Environmental Modeling And Sea Clutter Suppression Of High Frequency Hybrid Sky-Surface Wave Radar

High frequency hybrid sky-surface wave radar is a new over-the-horizon radar which makes full use of the sky-wave reflection/surface-wave diffraction hybrid propagation mode.It has the advantages of wide detection range and strong RF stealth ability.In this system,the inland sky-wave transmitting station and the shore-based surface-wave transmitting station send orthogonal signals.After being reflected by the target on the sea,they arrive at the sky-wave receiving station and surface-wave receiving station.After matched filtering,signals of four propagation mode are separated and obtained:surface-wave transmitting and surface-wave receiving mode;sky-wave transmitting and sky-wave receiving mode;sky-wave transmitting and surface-wave receiving mode;surface-wave transmitting and sky-wave receiving mode.However,the propagation channel of the radar system is complex and the severely broadened sea clutter existing in the echo signal will affect the target detection performance.In order to solve the above problems,this thesis relies on the key project of National Natural Science Foundation of China--research of maritime and air target information of the dynamic reconstructed high frequency hybrid sky-surface wave radar.The main work is as follows:(1)Building target echo signal model of four propagation modes.The ionospheric channel in the sky-wave path is studied deeply.Based on the ionospheric electron concentration model and analytical ray tracing method,the path parameters of signal are derived and the method to simulate the ionospheric phase disturbance is studied.Considering that the four propagation modes are the combination of sky-wave path and surface-wave path,the echo signal parameter model is studied under the sky-wave path and surface-wave path respectively,and the target echo signal model of four propagation modes is obtained by combining the corresponding path.(2)Building the broadened sea clutter spectrum model of four propagation modes.Firstly,based on Bragg resonance theory,the ocean surface cross section of four modes are derived under the condition that the bistatic angle is a constant.Then,considering that the bistatic radar existing sky-wave path is difficult to express the equidistant ring explicitly,and the bistatic angle of each resolution unit under wide receiving beam is variable,based on the scattering region equalization and simulation traversal,the division mode of clutter unit is discussed,and the wide-beam sea clutter power spectrum model is established.Finally,the clutter unit is regarded as a point target to generate sea clutter echo signal,and the sea clutter spectrum shift and broadening caused by variable bistatic angle and ionospheric phase diameter disturbance under wide receiving beam are simulated.(3)Studying sea clutter suppression algorithm based on the broadened sea clutter spectrum model built above.Firstly,ionospheric phase disturbance suppression method based on S-Method and S~2-Method time-frequency analysis is studied,and the performance of the algorithm under different disturbance amplitude and clutter to noise ratio(CNR)is simulated.When the ionospheric influence is weakened,the sea clutter suppression algorithm based on the optimal signal to clutter noise ratio(SCNR)filter and joint domain localized(JDL)is studied and simulated.