基于类等离子体的小型化天线及其在无线电监测中的应用基础研究

Reduce the size of antenna while maintaining its performance is the target of antenna miniaturization. In optical frequency band, plasmonic materials such as gold and silver are adopted to the design of optical antenna, of which the size is much small than wavelength. This is due to the fact that natural SPP occurring at optical frequencies is strongly confined, and the plasmon wavelength is much smaller than free space wavelength. It has been demonstrated that metals at radio frequencies can be induced to support surface modes by drilling an array of subwavelength holes or grooves in the surface. These modes share similar features to traditional SPP supported by noble metal films at optical frequencies and have been named spoof SPP. This project is aimed at building a bridge between optical frequency band and radio frequency band using plasmonic materials for antenna miniaturization. Firstly, plasmon wavelength and radiation characteristics of the plasmonic materials will be studied to obtain the wavevector conversion properties and establish a wavevector conversion interface between free space wave and surface wave. Secondly, spoof plasmonic materials will be adopted in microstrip antenna design instead of metals, and we will take the microstrip monopole antenna and Log-periodic antenna as examples to realize the miniaturization. Finally, applied basic research will be carried out for regional distributed and concealed monitoring of illegal radio emission, which may lay a solid foundation for the development of finer radio monitoring network.

在不降低天线主要性能的前提下尽可能的减小天线的几何尺寸是天线小型化追求的目标。在光频段，采用等离子体材料如金和银设计光天线，其尺寸远小于波长。这是由于光频段表面等离子体模（SPP）具有局域性，等离子体波长远小于自由空间波长。研究表明，在导体表面蚀刻周期性褶皱或小孔等结构将在射频频段形成一种类SPP模，具有亚波长性和局域性。本项目将利用褶皱结构类等离子材料在光频段和射频之间建立起一座桥梁，将光学效应用于射频，基于类SPP模进行天线的小型化：首先，研究类等离子体材料单元阵列与等离子体波长和辐射特性的关联，获得其波矢变换特性，建立表面波波矢与自由空间波矢的转换接口；其次，用类等离子材料代替传统射频天线中的金属材料进行天线设计，分别以微带型单极子天线和对数周期阵列天线为例实现小型化，并进行测试和验证；最后，针对局部区域无线电发射的分布式和隐蔽式监测开展应用研究，为精细化无线电监测奠定基础。

天线尺寸与工作波长相当才能达到良好的辐射特性，并且天线尺寸越大辐射性能越好。表面等离子体激元是沿着金属表面传播的波。而类表面等离子体是光波段表面等离子体激元在低频段的拓展，它利用周期性亚波长结构将低频电磁波紧紧地束缚在褶皱金属表面。基于类表面等离子体材料可以减小波的等效波长，实现天线的小型化设计。本项目研究了表面等离子体的传输特性以及微波频段亚波长周期阵列结构与电磁特性的关联，并以褶皱金属周期结构为重点，研究了其几何特性对等效电磁特性和等离子体波长的影响，实现了矩形波导TE模式和微带传输线准TEM模与类表面等离子体模的转换；基于褶皱金属结构超表面以及亚波长超材料单元结构阵列实现了天线的小型化设计,提出了一种加载超表面结构的单极子天线；研究了超材料阵列结构等效介电常数及其传输特性，并针对宽带无线电监测和现场测向的需求，分别采用分形以及分形与开槽、顶端加载相结合的方法设计了小型化的对数周期天线。结果表明，在保持了原天线的性能指标下，小型化后的天线与原始天线相比，在结构尺寸上均有了显著的减小，实现了对数周期天线小型化的设计目标。研究成果在手持式无线电监测设备小型化天线，无线电监测谱传感节点天线方面具有应用前景。