混合天线系统及基于散射矩阵的波束形成

【作者】 王静；

【导师】 郭陈江；

【作者基本信息】 西北工业大学 ， 电磁场与微波技术， 2007， 硕士

【摘要】 在过去的几十年中，许多学者对反射面天线馈源扫描技术进行了研究，但大部分馈源扫描是通过横向移动单点馈源或副反射面来实现的。通常使用喇叭天线或开口波导作为反射面天线的单点馈源，通过移动馈源的位置来实现天线的主波束指向的变化。如果天线波束扫描的范围较小，利用单点馈源馈电的抛物面天线就可以实现。但如果扫描范围较大，用单点馈源扫描抛物面天线时，会出现慧瓣，因而限制了扫描角度。 本文研究了一种由放置在反射面顶端的横向静态馈源阵列与反射面构成的混合天线系统，这种天线系统结合了阵列天线波束可以电控和反射面天线结构简单的优点，通过改变馈源阵列单元馈电的幅度和相位来实现电控波束扫描，而不需要移动馈源的位置。当波束扫描角范围不是很大时，混合天线系统能够利用较少的单元实现电控窄波束，从而可以大大降低电控波束天线系统的成本。本文根据物理光学法，将自由空间中的并矢格林函数应用于混合天线系统中接收时、发射时电磁场的计算，另外，还引入了描述阵列口面场与混合天线口面场之间的变换关系的散射矩阵。将整个混合天线系统看作一个N端口网络，其中一些端口与物理馈源(阵列孔径)相关，其他端口与反射面孔径面相关，同时利用并矢格林函数法对系统中阵列馈源面和反射面孔径面处的电、磁场进行计算，导出N端口的散射矩阵。通过对散射矩阵的数值计算和分析来研究该系统的接收和发射波束形成。本文就文献中优化的混合天线系统，即：反射面孔径的大小为60λ，馈源孔径面的大小为30λ的混合天线系统的波束形成进行分析，由分析结果可以看出：这种天线在±20°扫描角范围内，波束形状基本保持不变，实现了较大角域内的波束扫描。因而得出结论：通过合理的分析与设计可以使混合天线的波束扫描范围达到数百个波束宽度，而所采用的阵列的单元数量较常规阵列天线少得多。更多还原

【Abstract】 In the last few decades, much effort has been given to the development of methods for scanning reflector antennas. But most of them are accomplished by physically moving a single feed element or subreflector. The horn antenna or open-ended waveguide are usually used as a single feed element. Physically moving the position of feed element can steer the main beam in the desired direction. The main beam of a parabolic reflector can be steered by translation of a single feed element; however, a coma aberration will appear when a larger scan angle is required.In this thesis, a hybrid antenna system which is composed by placing a transverse static feed array near the apex of a compound reflector has been discussed. The advantage of hybrid antenna system is combining the electric scanning ability of feed array antenna with the structural simplicity of reflector antenna. Electric scanning can be achieved by adjusting the amplitude and phase between feed array elements instead of physically moving the feed array. When the scan angle is small, the electric scanning can be realized by using only a few feed arrays in the hybrid antenna system. Therefore, the cost of electric scanning is greatly reduced. Based on the physical optics (PO), the free space dyadic Green’s function is applied to the computation of transmitting and receiving field. Moreover, a scatter matrix which establishes the transformation between fields of the feed array and that of the aperture of hybrid antenna system has been discussed. A N-port network model is developed for the hybrid antenna system, some ports are located at feed array, others are related to the reflector aperture. Meanwhile, the electric or magnetic field at the feed array and aperture has been computed using the dyadic Green’s function in order to get the scatter matrix. The transmitting and receiving beamforming is analyzed by using the scatter matrix. In this thesis, the optimized hybrid antenna system which is brought up by reference, i.e.: the hybrid antenna system, in which the diameter of aperture is 60λ, the diameter of feed array is 30λ. From the results, we can conclude that when the scanning angle is within the range of ±20°, the beam keeps the same and the system realizes wide-scan. Therefore, through proper design of the hybrid antenna system, the beamscanning can reach hundreds of beamwidth and the elements of feed array are much less than the regular feed array.更多还原