The analytical expression of shortwave interference in the range-Doppler domain is derived and is found to exhibit a constant-amplitude spectrum ridge parallel to the range axis. The spatial nonstationarity of the shortwave interference induced by ionosphere perturbation is then analyzed and is found to be equivalent to the amplitude-phase error between the same frequency points of shortwave interference on different antenna elements; hence, the above mentioned spatial nonstationarity only a has a slight effect on the performance of Adaptive Digital BeamForming (ADBF). On the basis of the above analyses, this paper presents a post-Doppler ADBF approach for skywave radar. This approach involves transforming the received signal in each antenna element into a range-Doppler domain and then performing adaptive processing at each Doppler frequency point. The real radar data processing conducted in this study shows that the ADBF approach has a good interference suppression performance and strong robustness.
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