【摘要】：高頻無(wú)源分布式雷達(dá)采用天波反射/地波繞射的混合傳播模式,能夠探測(cè)視距以外的低空飛行目標(biāo)和海面艦船目標(biāo)。相對(duì)于傳統(tǒng)的天波高頻雷達(dá)和地波高頻雷達(dá),高頻無(wú)源雷達(dá)具有更大的靈活性,其可實(shí)現(xiàn)岸基接收與艦載接收;作為無(wú)源雷達(dá),只“靜默”接收回波信號(hào)而不發(fā)射能量,具備抗輻射打擊能力,提高了雷達(dá)的生存能力。本文所研究的高頻無(wú)源雷達(dá)是一種新體制雷達(dá),其照射源采用DRM數(shù)字廣播信號(hào),利用天/地混合傳播模式,其回波信號(hào)中包含強(qiáng)直達(dá)波、多徑干擾、電離層擾動(dòng)等多種干擾信號(hào),因而在信號(hào)處理過(guò)程中會(huì)出現(xiàn)諸多難點(diǎn)。本文將對(duì)該體制下雷達(dá)信號(hào)照射源、系統(tǒng)探測(cè)模型、信號(hào)處理等部分進(jìn)行探索,為后續(xù)研究工作提供必要的基礎(chǔ)。課題首先研究了該高頻無(wú)源雷達(dá)所采用的信號(hào)體制,完成了DRM數(shù)字廣播信號(hào)的仿真與波形特性分析。進(jìn)而研究了該信號(hào)的模糊函數(shù)以及幀結(jié)構(gòu)對(duì)信號(hào)波形的影響,以判斷其是否具有作為雷達(dá)照射源的可行性。仿真結(jié)果表明,該體制雷達(dá)具有圖釘狀模糊函數(shù),表明其具有良好的分辨性能。討論了該體制無(wú)源雷達(dá)系統(tǒng)信號(hào)傳輸模型,分別給出了參考信道、監(jiān)測(cè)信道的回波信號(hào)模型,推導(dǎo)了在天地混合傳輸模式下的雷達(dá)方程與目標(biāo)定位方程;同時(shí),對(duì)回波信號(hào)中的直達(dá)波功率與海雜波信號(hào)頻率進(jìn)行了分析。仿真結(jié)果表明,直達(dá)波相比目標(biāo)回波信號(hào),其功率高出70 d B以上,這會(huì)對(duì)目標(biāo)檢測(cè)構(gòu)成影響;理想的海雜波頻譜是兩根對(duì)稱(chēng)的譜線(xiàn),該性質(zhì)在信號(hào)處理過(guò)程中可作為一種特性加以利用。課題研究了切比雪夫準(zhǔn)則下的最佳陣列排布問(wèn)題,推導(dǎo)了最佳陣列排布方程,得到了無(wú)方向性等加權(quán)條件下的最佳陣列—指數(shù)間隔陣列,并分析了該陣列的近軸旁瓣電平、峰值旁瓣電平。由于該陣列旁瓣電平較高,本文討論了陣列波束優(yōu)化方案,仿真結(jié)果表明:利用改進(jìn)的窗函數(shù)加權(quán)后,所得陣列方向圖主波束展寬較嚴(yán)重,而最高旁瓣電平并沒(méi)有得到抑制,而利用凸優(yōu)化技術(shù)進(jìn)行加權(quán)后,所得方向圖主波束并未明顯展寬,而最高旁瓣電平得到了較好的抑制,對(duì)于指數(shù)間隔陣列,其最高旁瓣電平降低了1.2 d B,對(duì)于對(duì)稱(chēng)指數(shù)間隔,其最高旁瓣電平降低了1.6 d B。針對(duì)高頻無(wú)源分布式雷達(dá)信號(hào)處理技術(shù)進(jìn)行了相關(guān)研究。由于無(wú)源雷達(dá)采用DRM數(shù)字廣播信號(hào),其信號(hào)波形具有不確定性,需要利用參考信道信號(hào)與監(jiān)測(cè)信道進(jìn)行相干處理來(lái)實(shí)現(xiàn)目標(biāo)檢測(cè),這就要求對(duì)參考通道信號(hào)進(jìn)行重構(gòu),以便得到純凈的信號(hào)。在監(jiān)測(cè)信道回波信號(hào)中,由于強(qiáng)直達(dá)波、電離層干擾以及多徑干擾的存在會(huì)對(duì)目標(biāo)檢測(cè)形成干擾,強(qiáng)直達(dá)波會(huì)淹沒(méi)目標(biāo)信號(hào),而電離層引入的調(diào)制信息會(huì)引起海雜波的展寬,同樣會(huì)隱藏海雜波附近的目標(biāo)。本文研究了兩種自適應(yīng)波束形成算法進(jìn)行直達(dá)波、多徑干擾的抑制,利用相位梯度算法進(jìn)行電離層相位擾動(dòng)補(bǔ)償。仿真結(jié)果表明:MVDR算法與正交投影算法均可以很好的抑制直達(dá)波及多徑擾動(dòng),所得結(jié)果目標(biāo)檢測(cè)背景并無(wú)明顯差距,但是相對(duì)于MVDR算法,正交投影算法無(wú)需對(duì)期望信號(hào)導(dǎo)向矢量進(jìn)行估計(jì),這就避免了由于期望信號(hào)導(dǎo)向矢量估計(jì)不準(zhǔn)而引起的誤差。通過(guò)對(duì)電離層相位擾動(dòng)的分析,可以知道線(xiàn)性相位擾動(dòng)可以引起頻譜平移而不會(huì)造成展寬,而非線(xiàn)性相位污染會(huì)導(dǎo)致頻譜展寬。利用相位梯度算法可以很好地估計(jì)小幅度慢變電離層相位污染,較好的對(duì)污染結(jié)果進(jìn)行補(bǔ)償,而對(duì)大幅度、快變電離層相位污染,該算法并不適用。
[Abstract]:HF passive distributed radar uses the mixed propagation mode of sky-wave reflection and ground-wave diffraction, which can detect low-altitude flying targets and sea surface ship targets beyond the range of sight. The high frequency passive radar studied in this paper is a new kind of radar. Its illumination source adopts DRM digital broadcasting signal and uses space/ground hybrid propagation mode. Its echo signal contains strong direct wave and multi-path. In this paper, the radar signal illumination source, system detection model, signal processing and other parts of the system will be explored to provide the necessary basis for the follow-up research. First, the signal used by the high-frequency passive radar is studied. The simulation and waveform characteristic analysis of DRM digital broadcasting signal are completed. Then the influence of ambiguity function and frame structure on the waveform of the signal is studied to judge whether it is feasible to be used as radar illumination source. The performance of the passive radar system is discussed. The echo signal model of the reference channel and the monitoring channel is given. The radar equation and the target location equation in the mixed transmission mode are deduced. At the same time, the direct wave power and the sea clutter signal frequency in the echo signal are analyzed. It is shown that the power of direct wave is more than 70 D B higher than that of target echo signal, which will affect target detection. The ideal spectrum of sea clutter is two symmetrical lines, which can be used as a characteristic in signal processing. The optimal array-exponential spaced array without directional weighting is obtained by arranging the array equations. The paraxial sidelobe level and peak sidelobe level of the array are analyzed. The main beam broadening is serious, but the maximum sidelobe level is not suppressed. After weighted by convex optimization technique, the main beam of the pattern is not significantly broadened, but the maximum sidelobe level is well suppressed. For exponential spaced array, the maximum sidelobe level is reduced by 1.2 D B, and for symmetric exponential spaced array, the maximum sidelobe level is the highest. The sidelobe level is reduced by 1.6 D B. The signal processing technology of high frequency passive distributed radar is studied. Because the signal waveform of passive radar is uncertain due to the DRM digital broadcasting signal, it is necessary to use the reference channel signal and the monitoring channel for coherent processing to achieve target detection, which requires the reference channel signal. In the monitoring channel echo signal, the presence of strong direct wave, ionospheric interference and multipath interference will interfere with the target detection, strong direct wave will submerge the target signal, and the modulation information introduced by the ionosphere will cause the sea clutter to widen and also hide the eyes near the sea clutter. In this paper, two adaptive beamforming algorithms are studied to suppress direct wave and multipath interference, and the phase gradient algorithm is used to compensate the Ionospheric Phase disturbance.The simulation results show that the MVDR algorithm and the orthogonal projection algorithm can suppress the direct wave and multipath disturbance very well, and there is no significant difference between the results of target detection background, but the phase gradient algorithm can compensate for the Ionospheric Phase disturbance. Compared with the MVDR algorithm, the orthogonal projection algorithm does not need to estimate the expected signal steering vector, which avoids the error caused by the inaccurate estimation of the expected signal steering vector. The phase gradient algorithm can estimate the phase contamination of the slow ionosphere in small amplitude and compensate for the contamination. However, it is not suitable for the large and fast Ionospheric Phase contamination.
【學(xué)位授予單位】：哈爾濱工業(yè)大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2014
【分類(lèi)號(hào)】：TN957.51

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