【作者】 李雷；

【导师】 许荣庆；

【作者基本信息】 哈尔滨工业大学 ， 通信与信息系统， 2007， 博士

【摘要】 利用高频段垂直极化电磁波能够沿海洋表面绕射传播的机理,高频地波雷达能够实现对海上舰船目标和低空飞行目标的超视距探测,同时,为海洋资源管理和开发提供了新的途径。因此,世界上许多国家都投入了大量精力进行高频地波雷达的研制工作。电离层是目前影响高频雷达生存能力的最大障碍,一方面电离层反射高频雷达自身发射信号,通过复杂的调制和路径回到雷达接收机,形成电离层杂波;另一方面电离层传播远距离电台反射进入接收机,形成天波电台干扰。电离层杂波和天波电台干扰抬高了整个雷达探测谱基底,破坏了检测背景,给舰船等有用目标的探测带来了极大困难,直接影响到雷达的威力范围。因此,如何有效地抑制电离层杂波和天波电台干扰,改善检测性能,进而增大雷达的探测距离便成了高频地波雷达所必须解决的关键技术难题。本文的研究任务就是在上述课题背景下提出来的,全文主要贡献总结如下:1.基于长期观测和大量统计数据首次对赤道地区电离层杂波特性进行了详尽分析。分析了高频雷达电离层杂波的成因,路径及其传输特性。杂波按进入接收机路径被分为垂直向电离层杂波和海面传播电离层杂波。对电离层杂波的时域、距离域、多普勒域等特性进行了深入的比较分析,并着重研究了杂波的空间方向特性,比较了不同杂波(特别是垂直向和海面传播电离层杂波)的异同点,为电离层杂波抑制技术的研究提供了思路和可能的解决途径。2.首次提出了高频雷达阵列天线幅相误差实时盲校准方法,给出了接收机带内及路间不一致性补偿方法。高频雷达工作环境十分恶劣,阵列天线的幅相误差较大,破坏了雷达波束的旁瓣和凹口零值深度,为进行杂波干扰抑制,阵列幅相误差校准势在必行。本文选用了孤立的大信噪比目标作为校准源对雷达阵列天线幅相误差进行了测量和校准,并提出一种适合于实时处理的校准目标盲搜索方法,校准后阵列天线幅度误差从±2dB降低为±0.5dB,相位误差从±20o降低为±3o。对于接收机带内及路间幅相不一致性,提出了脉冲串补偿信号频域逐点补偿的方法,有效的保证了目标信号回波的脉压结果,同时降低了路间不一致程度,补偿后经模拟信号源测得路间幅度不一致性从0.776dB降低到0.005dB,相位不一致性从42度降至0.02度。接收系统误差校准降低了进入旁瓣的杂波能量,同时为自适应抗干扰的研究提供了保障。3.基于电缆移相的方法构造了新的接收天线,抑制了天顶及附近方向的垂直向电离层杂波,同时,提出了基于水平极化辅助天线和垂直向辅助波束的垂直向杂波旁瓣对消方法。在不增加信号处理复杂度前提下,新接收天线的垂直波束方向图凹口位于天顶方向,提高了接收系统对垂直面天顶及附近方向的抑制能力,降低了电离层杂波进入系统的能量。同时,探讨了利用水平极化辅助天线,垂直方向波束辅助通道进行旁瓣对消的方法,实测雷达数据处理结果均取得了一定的抑制效果。4.研究并系统实现了海面电离层杂波抑制,较弱杂波和阵列天线误差较小的情况下,提出了基于目标海杂波样本剔除的预检测对消方法(DBC),在强杂波或阵列误差较大情况下,提出了基于多次检测的迭代变加载预检测对消方法(RVDL-DBC),应用于实际系统,效果良好。针对空间单凹口滤波器辅助通道电离层杂波对消方法在实际处理过程中存在的目标损失和基底抬高等问题,提出了基于目标海杂波样本剔除的预检测对消方法(DBC),通过适当的数据选择准则,把预检测到的目标和海杂波信息从训练样本中剔除,保证了训练样本中仅含电离层杂波数据,获得了更有效的对消结果。在此基础上,针对强杂波或较大阵列误差情况,首次提出了基于多次检测的迭代变加载预检测对消方法(RVDL-DBC),逐步检测出淹没在杂波中的目标,有效的保证了杂波对消后的目标特性。最后给出了切合实际的电离层杂波抑制系统方案,通过大量实测数据处理,结果表明该方案在保证目标信息损失最小情况下有效的抑制了电离层杂波,改善了雷达检测背景,能够满足高频雷达系统自适应抗电离层杂波干扰的需要。5.研究了高频雷达电台干扰抑制技术,提出了基于稳健最小二乘(RLS)的电台干扰抑制方法,探讨了超分辨算法在电台干扰抑制中的应用。基于凸最优的思想,提出了稳健的最小二乘天波电台干扰抑制方法,通过修正水平接收通道的数据,在最差的误差环境下达到了最优的干扰抑制性能,并给出了有效求解方法,通过实际数据处理结果验证了算法的有效性。此外,本文最后探讨了超分辨算法用于电台干扰抑制的实验结果。通过本文的研究,突破了高频雷达电离层杂波和天波电台干扰抑制中的关键技术。改善了雷达的检测背景,保障了高频雷达全天候工作的能力,进而提高了雷达的总体性能。为整个雷达系统的研制提供了有力的帮助,具有非常大的应用价值和实际意义。更多还原

【Abstract】 High frequency surface wave Radar (HFSWR), utilizing vertical polarized electromagnetic wave which follows the curvature of the earth along the air-water interface with low propagation loss on highly conductive ocean surface, can detect and track targets beyond the horizon such as vessels on the sea or aircrafts at low altitude. It provides a new way to manage and explore oceanic resources in civil projects. Therefore, many countries devoted much energy to developing HFSWR in recent years. Ionosphere has proved to be the biggest obstacle to achieve consistently good performance in long-range detection and surface vessels tracking for HFSWR. On one hand, the ionosphere reflects the radar’s own signal, which returns to the receiver through complex modulation and path and forms ionospheric clutter; on the other hand, the ionosphere propagates and reflects the long-range radio signal to radar receiver, and forms skywave radio interference. Both ionospheric clutter and sky radio interference raise the floor of power spectrum and destroy the detection background, which cause huge difficulty for target detection and badly affect the detection range. Therefore, it is very crucial in HFSWR to effectively mitigate the ionospheric clutter and skywave radio interference, increase the signal to interference and noise radio (SINR) of target echo, improve the performance of detection, and increase the detection range. The current research was carried out under the circumstance mentioned above and the major contributions include:1. Characteristics of ionospheric clutter in equator were analyzed based on long term observation and abundant experimental data for the first time.The inducement, path and propagation characteristics of ionospheric clutter in HFSWR were analyzed. The clutter was classified into near vertical incident (NVI) clutter and sea propagated clutter based on propagation path. The Characteristics of ionospheric clutter were investigated in time, range and velocity domain, especially, spatial properties were studied with emphasis. The similarities and differences were compared (especially vertical clutter and sea propagated clutter). These studies provided the idea and possible approach for ionospheric clutter mitigation. 2. HFSWR antenna array amplitude and phase errors were real-time blind calibrated for the first time. And the compensation of receiver mismatch was proposed.HFSWR works in a short wave band. The antenna array amplitude and phase errors were very big which affect the sidelobe and null depth of radar beam. So it is imperative to calibrate the array antenna under this situation. Isolated targets with big SNR were selected as the calibration source to measure and calibrate array antenna error, and a suitable target blind search algorithm was studied. The antenna amplitude error was reduced from±2dB to±0.5dB and phase error was reduced from±20o to±3o. Narrow pulse sequence compensation method was proposed to compensate the mismatch of receiver amplitude and phase response. After the compensation, good match filter result was achieved and the receiver amplitude mismatch was reduced from 0.776dB to 0.005dB, and the phase mismatch was reduced from 42o to 0.02o. The calibration of receive system errors decreases the energy of ionospheric clutter from sidelobe, and guarantees the effective cancellation of clutter and interference.3. Based on the method of cable phase delay,new receive antenna was built to suppress the NVI ionospheric clutter at near zenith dirction. Sidelobe cancellation methods based on horizontal polar antenna and vertical beamformer were proposed to mitigate NVI ionsopheric clutter.New receive antenna was built to improve the mitigation ability of near zenith direction. The energy of NVI ionospheric clutter was reduced without increasing the complexity of signal processing. Based on horizontal polar antenna and vertical beamformer, NVI ionospheric cluter suppressed by the sidelobe cancellation method was discussed. Results show satisfactory suppression.4. A mitigation technology of sea propagated ionospheric clutter was studied and achieved. Detection before cancellation (DBC) method based on the exclusion of target and sea clutter was proposed for the case of weak clutter and small antenna errors. And recursive variational diagonal loading detection before cancellation based on multiple detections was proposed for the case of strong clutter or big antenna errors for the first time. Satisfactory results were achieved in real system. Detection before cancellation (DBC) method based on the exclusion of target and sea clutter was proposed to resolve target loss and floor hoist after traditional single notch filter auxiliary ionospheric clutter sidelobe cancellation for the case of weak clutter and small antenna errors. The sample data was trained to get the pure ionospheric clutter data by excluding the target and sea clutter information; for the case of strong clutter or big antenna errors, recursive variational diagonal loading detection before cancellation (RVDL-DBC) based on multiple detections was proposed for the first time. The small target was detected step by step through the multiple detections and cancellations, and effective cancellation results were achieved. The method keeps the target property after clutter cancellation. Finally, the whole clutter mitigation method was summarized. Experimental results showed that the method could effectively suppress ionospheric clutter without losing any target information, increase the SNR of target, improve radar detection background and meet the requirement of ionospheric clutter mitigation.5. Robust least squares radio interference mitigation method was proposed, and super resolution methods were discussed for radio interference mitigation.Based on the idea of convex optimization, the sample of horizontal auxiliary channel was modified, and the best performance of interference rejection in the worst case error circumstance under the limit of maximum error bound was obtained. A robust least squares method for skywave radio interference mitigation was proposed to settle the optimal weight coefficient effectively.In summary, the crucial techniques in ionospheric clutter and skywave radio interference mitigation of HFSWR were achieved. Radar detection background was improved; all-weather ability of radar was ensured; and the overall performance was improved. The current study is extremely useful for the development of whole radar system and has great potential to be employed in applications.更多还原