A Novel Composite Right/Left Handed Transmission Line And Its Application To Antennas

hi the near future, a variety of wireless applications will be integrated into one handheld terminal, which leads to the criterions for antenna design that are multi-band, low profile, small, high performing, accelerate time to market, low cost, and easy to integrate in the devices. Conventional materials or technologies can hardly satisfy all of them, one possible solution could be utilization of left-handed material and especially its micro-strip realization type that is the composite right/left-handed (CRLH) transmission line. CRLH transmission lines have been widely applied in microwave component field due to their characteristics of lower loss, wider bandwidth, and a nonlinear phase constant. In this thesis, the approaches to realize multi-band antenna and tunable antenna based on the novel CRLH transmission lines have been researched.First of all, this thesis has presented the basic characteristics of left-handed material and CRLH transmission line as well as their applications to antennas; the fundamental theories, LC network, and physical implementation technologies of CRLH transmission line are analyzed. According to the analysis, a novel type CRLH transmission line based on the asymmetric and symmetric coplanar waveguide (CPW) is proposed, which possesses advantageous properties such as a single layer, a compact size, via-less, and high design freedom of reactance parameters. The multi-band and tunable technologies have been summarized in this thesis as well.Then, the fundamental theories of CRLH-based half-and quarter-wave type resonators are analyzed in this thesis; the multi-band operation with arbitrary bands and low frequency ratios, achieved by controlling dispersion diagram and number of the unit cells, is proposed. According to the short-ended condition, dual-band, tri-band, and quad-band antennas based on the novel CRLH transmission line are designed and analyzed, respectively, which exhibit multi-band performance while keep a compact size with low frequency ratios. To validate the proposed approach, the tri-band prototype (Size:29x21.3x1mm3) was fabricated and measured, exhibiting good impedance matching as well as stably omni-directional radiation patterns at1.9GHz/2.1GHz/2.6GHz bands with frequency ratios of1.1/1.2. Additionally, by adding number of the unit cells, more working frequencies can be arbitrarily chosen, which offers a more straight forward design approach.Finally, this thesis has analyzed the characteristics of zeroth-order resonator (ZOR) as well as its performance parameters, such as input impedance, resonance frequency, and bandwidth; the approach that tuning the resonance frequency and widening the bandwidth by adjusting reactance parameters of the unit cell is proposed. By employing a varactor diode, a tunable antenna (Size:25x15x1mm3) based on the novel CRLH transmission line is designed, the variation of its performance parameters including bandwidth, gain, and radiation patterns when resonance frequency is varied are studied. The simulated results show a wide tuning range (1.18GHz), a tuning ratio of1.83, a little variation of gain, and stably radiation patterns have been obtained for the tunable antenna. To investigate the influences of varactor diode and its bias circuit on antenna performances, the HFSS-ADS co-simulation method is employed in this thesis, and the results reveal that the tuning range is deteriorated seriously, the resonance frequencies are shifted, and the bandwidth at each working frequency is widened as well.