Some studies on metamaterial transmission lines and their applications

This thesis work focuses mostly on investigating different potential applications of meta-transmission line (TL), particularly composite right/left handed (CRLH) TL and analyzing the new phenomena and applications of meta-TL, mostly left-handed (LH) TL, on other realization principle. The fundamental electromagnetic properties of propagation in the presence of left-handed material, such as the existence of backward wave, negative refraction and subwavelength imaging, are firstly illustrated in the thesis. The transmission line approach for left-handed material (LHM) design is provided together with a brief review of transmission line theory. As a generalized model for LHM TL, CRLH TL provides very unique phase response, such as dual-band operation, bandwidth enhancement, nonlinear dependence of the frequency, and the existence of critical frequency with zero phase velocity. Based on these properties, some novel applications of the now-existing CRLH transmission line are then given, including notch filters, diplexer, broadband phase shifters, broadband baluns, and dual band rat-ring couplers. In the design of notch filters and diplexers, CRLH TL shunt stub is utilized to provide high frequency selectivity because of the existence of critical frequency with zero phase velocity. The proposed wideband Wilkinson balun, which comprises of one section of conventional transmission lines and one section of CRLH-TL, is shown to have a 180°±10° bandwidth of 2.12 GHz centered at 1.5 GHz. In the analysis of the dual band rat-ring couplers, a generalized formulation of the requirements about impedances and electrical length of the branches are derived, and as an example, a compact dual-band rat-race coupler is designed utilizing the balanced CRLH TL. Furthermore, a low pass filter is also proposed and designed based on an Epson-negative Coplanar Waveguide (CPW). Various principles to realize the left-handed transmission line and composite right/left handed transmission line are investigated. The main conclusions are listed below: y Dual composite right/left handed (D-CRLH) transmission line, which is the dual structure of conventional CRLH TL, shows opposite handedness in the high frequencies and low frequencies with CRLH TL. Meanwhile, in the practical implementation, D-CRLH TL always shows a sharp stopband. A notch filter and a dual-band balun are designed based on D-CRLH TL. y The lattice type transmission line (LT-TL) shows the same magnitude response with the conventional right-handed (RH) TL, but a constant phase difference in the phase response over a wide frequency band. A wideband rat-race coupler is proposed as an application of the LT-TL. y Finger-shorted interdigital capacitors (FSIDCs) are …