Broadband And High Efficiency Antennas Based On Composite Right/Left Handed Transmission Line

With the rapid development of wireless communication systems, compact antennas with wide bandwidth and high efficiency are urgently needed for mobile terminals. Owe to the characteristics of anti-parallel wave, low loss, and adjustable phase constant, composite right/left-handed (CRLH) transmission line has been widely applied in microwave devices and antenna design. The epsilon negative (ENG) transmission line is a simplified form of the CRLH and has many applications. This thesis has also researched the approaches to design wideband and high efficiency antenna based on the ENG and CRLH transmission lines.First of all, the basic characteristics of Metamaterial (MTM) and CRLH transmission line as well as the research status of their applications to antenna have presented; the fundamental theories and physical implementation techniques of ENG and CRLH transmission lines are analyzed. Then, the basic concepts of antenna characteristic parameters are discussed. According to electrically small antenna (ESA) theory, this thesis points out the contradictions between compact size, radiation efficiency and broadband, which provide methods for good antenna design.Then, the characteristics of Zeroth-Order Resonator (ZOR) and First-Order Resonator (FOR), such as resonant frequency, quality factor and fractional bandwidth, have been analyzed in detail. The bandwidth characteristic of the FOR is analyzed and described using circuit parameters, and bandwidth extensions of ZOR and FOR are proposed. An equivalent circuit model for the FOR which has three unit cells is derived to understand its working principle. In order to verify the proposed bandwidth extension technique, we design an asymmetric coplanar waveguide (ACPW)-fed antenna with wide bandwidth and high efficiency. The antenna employed the co-simulation of CST MWS and Ansoft HFSS is fabricated and measured. The simulated and measurement results show good agreement with each other. The antenna has the advantages of dual-band, extended bandwidth and high efficiency, which is a good candidate for wideband wireless communication systems (GSM, UMTS, LTE, WLAN, WiMAX).Afterward, this thesis proposes the wideband and high efficiency antenna technique by merging the two resonant modes. By adjusting reactance parameters of the unit cell, the wideband antenna can be achieved when the extended-bandwidth ZOR and FOR are merged together. By designing the asymmetrical antenna structure, the odd current of transmission line is excited and large ground plane significantly affects the radiation to improve the radiation efficiency. Two wideband and high efficiency antennas based on different feed structures are designed. Compared to the CPW, the ACPW offers high design freedom. The measured results show that they not only have compact size and wide bandwidth, but also keep high efficiency and omni-directional radiation.Finally, we summarize the existed bandwidth expansion techniques, and propose a method which merges multi-modes to compensate the shortcoming of narrow bandwidth of a single resonant mode. By utilizing the low-loss distributed components of meander line, inter-digital capacitance and gap capacitance, we design a novel ACPW-fed wideband and high efficiency antenna based on CRLH transmission line. Compared to the same-type researches, the proposed antenna has the advantages of compact size, via-less, wide bandwidth and omni-directional radiation.