphere state. This research could provide important supporting functions for operating frequency selection, target detection, and location.