Researches On The Novel Planar Artificial Transmission Lines And Their Applications

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 permittivity?and permeability?determined 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.