【作者】 伍洋；

【导师】 龚书喜；

【作者基本信息】 西安电子科技大学 ， 电磁场与微波技术， 2013， 博士

【摘要】 相控阵馈源是作为多波束馈源使用的小型相控阵天线。在射电天文领域，相控阵馈源可用于产生几十个乃至上百个紧密交叠的波束，有效地扩大射电望远镜的视场，提高其巡天效率，还可以消除人为因素对射电望远镜的电磁干扰以及重力等因素引起的反射面形变，因此被称为下一代射电望远镜的关键技术之一。本文在综述国内外相控阵馈源技术发展的基础上，结合科研课题，对射电望远镜相控阵馈源技术进行了系统和深入的研究，所取得的主要研究成果总结如下：1.深入研究了相控阵馈源与射电天文观测需求之间的联系。基于射电望远镜高灵敏度、高分辨率以及快速巡天的要求，分析了各种多波束天线方案的可行性，得出了以焦平面阵列馈电的反射面天线更适合于射电天文观测的结论。针对这一方案，详细比较了相控阵馈源与传统的馈源组（通过增加馈源数量实现多波束）这两种焦平面阵列的特点，前者在波束数量、方向图灵活性、视场范围和连续性以及抗电磁干扰等方面更具优势，能够更好的满足射电天文观测的需要。2.深入研究了馈源与反射面系统之间的联系。总结了各种形式的反射面天线及其建立的条件。以“五百米口径球面射电望远镜(FAST)”、上海65m射电望远镜(SHAO65m)以及平方公里阵(SKA)中频阵列单元的中国设计方案DVA-C等不同形式的射电望远镜天线为例，通过计算平面波在天线焦平面形成的场分布，分析了各种形式的反射面天线及其几何参数对馈源设计的影响，得到了反射面系统对馈源影响最大的参数是照射角的结论。该参数决定了馈源的口径和需要的口径场分布。重点研究了多波束应用中，反射面系统的形式和参数，以及赋形对波束扫描性能的影响，得出了一些实用的设计参数和规律，可用于指导工程设计。3.建立了基于焦面场分析的相控阵馈源天线阵列的设计方法，并深入研究了其对射电望远镜性能的影响。对于给定的反射面系统的参数和波束覆盖，可利用焦面场分析计算出天线阵列的尺寸，并根据采样定律确定出馈源阵列最大的阵元间距。详细分析了焦平面阵列馈电射电望远镜各波束增益存在差别的原因，研究了阵元尺寸和间距变化对射电望远镜增益和视场的影响，比较了矩形和六边形两种排列方式的特点，得出了射电望远镜性能随馈源阵列变化的一系列规律。基于这一方法，针对FAST的观测需求，具体设计了一个在L频段能够实现上百个波束观测的相控阵馈源(FAST PAF)，并进行了初步的样机验证。4.针对FAST PAF的应用，提出了将背腔振子天线缩小尺寸、组阵使用的思路，其优点是展宽工作频带、提高方向图的对称性，同时抑制了阵元间耦合。通过比较背腔形状在六边形排列时的影响，选定以六边形背腔振子天线作为阵列单元，并进行了阵列单元和19元阵列的设计、加工、测试和验证。该单元形式能够充分利用阵列面积，适用于六边形排列的相控阵馈源阵列。5.建立了相控阵馈电射电望远镜天线系统性能分析的数学模型。在此基础上，分析了波束合成因子对射电望远镜性能的影响，比较了共轭匹配法、最大方向性系数和最大信噪比三种波束合成因子的特点，研究了波束合成因子与波束增益、系统噪声之间的联系。总结了射电望远镜系统噪声的组成和抑制方法，对阵列天线单元与低噪声放大器阻抗失配这一系统噪声的主要贡献进行了重点研究，并比较了各种阻抗匹配方法的特点和可行性。6.针对FAST的结构特点，提出以自适应波束合成消除馈源舱扰动引起的波束性能劣化和指向精度下降，建立了这一问题的数学模型、系统构架以及校准方案，并进行了初步的仿真验证。更多还原

【Abstract】 Phased Array Feed (PAF), which is a small phased array antenna, playing a role asmulti-beam feed of reflector antenna. In radio astronomy applications, PAF provides thepossibility of observation with dozens or hundreds of closely overlapped beams, whichgreatly extents the Field-of-View (FoV) of the radio telescope and enhances the SurveySpeed (SS). Moreover, PAF also helps to mitigate the radio frequency interference (RFI)from human activities and reflector deformation due to gravity and other environmentalfactors. Thus it is called one of the key technologies for next generation of radiotelescopes. This paper reviews the development of PAF in China and abroad,systematically investigates the analysis and design techniques of PAF considering theproject requirement. The main contributions and innovations of this thesis are listed asfollows:1. The relationship between the PAF performance and the requirements fromradio astronomical observation is investigated. To pursue a radio telescope of highsensitivity, high resolution and fast sky survey, several multi-beam antennaconfigurations are studied and a conclusion that the reflector antennas with Focal PlaneArrays (FPA) are most suitable for radio astronomical observation is made. In thisscheme, two types of FPAs, the PAF and cluster feed are investigated and compared indetail. The former is more competitive in several crucial aspects, e. g. beam amount,beam pattern flexibility, the range and continuity of FoV and RFI mitigation, and bettermeets the observation requirements.2. The interaction between the feeds and the reflector systems is investigated. Theconfigurations of reflector system, the law to establish a reflector system aresummarized. Taking the “Five-hundred-meter Aperture Spherical radio Telescope”(FAST), the Shanghai65m radio telescope (SHAO65m), and the Chinese DishVerification Antenna (DVA-C) for Square Kilometer Array (SKA) middle frequencyarray antenna element for examples, the effect of reflector configuration and geometryon feed design is analyzed via calculating the field distribution on the focal planeexcited by incident plane wave. And it is concluded that the feed design is mostsensitive to the (equivalent) illumination angle of the reflector system, which decidesthe feed aperture and the requisite aperture field distribution. Furthermore, since PAF isusually employed in multi-beam applications, the effect of reflector configuration andgeometry, as well as reflector shaping, on beam scanning performance is studied andsome design parameter and principles are reached. 3. The PAF design method is established based on the focal field analysis. Theperformances of radios telescope with various types of PAF are investigated. For agiven reflector system and FoV requirement, the dimension of the feed array and themaximum element spacing can be estimated via focal field analysis and Nyquist Law.From antenna array aspect, the gain distinction between beams and FoV of FPA fedreflector antenna is investigated, the differences between rectangular and hexagonalarray arrangements are compared. And the relationship between the radio telescopeperformance and feed array configuration are concluded. A PAF which is capable ofsimultaneously synthesizing more than one hundred beams is designed for FAST (FASTPAF) and a smaller prototype is built for preliminary verification.4. In the design process of FAST PAF, The cavity-backed dipole is proposed tooperate as the feed element. It is fit to broaden the operating frequency bandwidth,improve the symmetry of pattern, and mitigate the mutual coupling between elements.After the comparison between cavity-backed dipoles of different cavity shapes,hexagonal cavity is adopted for hexagonal arrangement feed array. A single element wasfabricated first and then a19-element array was designed, manufactured, tested andverified. This type of antenna element can make best use of the array aperture and fit forhexagonal arranged PAF.5. The model for phased array fed radio telescope system performance estimationis established. Based on this model, the effect of beam-former on the performance ofradio telescope is analyzed. The characteristics of three common beam-formers: theconjugate field matching (CFM), the maximum directivity (max-directivity), and themaximum signal to noise ratio (max-SNR) are compared, and the connection betweenthe beam-former and corresponding beam gain, system noise temperature is studied.The composition and reduction method of radio telescope system noise temperature arepresented. As a major contributor to the system noise, the dismatch between arrayelements and LNAs is introduced, and the characteristics and feasibilities of severalimpedance matching methods are compared.6. Subject to the structure feature of FAST, the core ideology that using PAF withadaptive beam-forming to compensate for the feed cabin vibration, mitigate the beampattern deterioration and pointing accuracy decline is presented. The mathematic model,system framework, and calibration scheme are established, and the feasibility ispreliminarily verified in simulation.更多还原