Dual-frequency Microstrip Antenna Based On Waveguided Metamaterials

Recently, with the development of wireless communication, communication systems have imposed higher requirements on antennas. Metamaterials have the advantage of flexible handling on electromagnetic wave, which makes them suitble for improving various antenna performances. This thesis focuses on the application of waveguided metamaterials on microstrip patch antennas. The main contents and contributions of the thesis are summarized as follows:1) Typical retrieval thechinque by inversion of scattering parameters was introduced.This technique was proposed for extracting the equivalent constitutive parameters of waveguide metamaterials. The validity of this technique in predicting scattering properties of multi-unit and stratified waveguide metamaterials was discsussed. The retrieval thechinque was then applied to waveguided metamaterials based on embedded meander line(EML) structure to find out the relationship between equivalent constitutive parameters and geometrical parameters of unit cells for this kind of metamaterials.2) A waveguided metamaterial with two-dimensional magneto-dielectric properties was dveloped. Such metamaterial, which is constitued by EML cells, has the advantages of weak dispersion and low-loss. The waveguided magneto-dielectric metamaterial was then used as the equivalent substrate of circular polarized(CP) microstrip antenna to improve the operational bandwidth of the antenna. Simulation and experimental results show that both the impedance bandwidth and axial ratio bandwidth of CP microstrip antenna can be obviously improved by loading the waveguide magneto-dielectric metamaterial.3) A stratified waveguided artificial metamaterial with double positive-near zero index(DPS-NIZ) properties was developed. The two segmens of such metamaterial are composed of EML cells and complementary split-ring resonator(CSRR) cells, respectively.The waveguided DPS-NIZ metamaterial was then used as the equivalent substrate of microstrip patch antenna to achieve a dual-band operation characteristic. Simulation andexperimental results show that the two lowest-order resonant modes of the dual-frequency antenna are TM010 and modified TM020 modes. The dual-frequency antenna has fairly consistent radaiation patterns in the two operational bands.