【作者】 李钢；

【导师】 杨仕文；

【作者基本信息】 电子科技大学 ， 电磁场与微波技术， 2010， 博士

【摘要】 随着现代电子技术的飞速发展,阵列天线——作为广泛应用于各种无线系统的传感器,通常工作在非常复杂的电磁环境当中。为了能够有效地抑制从天线副瓣进入系统的各种干扰,无线系统通常要求阵列天线具有很低的副瓣电平。然而,较高的激励幅度动态范围比以及苛刻的误差精度要求导致很难在常规相控阵中实现低或超低副瓣。如果在常规相控阵中引入新的一维自由度——时间自由度,对天线阵列的辐射和接收信号进行周期性的时间调制,所构成的四维天线阵则能够在较低的激励幅度动态范围比的情况下获得低/超低副瓣方向图。此外,由于时间自由度的引入,四维天线阵还表现出许多常规天线阵所不具有的新的特性。本文的研究内容主要有:四维天线阵的理论分析、设计与优化,四维天线阵中的信号分析和信号处理以及在雷达系统中的应用基础研究。本文主要分为五个部分进行讨论。1.回顾四维天线阵的相关研究背景。首先介绍了常规天线阵综合低副瓣方向图的方法,并说明常规天线阵在抑制副瓣电平时所遇到的困难和局限性。其次,介绍了四维天线阵的基本原理,包括“单向/双向相位中心运动”和“可变口径尺寸”三种常见的时间调制方式,及其综合低或超低副瓣方向图和各种赋形波束的方法以及四维天线阵的边带辐射抑制问题。2.将时间调制技术扩展应用至非等间距的直线阵和矩形平面天线阵,并在较低的激励幅度动态范围比的情况下抑制天线阵的副瓣电平。同时,利用差分进化(Differential Evolution,DE)算法对四维天线阵的边带辐射进行抑制。3.基于四维天线阵的基本原理研究了时间调制对四维天线阵幅度和相位加权的影响,并提出四维天线阵中的相位加权技术。该技术通过合理设计时间调制参数,可以在不采用移相器的情况下实现波束的电扫描。此外,还可以利用该技术进行各种赋形波束(如:平顶波束和余割平方波束)的综合。由于不需使用移相器,该技术可以极大地降低天线阵馈电系统的复杂度,从而降低天线阵成本。4.将广泛应用于常规天线阵的阵列信号处理技术应用于四维天线阵,实现四维天线阵中的信源个数估计、信号来波方向估计和自适应波束形成。首先,利用时间调制技术能够在四维天线阵中实现同时多波束的性质并结合相关阵列信号处理算法,由多波束的接收数据实现四维天线阵中信源个数的估计和远场信号来波方向的估计,其性能优于常规天线阵。其次,利用时间加权代替幅度和相位加权或者利用波束空间的方法将自适应波束形成算法应用于四维天线阵,实现对干扰信号和噪声的有效抑制。5.针对四维天线阵中的信号传输进行研究,并提出将四维天线阵应用于脉冲多普勒雷达的系统方案。结合脉冲多普勒雷达的工作体制,对四维天线阵传输信号的时域波形、频谱以及由于时间调制所导致的平均功率损失进行相关研究。本文对四维天线阵的阵列设计和信号处理进行了系统而深入的研究,并通过部分实验结果以及仿真结果验证了在四维天线阵中方向图综合和阵列信号处理的方法,以及所表现出的优于常规天线阵的性能。本文的研究工作表明了四维天线阵在实际工程应用中具有极大的优势和潜力,必将在未来的研究和工程应用中得到推广。更多还原

【Abstract】 With the rapid development of modern electronic technology, antenna arrays which act as the sensors for various wireless systems usually operate in very complex electromagnetic environment. In order to effectively suppress interferences received by the sidelobes of antenna arrays, low sidelobe levels (SLLs) are generally required in wireless systems. However, it is difficult for conventional antenna arrays to achieve low/ultra-low sidelobes due to the quite high dynamic range ratios of amplitude excitations and stringent requirements on various error tolerances. If an additional degree of design freedom, time, is introduced into conventional phased arrays, thus forming the four-dimensional (4-D) antenna arrays, the low/ultra-low sidelobes can be realized with lower dynamic range ratios of amplitude excitations by the time modulation. Furthermore, due to the introduction of time freedom, there are some new properties in 4-D antenna arrays which can not be obtained in conventional antenna arrays. The studies of this thesis are mainly concentrated on the theoretical analysis, design and optimization, signal analysis and processing, and applications in radar systems of the 4-D antenna arrays. The thesis is composed of the following five parts.1. The research background of the 4-D antenna arrays is reviewed. First, the methods of synthesizing low sidelobe patterns in conventional antenna arrays are introduced, which is to illuminate the difficulties and limitations of conventional antenna arrays on the suppression of SLLs. Next, basic theories of the 4-D antenna arrays are reviewed, including the“unidirectional/bidirectional phase center motion”and“variable aperture sizes”time modulation modes, the methods of synthesizing low/ultra-low sidelobe patterns, shaped patterns, and the suppression of sideband radiation in the 4-D antenna arrays.2. The time modulation technology is extended and applied to unequally spaced linear arrays and rectangular planar arrays to suppress the SLLs with lower dynamic range ratios of amplitude excitations. Moreover, the differential evolution algorithm is adopted to minimize the sideband radiation in the 4-D antenna arrays. 3. Based on the theory of the 4-D antenna arrays, the influences of time modulation on amplitude and phase weighting are studied, and a type of phase weighting technique in the 4-D antenna arrays is proposed. By appropriately designing time modulation parameters, the electronic beam steering can be realized in 4-D antenna arrays without using phase shifters. In addition, various shaped patterns such as flat-top pattern and cosecant-squared pattern can also be synthesized by the proposed technique. Due to the fact that phase shifters are not used in the antenna arrays, this technique can be used to simplify the complexity of feed network and reduce the cost of antenna arrays.4. The array signal processing technologies which are widely used in conventional antenna arrays are applied to the 4-D antenna arrays to realize the estimation of source numbers, direction of arrival of far-field signals and adaptive beamforming. Firstly, multiple beams can be obtained in 4-D antenna arrays by using the time modulation technique. Based on the data received by the multiple beams, the source number and the direction of arrival can be determined by relative array signal processing methods, which show better performances as compared to those of conventional antenna arrays. Secondly, by using time weighting instead of amplitude/ phase weighting or using the beamspace methods, adaptive beamforming algorithm can be applied to 4-D antenna arrays to suppress interference signals and noises effectively.5. The signal transimission in 4-D antenna arrays is studied, and the application of the 4-D antenna arrays to the pulsed Doppler radar is proposed. With the operation system of the pulsed Doppler radar, the waveform in time domain, spectrum, and average power losses caused by the time modulation are studied.The design and signal processing in the 4-D antenna array are studied systematically and deeply in this thesis. The simulated and some measured results validate the methods of pattern synthesis or signal processing in the 4-D antenna arrays, which show better performance as compared to conventional antenna arrays. The studies of this thesis demonstrate that the 4-D antenna array has great predominance and potential in practical engineering, and it will be extended in future research and engineering application.更多还原