【作者】 张洪林；

【导师】 胡斌杰；

【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】 左右手复合传输线(cRLH TL)是一种特殊的传输线，它同时具有左手传输线和右手传输线的特征。在较低的频率区间内，这种传输线呈现出左手特性，即相位的传播方向与能量的传播方向相反；在较高的频率范围内则呈现右手特性，它的相位的传播方向与能量的传播方向相同。此外，左右手复合传输线的传播常数和相速度在低频范围内小于零，在高频范围内大于零；而电磁波的群速度在整个通带内大于零。从相移常数与频率之间的色散关系来看，左右手复合传输线的传播常数在低频范围内具有较强的色散，在高频范围内则是弱色散的。左右手复合传输线作为一种新型的传输线还有一些其他独特性质，例如其特征阻抗和传输线上的相位关系可通过构成传输线的周期性结构单元的元件参数予以控制，其上的相位关系还可通过周期性结构单元的数目进行控制。最后，左右手复合传输线的的相位关系在低频区间为非线性的，在高频区间为准线性的。鉴于左右手复合传输线的这些特性，它在微波电路和天线中的应用具有极大的现实意义：它可实现任意频率比的双频器件，可实现任意频率比和功率比的功分器，也可以用于双频双异向圆极化天线设计，还可以用于实现器件的小型化。本文首先分析了左右手复合传输线的主要性质、判断方法，在此基础上研宄了基于交指电容的左右手复合传输线的带宽扩展方法、左右手复合传输线在功分器和圆极化天线中的应用。本文的具体研宄成果和创新如下：(1)提出并实现了使用地板开槽结构消除交指电容高频谐振，由此扩展了基于交指电容的左右手复合传输线的带宽。在构造左右手复合传输线时，交指电容的高频谐振会导致左右手复合传输线的带宽受限。本文采用地板开槽结构、过孑L和连接过孑L的金属条消除了交指电容的高频谐振，从而扩展了基于交指电容的左右手复合传输线的带宽。为这种交指电容提出了较为准确的电路模型和元件参数提取方法。通过该电路模型可判断基于这种交指电容设计的左右手复合传输线的左、右手频率特性区间。在大量存在这种交指电容的电路中，还可直接利用该电路模型获得较为精确的仿真结果，由此可节约大量的计算资源和时间。从电磁波仿真结果、实测结果与电路模型仿真结果的对比可知，该电路模型是有效、准确的，使用该电路模型判断左右手特性区间的方法也是有效、可靠的。(2)提出并实现了用左右手复合传输线设计工作频率比和功率分配比可控的双频功分器。首先从理论上证明了左右手复合传输线两端的90°相移可实现功分器的功率分配、全端口匹配和输出端口之间的良好隔离。据此提出可利用左右手复合传输线的相位超前／滞后特性设计双频功分器。通过理论分析证明了左右手复合传输线结构单元的元件参数和单元数目共同决定了传输线两端的相位关系，进而控制了功分器的工作频率比。此外，理论分析还证明左右手复合传输线的结构单元的元件参数可控控制传输线的特征阻抗，从而控制了功分器的功率分配比。研宄还证明采用Ⅱ型单元拥有与普通T型单元相同的性能，但用交指电容构造这两种结构单元时，Ⅱ型单元尺寸更小；因此Ⅱ型单元更容易满足电尺寸θ→0的等效均匀条件。在上述研究过程中，首次提出了左右手复合传输线Ⅱ形结构单元在给定阻抗、传输线两端相位关系以及所需单元数目的条件下的元件参数的设计公式。利用这些元件参数设计公式可以得到任意特征阻抗和任意相位关系的左右手复合传输线。设计和加工了两款工作在2.45 GHz和5.2 GHz频段、具有不同功率分配比的双频功分器。仿真和测试结果相互吻合，与其他方法实现的双频功分器相比，基于左右手复合传输线实现的双频功分器具有如下优点：体积更小，功率分配比更接近理论值，高频带宽更大。理论分析与实测结果表明使用基于左右手复合传输线设计频率比和功率分配比可控的功分器是可行的。(3)提出了并实现了一种频率比可控的新型双频双异向圆极化天线。新型天线的辐射体为两个层叠放置的圆形贴片和环形贴片，它们谐振在不同的工作频段，并采用放置在天线顶部的两个圆形贴片进行容性耦台激励。在天线的底部是利用左右手复合传输线设计的双频双正交相位功分馈电网络，它为天线顶部的两个正交位置的圆形耦台贴片提供幅度相等、相位正交的信号。双频双正交相位功分馈电网络的两个工作频率对应于两个辐射体的工作频段，并在上述两个频段输出相位关系分别为超前90°和滞后90°的等幅度信号。仿真和测试结果表明，这种基于左右手复合传输线馈电网络的新型的双频双异向圆极化天线在选定的两个频段上可形成较大的轴比带宽。采用左右手复合传输线实现的双频双正交相位输出功分馈电网络可有效地简化双频双圆极化天线的设计。（4）提出了一种基于双面带状线的新型左右手复合传输线，设计和测试了基于该新型左右手复合传输线的双频功分器。这种新型的左右手复合传输线基于双面带状线，它的两条完全相同的平行金属线『呆证了这种新型传输线是一种平衡型传输线。通过等效电路对该新型传输线进行了理论分析，分析表明该传输线的相位在其通带内较低频率范围内沿传输线呈反向传播、在较高频率范围内沿传输线呈正向传播，而在整个通带内群速度始终大于零。这证明这种基于双面带状线的新型传输线是一种左右手复合传输线。为验证新型传输线的左右手特性，使用这种平衡型的左右手复合传输线设计了一款工作在2.45 GHz和5.2 GHz的双频功分器。仿真与测试结果表明，采用这种新型平衡型左右手复合传输线设计的双频功分器能在这两个频率实现平均的功率分配，并能在子端口取得良好的端口匹配，还能实现输出端口之间的良好隔离。这证实了该功分器中的两条平衡型左右手复合传输线在功分器的低频、高频工作频率上的相移分别为90°和+90°，且它们的特征阻抗和相位关系由传输线的结构单元控制。更多还原

【Abstract】 The composite right/left-handed transmission lines(CRLH TLs)are artificial transmissionlines They possess both left-handed and right handed characteristics at the same time The lefthanded characteristics dominate the lower~equency band while the right handed characteristicsdominate the higher~equency region While operate at lower band，the phase velocity andgroup velocity aJ’e anti-parallel compared to the parallel velocities at higher frequencies Thedispersion relations of the CRLH TLs reveal that the CRLH TLs are extremely dispersive atlower frequencies and are much less dispersive at high frequencies The CRLH TLs posses otherdistinctive characteristics as well Their characteristic impedaaces and phase shifts along theCRLH TLs can be controlled by the element values oftheir constructing unit cells The numberof the cells can be use to tune the phase shifts as well In addition，the phase relations of theCRLH TLs are non--linear in the lower frequency band while they are quasi--linear in the higher~equency band Due to these characteristics the CRLH TLs are important for microwave circuitsand antennas By using them，one can achieve arbitrary frequency ratio dual band components，which includes Wilkinson power dividers with arbitrary~equency ratios and power-splittingratios They can also be used to implement dual~equency dual circularly polarized aatennasand other compact devicesThe thesis studied the main characteristics and determination methods ofthe CRLH TLsIt also conducted analysis on bandwidth expansion method ofthe CRLH TL constructed withinterdigital capacitors(IDCs)The thesis also provided the applications of the CRLH TLs individers and circularly polarized antenna The main contribution ofthis thesis are as follows(1)、Proposed and implemented a wide band CRLH TL by eliminate the high-frequency reso-nance ofthe IDCs in the CRLH TL The high~equency resonances ofthe IDCs are removedby connecting the finger tips at either side ofthe IDCs through vias and metal strips in theslots on the ground plaae An accurate circuit model and extraction method for the mod-ified IDC is proposed The circuit model can be used to determine the left/right-handedcharacteristic frequency region when the modified IDC is used to implement CRLH TLsThe circuit model can accelerate the simulation time with much less computing resources Electromagnetic simulation，measurement mad circuit simulation show-that the circuit modeland the extraction method are reliable mad the frequency regions are correctly predicted bythe circuit model(2)Proposed and implemented two dual~equency Wilkinson power dividers with the samecontrollable frequency ratio and different power splitting ratios by using CRLH TLs，whichare constructed with IDCs mad stub inductors Theory analysis show-that the90°phaseshift along the two arms ofthe proposed divider allow-the divider split power efficiently andensure perfect match at all ports and perfect isolation between the output ports Theory anal-ysis also reveals that theπ-shaped unit cell has the same dispersion relation and bandwidthas that of the T-shaped cell As theπ-shaped cell has shorter electrical length．thereforeit is easier to meet the effective homogeneous conditionθ→0when the both cells areimplemented with IDCs and shorted stubs The element values in the cell control the phaseshift and characteristic impedance ofthe CRLH TL，which therefore controls the~equencyratio and power splitting ratio ofthe divider．Two divider with the same frequency ratio anddifferent spitting ratios are designed and tested to verify the theory analysis Simulation andmeasurement results show-the two dividers w-ork as expected which verifies the theory(3)Proposed a novel dual~equency dual circularly polarized antenna with controllable fre-quency ratio The antenna has two stacked radiating elements excited by two capacitivepatches，which connected to the two ports of a dual~equency feeding network The feed-ing network provides equal power with quadrature phase to the two output ports The new-feeding scheme allow-easy design of dual~equency matennas having different circular po-larizations at the two operating frequencies A dual frequency dual circularly polarized an-tenna is designed，fabricated and measured，which works well at the up-link and down-linkfrequencies ofthe Chinese Beidou satellite navigation system(4)Proposed and implemented a new-balmaced CRLH TL based on double sided parallel striplines(DSPSLs)The new-CRLH TL has two identical parallel strips printed on the top madbottom sides of the substrate Theory analysis based on the circuit model show-that thephase propagates backwards along the transmission line in the lower~equency region and forwards along the transmission line in the higher frequency region With regards to theforward group velocity propagation direction．the new trmasmission line is a CRLH TL‘Ibverify the new balanced CRLH TL，a dual frequency Wilkinson power divider is designedand implemented with the CRLH TL The simulation and measurement results show thatthe divider can work efficiently at the two working frequencies as expected The power issplit equally to the two output ports，all the ports are matched and the isolation betweenthe two output ports are quite good Judging with the performances ofthe dividec the newbalanced CRLH TL provide90°and+90°phase shifts to the output ports at the lowerand higher working frequencies，respectively The results also verify that the characteristicimpedances ofthe two CRLH TL in the divider are controlled by the element values oftheconstructing unit cells更多还原