Research On Compact And Wideband Planar Metamaterial Antenna

Metamaterials are loaded with many special geometric structures in traditional medium, so as to construct artificial electromagnetic material with unique electromagnetic properties. Their element dimensions are much smaller than the operation wavelength of the electromagnetic wave. The attributes of atoms or molecules of the traditional medium determine its electromagnetic properties. The singular electromagnetic properties of metamaterials come from all kinds of man-made special structures of the metamaterials. In microwave devices, antennas, and other fields,metamaterials have very broad applied prospects, so many researchers launch extensive researches. The applications of planar metamaterials in miniaturization, broadband and circularly-polarized antennas have been done in this dissertation. The macro equivalent circuit models of electromagnetic characteristics of different structural metamaterials have been established. The dissertation has mainly the following contents:In the second chapter, two electrically small antennas loaded with metamaterials are designed and researched. Based on metamaterial unit, the theories of microwave equivalent medium parameter and subwavelength resonance are researched, the singular characteristics of the composite right/left-handed(CRLH) transmission line structure are analyzed, and the physical mechanism of reducing the antenna resonant frequency is explained. A simple and compact comb line structure with left-handed equivalent inductance has been put forward. Many periodic strip gaps are etched on the ground.The coupling of the microstrip feeder, main radiating element and the strip gap ground provides left-handed character, which composes a CRLH transmission line. Based upon analyzing the equivalent circuit and resonant characteristics, the analytical expression of the zeroth-order resonance(ZOR) antenna bandwidth is deduced. A CRLH transmission line resonant antenna, which is electrically small, is proposed. The ENG ZOR principle and characteristics of the resonator are investigated. With the flexible characteristics and easy integration of the coplanar waveguide feed line, the left-handed comb line inductances are directly used to connect the coplanar waveguide feed line to the ground.Two-unit ENG equivalent circuit model is researched, and an ENG transmission line resonant electrically small antenna is proposed. The problem of increasing bandwidth of the electrically small antenna is solved.In the third chapter, an ENG broadband antenna and a CRLH transmission line end-fire antenna are researched. Artificial impedance surface(AIS) is a kind of periodic metal cell array etched in dielectric substrate. Y type patch is connected with the AIS through two metallic vias. The asymmetric Y type patch and AIS constitute the ENG transmission line resonant antenna. The equivalent dielectric constant of CRLH transmission line and the relation between permeability and the distribution parameters are researched. In the ENG transmission line antenna, the ZOR, the first-order resonance(FOR) and the second-order resonance(SOR) modes are excited. The FOR and SOR are merged into a pass band, which results in a broadband characteristic. The SRR array can excite magnetic resonance. The complementary split resonance ring(CSRR) array is etched in the radiation patch, and many strip gaps are etched in the ground periodically. With the coupling between the CSRR array and the ground, a CRLH transmission line antenna is achieved. The ZOR and FOR are excited, which are merged into a broadband. In general, the main radiation direction of the conventional antenna is in the normal direction of the patch. However, the radiation direction of the CRLH antenna is end-fire. The problems of the miniaturized antenna, such as decreasing profile, increasing bandwidth and decreasing size of the ground are solved.In the fourth chapter, compact and circularly-polarized CRLH transmission line resonant antennas are researched. The equivalent circuit theory and circularly-polarized mechanism of the antennas are investigated. The dispersion characteristic of the CRLH transmission line structure is analyzed. With the CRLH transmission line structure, two circularly-polarized antennas are designed. The distributed parameter components, such as the comb line inductance with compact structure and gap capacitance, constitute a left-handed parallel inductance and a left-handed parallel capacitance, respectively.Through the equivalent circuit of the CRLH transmission line, the principle of sub-wavelength resonant and bandwidth expansion mechanism are analyzed. By adjusting and optimizing the capacitance and inductance parameters of the series/parallel equivalent circuits, the ZOR and FOR are excited at the same time, so the antenna bandwidth is broadened. Three-unit comb line left-handed parallel inductances are designed. The asymmetry structure resultes in perturbation, and excites the circularly-polarized electromagnetic wave. A dual band CRLH transmission line circularly-polarized antenna is proposed. Two-unit comb line left-handed parallel inductances are designed and a CRLH transmission line linearly/circularly-polarizedantenna is proposed. The problems of circularly-polarized antenna, such as decreasing size and simplifying complex feed network are solved.In the fifth chapter, the research content of this metamaterial antenna is summarized and future research is proposed.