Research Of Sky-Wave OTHR Signal Detection

Sky-wave Over-the-horizon radar (OTHR) works at high frequency band and can achieve long range detection via refraction by the ionosphere. It is significantly characterized by capabilities of detecting targets at long distance, resisting anti-radiation missile and stealth aircraft, and countering electronic jam, which badly threat conventional radars at present. Sky-wave OTHR plays an important role in the field of modern aerial defense and consequently fills the vacancy of strategic early warning of our country.OTHR works at a hostile electromagnetic environment and its echoes are confronted with all kinds of interferences from man-made and natural sources, and external noise, so it has a complicated background when detects targets. Besides, time-varying ionosphere will lead to serious clutter spectrum spread. All of the above makes target detection a key technique in OTHR signal processing. OTHR targets can be classified into two kinds, i.e. air targets and ship targets. This thesis aimed at air target detection with sky-wave OTHR.The thesis was organized as follows: introduced the features of sky-wave OTHR environment and the main task of corresponding signal processing; signal processing flow at sky-wave OTHR was introduced and techniques involved were analyzed and deduced, especially the range-azimuth-speed joint processing; Analysis of target signature, interference feature and clutter characteristics was centralized. Statistics of much data recorded with sky-wave OTHR showed that, target, interference and clutter consisted of nonstationary signal detection background; Two kinds of classical CFAR detectors were illustrated. The performance of CA-CFAR and OS-CFAR was compared, and both of their deficiencies appearing in the application to real radar data were analyzed; Based on the preceding detectors performance comparison and real echo analysis, It presented a new target detection scheme. Firstly, interference-suppressing measure was taken in the scheme to remove interference remains to keep background stationary and homogeneous. Secondly, CFAR based classical detector was adopted. The last step was false alarm filtering. Due to the inconsistency of real background with CFAR model, false alarm is possibly higher than expected. False target filtering technique was developed to discriminate false targets among all the detected. Furthermore, CFAR-based correlative detection method was advanced for fluctuant target to promote probability of detection, which had fluctuating SNR during sky-wave radar's scanning time. At last, the thesis summarized the whole thesis and pointed out future work remained to study further.The techniques provided in this thesis has been proved by sky-wave OTHR data to be effective and applied in engineering practice.