Study Of Target Simulation And Signal Processing Algorithm For Skywave Over-The-Horizon Radar

The skywave Over-the-Horizon Radar (OTHR) is a special type of radar which operates in high frequency band (3-30MHz) and employs the ionosphere to reflect signal to detect target from the top down. OTHR has some native advantages, such as the capability of detecting low-flying target and stealth target, avoiding the attack of anti-radiation missile, as well as providing wide area surveillance with longer early warning time than some other common radar. Therefore, OTHR play a more and more important role in modern air defense system and has potential significant contribution to military applications. However, OTHR's operating modes (high frequency operation band, ionospheric propagation medium and looking-down mode) bring some great challenges to the signal processing. The success in resolving these problems will be crucial to enhance OTHR's performance and extend its advantages.This paper focuses on the decontamination of ionospheric distortion and the ship detection in OTHR's operation. First of all, the mathematical derivation of the range-azimuth-Doppler joint signal processing of OTHR presented in detail. And based on the ocean scattering intensity formula proposed by Barrick, the sea clutter spectrum is simulated, with which the characteristics of clutter distribution and its dependence on sea-state are deduced. Then, the decontamination of ionospheric distortion is studied in detail, and the emphasis is placed on ionospheric phase perturbation correction. The several existing methods of ionospheric phase perturbation correction are introduced and compared, and their advatages and disadvantades are analysed. Futher, the analysis of the condition that real targets are near Bragg peaks in phase perturbation correction using PGA is presented, with which a method that can effectively detect the real targets using PGA by positive and negative Bragg peaks is proposed. Finally, the ship detection is disscused in OTHR's operation, respectively with long coherent integration time and short coherent integration time (CIT). The emphasis is placed on the ship detection with short CIT. The simulation examples proved that the new improved ocean clutter cancellation method based on FFT phase analysis, compared to the traditional clutter cancellation method, can obtain much higher estimation precision in ocean clutter parameter estimation, and achieve better clutter cancellation performance. As the result, the power and spreading of the clutter residue are decreased significantly, that will benefit the ship visibility and identification from the clutter residue.