一种新型SCRLH传输线结构的设计与分析

Design and Analysis of a Novel SCRLH Transmission Line Structure

传统的混合右左手(CRLH)传输线(TL)若要实现较宽的阻抗匹配带宽则须工作于平衡态,即左手和右手通带无缝过渡,而在现实中平衡态条件往往不易满足.为此,文中提出了一种新型的简化混合右左手(SCRLH)TL结构.该新结构具有类似带通滤波器的特性:通带内衰减常数为零,特性阻抗为实数并随频率连续平滑分布,具有宽带甚至是超宽带的阻抗匹配带宽;带外特性阻抗为纯虚数,电磁波传播受到抑制.文中还采用微带高低阻抗线以及短路枝节实现了一种中心频率为6.85 GHz、相对带宽约为110%的超宽带微带SCRLHTL结构实例,针对该结构实例进行了全波、电路仿真分析以及实验测量,三者所得的传输特性吻合良好,并且基于三者传输特性提取出的色散特性皆能很好地逼近色散特性理论值,从而证明了新型SCRLH TL结构的可实现性以及其适用于超宽带滤波器设计的潜在价值.

In order to realize a relatively wide impedance matching bandwidth,the traditional composite right/left-handed（CRLH） transmission line（TL） must operate in a balanced state,in which a seamless transition exists between the left-handed and the right-handed passbands.However,it is difficult to satisfy such a balanced condition in practice.To solve this problem,a novel simplified CRLH（SCRLH） TL structure is proposed.The novel structure is similar to the bandpass filter in property,that is,the attenuation constant keeps zero with a continuous and smooth characteristic impedance distribution within the passband, the bandwidth may be wideband or even uhrawide band, and the characteristic impedance is respectively a real number within the passband and a pure imaginary with the inhibition of electromagnetic wave propagation outside the passband. Then, a practical microstrip SCRLH TL structure with the center frequency locating at 6.85 GHz and the relative bandwidth of 110% is implemented by adopting the microstrip high/low-impedance lines and the grounded stub, and its transmission properties obtained from full-wave/circuit simulation analyses and experimental measurement accord well with each other. In addition, the dispersion characteristics extracted from the above-mentioned transmission properties approach the theoretical ones well, which justifies the feasibility of the novel SCRLH TL structure and its potential application prospects in the design of ultra-wideband filter.