Study On The Compact Electromagnetic Band-gap Structure And Double Negative Medium Structure

Compact electromagnetic band-gap (EBG) structure and double negative (DNG) structure are new types of electromagnetic material presented recently, which have greatly potential applications on the field of microwave and optics. Generally, EBG structure is periodic metal-dielectric structure, whose distinct property is artificial control of the electromagnetic wave. The electromagnetic wave in the band-gap can not propagate. Compact electromagnetic band-gap structure has narrow bandwidth characteristic and mostly applied to narrow band-width antenna or equipment due to its bandwidth bottleneck. In this thesis, cascaded electromagnetic band-gap structure is presented to broaden the bandwidth or achieve dual band operation. The structure is applied to antenna in order to restrain the backward radiation, decrease mutual coupling between units and eliminate scan blindness of phased array antenna. The study on theory and application of DNG structure is at initial stage. The DNG structure is applied to waveguide antenna and arrays in this thesis to enhance the gain of antennas. The work of the author is mainly focused on:1. The effect of five configuration parameters of Mushroom-like EBG structure unit (including metal patch width, gap width, permittivity of dielectric board, thickness of dielectric board, metal via radius) on surface wave and reflection phase band-gap is studied based on unit model of infinite periods using periodic boundary condition (PBC). The inductance loops are integrated to EBG structure to broaden the band-gap width.2. The transmission characteristic and reflection phase of non-uniform EBG structure are analyzed. The direct transmission method is used to analyze the band-gap of finite periodic EBG structure. The equivalent circuit of EBG structure in waveguide is developed. The method of different parameters cascading is presented to broaden the band-gap. The EBG structures with different radius of via or periodic size are cascaded. The band-gap of the cascaded EBG structure almost covers the band-gap produced by the uniform structure respectively. The EBG structures with uniform radius of via and cascaded one are fabricated and measured. The experimental results are consistent with the simulation data, which proves the validity of the method. In the aspect of reflection property, the model to analyze finite periodic EBG is also founded. The nest-like EBG structure are presented using different patch size cascaded, which can obtain in-phase reflection phase in two frequency-bands simultaneously. 3. The applications of EBG structure on microstrip antennas are studied. The band-gap of EBG structure is confirmed exactly by the method of united simulation with EBG structure and microstrip antennas. The EBG structure is integrated between two microstrip antennas to reduce the mutual coupling. The EBG structure is also integrated around the microstrip antenna unit to reduce the backward radiation, enhance forward gain and improve the radiation property. Dual-band microstrip antenna is designed and fabricated. The dual-band EBG structure using cascaded idea is integrated between two dual-band antenna units. The simulation and experimental results show that the mutual coupling of two dual-band antennas can be reduced in two operational frequency-bands simultaneously.4. The scan blindness of circular waveguide dielectric rod phased array is analyzed. The relation between the active element pattern of central unit and scan characteristics of phased array is compared. Fifteen units of circular waveguide dielectric rod antennas are arranged along the E plane to form linear array. In the angle of scan blindness, there are sharp and deep depression in the active element pattern. The EBG structure is applied to circular waveguide dielectric rod phased array to effectively restrain the mutual coupling between units, eliminate the scan blindness of phased array and increase the ability of the array to scan wider angular sectors.5. The DNG structure unit is composed of square split ring resonator (SRR) and strip wire (SW). The modified NRW method is used to extract the equivalent permittivity, permeability, and refractive index from the scattering parameters of the two-port waveguide with DNG structure. At the designed operating frequency, the refractive index approximates zero, which makes the nondirective electromagnetic wave tend to approximate plane wave along the normal direction of the superstrate and congregate the radiation energy. The gain patterns of the rectangular waveguide antenna and arrays with and without DNG structure are compared. Simulation and experimental results show that the forward gain of antenna is enhanced distinctly and backward radiation is somewhat restrained with the DNG structure.