【作者】 黄健全；

【导师】 褚庆昕；

【作者基本信息】 华南理工大学 ， 电磁场与微波技术， 2011， 博士

【摘要】 异向介质是由人工微结构组成的等效均匀电磁材料,由于电磁波在其传播时具有特殊的传导或辐射特性,已成为材料科学、光学和微波工程领域的前沿研究热点。广义地说,异向介质包括所有对电磁波传播具有特定影响且满足亚波长条件的人造材料或结构,如慢波结构、左手材料和复合左/右手结构等等。人工传输线通常由周期性微结构组成,可视为一维异向介质,其等效媒质参数可由单元结构控制。同时,由于人工传输线具有均匀传输线难以实现的可控奇特色散特性,为新型微波器件与电路的设计提供了新思路。本文主要研究平面人工传输线及其在微波器件中的应用。论文提出了多种新型平面人工传输线结构,包括具有高慢波因子和线性相位特性的慢波传输线、左/右手通带可独立控制的复合左/右手传输线及具有近零相位常数的负介电常数传输结构;并进一步探索新型平面人工传输线在微波器件如滤波器、耦合器、天线等小型化、多频/宽带化中的应用。主要工作如下:1、概述了分析人工周期性结构的基本理论和方法——Floquet定理和Bloch阻抗分析法,重点研究了平面人工传输线等效媒质参数的散射参数提取方法,阐述了人工传输线的等效媒质思想和控制方法;并且根据其等效媒质参数,把人工传输线分为慢波、复合左/右手和单负传输线;2、提出了基于混合型单元传输网络的新型慢波传输线。新结构不仅获得了较大的慢波因子和较小的插损,还具有线性相位特性,可以在宽带范围替代均匀传输线;1)由于X形传输网络具有与π形传输网络互补的相位响应,混合单元传输网络的相位响应和截止频率可以通过调整二者比例进行控制,在很宽的频带内实现类似均匀传输线的传输特性;2)基于混合型传输单元网络的新型平面慢波传输线具有较大的等效介电常数和磁导率,应用于微波器件中,可获得明显的小型化效果。其在环形混合网络中的应用表明,与采用均匀传输线的相比尺寸缩减54%,而性能相当;3、提出了一种改进的复合左/右手结构单元网络,在传统的复合左/右手结构单元内部引入交叉耦合,使其左/右手通带可独立控制;设计并制作了基于该网络的平衡型超宽带复合左/右手传输线,应用面耦合结构,显著改善传输线的高频特性,获得了超宽通带。并采用一单元该改进型复合左/右手结构设计了小型超宽带滤波器,其高端阻带由单元内部交叉耦合形成,具有小尺寸、低插损和良好选择性等优势;4、研究了谐振单元的负本构参数的形成机理,并由此提出了两种新型ENG传输结构,应用该ENG传输结构的窄带阻/陷波特性设计并制作了双陷波的超宽带滤波器。在不增加器件尺寸的前提下,实现了有实用水平的可控双陷波,从而有效降低了超宽带通信系统与其他通信系统(如WLAN等)间的相互干扰;5、研究了人工传输线零阶(Zeroth-Order Resonator, ZOR)和负数阶谐振器的特性和控制方法;提出了由一单元ENG传输结构构成的新型零阶谐振天线,通过在传输单元并联支路引入串联电容的方式降低Q值,从而使电小天线也获得了较高的辐射效率和增益。更多还原

【Abstract】 Meta-materials (MTMs), which are broadly defined as effectively homogenous materials composed of artificial micro-structures, become the foreland and hotspot field of material science, optics and microwave engineering since they can guide or radiate electromagnetic waves in some unusual manners without violating the basic laws of physics. Generally speaking, all the artificial structures can be called meta-materials if they exert a special influence on the wave propagation and satisfy the sub-wavelength condition, such as the slow-wave structures, left-handed mediums (LHMs), composite right/left-handed (CRLH) structures and so on. Artificial transmission lines (ATLs), commonly composed of periodical unit cells, can be regarded as 1-D meta-materials. They have the effective permittivityεand permeabilityμdetermined by their micro-structures. Moreover, due to their fantastic controllable dispersion characteristic which cannot be achieved by the uniform transmission lines, the artificial transmission lines can pave the way for a novel generation of microwave devices and circuits.In this dissertation, the attention is paid to the novel planar artificial transmission lines and their applications in the microwave components. Several kinds of artificial transmission lines are proposed, such as a slow-wave transmission line with the large slow-wave factor and linear phase response, an ultra-wide-band composite right/left-handed transmission line of which RH/LH passband can be adjusted respectively, single negative transmission lines with near zero phase constant and so on. The design methods of the miniaturized, multi/wide-band microwave components such as couplers, filters and antennas are investigated by using the artificial transmission lines as well. The main contents and contributions are listed as follows:1. The basic method of analyzing the periodical artificial structures has been established. Firstly, by means of Floquet theorem and Bloch impedance analysis, the effective constitutive parameters of artificial transmission lines are retrieved from the scattering parameters. Secondly, the effective medium theory and control method of the artificial transmission lines are analyzed. Finally, the artificial transmission lines are classified as slow-wave, double negative and single negative transmission lines according to their effective constitutive parameters.2. A slow-wave structure based on the mixed lattice topology has been proposed. Both large slow-wave factor and low insertion loss are achieved by the new structure. Besides, due to its linear phased response, the uniform transmission line can be replaced by the slow-wave one within a wide band.1) Owing to the complementary dispersions of the lattice and pi-shaped topology, the phase characteristic and cutoff-frequency of the mixed structure can be well controlled by varying the proportion of lattice to pi-shaped part. As a result, the mixed slow-wave structure has the similar phase shift characteristic to that of the ideal transmission line within wideband.2) Because the proposed slow-wave transmission line has large effective permittivity and permeability, significant miniaturization can be achieved if the uniform transmission lines in the microwave devices are replaced by the proposed structures. A rat-race coupler using this slow-wave structure demonstrates the evident size reduction (54%) with a little performance degradation compared with the one using uniform transmission lines.3. A modified composite-right/left handed (CRLH) unit cell has been proposed. By introducing the cross coupling to the conventional CRLH structure, the right-handed pass-band can be controlled with little effect on left-handed pass-band. An ultra-wide-band balance CRLH TL based on this topology has been presented. The surface coupling structure improves the transmission response at high frequencies evidently. Moreover, an ultra-wide-band bandpass filter has been designed and fabricated based on this modified CRLH structure. A wide stopband at high frequencies is generated by the cross coupling in the CRLH structure. The fabricated filter has a compact size and exhibits good selectivity and low insertion loss.4. Two epsilon negative transmission structures have been proposed based on the study of the essential principle for the single negative resonant unit cell. By using these ENG structures, two ultra-wide-band bandpass filters with dual notched bands have been designed and implemented. The rejection level of those notched bands is good enough for the practical application without additional circuit size. The notched bands can restrain the interference between the UWB communication system and other undesired narrow band radio signals, such as wireless local area network (WLAN).5. The characteristics and control methods of the negative and zeroth-order resonators based on the artificial transmission lines are studied. A novel zeroth-order resonator (ZOR) antenna has been presented, which comprises a single unit cell of the epsilon negative (ENG) transmission line (TL). Its Quality factor can be substantially reduced by introducing a series capacitor in connection with the shunt branch of the ENG TL unit cell, which produces higher radiation efficiency and gain with a very compact size.更多还原