Adaptive suppression of skywave interference in HF surface wave radar using auxiliary horizontal dipole antennas

This paper presents the results of a study to evaluate the effectiveness of an adaptive technique using horizontal dipoles to suppress the skywave interference in HF surface wave radar (HFSWR). Four auxiliary horizontal dipole antennas, configured in the form of two separate crosses, are used to form an adaptive system with the vertically polarized antennas (VPA) of a HFSWR system. The outputs of the horizontal dipoles are correlated with the summed output of the VPAs to cancel the interference component in the output of the VPAs. Two slightly different methods are used in the estimation of the correlation coefficients. The first method uses the samples at the far ranges of the radar. The second method uses the samples in the nearby range bins. The results of using the first method have been presented by Leong (see RADAR'97, IEE Conf., Edinburgh, Scotland, p.26-30, 1997). Here we present the results of using the second method. With the first method, the interference-plus-noise power (INP) is reduced by more than 13 dB, and the Bragg-to-interference-plus-noise-ratio (BINR) increases by up to 21 dB. With the second method, the INP is reduced by more than 17 dB, and the BINR increases by up to 25 dB. Both sets of the results show that the adaptive techniques are effective in suppressing the skywave interference.