Research On Slowly Moving Target Detection Algorithm For Sky-wave Over-the-horizon Radar

The sky-wave over-the-horizon radar(OTHR) has a special working mechanism, which uses the reflection of ionosphere for the high-frequency electromagnetic wave to detect targets. It has wide detection distance and monitoring range, can effectively detect low-altitude targets, stealth aircraft and anti-radiation missiles, which has important military application and civil values. Due to the special detection mechanism, OTHR echo usually contain strong sea clutter signal, slowly moving targets likely to be overshadowed by the first-order sea clutter spectrum, resulting in missed targets. Moreover, the working band of OTHR is busy, there are more active radio frequency interference in the high frequency band, RF interference into the radar receiver would seriously interfere the target detection.Aiming at the existing problems in the slowly moving targets detection, this paper focus on research the OTH radar RF interference suppression algorithm, sea clutter suppression and slow ship targets detection, the main innovation includes:1、Firstly, in-depth study of the RF interference suppression method of the skywave radar. Based on the analysis of RF interference sources and hazards, this thesis propose a RF interference suppression algorithm based on the optimal filter design, this method can suppress RF interference while achieving matched filtering, and does not affect the target signal. Measured data processing results demonstrate the effectiveness of the algorithm.2、Secondly, a variety of sea clutter suppression method is studied, such as traditional sea clutter cycle cancellation algorithm and subspace projection algorithm, and analyzes the characteristics and application scenarios of the two algorithms. For practical application, a new sea clutter algorithm based on high-precision frequency estimation is proposed. This method can precisely estimate the frequency, amplitude and initial phase of each sinusoidal component, which reduces the residual clutter energy. In addition, the use of clutter frequency margin can avoid the target signal being mistakenly cancelled, further improve the target detection performance.3、Thirdly, a slowly moving target detection algorithm under short coherent accumulation condition is proposed. This method firstly construct a local clutter covariance in frequency domain, then do weighted adaptive processing for each detect Doppler channel, thus the problem is transformed into an optimization problem of extremum. The Wiener filtering method used to keep the detected frequency channel signal gain constant, while trying to suppress signals from other frequency channels. The measured data results show that the algorithm still has a good performance under the condition of the slow target.