Research On Array Signal Processing Of High Frequency Passive Bistatic Radar

The high frequency passive radar utilizes ionosphere reflection and surface diffraction propagation modes to detect targets beyond the horizon such as vessels on the sea and low altitude flying targets. Compared with traditional HF sky wave and surface wave radar, HF passive radar is more flexible to build shore-based and shipboard receiver. The HF passive radar can be classified as bistatic radar, it will not emit signal with powerful energy and only receive echos in silence, which improves invisibility and survival of the radar in wartime.The HF passive radar studied in this paper is a new radar system, which uses DRM broadcast signals as radiation sources and utilizes ionosphere reflection/surface diffraction propagation modes. The echos contains powerful direct path wave, multipath interference and ionospheric disturbances. Therefore, there is a lot of difficulties in signal processing. This article will explore the DRM radiation source, detection model and signal processing in this new radar system to provide the necessary foundation for further research.This article studied the radiation signal system of HF passive radar. Completed simulation and waveform characteristics analysis of DRM digital broadcast signal based on theoretical analysis of the principle of OFDM modulation and demodulation, and the analysis of protection unit. And then make a further study on the influence of the ambiguity function and waveform frame structure so as to determine whether it is feasible as the radar illumination source.The article researched the signal transmission model of this HF passive radar system. Established the echo model of the reference channel and monitoring channel, and derived the radar equation and localization equation on hybrid sky-surface wave transmission mode. And also, the article analyzed the direct wave power and the sea clutter frequency in monitoring channel echo.The article discussed the optimum array under the criterion of Dolph-Chebyshev. Derived the equation of optimum element distribution, and then got a best array on condition that each element uses non-directional equal weighting—exponentially spaced array, and also analyzed the nearby side-lobe level and peak side-lobe level of this array. Since the side-lobe level is a little high, this paper used convex optimization. Meanwhile, this paper also discussed another two array—Symmetry exponentially spaced array and improving generalized cosine weighted array.This article researched signal processing techniques based on HF passive bistatic radar. Since the radar uses DRM digital broadcast signal as its radiation sources, the waveform is uncertainty, so it need to use coherent process between reference channel and monitoring channel signals to achieve the target detection. This asks the reference signal need to be pure, so it reconstructed the reference channel signals. In the Monitoring channel echo, there is a lot of interference signals such as powerful direct-path wave, ionospheric disturbances and multipath interference, these signals would cause interference with target detection: The powerful direct path wave would hide the target signal, and ionospheric disturbances would make the sea clutter spectral broadening, which hid the target closed to sea clutter spectral. This paper completed the direct path wave and multipath disturbance suppression by using adaptive beamforming technology, and phase ionospheric disturbance compensation hrough the phase gradient algorithm.